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Critical considerations in the formulation development of parenteral biologic drugs
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Critical considerations in the formulation development of parenteral biologic drugs Q3
Bilikallahalli K. Muralidhara1 and Marcus Wong2
1 Q4 2 Technical Operations, Acceleron Pharma, Cambridge, MA 02139, USA Technical Operations, Allakos Inc., Redwood City, CA 94065, USA
Biopharmaceuticals, unlike chemically synthesized small-molecule drugs, are marginally stable, with most of them requiring 3D structures to retain their activity and/or potency. This implies challenges to formulate these molecules for a shelf life >2 y of and also to minimize the cost of goods for manufacturing. Patient compliance has become a key consideration in the design and development of suitable dosage forms in the modernized world. Thus, here we describe different classes of biological therapeutic, with an emphasis on molecular properties, formulation challenges, and development strategies. We also present statistics on the different classes of approved biologic drugs and dosage forms.
Introduction Q6 Since the advent of the first recombinant therapeutic protein (i.e.,
insulin in 1982), there has been a major shift toward biologic drugs
Q7 within the pharmaceutical industry. Approximately two decades
ago, biologics comprised <1% of the pharmaceutical portfolio, but this has increased to nearly 20% currently and is expected to continue to grow (Fig. 1). The popularity and success of biologics has resulted mainly from their roles in disease modification and targeted treatment compared with conventional, chemically synthesized small-molecule drugs. While maximizing the target specificity, biologics often minimize the potential off-target toxicities, enhancing the ability of the drug to alter and terminate a disease state [1]. Such distinct advantages have established biologics as a major pillar of the pharmaceutical industry in a relatively short period of time and have added tremendous value to the global healthcare system by providing new treatment opportunities and bringing hope to millions of patients worldwide. Despite their inherent superiority from the therapeutic standpoint, biologics often introduce significant development challenges because of their large size, high structural complexity, and marginal stability. Their high propensity to undergo physical and chemical degradation, which directly impacts their structure and function, can jeopardize the utility of biologics as efficacious
Corresponding author: Muralidhara, B.K. ([email protected]) 1359-6446/ã 2020 Published by Elsevier Ltd. https://doi.org/10.1016/j.drudis.2019.12.011
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and life-saving therapeutics [2–6]. The development of patient friendly dosage forms with the goal of enhancing and maintaining the stability and efficacy of biologics over their intended shelf life (2–3 years) is key to ensuring the successful transformation of lead drug candidates into widely accessible and commercially viable products. A well-designed formulation strategy, while maximizing the ‘usability’ of a drug by enhancing its stability and maintaining its efficacy, should improve the safety, convenience, and patient compliance. The modality of the biologic (e.g., proteins, nucleic acids, and cells), stability or lack thereof, intended dosage configuration, and designated route of administration in combination with device strategies, as applicable, are some of the more common considerations for ensuring the development of a successful drug product [7]. Here, we provide a high-level overview of these considerations and their corresponding challenges within the context of formulation strategy and design space.
Common considerations in the formulation development of biologics Molecular modality Biological therapeutics cover a range of molecular modalities. Proteins have revolutionized the pharmaceutical industry following conventional small-molecule therapeutics and now represent the largest fraction of approved biologic drugs (74%). Difficultto-treat diseases, such as oncology and infectious diseases, are now
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Total (approved products, worldwide)
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5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0 Through 1995
Through 1998
Through 2005
Small molecule
Through 2008
As of November 2015
Biologic
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FIGURE 1
Total number of approved drugs over the past 20 years by global regulatory agencies. Biologic drugs grew significantly, especially over the past 7 years because of decreased attrition rates and improved production technologies. The data were compiled from various sources, including www.pharmacircle.com and www. citeline.com, using a 2016 year cut-off.
979 No. of surveyed biologies biologies
3.4%
Cellular therapies
0.8%
Nucleic acids
74.0%
7.4%
14.3%
Proteins
Peptides
Virus particles Drug Discovery Today
FIGURE 2
Proteins as therapeutic modalities constitute the majority of approved biologics. A large number of cell-based therapies under regenerative medicine, peptides as conjugates, and virus particles for nonvaccine use are also in late-stage clinical development.
