Cynthia A. Challener is a contributing editor to Pharmaceutical Technology.

Cynthia A. Challener

Although inspections are critical, according to US Food and Drug Administration Commissioner Stephen M. Hahn, they are one part of a robust and multi-pronged approach to overseeing the safety and quality of FDA-regulated products. “Safety and quality must be part of the daily routine at a firm for their products to be high quality and reliably suitable for the US consumer,” he explained in previous press statements from the FDA press office.

Under normal circumstances, the agency uses risk-based models to identify firms for inspection. FDA prioritizes for inspection facilities deemed as higher-risk based on specific, defined criteria. For drug and device inspections, these criteria can include inherent product risk. To supplement inspections, FDA also uses a number of other tools, including denying entry of unsafe products into the United States; physical examinations and/or product sampling at US borders; reviewing a firm’s previous compliance history; using information sharing from foreign governments as part of mutual recognition and confidentiality agreements; and requesting records “in advance of or in lieu of” on-site drug inspections.

Furthermore, FDA will conduct inspections when a potential risk to public health is detected, and the agency has remained in contact with domestic and foreign regulatory counterparts to identify emerging risks in the medical products and food supply systems, according to an FDA spokesperson. “When we suspended routine operations, mission critical inspections were conducted for products deemed as mission critical drugs because of reasons including medical necessity, drugs for which there is a shortage, and pre-approval inspections for novel drugs or drugs related to the potential treatment of COVID-19,” says the spokesperson.

Both for-cause and pre-approval inspections can be deemed mission critical. They are identified on a case-by-case basis by the agency and conducted with appropriate safety measures in place.

Where routine domestic and foreign surveillance inspections have been postponed during the COVID-19 pandemic, FDA has used and implemented additional alternative approaches and records reviews, including, among other things, when appropriate evaluating records in lieu of conducting certain onsite inspections on an interim basis when travel is not permissible, according to an FDA spokesperson. The agency’s labs also continue to analyze high-priority samples.

“The resumption of prioritized domestic surveillance inspections has been an important area of focus for us,” the FDA spokesperson observes. As of July 10, 2020, FDA was working toward the goal of restarting routine on-site domestic inspections during the week of July 20. Resuming prioritized domestic inspections is, however, dependent on the data about the virus’ trajectory in a given state and locality and the rules and guidelines that are put in place by state and local governments, according to whom. “In order to move to the next phase, we must see downward trends in new cases of COVID-19 and hospitalizations in a given area,” noted Hahn in an FDA statement.

Preparation for restarting on-site prioritized domestic inspections involves using the tools available while considering other factors including the operational status of the facility, the ability for the appropriate investigator to travel, evolving local, state, and federal requirements, and updates to Centers for Disease Control (CDC) guidance. “We are using a newly developed risk assessment system to help it, and individual states make informed risk-based decisions on when and where to resume prioritized domestic surveillance inspections,” says the FDA spokesperson.

In addition, for the foreseeable future, prioritized domestic inspections will be pre-announced to FDA-regulated businesses to help assure the safety of the investigator and the firm’s employees. This approach will provide for the “safest possible environment to accomplish our regulatory activities while also ensuring the appropriate staff are on-site to assist FDA staff with inspection activities,” Hahn says.

Articles

FDA relies on risk assessments, border inspections, and compliance histories in place of routine audits during the COVID-19 pandemic.

FDA Takes Calculated Approach to Auditing during COVID-19

Continuous manufacturing is being encouraged by regulatory authorities as a means for improving product consistency and quality while also potentially reducing cost. For continuous manufacturing of oral solid dosage drugs, excipients play important roles not only in the performance of the formulated product, but also during processing. Excipients must address the specific needs of the API, such as the desired drug release rate, solubility enhancement, crystallization inhibition, or improved API uniformity while also enabling processing of the final intended dosage form. In the latter case, physiochemical properties such as flowability, density, particle morphology, and glass-transition temperature are crucial considerations for designing an optimal continuous process.

For each given excipient, the impact on a continuous process may be small or substantial depending on the quantity of excipient present and its difference in properties from that of the API. Many excipients available today are well suited for continuous processing, but there remain significant opportunities for increasing knowledge about the impact of material property changes in process output and, ultimately, drug product quality.

“The excipient impact on continuous drug product manufacture is profound,” asserts Joseph Zeleznik, technical product manager for IMCD US Pharmaceuticals. “The proper choice and use level influence product and process robustness, throughput and yield, development and manufacturing costs, and drug product quality. It is important that any excipient used is not only effective in its application within the formulation but is well-suited to maximize continuous manufacturing process efficiency,” he adds.

For oral solid dosage (OSD) drugs, excipients can have an impact on the physical characteristics (i.e., flow, density, homogeneity, and compactability) of the mixture in the equipment during processing and ultimately at compression or encapsulation, notes Anthony Carpanzano, director of R&D at JRS Pharma in the United States. Blend homogeneity is critical for achieving content uniformity in the finished tablet, according to Mark Dreibelbis, associate research scientist with DuPont Nutrition & Biosciences. “Large mismatches in particle size and flowability between excipients and the API can lead to segregation, impacting dosage consistency and possibly leading to excursions from the therapeutic window,” he explains. Inter- and intra-lot excipient variability should be understood, as well as its potential impact on process and product quality Zeleznik observes.

“Excipients can be a double-edged sword for OSD continuous manufacturing processes,” states Krizia Karry, global technical marketing manager at BASF Pharma Solutions. “They can be used to improve flowability and tabletability, but they may also affect dissolution performance if they are shear dependent, for example. My recommendation is to steer away from excipients that are very shear dependent as these can lead to inconsistent residence time distributions, and those with broad particle size ranges and/or high specific surface area, as fines are more prone to gaining static charge and bridging,” she says.

A quality-by-design (QbD) development program supported by an appropriate process analytical technology (PAT) strategy is essential in understanding and controlling excipient impact on continuous manufacture and drug product quality and performance, according to Zeleznik. Lubrication strategies also need to be rethought not only with respect to the right choice of lubricant, but the right use level and when it should be added.

In batch manufacturing, Krizia explains, there is not too much emphasis placed on flow characteristics, shear, or electrostatics because the batch dispensing process is manual (you open a bag and dispense into an [intermediate bulk container] IBC, or you use a vacuum system) and subsequent unit operations are discrete. “In continuous processing, the impact of compactability (change in volume with force) when refilling materials, flowability (how easy the material moves through the line), and shear (which also dictates your feeder screw set-up because you want to feed accurately and without breaking the material) must be considered, among other factors,” she says.

Overall, Zeleznik comments that continuous manufacture is no different than batch manufacture regarding choosing the “right” excipient. “Excipient choice is predicated on several factors, including API physicochemical characteristics, targeted dose, route of administration, and most importantly, the manufacturing equipment and process used during continuous manufacture,” he says. “Another consideration in choosing an excipient is its multifunctionality and flexibility with respect to the formulation and process. Excipients to avoid are those having limited performance attributes or that are unsuitable for continuous operations. Because of the limited feeders, more has to be accomplished with less.”

