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Editor of Pharmaceutical Technology Europe
The right partner can help companies overcome key formulation challenges for biologic drugs.
Biologic drugs are entering the development pipeline with increasing frequency for the treatment of complex diseases, such as cancer, autoimmune disorders, and infectious diseases. However, formulating a biologic drug substance that is optimally effective and safe, while also keeping cost and time for development under control, is no easy task.
“Due to the complexity and fragility of biologic active compounds, several challenges exist in formulation development,” explains Anand Khedkar, senior vice-president R&D, Stelis Biopharma. “First, stability and preservation present a significant challenge as the API of a biologic is more unstable than in small-molecule drugs. In addition, protein-based therapeutics have the potential to cause an immunogenic response leading to adverse events that are often not discovered until after the medicine is on the market. Lastly, most of these medicines must be developed in a liquid form for compatibility with subcutaneous, intramuscular, or intravenous administration.”
“Biologic molecules are large and inherently more heterogeneous when compared to small molecules,” says Aaron Frimel, senior scientist/group lead, Pharma Services, Thermo Fisher Scientific. “This translates to increased opportunity to generate degradants due to environmental stresses.”
Gary Watts, senior scientist and formulation lead—Analytics Group, Abzena, adds that many different degradations pathways, such as aggregation, fragmentation, deamidation, and oxidation, can occur when formulating biologics. “Typically, more than one of these pathways occur, and all need to be addressed within the formulation evaluation process to ensure the stability of the biologic drug candidates,” he states.
Sensitivity of biological molecules to the microenvironment can be challenging, particularly as changes can occur during various manufacturing procedures, asserts Khedkar. “Additionally, biologic molecules are sensitive to temperature, shear, exposure
to oxygen, air-water interface, and many other factors,” he adds. “It’s vital to bear all of these factors in mind during formulation to ensure that exposure to any unfavorable environment is minimized.”
“Any changes to the process can yield changes to the analytical and stability profile of the molecule,” confirms Frimel. “It is, therefore, not only important that an ideal formulation be selected, but that the design space of the specification range is robust.”
All biologics, standard or novel, present unique developmental challenges, such as solubility and viscosity issues, Watts continues. “For early screening, a wide scope of formulations needs to be tested to find optimal conditions that manage the concentration requirements for future storage and dosing purposes,” he says. “Capabilities to explore liquid and lyophilized forms allow flexibility to formulate challenging molecules.”
Formulation alignment with early manufacturing stages is important, according to Watts, to ensure the integrity of the biologic can be maintained throughout purification and filtration. “A particular consideration is that the formulation buffer is compatible with the manufacturing process,” he comments. “The ideal final dosage form is a liquid, which is preferred to a lyophilized form at this stage as this can reduce manufacturing costs and ultimately allows for easier administration to the patient. However, some biologics may not be sufficiently stable in a liquid form, and thus a lyophilized product will have to be considered.”
Once a company has decided to pursue early phase development with a contract development and manufacturing organization (CDMO), a key driver for the project becomes the timeline, which is critical to maintaining project viability and investor interest, specifies Frimel. “This means that an acceptable formulation must be developed from material generated from, ideally, a final clone and finalized before ultrafiltration/diafiltration development by a process development team,” he says.
“If the investigational new drug application has to be filed faster and time is critical, then other sources of material for formulation development have to be considered,” asserts Elena Gontarz, manager of Scientific and Technical Affairs, Pharma Services, Thermo Fisher Scientific. It is possible to use material generated from one of the leading clones or from mini pools, in cases of immunoglobulin G subclasses (IgG1/IgG4), Gontarz explains.
“Because first to market is such a competitive place, a formulation screening approach can be taken for IgG1/IgG4, where an array of predefined formulations is screened to finalize a formulation that works,” Gontarz says. “This is a riskier approach that is appropriate for early-stage development, where money and time are of an essence. Although taking this approach will prompt additional robustness work to be done before Phase III clinical studies and commercialization.”
Sometimes, companies seek to redevelop a formulation prior to Phase III clinical studies and commercialization, either to scale up the concentration for subcutaneous injection formats, or to simply find a more optimal or robust formulation, notes Frimel. “The timing of when these late-phase studies will be pursued is a balancing act between client finances, confidence in project viability, and the ability to allow the time to and execute a study that is conservative enough to yield the favorable results,” he states.
“Any final formulation must also be compatible with a variety of drug delivery systems, and issues such as leachables, extractables, and surface adsorption need to be mitigated for, as appropriate,” Watts adds.
Although similar formulation parameters are evaluated for vaccines as are for biologics, vaccines can be more complex in terms of the antigenic composition and include extra components such as adjuvants, explains Watts. “All components need to be characterized and compatible to ensure that the final formulation optimally supports the stability and activity of the antigen and adjuvant components,” he notes.