being targeted using natural biologics (cells, genes, and viruses) that have multiple modes of interaction (Fig. 2). Among protein therapeutics, growth factors and monoclonal antibodies (mAbs) constitute the largest portion. Hormones, interferons, cytokines, coagulation factors, and enzymes comprise some of the other main classes, providing a largely diverse class of protein therapeutics (Fig. 3). In terms of molecular constructs, these can be individual proteins, fusion and conjugated proteins, bispecific antibodies, and so on. For the purpose of the discussion herein, peptides and/ or peptide conjugates (8% of the biologics portfolio, Fig. 2) are categorized as protein therapeutics because of their similar amino acid-based structural building blocks. In general, a common salient feature of protein therapeutics is their large and complex 3D structure, requiring proper folding and conformational stability for efficient functionality. The difference in the free energy between the folded and unfolded states of proteins is typically in the range of 5–20 kCal/mol, which is equivalent to a few hydrogen bonds or ion pairs [8–10]. Challenges to developing these fragile macromolecules as stable therapeutics drugs are detailed herein. Another class of biologics includes nucleic acids (e.g., DNA, mRNA, and synthetic oligonucleotides) and, although currently constituting only 1% of the commercial biopharmaceutical landscape (Fig. 3), they represent one of the fast-growing classes 2
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of biologics and are currently being studied in a large number of ongoing clinical programs [11]. Such interest in nucleic acids stems from their ability to target and bind gene sequences and inhibit disease gene expression and transcription, offering distinct advantages in disease modification and treatment by attacking conventionally out-of-reach targets using proteins and peptides. A salient liability feature of nucleic acids is their high susceptibility to in vivo degradation from nuclease attacks, which often require chemical modifications of their backbone to increase their stability, extend their circulation half-life, and increase their transcription and translation efficiency. Such modifications include, but are not limited to, a 20 -methylene bridge to sugar backbone, 30 methylation, and replacement of oxygen by sulfur in the phosphodiester bond (phosphorothioate). Finally, the latest and fastest growing class of biologics, with potential advantages over both small- and large-molecule therapies, is the category of cell and gene-based therapeutics (e.g., gene delivery vectors/viruses, transgenic cells, and stem cells), comprising 3–5% of the biopharmaceutical portfolio. A salient feature of cells includes their extremely sensitive architecture, pleomorphic shape, and surface-expressed antigens with a diverse chemical nature (e.g., lipids, proteins, and carbohydrate chains). From the standpoint of biology, cell and gene therapies offer distinct
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Growth factors Antibodies (mAb, non-mAb, biosimilars) Interferon (biosimilar, recombinant) Interleukins Hormones
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Blood fractions Enzymes Fusion proteins Antibody–drug conjugates 0
50
100
150
200
No. of products approved by a Governing Agency Drug Discovery Today
FIGURE 3
Agency-approved protein drugs are further classified according to their mode of functionality. Therapeutics based on novel and unnatural constructs, such as antibody–drug conjugates (ADCs) and fusion proteins with multiple modes of interaction, have gained traction in recent years. Abbreviation: mAb, monoclonal antibodies.
advantages in information processing and targeting compared with small and large molecules and sometime offer cure. These have broadened their applications from conventional tissue regeneration and/or repair and vaccines to other therapeutic areas, such as infectious diseases, autoimmunity, cancer immunotherapy, and metabolic diseases. Currently, industry is working towards reducing the cost of their development and manufacturing to make them more affordable for patients.
Stability In general, biologics, regardless of the modality, are subject to a variety of environmental stresses throughout their product life cycle [12], including suboptimal solution conditions during purification, freeze-thaw and mechanical stresses (e.g., agitation and shear) during fill-finish and manufacturing, temperature
excursions and light exposure during transportation and storage, and interaction with the surfaces of a variety of container-closure systems. In combination with their large size, high structural complexity, compositional variability, and inherent marginal stability, biologics can undergo a variety of different physical and chemical degradations, leading to loss of their stability and activity [12–14]. In brief, there can be physical degradation from conformational (e.g., unfolding), colloidal (e.g., aggregation and particulate formation), interfacial (e.g., adsorption and degradation at interfaces), or morphological (e.g., disruption of epitope presentation on cell surfaces) instabilities, whereas chemical degradation involves modifications of the covalent bonds and can include oxidation (e.g., tryptophan and methionine in proteins, and guanine in nucleic acids), deamidation (e.g., Asn and Gln in proteins, and cytosine in nucleic acids), isomerization (e.g., Asp
TABLE 1
Q1 A generic toolbox for the formulation of different modalities of biologic drugs Formulation agents/ingredients
Purpose of action
Examples
Buffers Salts
pH modulator Tonicifiers Stabilizers/destabilizers (Hofmeister series) Surface adsorption inhibitors Interfacial stabilizers Inhibitors of microbial growth (multidose formulations) Free radical scavengers Inhibitors of metal-induced degradation Tonicifiers Cryoprotectants Stabilizers (preferential hydration) Stabilizers Antioxidants Tonicifiers Rheology modulators Sustained release/extended half-life Surface adsorption inhibitor Bulking agents Condensing agents for nucleic acids Viscosity modifiers, cofactors, cell stabilizers
Citrate, acetate, histidine, phosphate, tris Sodium chloride, potassium chloride
Surfactants Preservatives Antioxidants/chelators Osmolytes/sugars
L-amino acids
Bio-/polymers
Polycations Metal ions
Polysorbate-20, pluronic-188 Phenol, m-cresol EDTA, DTPA, methionine, ascorbic acid Sucrose, trehalose, sorbitol, TMAO
Arginine, glycine, proline, lysine, methionine
HSA, PLGA, PEG, cyclodextrins
Cationic lipids, spermidine, tetra-arginine Calcium, magnesium, manganese
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in proteins), disulfide bond shuffling (e.g., strand separation and desulfurization in DNA and mRNA), and clipping of functional groups and/or linkers (e.g., payload deconjugation in ADCs), among others. The most common chemical liabilities are often mitigated via genetic engineering efforts during the discovery stage. The mechanisms of physical and chemical degradation and the variety of molecular and environmental factors impacting the stability of biologics have been extensively reviewed elsewhere. [15]. Herein, only a high-level risk-based analysis of the main degradation pathways according to the modality of the biologic is provided to aid discussions on formulation development (Table 1). In addition, computational modeling and theoretical predictions of potential liabilities (e.g., aggregation and selected chemical degradation hotspots) can further help the formulation design space [16]. Selection and optimization of appropriate formulation components that protect the biologics against potential physical and chemical degradation can be rationally conducted according to the identified routes of degradation [17,18]. Table 2 classifies some of the more common formulation excipients and their intended modes of action that are used to stabilize a range of biological modalities. These excipients should have a proper safety profile and be approved for parenteral use. Other potential considerations, such as the compatibility of the selected formulations with the intended dosage form configuration, the route of administration, and the designated device component, as applicable, might also have roles in formulation selection and optimization strategies, as discussed in the following sections. Another important consideration when utilizing pharmaceutical additives is their purity and stability profile. Impurities within pharmaceutical excipients, such as trace metal ions, hydroperoxides, and bacterial endotoxins, have been observed and can impact the stability and potency of the biologic. Regulatory guidelines often outline the type of analytical data as well as vendor manufacturing information required for pharmaceutical excipients that are intended for use in the formulation of biologics to meet quality standards [19].