It is important, therefore, to develop a formulation with the desired functionality. The flow, density, particle size, and electrostatic properties of excipients are more important in continuous processes versus traditional batch processes, according to Mara van Haandel, innovation manager at DFE Pharma. “During continuous manufacture, it is essential that product flows in a continuous manner in the processing units (and is consistently transported from one unit to the next), as clogging of material/material build up can impact the residence time distribution,” she says. Hence, the “right” excipient choices have to be made from the start of developing a formulation on a continuous process.

That can be a challenge for OSD formulations because powders of various particle sizes and densities must be meter-fed into the system at the correct ratios and then make their way through the production path, notes Becca Putans, an associate chemist from DuPont. “Materials that have a poor flowability or high cohesive properties pose a risk of accumulating in corners, causing blockages, downtime for cleaning, and non-uniform dosage forms,” she says.

Any excipient chosen also needs to demonstrate a non-segregation potential for the final blend. “Since the materials move continuously together through the unit operations, the mixture must stay at the correct ratio, otherwise the resulting dosage forms will not have a uniform distribution of the active ingredient,” Putans adds. Therefore, excipients with higher flowability, optimized density, morphology, and moisture content, low batch-to-batch variability, and compactability are preferred.

The physical behavior of an excipient when under shear stress is a major determining factor in its suitability for continuous processing, adds Carpanzano. “Excipients that perform well in continuous manufacturing can be easily fed into the process at a uniform rate, promote blending with the active ingredient and other excipients, maintain flow and do not break down or compact in the mixing phase, and can be compacted into tablets or filled into capsules after blending,” he concludes.

Many direct compression excipients have been designed for use in a continuous tableting operation, according to Putans. The particle size and morphology have been tailored to provide a high level of flowability while retaining compactability. “These materials are designed to flow through a continuous manufacturing process with little build-up, while maintaining content uniformity and good final dosage consistency,” she observes.

In some cases, a pre-blending strategy is adopted to improve flowability, such as with fumed silica when used as a glidant, according to Karry. “Fumed silica has a low density of 0.03 g/mL, which presents challenges when trying to individually dispense via loss-in-weight feeders. “To overcome this issue, formulators pre-blend the glidant with another excipient to ensure accurate feeding and good flow properties of the blend. Undoubtedly, pre-blending with silica is not ideal—especially in a continuous manufacturing setting—but it is a proven strategy for improving powder flowability,” she says.

“Improving flow properties with excipients is a proven strategy, but for troublesome low-density and/or poor water-soluble APIs, additional unit operations have also been adopted to continuous platforms,” adds Karry. Twin-screw granulation or hot-melt extrusion excipients intended for preprocessing of these APIs should have wide operating temperature ranges and resist degradation, discoloration, or drastic changes in viscosity, according to Dreibelbis.

Binder selection is also critical for continuous granulation processes for uptake of granulation liquid and quick drying to produce robust granules. Less hydrophilic grades of common binders exist to facilitate faster moisture removal from the resulting granules, which ultimately reduces cost and improves throughput, he adds.

Compared to batch processes, electrostatics (measured as static charge) is a critical piece of the puzzle for both APIs and excipients. “When a material bridge occurs due to electrostatics,” Karry explains, “material is likely not being fed through the conveying screw elements, and thus, there is no registry of weight change over time. This absent change triggers a control reaction (since feeders have Level 1 control) that involves increasing the screw speed to ‘try’ to dispense more material. Since the material is stuck on the hopper, no material is fed and the result is a subpotent (for the case of API) or superpotent (if the case is for filler) blend. The blend amount produced during this time will depend on the total mass flowrate of the process, the mean residence time, the alarm limits, and the controller dead-time.”

The problem, Karry adds, is that few options exist for accurately measuring this attribute and electrostatic properties depend on the humidity, temperature, and contact material. It is therefore important when evaluating performance to replicate the manufacturing conditions.

van Haandel notes it is unlikely that a powder will bridge due to electrostatic behavior in a hopper/feeder, but due to the combination of wall friction and hopper/feeder flow mostly caused by powder consolidation and/or incorrect powder flow in relationship to the opening diameter.

In a continuous process, ingredients need to be fed in at an appropriate rate and at the correct ratio. When there are many different ingredients, it can be challenging and costly to have feeders dedicated to each individual component. To reduce the number of feeders that must be aligned, co-processed excipients offer an effective solution, and also reduce the number of variables and opportunities for variability in a process, according to van Haandel.

“A single high-functionality co-processed excipient can accomplish the same task using only one feeder, thus enhancing finished product performance while keeping variability to a minimum,” Carpanzano agrees. A typical coprocessed excipient has a filler, a binder, and a disintegrant as part of its structure, as well as a low concentration of glidant to ensure excellent flow, according to Karry. “In addition to eliminating the need for multiple feeders, the use of such co-processed excipients simplifies the control architecture and control strategy for continuous processes,” she notes. There is also less chance of segregation of the components during mixing, according to Carpanzano.

In fact, Zeleznik asserts that multifunctional excipients are an essential part of a successful, robust formulation and process. “While not new, co-processed excipients offer the increased, multifunctional performance needed for continuous operations,” he says. DuPont, BASF, DFE Pharma, and JRS Pharma all offer advanced co-processed excipients with the flexibility and enhanced multifunctionality ideal for use in continuous production of OSD formulations. “Modifications to existing excipients, such as particle engineering, and advances in excipient performance through co-processing have accelerated the development of continuous processing, and specifically, continuous manufacture of directly compressed tablets,” Zeleznik concludes.

Consistent performance of excipients is essential for continuous manufacturing. So is a constant feed in and out of a continuous process to ensure traceability and control of all critical process parameters. “Because excipients have inherent variation, it is important to understand the implications of this variation on continuous processes and thereby final products,” states van Haandel.

Therefore, simplification of a formulation combined with the use of very consistent excipients is important. DFE Pharma is applying fundamental and mechanistic analyses to gain an understanding of the impact of potential excipient variation on continuous manufacturing processes and the performance of final products. Using this knowledge in formulation development is essential for successful implementation, according to van Haandel. “Formulations should be designed in such a way that they can cope with the variation proven in historical data and analyzed using multivariate statistics,” she states.

Specifically, DFE Pharma is applying multivariate analysis on all physical/chemical parameters to gain that needed better understanding of historical product variation and is offering stretch batches, or batches showing high multivariate variation to ensure they are representative of the historical product variation (five years of manufacturing-based data), to enable formulators to efficiently test the impact of this variation on their formulations.

DuPont is also analyzing critical excipient attributes, providing historical (four to five years) manufacturing data to establish inherent excipient variability, and performing comprehensive multivariate analysis on many grades to understand the variability within batches and at different manufacturing sites, according to Dreibelbis.

Karry adds that research centers and companies alike have developed excipient libraries that serve as input to mechanistic models that predict the impact of raw material property changes on feeding accuracy, hold-up mass, mean residence time, and downstream drug product concentration. These models are verified with tracer experiments that seek to measure the change in concentration as a function of time and total mass flowrate.

Unfortunately, according to Karry, the selection of these tracers is not a trivial task, because formulators need to consider the strengths of their spectroscopic signals (near-infrared or Raman, typically), and their bulk properties, as their addition into the blend should not affect the bulk flowing properties that one intends to study. “Such a perfect tracer does not currently exist,” she says.