There are many different types of vaccines and each one comes with its own set of challenges, continues Khedkar. “For example, if the vaccine is a peptide vaccine in a liquid formulation, the formulation development mimics any other peptide/protein formulation, and the transport of the drug substance, manufacturing process, storage, and distribution of final vaccine can be expected to be very similar to most biologic products,” he says.
“Thermal stability of vaccines can be approached in a similar way to biologics, with temperature excursions needing to be carefully considered,” comments Watts. “For instance, a cold chain may be required for shipment and storage; however, if frozen during transit, the antigens could be degraded and lose efficacy. [Whereas], if stability at ambient temperature is critical, lyophilization can be considered a more viable format.”
Watts adds that it is also imperative to understand the interactions between the antigens and the adjuvant, such as aluminum solutions that are commonly used. Investigation into the compatibility of the vaccine with the selected adjuvant is required, as well as any potential impact there may be on stability, he stresses.
Concerning many of the vaccines in development for COVID-19, Christy Eatmon, global subject matter expert, Sterile Drug Products, Thermo Fisher Scientific, specifies that, they utilize RNA technology, in addition to other platform vaccine technologies and DNA plasmids, are comprised of lipid nanoparticles, and therefore, are delivered as dispersions. “Biologics are typically true solutions and don’t have the same manufacturing and processing challenges as a dispersion,” she says.
In cases of RNA vaccines, contamination of the RNAase enzyme is detrimental to the product’s stability, concurs Khedkar. “Delivery of mRNA and DNA vaccines is a challenge compared to routine vaccines,” he continues. “Formulation to support the delivery systems to minimize the reactions at the administration site, and also to maintain the effectiveness post-administration, plays a significant role in formulation development.”
Carrier molecules may be used to resolve delivery challenges of RNA vaccines, or traditional/novel adjuvants can be used to augment the immune response of the RNA vaccine, Khedkar adds. “RNA’s inherent immunogenicity also needs to be modulated,” he says. “Moreover, RNA degrades very quickly once injected due to normal cellular processes and may not provide adequate exposure to ensure the desired therapeutic effect. With this in mind it is critical that formulation development takes care of stabilization of the RNA, during circulation and during distribution.”
There are numerous new technologies available to drug developers that aid with stability and can protect the biologic drug substance, such as encapsulation and the application of buffers, confirms Khedkar. “Many companies are also working on ways to adjust the pH of drug solutions to improve solubility; however, this often destabilizes the product,” he says. “Introduction of a water-miscible solvent into the product, can suppress ionization, reduce the extreme pH required to achieve this solubility, and reduce the water activity by reducing the polarity of the solvent.”
“In addition,” Khedkar adds, “techniques to facilitate moisture control and promote microbial growth and catalyst reactions are growing in popularity, as well as the use of specific vessels that remove light from the reaction, or nitrogen sparging, to avoid oxidation.”
According to Watts, the testing of stability must be included at different pH levels across a range of buffers, with observation of increasing or decreasing ionic strength trends and any effects of the addition of surfactants, during initial screening. “This technique would highlight any inherent preferences and would also indicate whether the use of traditional excipients would suffice, or whether a more tailored formulation is needed,” he says. “If a biologic was found to have a high propensity for deamidation, for example, this could be mitigated by pH optimization, increase in viscosity, or altering of the dielectric constant of the media. Also, a high tendency towards aggregation could be reduced by the use of a surfactant.”
Eatmon adds that protection of the product from microbial ingress is possible through the use of single-use disposables with closed transfer systems, and that the route of administration can sometimes dictate a target set of formulation components, such as the use of arginine in high concentration formulations to lower viscosity. “Excipients and buffer selection are the key to protect the molecule from degradation and other stability issues,” she asserts.
“At present, there are a number of alternative excipients that are being used by formulation groups,” continues Watts, “most notably, cyclodextrins with their capacity to solubilize hydrophobic molecules, polysaccharides with their complex-forming and solubilizing properties, and nanoparticles on account of their observed positive effects in increasing bioavailability and their potential to assist targeting the drug to as specific location within the body.”
“For biologics and vaccines, the role of the excipient is to enhance solubility, enhance processing, and ensure shelf-life stability of the active,” Khedkar specifies. “In a biologic, however, they are also used to control pH and tonicity, maintain preferred stable conformation for proteins or vaccines, including exposure of the functional epitopes, and prevent aggregation or degradation of the active, as well as perform several other functions, such as acting as bulking agents, antioxidants, or preservatives.”
Adjuvants are another class of excipients that are used for vaccines, Khedkar notes. “Adjuvants are defined as substances that enhance the pharmacological effect of a drug or increase the ability of an antigen to stimulate the immune system,” he says.