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Despite commonalities in the mechanisms of physical and chemical degradation as well as the stabilizing effect of formulation additives, the development of a generalized universal approach to stabilize all biologics has proven unsuccessful thus far. One example includes the formulation of nucleic acids, in which their large size, highly charged nature, and high susceptibility to nuclease degradation often result in their poor uptake and suboptimal in vivo stability, demanding delivery-focused formulation and stabilization strategies that facilitate the transfection efficiency of the molecule [20]. Such strategies can include nucleic acid condensation using polycationic agents (e.g., lipids, polyamino acids, and polymers), conjugation (e.g., cholesterol), and encapsulation (e.g., liposomes, lipoplex, chitosan, and dendrimers) methods [21]. In terms of chemical stability, cytosines can spontaneously deamidate into uracil and the process is >100-fold faster in single-stranded nucleic acids. Sequence-independent depurination is also observed at higher temperatures and above neutral pH. Reactive metals, such as Hg, Zn, Co, and Ni, are known to form metal-base pairs by chelating between strands through connecting two adenines, cytosines, or mixtures thereof, thereby destabilizing and/or initializing strand separation and/or breakage [22,23]. Another example includes antibody–drug conjugates (ADCs), a hybrid of small and large molecules, with wide therapeutic applications, particularly as oncolytic agents [24,25]. ADCs combine the superior target specificity of mAbs and target-killing ability of small cytotoxic drugs (known as payloads), which are covalently conjugated to mAbs via a linker [26]. In addition to the formulation challenges associated with mAbs, the physicochemical properties of the payloads and linkers, conjugation chemistry, drug: antibody ratio, and location of the conjugation sites can all impact the overall conformational, colloidal, and in vivo stability of the ADC, which introduces unique challenges to formulation [26–29]. Finally, cell and gene-based therapies offer unique formulation development challenges because of various compounding factors, including multiple reporter genes, multiple and complex antigen epitopes, membrane fluidity and permeability, and vector heterogeneity, all of which have key roles in the stability and function of
TABLE 2
Associated formulation development risks for the most common macromolecular modalitiesa
a The risk classification of low (green), medium (yellow), and high (red) is a qualitative interpretation of the degree of formulation development challenges recognized based on authors’ experience and literature data. The list of modalities and their corresponding degradations represents a collection of the most common categories currently in biopharmaceutical development. In vitro degradations refer to those observed during drug product development, storage, and distribution life cycle. The in vivo pathways occur post administration and directly reflect the serum stability and half-life of the molecule. b* , desulfurization; **, adhesion.
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Route of administration Other parenteral 5.9%
Intramuscular 18.8%
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(a)
Intravenous 42.7% Subcutaneous 32.6%
Drug product presentation
(b)
Solid dose (other) 19.0% Liquid (not dried) 51.5% Lyophilized 29.5%
Drug Discovery Today
FIGURE 4
Two major considerations in the formulation and development of biological drugs. (a) The route of administration is mainly driven by mechanism of action of the drug and patient convenience. (b) Liquid dosage forms are the preferred configuration because of the low cost of manufacturing and ease of administration. Nonliquid dosage forms (lyophilized, spray dried, or frozen) are dictated by, but not limited to, product instability, scale of manufacturing, transportation, and storage concerns.
the cells and/or viruses [30]. Although detailed mechanisms of instability in cell-based therapeutics are generally not well understood, the substantial loss of transplanted cells has been observed upon delivery [31]. Extreme sensitivity and apoptosis to freeze-thaw and mechanical shear have been well documented during the thawing of frozen cells and their subsequent administering using various needle sizes and flow rates [31,32]. Specific classes of additive, such as polyhydric alcohols (e.g., glycerol), sugars (e.g., trehalose), and carrier proteins (e.g., gelatin and human serum albumin; HSA), have been proven effective cryoprotectants, although their mechanisms of stabilization of cells are not well understood. Cryoconcentration cells and excipients have been shown to occur for viruses during freezing and cell adhesion and/or agglomeration during diafiltration potentially impacting the viability and/or integrity of surface antigens [33]. Viscus carriers (e.g., sodium alginate or PEGs) and carrier proteins (e.g., gelatin and HSA) have been used to
overcome shear stress during administration of low cell density (104–106) dosage forms [31]. As the field evolves further, an industry consortium working with regulatory agencies would be useful to put together guidelines to accelerate the development and manufacturing of cell and gene therapy products.