Another important issue that needs to be addressed, according to Karry, is cleaning. “Taking apart, cleaning, and correctly reassembling every component of a continuous manufacturing line is basically a work of art,” she stresses. “Companies that have implemented continuous manufacturing processes agree that this task requires much more attention than with batch processes and that it has an impact on the supply chain because turnover times are greatly increased,” Karry says.

Modular equipment that can be easily cleaned in place has advantages, but piping, mixers, and contact parts still need to be disassembled for proper cleaning and reassembled prior to starting the next campaign. “An integrated line can have hundreds of parts, so the question we must ask ourselves is ‘Why disassemble?’,” Karry poses. With the right excipient, she envisions a ‘flushing’ type of cleaning process based on electrostatics. “The adequate balance of charges would pull everything in its path, and a non-contact hand-held spectroscopic device could be used for measuring the ‘cleanliness’ of the surface,” explains Karry.

Need for a novel excipient approval pathway

While formulation and process challenges for continuous manufacturing are being addressed through advances in excipient technologies such as particle engineering and co-processing, a regulatory gap continues with novel excipient acceptance, according to Zeleznik. “New or novel excipients are often avoided due to the perceived risk associated with using a new excipient even when a novel excipient’s performance could expedite drug product development and enhance continuous manufacturing processes,” he says.

There might be some changes coming, however. FDA is now considering a pilot program for novel excipient assessment (1). “Should this program be formalized and novel excipients have an acceptance pathway, it could do much to advance continuous manufacture growth going forward,” Zeleznik believes.

Novel Excipient Review Program Proposal; Request for Information and Comments

Cynthia A. Challener, PhD, is a contributing editor to 


Vol. 44, No. 8
August 2020
Pages: 21­-24

When referring to this article, please cite it as C. Challener, “Key Ingredients Needed to Drive the Success of Continuous Manufacturing,” 

Understanding and overcoming excipient variation are crucial for successful continuous processes.

Key Ingredients Needed to Drive the Success of Continuous Manufacturing 

Originally it was thought that the only role of ribonucleic acid (RNA) was to translate genetic information encoded in DNA into protein sequences that perform critical biological functions. While messenger RNA (mRNA) is crucially important, it is just one of many types of RNA involved in a range of activities that affect the transmission of genetic information and the functioning-or dysfunctioning-of cells. Appropriately designed RNA-based therapies can thus modulate genetic information in a controlled and targeted manner, effectively acting as gene therapies. They also offer several advantages over DNA plasmid-based therapies.

	Strands of RNA by themselves, however, are unstable and degrade rapidly in the bloodstream. Delivery to specific targeted cells is one of the main challenges that developers of RNA-based gene therapies are tackling today.

	RNA technologies fall into two main categories: those that directly interfere with expressed mRNA or mRNA expression, blocking protein production, and those that cause the expression of target proteins whose deficiencies can lead to disease.

	The first type includes RNA interference (RNAi) and antisense therapies, which in effect silence the expression of specific genes that are drivers of disease mechanisms. One example is small interfering RNAs (siRNAs), which according to David Evans, chief scientific officer at Sirnaomics, are useful as therapeutics where the gene(s) to be targeted is (are) overexpressed in the diseased state and where silencing these genes may produce a therapeutic benefit.

	Indeed, Doug Fambrough, president and CEO of Dicerna Pharmaceuticals, believes that while supporting protein production is useful in a few contexts, such as treating rare genetic diseases or making vaccines, there are far more uses for silencing genes. “For example, silencing can be used to treat viral diseases, cardiovascular conditions, cancer, inflammatory diseases, fibrotic diseases, select rare diseases, and generally any condition where biological processes are inappropriately activated,” he asserts.

	Sirnaomics and Dicerna are both focusing on RNA interference therapies. Belgium-based biotech company eTheRNA immunotherapies, on the other hand, has elected to focus on mRNA-based technologies that lead to the expression of proteins the body is unable to produce on its own, according to Wim Tiest, a special advisor at the company.

	Unlike DNA-based gene therapies that must be delivered into the nucleus and create permanent changes, RNA therapies only need to reach the cytoplasm to perform their post-transcriptional activity and are not permanent, thus treatment can be modified or halted if necessary. They are also smaller, more easily manipulated, and do not present the risk of unintentional genetic effects.

	“Messenger RNA and other RNA-based therapies have the advantage of being versatile (they can code for a broad range of targets), easy to produce (basically the production process is transposable between mRNA designs), and safe (due to the transient expression of the target and absence of risk for integration into the patients genome),” asserts Tiest. “Additionally,” he says, “mRNA is compatible with a range of systemic and local delivery modalities and can be designed to be nearly invisible to the host’s immune system, thus avoiding any vector-directed immune responses.”

	RNAi technologies such as siRNAs also provide high target specificity by using gene sequences that match with targeted genes and rely on naturally occurring cellular enzymes to mediate gene silencing, according to Fambrough. Due to this high specificity-and reversibility-they offer the potential of fewer side effects. “Unlike gene therapy or gene editing, which can be permanent and could have unknown, unwanted, and irreversible consequences, RNAi therapies can offer targeted, effective treatment that does not permanently edit or change DNA. An RNAi therapy’s effect is targeted, precise, and can be stopped at any time by discontinuing treatment,” he explains.

	With the rapid progress made in sequencing the human genome, there is now a wealth of information on sequences of genes, some of which have been identified as playing a direct role in the etiology of diseases, according to Evans. “Many of these therapeutic targets, however, are undruggable by traditional small molecules or antibodies but are upregulated in disease states like cancer and fibrosis,” he notes. “siRNAs are readily designed against these gene sequences and can silence expression of the proteins that are driving disease, producing therapeutic benefit to patients with disease,” Evans says.

	In addition, RNAi therapies offer a highly versatile approach that can benefit patients with an array of diseases, Fambrough points out. “Today, we can create siRNAs to match almost any messenger RNA. In effect, the RNAi approach to drug development can silence virtually any gene,” he notes.

	Another benefit of RNA therapies compared to many conventional small-molecule and biologic drugs is the possibility of reducing the treatment burden for patients, according to Fambrough. “With a longer duration of effect, RNAi therapies can be administered with infrequent subcutaneous injections, and depending on the disease modality, can be self-administered at home,” he observes.

	RNA by its nature is rapidly degraded once injected. As such, delivery to the targeted cells is the main hurdle at this time. “We need to ensure that the siRNAs are able to reach their target tissue and cell types,” Evans states. In cancer, for example, that means accumulation of nanoparticles, for instance, at the tumor site with delivery of the RNA into the tumor cells specifically. Stabilization of RNA by modification of the chemical backbone is possible, and this approach can also help to make the RNA less immunogenic, Tiest notes.

	Similarly, the inhibitory or expression effect wanes as the RNA degrades inside the cell. Self-amplifying RNA can to some extent prolong this active period, according to Tiest. The need for regular, repeated dosing and maintenance of a sufficient active dose is therefore also a major bottleneck. He does note that local administration helps to overcome some of this limitation.

	Overall, careful selection of targets that require short interventions and can benefit from the increased safety profile of RNA is required to fully profit from RNA-based therapy development, Tiest concludes.