Due to the unstable nature of biologics and vaccines, a variety of excipients are usually required to stabilize the active ingredients for processing and storage, Khedkar continues. “Selection and use of the appropriate excipients enable development of novel therapies and robust pharmaceutical products,” he states. “Biological drug products, however, do contain fewer inactive ingredients than small-molecule medicines.”
Biologics are mostly delivered systemically or subcutaneously, as a result of the size of the molecules, leading to the use of carbohydrates (mannitol) or polyols as cryoprotectors (for lyophilization) and stability enhancers (for high viscous formulations), respectively, Khedkar explains. “There are several options that are available for proteins and peptides; however, as the technology is evolving, along with the type of drug substance, there is a need to research new excipients and adjuvants,” he says. “Especially, in case of RNA/DNA as the therapeutic agents, the choice of excipients is limited, and the capacity available for few of the excipients (e.g., liposomes or adjuvants) is limited.”
“While the number of approved excipients is small, combinations of excipients may be used in some cases,” asserts Eatmon. “A design-of-experiment approach during formulation development can be executed to determine the best matrix for the molecule and to ensure long-term stability.”
For Watts, the limitation in excipient availability is ultimately due to there being a lack of excipients considered safe for use by the regulatory authorities. “Steps taken by industry towards the approval of novel excipients involves rigorous toxicological testing before they can be deemed safe for use, which is time-consuming and costly and, therefore, poses a significant hurdle,” he adds. “Excipient development could be expedited through subsidized incentives to provide for regulatory guidance and support as well as developers openly sharing information on their experience.”
“When considering a subcutaneous (SC) formulation, particular attention needs to be paid to excipients that aid drug dispersion once administered as well as in-vivo stability,” Watts says. “These [excipients] could be ones that prevent precipitation and are more closely matched to physiological conditions.”
Injection pain is another consideration when approaching an SC formulation, Watts notes, which can be reduced by matching the formulation tonicity with the physiological tonicity. “Excipients known to cause ISRs [injection site reactions] (such as inflammation/redness/swelling) should be avoided if possible,” he asserts. “A formulation with a low viscosity is preferable to enable quick administration without undue force applied.”
Delivering biologics subcutaneously requires small volumes and, hence, higher drug concentrations, confirms Khedkar. “High drug concentration can lead to aggregation, which interferes with protein absorption, can increase immunogenicity, and also cause safety concerns due to the higher doses required,” he says. “There are several approaches that can be taken to overcome these challenges; for example, stabilizers to avoid aggregation and denaturing, introducing salts to increase stability, and the use of surfactant to avoid protein–protein interaction, among others.”
“The trade-off between viscosity and concentration is inherent to scaling up concentration to meet the ≤ 1 mL requirement for autoinjector compatibility,” adds Frimel. “Moderate viscosity can be desired as it reduces pain associated with injection. Too high of viscosity has the potential to cause issues with shear stress.”
Achieving a balance between desired viscosity and excipient compatibility is vital, Frimel stresses. He states that it is worthwhile to employ a well-designed syringeability study for subcutaneous injection so that product stability during use and patient comfort are assured.
“A final thought,” continues Watts, “must be paid to device compatibility in that interactions between excipients and components of the device should be avoided as these can lead to degradation of the device and reduced shelf life of the product, and, in worst cases, an immunogenic response in patients.”
From the perspective of the sponsor company, an outsourcing partner will provide access to solutions that will aid in overcoming challenges without requiring investment in new infrastructure, Khedkar reveals. “The right outsourcing partner can bring the expertise and experience required to develop the formulations, as per regulatory expectations,” he says. “It [the outsourcing partner] can also bring the necessary manpower to expedite the work and ultimately avoid capex expenditure on internal resource and infrastructure.”
In concurrence, Watts agrees that an outsourcing partner should offer services that the client would not necessarily have access to, including deep industry experience and a strong track record of success. “[Provision of these services] would be achieved through strong links with other multidisciplinary groups during product development, starting from discovery right through to lead candidate selection,” he notes. “Added bonuses would include access to process development and good manufacturing practice manufacture.”
Furthermore, CDMOs can advise new late-stage clients on the best approach for formulation prior to Phase III clinical studies, Gontarz continues. And, she adds, CDMOs can help guide their clients as to which formulation related characterization studies are required to ensure a successful biologics license application.
Outsourcing has the potential to be transformative to business models, Khedkar asserts. “Each individual piece of discovery, development, and manufacturing can be effectively addressed by experts in the field and this combined with effective project management can really expedite project timelines. It can also help to free up capital and help in make the companies nimble,” he summarizes. “The key is to find the right set of partners and together increase the chances of project success.”
Felicity Thomas is the European editor for Pharmaceutical Technology Group.
Vol. 45, No. 1
When referring to this article, please cite it as F. Thomas, “Overcoming Biologic Drug Formulation Hurdles,” Pharmaceutical Technology 45 (1) 2021.