Dosage form configuration The designation of the optimal dosage form configuration of a biological drug product depends on a variety of factors, including the efficacy, intended dose, dosage regimen, stability of the macromolecule, material compatibility, designated therapeutic area, route of administration, patient compliance, and cost-of-goods analysis from a commercialization perspective. Liquid and lyophilized formulations constitute the most common dosage form configurations for biologics development, comprising 52% and 30% of all biologic dosage forms, respectively (Fig. 4). Frozen www.drugdiscoverytoday.com
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formulations, although not common for protein and nucleic acid drug products, have wide utility in the formulation of cell therapeutics, and the three are discussed herein. Spray-dried [34] and protein microcrystal dosage forms are being developed to reduce developmental costs and to achieve high concentration doses for subcutaneous delivery, respectively. Liquid dosage forms, when feasible, are the most preferred because they provide the highest level of compliance for clinicians and patients by simplifying the dose preparation procedures (e.g., elimination of reconstitution or thawing steps with lyophilized or frozen forms). In addition, they allow self or at-home administration with prefilled syringes and auto-injectors, particularly for the treatment of chronic diseases that require frequent dosing (e.g., diabetes and arthritis). Despite such advantages, there are significant challenges to their development, including the higher instability and risks involving a variety of physical and chemical forms of degradation, greater need for cold-chain storage, and more stringent transportation criteria [35–37]. In addition, in cases where high-concentration liquid formulations are needed for subcutaneous delivery because of injection volume restrictions (e.g., mAb formulations in prefilled syringes at >100 mg/ml and <1.5 ml), issues such as induced viscosity, phase separation, opalescence, or self-association can be observed from molecular crowding effects. This introduces significant processing, formulation, and delivery challenges, which impact the product quality as well as patient comfort and convenience. When the shelf-life stability, handling, or distribution become development risks (e.g., in the case of ADCs and nucleic acids) for liquid-dosage forms, lyophilized formulations present a viable alternative by improving the formulation stability based on a general phenomenon of reduced molecular mobility and degradation kinetics in the dried state [38,39]. Recent advances in lyophilization technologies, including ‘SMART’ freeze-drying based on manometric temperature measurements (MTM) and process analytical technologies (PAT) to monitor critical freeze-drying process parameters, have paved the way for more systematic and less empirically designed lyophilization processes, enhancing the freeze-drying capabilities of biologics [39,40]. Despite such advantages, from a commercial perspective, lyophilized formulations can introduce certain challenges because of the more complex dosing preparation procedures with additional reconstitution steps and also the limitations of device usability in self and/or at home set-ups. Incompatibility of certain formulation additives (e.g., salts) with the freeze-drying process can further restrain the formulation space design. Lyophilization process also adds to costof-goods, which might be reflected in the market pricing [41,42]. In addition to conventional freeze-drying, referred to as lyophilization, alternative approaches, such as spray freeze-drying, have also been utilized in the formulation of biologics to, for example, generate particles of a specific size and morphology for pulmonary delivery of aerosol powders deep into the lungs (i.e., inhaled insulin or interferons). In such cases, formulation optimization efforts via the use of appropriate excipients, such as sugars, surfactants, and, in some cases, polymeric compounds, have to be implemented to avoid macromolecular denaturation and aggregation, which are common during these processes [43]. Frozen formulations offer another alternative to their liquid counterparts and, although less desirable in the field of protein 6
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therapeutics, they are widely utilized in the formulation of cell therapeutics for which achieving liquid or lyophilized shelf-life stability is currently a significant challenge. Although they provide enhanced long-term stability compared with their liquid counterparts, the development of frozen formulations can present with unique challenges, including denaturation at the ice–water interfaces during freeze-thaw [44,45], potential buffer and/or excipient crystallization [46],and precipitation upon freezing [47], resulting in aggregation or pH shifts that might impact product quality and efficacy [48]. Additionally, heterogeneous freezing profiles, particularly at large scales because of cryoconcentration effects, can be a major issue for cell therapeutic formulations, especially given their high sensitivity to osmotic stress [49]. The higher costs associated with storage, shipping, and handling of frozen formulations can further complicate their utility from the cost of goods and compliance perspective [14].