	Like most DNA plasmid-based gene therapies, RNA therapies can also be delivered into cells using viral vectors, but the majority of these therapies under development today rely on nonviral methods, such as organic (lipid) or inorganic nanoparticle-encapsulated complexes, extracellular vesicles, and patient-derived dendritic or mesenchymal stem cells, allowing delivery even across the blood-brain barrier (1).

	Delivery technologies for intravenous, subcutaneous, and intramuscular administration are largely focused on preventing RNA-based therapies from degrading in the blood stream. For mRNAs administered in this manner, lipid nanoparticle solutions appear to be most common. Other delivery technologies are designed to enable local administration of mRNAs to the target site or organ, according to Tiest. “For cancers,” he explains, “intratumoral injection of mRNA offers advantages in safety (very local effect), dosage (no need to saturate circulation and reach the target), and easier combination with other existing therapies.”

	Lipid-based nanoparticles have also been used for siRNA-based drugs, including some that have been approved by regulatory authorities. N-Acetylgalactosamine (GalNAc)-mediated delivery of chemically modified siRNAs has been demonstrated to result in significant delivery and silencing of genes within the hepatocytes of the liver and has also resulted in an approved product.

	Dicerna’s GalXC platform is a leading example. “This approach uses a unique, proprietary, and rationally designed tetraloop configuration of double-stranded RNA molecules that interfaces effectively with the RNAi process and allows us to easily modify a compound’s chemical structure to maximize stability and potency,” Fambrough explains. He adds that it offers the potential for more convenient administration, infrequent dosing, high specificity, a high therapeutic index, and scalable, straightforward manufacturing. So far, the company has focused on treating diseases of the liver, but is now exploring the use of its GalXC platform across different organs, systems, and rare and common diseases.

	Sirnaomics uses a polypeptide nanoparticle consisting of a histidine-lysine branched-chain polypeptide (HKP). HKP mixed with siRNAs spontaneously forms nanoparticles due to the charge-charge interaction between the negative phosphates on the siRNAs and the positively charged lysines, Evans notes. An advantage of this technology over some other delivery mechanisms, he says, is its ability to deliver multiple siRNAs to a cell at the same time, allowing synergistic effects of two siRNAs to be utilized as a therapeutic.

	HKP-based nanoparticles can also accumulate near tumors, possibly mediated by the enhanced permeability and retention (EPR) effect, according to Evans. They further benefit from the presence of histidines, because these moieties have a pKa of approximately 6.3 and become protonated during acidification of the endosomes that are intermediary in the uptake of siRNAs by the nanoparticles. “This protonation helps release the siRNA payload into the cytoplasm where the siRNAs function to silence targeted genes,” he observes.

	A third challenge has been regulation of mRNA activity once it is delivered to the right cells, which is needed to ensure the right dose of the targeted therapeutic protein is expressed. A research team at the Massachusetts Institute of Technology developed one possible solution: incorporation of additional genes for RNA-binding proteins (2). The interaction between the mRNA and RNA-binding proteins is controlled using a small-molecule drug, and thus dosing of the small-molecule drug regulates the mRNA activity.

	Inhibitory RNA approaches are most advanced, while mRNA therapies are at earlier stages, with some vaccines in Phase II trials and candidates using mRNA for in-vivo expression of antibodies that target a specific therapeutic effect, according to Tiest.

	The two RNAi therapies that have received approval to date were both developed by Alnylam Pharmaceuticals. Onpattro (patisiran) was granted approval by FDA in August 2018 for the treatment of the polyneuropathy of hereditary transthyretin-mediated amyloidosis (3). It has received marketing authorization from the European Medicines Agency. This drug halts the production of faulty transrethrytin.

	In November 2019, Alnylam received FDA approval for Givlaari (givosiran) for the treatment of adults with the rare genetic disease acute hepatic porphyria (4). This RNAi therapy targets aminolevulinic acid synthase 1.

	The three companies interviewed for this article alone have several RNA-based therapies in development, but they represent only a small portion of candidates moving through clinical development.

	eTheRNA is mainly active in oncology, with both vaccines against tumor targets and intratumoral injection of mRNA expressing targets involved in cell death and immune stimulation in its portfolio that leverage propriety LNP and immune stimulation (Trimix) technologies. Currently, the company has an ongoing Phase I/II program in melanoma and breast cancer. It also recently entered the field of infectious diseases and is working on a cross-protective coronavirus vaccine based on T-cell response that is administered intranasally, according to Tiest.

	Sirnaomics has developed a combination of two siRNAs targeting TGFbeta 1 and Cox2 within an HKP nanoparticle that it has formulated for intratumoral delivery (STP705 in Phase IIs in non-melanoma skin cancer) and intravenous administration (STP707 for delivery to key liver cells for fibrosis treatment; it also has demonstrated in animal models to mitigate hepatocellular carcinoma [HCC]). STP707 has further been shown to increase the activity and improve the efficacy of anti-PDL1 antibodies against HCC, according to Evans.

	The company is also working on chimeric siRNAs that combine a small-molecule therapeutic into the structure of the siRNA. “Once inside the tumor cell, the small molecule is released from the sense strand where it is designed to augment the activity of the siRNA inhibitor and produce a synergistic effect,” Evans says. The activity of these constructs has been demonstrated against a number of tumor types including pancreatic tumors, colon cancers, bladder cancer, and head and neck cancers.

	Dicerna is leveraging its GalXC technology on its own and through several collaborations. The company’s lead candidate, nedosiran, is in development to treat primary hyperoxaluria (PH), an ultra-rare and devastating condition that causes calcium oxalate crystals to form in the kidneys and often results in kidney failure. Nedosiran silences the lactate dehydrogenase enzyme, which is implicated in all three types of PH. It is currently being evaluated in the PHYOX clinical development program, which includes an ongoing registrational trial.

	Two other top candidates include an siRNA therapy to treat alpha-1 antitrypsin-associated liver disease (Phase I/II) and RG6346 for the treatment of hepatitis B virus infection (Phase I), which is being pursued in collaboration with Roche. “Between Dicerna and our collaborative partners, we currently have more than 20 active discovery, preclinical, or clinical programs focused on rare, cardiovascular, cardiometabolic, viral, chronic liver, and complement-mediated diseases, as well as neurodegeneration and pain,” Fambrough notes.

	Both mRNA and siRNA therapeutics and vaccines are advancing through the clinic, with a steady stream of readouts expected in the next few years. “Apart from clinical data, these results should validate a number of delivery and chemical modification platforms that can then open up the field into an increased development of RNA-based therapeutics,” Tiest states.

	Over the next year, Evans expects an influx of additional siRNAs targeting liver diseases and being targeted to the hepatocytes using GalNAc conjugates because this approach has already demonstrated success. “Efforts will also be focused on additional chemically modified siRNAs with different targeting ligands that enable delivery to tissues and cells outside the liver, with the biggest obstacle being avoidance of uptake by the liver for any and all systemically delivered siRNAs,” observes Evans.

	Fambrough agrees that the next frontier for RNAi therapies will be non-hepatic tissues. “There is significant interest and persistent unmet need across a range of disorders,” he says.

	Moving new therapies on to the main stage

	Going forward, the key advantages of RNA-based therapies compared to DNA-based gene therapies will continue to drive greater interest in all types of RNA treatments. “RNA combines the advantages and versatility of genetic-based therapy modalities with the lack of (perceived) risks associated with DNA-based gene therapy. Technology has now reached a level of maturity, particularly around stabilization and delivery of RNA, and the upcoming flow of clinical data could enable the break-through of this technology onto the main stage of drug development,” comments Tiest.

	Looking specifically at RNAi therapies, Fambrough notes that while the technology is a newer approach to treating disease, it has experienced a “coming of age” in the past couple of years. “We have seen not only the first approvals in the space, but also a surge of interest among big pharma and big biotech companies seeking an entry into RNAi,” he says.

., 9:1208 (2019).
	2. MIT, “This RNA-Based Technique Could Make Gene Therapy More Effective,” Press Release, Oct. 16, 2018.
	3. Alnylam Pharmaceuticals, “Alnylam Announces First-Ever FDA Approval of an RNAi Therapeutic, ONPATTRO (patisiran) for the Treatment of the Polyneuropathy of Hereditary Transthyretin-Mediated Amyloidosis in Adults,” Press Release, Aug. 10, 2018.
	4. FDA, “FDA Approves Givosiran for Acute Hepatic Porphyria,” Press Release, Nov. 20, 2019.


	Vol. 44, No. 7
	July 2020
	Pages: 22–25, 64

	When referring to this article, please cite it as C. Challener, “Can RNA Simplify Gene Therapy Development?" 

RNA is easier to manipulate than DNA but challenging to deliver to the right cells.

Can RNA Simplify Gene Therapy Development?

Today, FDA expects drug formulators to not only consider patients outcomes when developing new products, but to also focus on the overall patient experience. Four main factors address the patient experience, according to Sarath Chandar, chief science officer with SPI Pharma: convenience, compliance, safety, and efficacy. Orally disintegrating tablets (ODTs) and other fast-dissolving oral dosage forms address the first two factors-and to some extent efficacy as well- from the standpoint of sublingual delivery, which can lead to increased bioavailability for poorly soluble APIs.

	Convenience is increased with ODTs and fast-dissolving products across all patient populations. “Pediatric patients benefit from this group of products because they dissolve faster than what they are able to spit-out and can also be mixed with foods for easy administration. These products can also be taken without water, so they are also amenable for adults on the go,” says Krizia Karry, global technical marketing manager at BASF Pharma Solutions.

	The fact that ODTs do not need to be washed down with water provide additional benefits as well. ODTs are, for instance, attractive to those who do not want to swallow liquids or hard tablets because they are feeling nauseous, adds Ralph Gosden, head of product development at Catalent Swindon. They are also useful when there is a need for rapid drug release, such as to relieve a headache, according to Torkel Gren, science and technology officer for Recipharm. “Orally disintegrating products are an ideal platform for delivery of active ingredients for the treatment of pain, allergies, diarrhea, Parkinson’s disease, travel-related illness, and other indications where rapid dosing and absorption is required,” he observes.

	In addition, ODTs can help patients who have an aversion to swallowing a tablet or capsule, and those who find it extremely difficult to take standard tablets because they may have dysphagia or other problems with swallowing (e.g., the elderly and infirm), Gosden notes. “Patients suffering from mental impairments can benefit as well,” he adds, “as they will sometimes deliberately avoid taking medications or pretend to have swallowed a standard tablet or capsule by hiding it in their mouth to spit out later-a practice referred to as ‘cheeking’. This tactic is nearly impossible with an ODT as it disintegrates quickly and completely.”

	Other benefits of orally disintegrating products in some cases are higher bioavailability and the fact that faster drug uptake can be achieved, according to Gren. “Instantaneous disintegration allows the drug to be dissolved and absorbed more rapidly, and for drugs that can be absorbed via the mucous membranes within the oral cavity, it can help to avoid the harsh environment within the gastrointestinal tract and bypass first-pass metabolism by the liver.”

	Orally dissolving products include tablets, granules, and films. “For tablets, the most common manufacturing technology is direct compression into tablets or minitablets,” Karry asserts. The use of 3D printing is also being explored for the production of ODTs, Gosden notes. “Granules are mostly produced via fluid bed granulation/drying and twin-screw granulation to ensure adequate size control. On the other hand, films are cast and dried on moving Teflon membranes from solutions or suspensions of APIs and soluble polymers,” Karry comments. More advanced technologies are often protected by patents, which may restrict competition, according to Gren. “In addition,” he stresses, “a more complex technology should not be used if it does not result in significantly better product properties.”

	Thin film strips are a delivery technology that can be used for both systemic and local delivery by oral, buccal, and sublingual routes, according to Gosden. “Although they dissolve rapidly in the mouth and are considered self-administrable, the application of thin-film strips is somewhat limited as the maximum dose that can be formulated for delivery via the digestive tract is only in the 20–50 mg range,” he says.

	In addition, Chandar adds that FDA has not approved many thin-film products for pharmaceutical applications because the strips can stick together, resulting in the patient taking multiple doses at once. This challenge has been addressed by individually packaging the oral strips, according to Karry.

	The distinguishing properties between orally dissolving products are the form factor and drug delivery methods (e.g., sublingual, buccal, oral, etc.). “The form is selected taking into consideration the target population and the API solubility. For example, a drug dissolved in a polymeric matrix in the form of a fast-dissolving film may avoid first-pass effects through buccal drug delivery and thus show higher bioavailability due to the design of the drug product,” Karry says.

	To be successful, orally disintegrating formulations must have certain features. The most important property is rapid-within 30 seconds or less-disintegration or dissolution in the oral cavity with or without water, according to Chandar. Because they are placed in the mouth, they also ideally should have a pleasant mouth feel that is creamy rather than chalky. An attractive taste is also ideal, which requires taste masking if the API is bitter, which many are.

	Excipients: The most important component

	Excipients are the most important part of orally disintegrating/fast-dissolving products, according to Karry, because they ensure good sensory properties and adequate technical performance. “When developing conventional tablets, the drug developer will focus on a limited number of characteristics that are easy to measure quantitatively, such as hardness, friability, disintegration, and 

 dissolution. When working with ODTs, several parameters that are difficult to measure are affected by the excipient,” Gren explains.

	“Examples include creating a clean mouth feeling, or creaminess and overall good palatability, as opposed to grittiness and lingering bad flavors, all the while leading to tablets with high tensile strength, low friability, and fast disintegration,” Karry says. She also points out that the interplay between tensile strength and disintegration is particularly important, because the stronger the tablet, the lower its porosity and the slower it disintegrates. “In this case, having both an efficient binder and a super-disintegrant is necessary for good performance of the drug product,” she comments.

	Compressed tablets require super-disintegrants, which either swell or wick up saliva, disrupting the tablet’s structure and encouraging dispersion, according to Gosden. Other important excipients include binders and fillers, according to Karry. Numerous other excipients can also be added to impart specific properties, such as lubricants, sweeteners, colors, and flavorings. “However,” Gosden notes, “some of the additional ingredients that may be required to manufacture the tablet can impede its disintegration. For example, if high levels of lubricant are necessary, the particle size must be carefully considered. If the particle size is too large, then the tablet may give a gritty and unpleasant mouthfeel as it disperses.”