Route of administration Biologics are often difficult to deliver via nonparenteral routes (e. g., oral) of administration because of issues such as enzymatic degradation, poor permeation, variable pharmacokinetics/pharmacodynamics (PK/PD) profiles, and low bioavailability [50]. Therefore, substantial attention has been paid to the parenteral routes of administration, which currently comprise 85% of all biological deliveries (Figure 5). There are a few recent clinical Q8 studies advancing the intratumoral delivery of oncology drugs. Within the parenteral portfolio, intravenous and subcutaneous administrations, at 37% and 28%, respectively, constitute the most common categories and, therefore, are the main focus of the discussions herein. The regulatory guidelines require demonstration of the compatibility of the biological drug product with the intended route of administration and associated material components to ensure patient safety and compliance. In recent years, the study of ‘human factors’ has been mandated to evaluate the advantages and compliance with patients where a device is implemented to deliver a drug. These are called combination products. ICH-M4Q Common Technical Document, Quality Section 3.2. P.2.6 states that ‘the compatibility of the drug product with reconstitution diluents or dosage devices should be addressed to provide appropriate and supportive information for the labeling.’ A set of formulation studies, often referred to as ‘clinical compatibility,’ is then executed to support drug product compatibility claims and must be included in regulatory submissions, such as the Investigational New Drug (IND) and Biologics License Application (BLA). Depending on the route of administration, a unique set of incompatibility issues can arise. For example, in intravenous (IV) delivery, incompatibility of the drug product (formulation) with the construction materials used in the bag or components of the infusion sets (e.g., polyvinylchloride or polyolefin) as well as with the bag diluent (e.g., saline or dextrose) has been observed to impact the stability and activity of the drug. Common incompatibility issues often include adsorption of the active pharmaceutical ingredient (API) to the surface of the IV bags and infusion sets as well as the formation of aggregates, subvisible, and visible particulates [51], which are of concern from the product immunogenicity perspective. Although the former can often be mitigated via the use of an optimal surfactant type and concentration (in some
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importantly, the choice of the delivery system involving excipients and delivery mechanisms (i.e., electroporation), impacting the targeting and transfection efficiency [58,59]. Although systemic delivery mainly in the form of intravenous administration is used in some cases, susceptibility to nuclease-induced degradation as well as high clearance rates often demand local delivery in the form of intratumoral, intraocular, and intravaginal routes of administration. Some of the unique formulation challenges associated with these administration routes include the limited volume of injection, high viscosity, photosensitivity, and high sensitivity of leachable metal ions and shear stress [30,32]. In the case of other nonparenteral routes of administration, such as transdermal, nasal, buccal, rectal, vaginal, and oral deliveries, one commonly faced challenge is the issue of poor tissue permeation, which mainly results from the large size and charged nature of the biologics. The utilization of penetration enhancers has traditionally been explored as a potentially effective formulation strategy; however, observed induced toxicities associated with the use of enhancers have limited their applications and therefore the use of these delivery routes in humans.
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cases used as an IV bag stabilizing solution), the latter might require more drastic changes in the formulation as well as more careful selection of IV administration sets with more compatible construction materials [51,52]. In the treatment of chronic diseases with a higher frequency of dosing, subcutaneous administrations with prefilled syringes, auto-injectors, pens, and so on, can enhance patient compliance by allowing self and/or at-home administration. However, the use of such devices can introduce formulation and/or incompatibility challenges, mainly because of the interaction of the API with device components, such as silicone oil and/or tungsten, causing aggregation and particulate formation [53–56]. Optimized formulations that are designed to minimize such interactions are then needed to provide the required shelf-life stability (e.g., optimization of the surfactant type and concentration). In addition to the incompatibility issues, because of the low volumes of injections associated with subcutaneous administration, high-concentration formulations might be needed to deliver the required clinical doses. Suboptimal solution properties, such as induced viscosity with an impact on pain upon injection, irritation, or injection site erythema, opalescence, and phase separation can jeopardize patient confidence in the drug. Reversible self-association with potential immunogenicity risks might arise, demanding formulation optimization strategies, including modulation of the pH, ionic strength, and excipients. Extensive details of the high-concentration formulation development challenges and strategies are detailed elsewhere [37]. To further enhance patient compliance during the treatment of chronic diseases, sustained controlled-release formulations can offer real advantages by reducing the frequency of dosing. Historically, biologic instability and degradation within the delivery system over the long designated release periods (days to months) have posed significant formulation development challenges, limiting the utility of this approach. In such cases, formulation strategies involving sustained controlled-release methods with the use of, for example, PEGylation or carrier protein fusion (e.g., somatropin, FC fusion, or HSA fusion), can offer distinct advantages. Compared with protein-based therapeutics, nucleic acids rely more heavily on the route of administration and, more
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Concluding remarks Formulation/stability/shelf-life are interlinked and have direct impact on the cost-of-goods (COGs) of parenteral biologic therapies. There are numerous efforts to develop parenteral dosage forms to minimize or eliminate cold-chain (refrigerated/frozen) using lyophilization, spray-drying or immobilization technologies. In the coming years its critical to integrate the advanced computational methods for the development of patient-centric dosage forms and devices with connected/remote monitoring and Q9 data transfer capabilities.
Uncited reference
Q10 Q11
[57].
Acknowledgements Authors would like to thank Reza Esfandairy of Biopharmaceutical Development, AstraZeneca LLC for the critical reading of the manuscript.