	Certain excipients also enhance the bioavailability of poorly soluble APIs (e.g., Biopharmaceuticals Classification System [BCS] II and IV) by helping to increase the dissolution rate, according to Chandar.

	The type and amount of excipient needs to be carefully selected in order to get the right balance between a number of technical characteristics, including stability, flavor, and mouthfeel, Gren comments. It is particularly important to choose the right filler(s), he says, because the filler is often present in large quantities and has a significant impact on the taste and mouthfeel of the product. “A judicious use of quality-by-design and multivariate methods are helpful here,” notes Gren.

	Some excipients found in orally dissolving products such as sweeteners and flavoring agents are not normally used in conventional tablets, according to Gren. “Here it is extremely important to work in close collaboration with the marketing professionals when selecting the type and amount of all excipients, but especially the flavoring agents. The taste of the product should be developed in order to suit the intended patient population,” he says. “In my experience, sugar alcohols, mannitol in particular, are extremely useful in orally disintegrating products; they provide sweetness and pleasant mouthfeel and also have relatively favorable technical properties,” Gren observes.

	The most important excipients are those that ensure adequate technical and sensorial performance, notes Karry. She lists binders to give strength to the formulation, super-disintegrants to ensure fast hydration and disintegration, taste-masking polymers to decrease the interaction between the bitter or acidic drugs and tongue receptors, and flavors, which are used as needed based on the target population and to stimulate saliva secretion. Strawberry and apple flavors stimulate more saliva than cinnamon, for example.

	“The absolute most important excipient for these products, in my opinion, are disintegrants,” Karry says. “As a patient, I can accept having a bad tasting medicine-there are many out there already-but what I cannot accept is having a bad taste in my mouth for minutes or hours. Disintegrants help to ensure this does not happen. They enable complete drug product disintegration in the mouth so that the small particles can be swallowed, and if designed right, they clean our mouth as well,” she explains.

	Karry notes that studies have shown that both particle size and shape play an important role in mouthfeel. Hard irregular particles are perceived as larger than soft and smooth particles (1), while particles of 100 µm in size are perceived as creamy or fatty and thus activate salivary secretions and swallowing (2). “These studies demonstrate that a systematic science-based approach is needed when formulating orally disintegrating products,” Karry concludes.

	For lyophilized ODTs, Gosden says the most critical excipients are those that form the porous structure, specifically gelatin and mannitol. “While the freeze-drying process is under way, it is important to ensure that all of the mannitol remains crystalline, or there will be a risk that the finished dosage form will collapse during storage,” he explains.

	Chandar notes that for poorly soluble APIs, surfactants and plasticizers are used for bioavailability enhancement. He stresses, though, that no excipient should be used unless there is a demonstrated need and each ingredient in an ODT formulation should be justified.

	It is also worth noting, according to Gosden, that some excipient suppliers have developed proprietary blends of excipients in ready-to-use form (i.e., co-processed excipients) for the creation of compressed ODTs.

	Co-processed excipients based on microcrystalline cellulose (Prosolv ODT from JRS Pharma) and mannitol (Ludiflash from BASF and Pharmaburst from SPI Pharma) have been increasingly used in orally disintegrating/fast-dissolving products owing to their ease of use and overall particle characteristics, according to Karry. “In particular,” she observes, “those containing mannitol have the advantage that this alcohol sugar has a negative heat of solution and upon dissolving in the mouth imparts a cooling effect with a sweet taste. Mannitol is also amenable for ketogenic diets (important for epileptic patients) and diabetics (due to the low carbohydrate count).”

	Co-processing, unlike simple blending or mixing, of different excipients, enables the enhancement of functional performance, according to Chandar. “Whether via spray drying, granulation, congealing, or other methods, co-processing-when done effectively-creates synergies between the excipients involved, leading to unique properties and functionality not achievable any other way,” he states.

	As an example, Chandar points to SPI Pharma’s latest addition to the Pharmaburst line (500), in which the excipients are subjected to a three-step process that includes spray drying and granulation. “The result is a microplate structure of the combined excipients that exhibits a 30–40% improvement in compactability compared to simple, physical mixing. This higher compactability opens up a broader design space for formulating robust ODTs by providing a much higher API carrying capacity of up to 500–600 mg,” he remarks.

	Catalent has developed Zydis Ultra, a next-generation ODT technology that provides better taste-masking properties in a lyophilized ODT combined with an increased drug loading capacity, according to Gosden. A coating is applied to the outside of micronized API particles (as small as 100 µm in diameter) using a dry-coating process.

	“Gelatin forms the overall polymeric structure of the tablet, while mannitol increases robustness and makes the tablet look aesthetically elegant. Both ingredients dissolve readily in saliva, giving a quick-acting, melt-in-the-mouth experience for the patient,” Gosden says. In addition, he observes that unlike compressed ODTs, they are not reliant on the use of super-disintegrants to provide rapid dispersion. Instead, the rapid disintegration results from the way in which lyophilized ODTs are manufactured as well as the formulation of excipients.

	BASF, meanwhile, has developed Kollidon CL-SF, a superfine disintegrant with unique properties for ODTs, according to Karry. “This super-fine version of crospovidone was specifically designed to provide formulators a disintegrant that generates upon hydration smooth particles that are less than 100 µm for a non-gritty, melt-in-your-mouth feeling,” she explains.

	Separately, Karry notes that many companies in South America and Europe are moving to twin-screw granulation methods for manufacturing fast-disintegrating granules. “Twin screw allows for better control of granule size and is easily converted and integrated into continuous manufacturing processes,” she says.

	Regardless of the technology, the advantageous properties of new and more advanced excipients should be balanced against the higher costs that are often associated with them, asserts Gren. “For example,” he comments, “a more expensive excipient may allow you to avoid complex process steps and hence reduce manufacturing costs. As a result, the overall costs must be considered.”

	Compatibility and flexibility are important

	As with any formulation, one of the biggest challenges to developing orally disintegrating/fast-dissolving products is ensuring API-excipient compatibility. “Even though the majority of the excipients are pharmacologically inert, sometimes physical and chemical interactions between the API and excipients can occur that affect the stability, safety, and efficacy of the drug,” Gosden explains.

	For fixed-dose combinations involving two or more APIs, the question of whether the APIs are chemically compatible or prone to interact when combined must also be considered. Catalent addresses this issue when using its Zydis technology by using two or more homogenous formulations that are dosed sequentially under different conditions prior to freeze-drying. “This approach addresses issues of incompatible APIs/excipients and temperature-sensitive APIs,” says Gosden.

	ODT formulators should also prioritize exploring the relationship between tensile strength, friability, and disintegration, according to Karry. “Tensile strength is lower for ODTs compared to regular tablets due to fact that you need higher porosity for solvent uptake and core hydration. Similarly, disintegration tests are decent 

 predictors of palatability as patients prefer dosage forms that do not linger in their mouth for too long,” she adds.