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19 Wang, W. et al. (2014) Impact of residual impurities and contaminants on protein stability. J. Pharm. Sci. 103, 1315–1330 20 Mastrobattista, E. et al. (2007) Delivery of nucleic acids. Pharm. Res. 24, 1561–1563 21 Guzman-Villanueva, D. et al. (2012) Formulation approaches to short interfering RNA and MicroRNA: challenges and implications. J. Pharm. Sci. 101, 4046–4066 22 Medley, C.D. et al. (2010) Quantitation of plasmid DNA deposited on gold particles for particle mediated epidermal delivery using ICP-MS. Anal. Bioanal. Chem. 398, 527–535 23 Boerner, L.J. and Zaleski, J.M. (2005) Metal complex-DNA interactions: from transcription inhibition to photoactivated cleavage. Curr. Opin. Chem. Biol. 9, 135– 144 24 Polakis, P. et al. (2005) Arming antibodies for cancer therapy. Curr. Opin. Pharmacol. 5, 382–387 25 Chen, T. et al. (2015) Chemical de-conjugation for investigating the stability of small molecule drugs in antibody-drug conjugates. J. Pharm. Biomed. Anal. 117, 304– 310 26 Teicher, B.A. et al. (2011) Antibody conjugate therapeutics: challenges and potential. Clin. Cancer Res. 17, 6389–6397 27 Adem, Y.T. (2014) Auristatin antibody drug conjugate physical instability and the role of drug payload. Bioconjug. Chem. 25, 656–664 28 Shen, B.Q. et al. (2012) Conjugation site modulates the in vivo stability and therapeutic activity of antibody-drug conjugates. Nat. Biotechnol. 30, 184–189 29 Singh, S.K. et al. (2015) Antibody-drug conjugates: design, formulation and physicochemical stability. Pharm. Res. 32, 3541–3571 30 Amer, M.H. et al. (2015) The effect of injection using narrow-bore needles on mammalian cells: administration and formulation. J. Pharm. Pharmacol. 67, 640– 650 31 Chen, F.M. et al. (2011) Homing of endogeneous stem/progenitor cells for in situ tissue regeneration: promises strategies and translational perspective. Biomaterials 12, 3189–3209 32 Agashi, K. et al. (2009) The effect of delivery via narrow-bore needles on mesenchymal cells. Regen. Med. 1, 49–64 33 Zhai, S. et al. (2004) Effect of freezing rates and excipients on the infectivity of a live viral vaccine during lyophilization. Biotechnol. Prog. 4, 1113–1120 34 Lee, G. (2002) Spray-drying of proteins. Pharm. Biotechnol. 13, 135–158 35 Wang, W. et al. (1999) Instability, stabilization, and formulation of liquid protein pharmaceuticals. Int. J. Pharm. 185, 129–188 36 Chi, E.Y. et al. (2003) Physical stability of proteins in aqueous solution: mechanism and driving forces in nonnative protein aggregation. Pharm. Res. 20, 1325–1336 37 Shire, S.J. et al. (2004) Challenges in the development of high protein concentration formulations. J. Pharm. Sci. 93, 1390–1402 38 Wang, W. et al. (2000) Lyophilization and development of solid protein pharmaceuticals. Int. J. Pharm. 203, 1–60 39 Tang, X.C. et al. (2004) Design of freeze-drying processes for pharmaceuticals: practical advice. Pharm. Res. 21, 191–200
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40 Gieseler, H. (2007) Use of manometric temperature measurement (MTM) and SMART freeze dryer technology for development of an optimized freeze-drying cycle. J. Pharm. Sci. 96, 3402–3418 41 Chang, L.L. et al. (2009) Mechanisms of protein stabilization in the solid state. J. Pharm. Sci. 98, 2886–2908 42 Lai, M.C. et al. (1999) Solid-state chemical stability of proteins and peptides. J. Pharm. Sci. 88, 489–500 43 Costantino, H.R. et al. (2005) Protein spray freeze drying. 2. Effect of formulation variables on particle size and stability. J. Pharm. Sci. 91, 388–395 44 Tang, X.C. et al. (2005) Freeze-drying process design by manometric temperature measurement: design of a smart freeze-dryer. Pharm. Res. 22, 685–700 45 Chang, B.S. et al. (1996) Surface-induced denaturation of proteins during freezing and its inhibition by surfactants. J. Pharm. Sci. 85, 1325–1330 46 Piedmonte, D.M. et al. (2007) Sorbitol crystallization can lead to protein aggregation in frozen protein formulations. Pharm. Res. 24, 136–146 47 Murase, N. et al. (1989) Salt precipitation during the freeze-concentration of phosphate buffer solutions. Biophys. Chem. 34, 293–300 48 Kolhe, P. et al. (2010) Impact of freezing on pH of buffered solutions and consequences for monoclonal antibody aggregation. Biotechnol. Prog. 26, 727–733 49 Singh, S.K. et al. (2009) Large-scale freezing of biologics. Bioprocess Int. 39, 230–239 50 Mcleod, A.G. et al. (2000) Loss of factor VIII activity during storage in PVC containers due to adsorption. Haemophilia 6, 89–92 51 Kumru, O.S. et al. (2012) Compatibility, physical stability, and characterization of an IgG4 monoclonal antibody after dilution into different intravenous administration bags. J. Pharm. Sci. 101, 3636–3650 52 Chang, J.Y. et al. (2010) Leachables from saline-containing IV bags can alter therapeutic protein properties. Pharm. Res. 27, 2402–2413 53 Jones, L.S. et al. (2005) Silicone oil induced aggregation of proteins. J. Pharm. Sci. 94, 918–927 54 Liu, W. et al. (2010) Root cause analysis of tungsten-induced protein aggregation in pre-filled syringes. PDA J. Pharm. Sci. Technol. 64, 11–19 55 Seidl, A. et al. (2012) Tungsten-induced denaturation and aggregation of epoetin alfa during primary packaging as a cause of immunogenicity. Pharm. Res. 29, 1454– 1467 56 Thirumanagalathu, R. et al. (2009) Silicone oil- and agitation-induced aggregation of a monoclonal antibody in aqueous solution. J. Pharm. Sci. 98, 3167–3181 57 Ibraheem, D. et al. (2014) Gene therapy and DNA delivery systems. Int. J. Pharm. 459, 70–83 58 Anwer, K. (2008) Formulations for DNA delivery via electroporation in vivo. Methods Mol. Biol. 423, 77–89 59 Trimble, C.L. et al. (2015) Safety, efficacy, and immunogenicity of VGX-3100, a therapeutic synthetic DNA vaccine targeting human papillomavirus 16 and 18 E6 and E7 proteins for cervical intraepithelial neoplasia 2/3: a randomized, doubleblind, placebo-controlled phase 2b trial. Lancet 386, 2078–2088