	Given the wide range of APIs and the drive to develop more patient-centric formulations including orally disintegrating fast-dissolving products, it is also important for formulators to have access to broadly flexible platform technologies that can be used for multiple drugs, Chandar asserts. “An antiretroviral drug may require a very high dose, while a cardiovascular therapy may need minimal loading. A universal excipient platform that can be used for both types of formulations and generate robust tablets that don’t apart when the patient opens the package dramatically simplifies the process,” he comments.

	Chandar goes on to note that excipient technologies that provide rapid dissolution and can also aid in enhancing bioavailability are particularly attractive given than nearly 75% of pipeline candidates fall in BCS Class II or IV. In addition, ODT excipient technologies if designed appropriately may even be able to facilitate the oral delivery of some smaller biologic drugs- notably peptides-by enabling sublingual dosage forms that dissolve under the tongue in just five seconds, avoiding first-pass metabolism in the liver.

, online doi.org/10.1111/j.1745-4603.2005.00022.x. (Sept. 19, 2005),
	2. J. R. Stokes, M. W. Boehm, and S. K. Baier, 

Vol. 44, No. 6
	June 2020
	Pages: 20–23, 60

	When referring to this article, please cite it as C. Challener, “Formulating for Convenience and Compliance," 

The correct mix of excipients is crucial to the success of fast dissolving/orally disintegrating dosage forms.

Formulating for Convenience and Compliance

Ensuring the quality of data in process monitoring and control systems starts in process development phases. Maintaining data integrity during scale up and technical transfer phases is crucial. Building quality features into data management systems is a recommended strategy.

	Pharmaceutical Technology
	eBook: Biologics and Sterile Drug Manufacturing, May 2020
	May 2020
	Pages: 4–9

	When referring to this article, please cite it as C. Challener, “Building Data Quality In Generates Quality Data Out,"

 Pharmaceutical Technology Biologics and Sterile Drug Manufacturing eBook 

Ensuring the quality of data in process monitoring and control systems starts in process development phases. 

Building Data Quality In Generates Quality Data Out

The concept of bioconjugation has been recognized for many decades, as has the specific idea of antibody-drug conjugates (ADCs). Technology for the production of ADCs did not advance sufficiently until the late 20th century. Even then, the first ADC approved by FDA-gemtuzumab ozogamicin (Mylotarg) from Pfizer in 2000-was voluntarily withdrawn in mid-2010 due to its association with the serious liver condition called veno-occlusive disease.

	Gemtuzumab ozogamicin was ultimately re-approved in 2017 at a lower recommended dose and schedule in a different patient population. There are now six additional FDA-approved ADCs on the market: brentuximab vedotin (Adcetris, Seattle Genetics/Takeda); (ado-) trastuzumab emtansine (Kadcyla, Genentech/Roche); inotuzumab ozogamicin (Besponsa, Pfizer); polatuzumab vedotin-piiq (Polivy, Genentech/Roche); Fam-trastuzumab deruxtecan-nxki (Enhertu, Daiichi Sankyo and AstraZeneca); and Enfortumab vedotin (Padcev, Astellas Pharma/Seattle Genetics), the latter of which received approval in February 2020. And, there are approximately 80 ADC candidates undergoing nearly 600 clinical trials (1).

	Why have more not already been approved? The issue of toxicity has been a challenge, as has the complexity of ADCs and the consequent manufacturing challenges.

	Finding the right target, protein, linker, and payload all belong to the discovery phase. “This phase is very challenging, as the correct definition of the drug is key to move it into the clinic successfully. ADCs represent a product class that is also highly complex and difficult to predict,” comments Iwan Bertholjotti, director of commercial development for bioconjugates with Lonza. It is, in fact, one of the key questions in the development of ADCs since the rules are still being written, as data from clinical trials are used to guide ADC technology improvements, according to Steve Coats, global project leader at AstraZeneca.

	Finding the right targets and crafting an effective molecule has proven to be much more difficult than many researchers had expected at the outset of ADC research, adds Justin Sweeley, senior technology manager, biologics at Novasep. “It was initially understood that finding a good target antigen for an ADC-based compound would require a target with rapid internalization once it had reached the cell,” he notes. “The result,” he says, “was that in many cases targets that were ineffective for monoclonal antibody (mAb) therapies because of rapid internalization became perfect targets for ADC therapies.”

	This picture became much more complex upon the addition of payloads to these mAb candidates, however. This issue can be seen most clearly in the fact that the clinical trial landscape includes well over 50 different payload candidates, but only seven have successfully made it into commercial production, according to Sweeley.

	“As a result, there has been a recent shift in the industry to recognize that when trying to predict ADC effectiveness, researchers must take into account the target epitope, the physical attributes of the payload on the mAb once conjugated, and also the effect of the payload mechanism of action on the specific kind of cancer being targeted,” Sweeley observes.

	AstraZeneca takes an empirical approach to target and payload selection, keeping the patient population top-of-mind, using data from clinical trial results and non-clinical data to help validate target and payload selection. “With potency being driven by the strength of the warhead, we optimize the therapeutic index of our molecules by selecting the most favorable drug-to-antibody ratio (DAR) in designing our ADCs,” Coats says. “We believe,” he adds, “that establishing target rationale and strategy early on are key to determining the right payload.”

	Site-specific conjugation is looked at as the second generation of ADC conjugation techniques. “The homogeneity of these molecules allows for much tighter control at both the manufacturing and characterization levels,” Sweeley explains. Better definition for an ADC means that its therapeutic index can be further improved, adds Bertholjotti.

	Additionally, the technology allowing for site-specific conjugation has evolved dramatically from the Thiomab concept piloted by Genentech to current techniques allowing site-specific conjugation with any native mAb, such as Synaffix’s glycogen modification techniques or Ajinomoto’s AJI-cap technology, Sweeley remarks. Many of the ADCs in preclinical and clinical stages are based on site-specific conjugation technology of one form or another, Bertholjotti adds.

	On the other hand, Sweeley notes that even though more site-selective ADCs are expected in the future, ADCs with stochastic conjugation can still be successful. Coats agrees that site-selective conjugation does not seem to demonstrate significant differences in terms of clinical activity and safety when compared to classic non-site-selective conjugation. In fact, the seven commercially approved ADCs are not based on site-specific conjugation.

	It is possible, according to Sweeley, that the lack of a commercially available site-specific conjugated molecule is just a result of the head start that stochastic conjugation has had, but it is also possible that simplicity in manufacturing and homogeneity in analytic testing methods doesn’t directly result in better outcomes for patients.

	Finding an ADC that is better than standard therapy or that provides a solution to an unmet need definitely represents a challenge, just as with other drugs based on different approaches, according to Bertholjotti. The linker chemistry is an important component of ADC and has a significant impact on performance.

	“Linker chemistry plays a critical role in 

 stability, but initially was assumed to have a passive role with the exception of either being stable or labile in the acidic cytosolic cellular environment,” observes Sweeley. More recently, however, he notes that there has been growing recognition that the linker plays an active role in conjugate hydrophobicity and therefore stability of the ADC as a whole.

	The technology, according to Coats, has advanced and matured during the past 20 years to a point where linker technology is stable and molecules in development demonstrate low levels of deconjugation in patients. Both protease cleavable and non-cleavable linkers are in development and on the market.