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Critical considerations in the formulation development of parenteral biologic drugs Q3
Bilikallahalli K. Muralidhara1 and Marcus Wong2
1 Q4 2 Technical Operations, Acceleron Pharma, Cambridge, MA 02139, USA Technical Operations, Allakos Inc., Redwood City, CA 94065, USA
Biopharmaceuticals, unlike chemically synthesized small-molecule drugs, are marginally stable, with most of them requiring 3D structures to retain their activity and/or potency. This implies challenges to formulate these molecules for a shelf life >2 y of and also to minimize the cost of goods for manufacturing. Patient compliance has become a key consideration in the design and development of suitable dosage forms in the modernized world. Thus, here we describe different classes of biological therapeutic, with an emphasis on molecular properties, formulation challenges, and development strategies. We also present statistics on the different classes of approved biologic drugs and dosage forms.
Introduction Q6 Since the advent of the first recombinant therapeutic protein (i.e.,
insulin in 1982), there has been a major shift toward biologic drugs
Q7 within the pharmaceutical industry. Approximately two decades
ago, biologics comprised <1% of the pharmaceutical portfolio, but this has increased to nearly 20% currently and is expected to continue to grow (Fig. 1). The popularity and success of biologics has resulted mainly from their roles in disease modification and targeted treatment compared with conventional, chemically synthesized small-molecule drugs. While maximizing the target specificity, biologics often minimize the potential off-target toxicities, enhancing the ability of the drug to alter and terminate a disease state [1]. Such distinct advantages have established biologics as a major pillar of the pharmaceutical industry in a relatively short period of time and have added tremendous value to the global healthcare system by providing new treatment opportunities and bringing hope to millions of patients worldwide. Despite their inherent superiority from the therapeutic standpoint, biologics often introduce significant development challenges because of their large size, high structural complexity, and marginal stability. Their high propensity to undergo physical and chemical degradation, which directly impacts their structure and function, can jeopardize the utility of biologics as efficacious
Corresponding author: Muralidhara, B.K. ([email protected]) 1359-6446/ã 2020 Published by Elsevier Ltd. https://doi.org/10.1016/j.drudis.2019.12.011
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and life-saving therapeutics [2–6]. The development of patient friendly dosage forms with the goal of enhancing and maintaining the stability and efficacy of biologics over their intended shelf life (2–3 years) is key to ensuring the successful transformation of lead drug candidates into widely accessible and commercially viable products. A well-designed formulation strategy, while maximizing the ‘usability’ of a drug by enhancing its stability and maintaining its efficacy, should improve the safety, convenience, and patient compliance. The modality of the biologic (e.g., proteins, nucleic acids, and cells), stability or lack thereof, intended dosage configuration, and designated route of administration in combination with device strategies, as applicable, are some of the more common considerations for ensuring the development of a successful drug product [7]. Here, we provide a high-level overview of these considerations and their corresponding challenges within the context of formulation strategy and design space.
Common considerations in the formulation development of biologics Molecular modality Biological therapeutics cover a range of molecular modalities. Proteins have revolutionized the pharmaceutical industry following conventional small-molecule therapeutics and now represent the largest fraction of approved biologic drugs (74%). Difficultto-treat diseases, such as oncology and infectious diseases, are now
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Total (approved products, worldwide)
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5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0 Through 1995
Through 1998
Through 2005
Small molecule
Through 2008
As of November 2015
Biologic
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FIGURE 1
Total number of approved drugs over the past 20 years by global regulatory agencies. Biologic drugs grew significantly, especially over the past 7 years because of decreased attrition rates and improved production technologies. The data were compiled from various sources, including www.pharmacircle.com and www. citeline.com, using a 2016 year cut-off.