	Classic conjugation chemistry approaches include maleimide and N-hydroxysuccinamide-ester moieties (Seattle Genetics, Roche, and Pfizer). There are also various newer technologies for linkers, with some, Bertholjotti comments, at the proof-of-concept stage and others already in preclinical evaluation.

	An example pointed out by Sweeley is the use of non-natural amino acid-based click-chemistry (Ambrx and Sutro). “To my knowledge, these technologies have clearly simplified the conjugation process, but have not shown a clear improvement in product effectiveness in the clinic,” he states.

	ADCs are designed to be more selective than traditional chemotherapy agents. The mAb enables targeting of cancer (or other disease) cells where the payload is delivered with high selectivity, thus reducing the systemic toxicity in comparison with standard chemotherapeutic drugs.

	Unfortunately, undesired immune responses have presented a problem that has been difficult to overcome. These responses are largely due to the massive number of variables being examined and the relatively small number of clinical trials going on, according to Sweeley. “Many of the warheads being investigated for ADCs induce immunogenic cell death, which may enhance anti-tumor immunity,” adds Coats. He also observes that there are recent examples demonstrating clinical activity with a combination of an ADC with PD-1 inhibition.

	“In the process of taking any ADC through the approval process, it is necessary to look at the mAb, the linker, and the payload chemistries individually, the ADC as a whole, and the payload and linker residues after the ADC has been internalized and digested within the cell. The end result is that for each ADC trial, researchers must monitor all of the normal undesired immune responses that occur during any oncology trial, but then try to attribute the cause of any that are observed to one of the five different potential sources,” Sweeley explains.

	“Factoring these additional considerations into the normal variables of any trial, such as the specific cancer type, patient population, and level of pretreatments, etc., the picture becomes incredibly complex. Even after 20 years of clinical testing, the issue is still not fully understood,” he concludes.

	The primary issue affecting ADC approvals today, according to Sweeley, is the lower-than-expected therapeutic window of these therapies. “If the therapeutic window of ADCs were as large as people expected when ADCs first came to light, then many more approvals would already be on the market,” he asserts. This window has proven to be much more complicated than originally hoped, however, and therefore the clinical impact less significant than originally imagined.

	Here again, the complexity of ADCs themselves is the main problem. For instance, Sweeley notes that if an innovator company wants to test a new conjugation method, they might choose a mAb and payload pair that have already shown success in the clinic. Similarly, a mAb company with a new antigen target is likely to use an established conjugation approach (e.g., that for Adcetris) to lower their risk. “The best molecule, however,” Sweeley explains, “might be a combination of multiple new technologies that are too risky to investigate for a small company with a limited budget.”

	The supply chain for ADCs is highly complex as well. ADCs are unique in that their manufacture is an amalgamation of classical small-molecule production and traditional mAb manufacturing with the added complexity of highly potent drug manufacturing. “All three characteristics are complex on their own, and combining them brings the complexity to a level where it is no surprise that the vast majority of ADCs are manufactured by outsourcing partners,” Sweeley says.

	For the most part, he notes that innovator companies treat the manufacturing of an ADC as three separate processes:

		mAb manufacturing using traditional mAb techniques

		Payload synthesis using traditional highly potent synthesis techniques

		ADC conjugation using specialty contract manufacturing organizations capable of both working with both biologics and highly potent payloads.

	“Taken individually, all three of these steps are actually defined quite well and have been orchestrated successfully for a long time. But because ADC manufacturing requires all three to happen together, any delays or issues in one process will necessarily affect the other two. The reality, therefore, is that ADC supply-chain management is one of the most complex processes in the pharmaceutical industry and must be managed by an experienced team who can mitigate risks whenever possible,” observes Sweeley.

	Bertholjotti agrees. The supply chain for ADCs is complex and requires specialized companies to manage different steps in a safe way and with the necessary quality. “If the supply chain is not properly managed, delays and supply issues may arise. Therefore, compromises related to the supply chain can result in critical impacts on timelines and costs to bring a drug to market,” he asserts.

	FDA has shown willingness to work closely with sponsors to ensure that ADCs that truly benefit patients are brought to market expeditiously, says Coats. For example, he comments that AstraZeneca’s ADC Enhertu (developed in collaboration with Daiichi Sankyo) demonstrated significant benefit in a high unmet-need cancer population. FDA approved Enhertu four months prior to the FDA goal date for the treatment of adult patients with unresectable or metastatic HER2-positive breast cancer who have received two or more prior anti-HER2 based regimens in the metastatic setting. Enhertu is manufactured using site-selective conjugation and contains a cleavable linker technology that releases a warhead with bystander activity. It has also shown encouraging clinical activity in other HER2-driven cancers.

	Over the past decade, awareness of these issues has increased dramatically, leading to the development of more optimized molecules. Even so, Sweeley emphasizes that the complexity of the space means that it is still prudent to go slowly and only tackle one challenge at a time. “Progress is therefore slow, but continually happening. Each success creates a new platform for companies to reach out a little bit farther. And as the industry matures, the rate of success will increase, just as it has in every other area of pharmaceuticals,” he asserts.

	Novasep has strong expertise in highly potent compound synthesis and for the past three years has brought this expertise into the realm of ADC conjugation, Sweeley notes. “Our focus has always been on producing the highest quality materials by developing the simplest possible procedures and coupling them with world-class analytics. The end result of these efforts is a simplification of the payload synthesis and conjugation steps along the supply chain, enabling rapid development of the two most complicated parts of the manufacturing of ADCs,” he states.

	Since 2006, Lonza has been establishing a center of excellence for the development and manufacture of ADCs. Today the company offers an integrated solution, which helps to reduce the challenges presented by such a complex supply chain, according to Bertholjotti. “Integrated offerings such as that offered by Lonza represent a competitive advantage. They afford ADC developers with better predictability of timelines and costs, along with substantially reduced complexity and supply risk,” he says.

	AstraZeneca is developing novel ADCs and building a library of payloads using its antibody engineering expertise for site-specific conjugation and next-generation ADCs. “ADCs form one of AstraZeneca’s key oncology scientific platforms, along with immuno-oncology, DNA damage response, and tumor drivers and resistance mechanisms. Within these platforms, multiple technology and scientific options offer great potential to yield effective medicines for cancer patients,” Coats says.

	As more ADCs are approved commercially, Sweeley believes a roadmap will be established for other companies to follow, leading to more success in the near future. “In the last 12 months alone, the number of approved ADCs on the market has more than doubled, and I would expect that this track record will be followed by a sizable increase in the amount of research being put into the molecule discovery and preclinical trial stage,” he observes. “With the healthy increase in candidates being brought into the preclinical stage, it is only a matter of time until some of those candidates make it through the rigorous demands of clinical testing and reach the market in the not-so-distant future,” Sweeley concludes.

	The increased number of ADC candidates in the pipeline in combination with ever improving knowledge and the further development of new conjugation technologies will result in an increased rate of approvals, agrees Bertholjotti. Lonza expects that the number of ADC molecules will in fact rise at a 10% compound annual growth rate until 2029.

Vol. 44, No. 5
	April 2020
	Pages: 22–27

	When referring to this article, please cite it as C. Challener, “Formulating an ADC Development Solution," 

Many antibody-drug conjugate therapies are in the pipeline; however, only a handful have been approved. What are the bottlenecks? 