979 No. of surveyed biologies biologies
3.4%
Cellular therapies
0.8%
Nucleic acids
74.0%
7.4%
14.3%
Proteins
Peptides
Virus particles Drug Discovery Today
FIGURE 2
Proteins as therapeutic modalities constitute the majority of approved biologics. A large number of cell-based therapies under regenerative medicine, peptides as conjugates, and virus particles for nonvaccine use are also in late-stage clinical development.
being targeted using natural biologics (cells, genes, and viruses) that have multiple modes of interaction (Fig. 2). Among protein therapeutics, growth factors and monoclonal antibodies (mAbs) constitute the largest portion. Hormones, interferons, cytokines, coagulation factors, and enzymes comprise some of the other main classes, providing a largely diverse class of protein therapeutics (Fig. 3). In terms of molecular constructs, these can be individual proteins, fusion and conjugated proteins, bispecific antibodies, and so on. For the purpose of the discussion herein, peptides and/ or peptide conjugates (8% of the biologics portfolio, Fig. 2) are categorized as protein therapeutics because of their similar amino acid-based structural building blocks. In general, a common salient feature of protein therapeutics is their large and complex 3D structure, requiring proper folding and conformational stability for efficient functionality. The difference in the free energy between the folded and unfolded states of proteins is typically in the range of 5–20 kCal/mol, which is equivalent to a few hydrogen bonds or ion pairs [8–10]. Challenges to developing these fragile macromolecules as stable therapeutics drugs are detailed herein. Another class of biologics includes nucleic acids (e.g., DNA, mRNA, and synthetic oligonucleotides) and, although currently constituting only 1% of the commercial biopharmaceutical landscape (Fig. 3), they represent one of the fast-growing classes 2
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of biologics and are currently being studied in a large number of ongoing clinical programs [11]. Such interest in nucleic acids stems from their ability to target and bind gene sequences and inhibit disease gene expression and transcription, offering distinct advantages in disease modification and treatment by attacking conventionally out-of-reach targets using proteins and peptides. A salient liability feature of nucleic acids is their high susceptibility to in vivo degradation from nuclease attacks, which often require chemical modifications of their backbone to increase their stability, extend their circulation half-life, and increase their transcription and translation efficiency. Such modifications include, but are not limited to, a 20 -methylene bridge to sugar backbone, 30 methylation, and replacement of oxygen by sulfur in the phosphodiester bond (phosphorothioate). Finally, the latest and fastest growing class of biologics, with potential advantages over both small- and large-molecule therapies, is the category of cell and gene-based therapeutics (e.g., gene delivery vectors/viruses, transgenic cells, and stem cells), comprising 3–5% of the biopharmaceutical portfolio. A salient feature of cells includes their extremely sensitive architecture, pleomorphic shape, and surface-expressed antigens with a diverse chemical nature (e.g., lipids, proteins, and carbohydrate chains). From the standpoint of biology, cell and gene therapies offer distinct
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Growth factors Antibodies (mAb, non-mAb, biosimilars) Interferon (biosimilar, recombinant) Interleukins Hormones
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Blood fractions Enzymes Fusion proteins Antibody–drug conjugates 0
50
100
150
200
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FIGURE 3
Agency-approved protein drugs are further classified according to their mode of functionality. Therapeutics based on novel and unnatural constructs, such as antibody–drug conjugates (ADCs) and fusion proteins with multiple modes of interaction, have gained traction in recent years. Abbreviation: mAb, monoclonal antibodies.
advantages in information processing and targeting compared with small and large molecules and sometime offer cure. These have broadened their applications from conventional tissue regeneration and/or repair and vaccines to other therapeutic areas, such as infectious diseases, autoimmunity, cancer immunotherapy, and metabolic diseases. Currently, industry is working towards reducing the cost of their development and manufacturing to make them more affordable for patients.
Stability In general, biologics, regardless of the modality, are subject to a variety of environmental stresses throughout their product life cycle [12], including suboptimal solution conditions during purification, freeze-thaw and mechanical stresses (e.g., agitation and shear) during fill-finish and manufacturing, temperature
excursions and light exposure during transportation and storage, and interaction with the surfaces of a variety of container-closure systems. In combination with their large size, high structural complexity, compositional variability, and inherent marginal stability, biologics can undergo a variety of different physical and chemical degradations, leading to loss of their stability and activity [12–14]. In brief, there can be physical degradation from conformational (e.g., unfolding), colloidal (e.g., aggregation and particulate formation), interfacial (e.g., adsorption and degradation at interfaces), or morphological (e.g., disruption of epitope presentation on cell surfaces) instabilities, whereas chemical degradation involves modifications of the covalent bonds and can include oxidation (e.g., tryptophan and methionine in proteins, and guanine in nucleic acids), deamidation (e.g., Asn and Gln in proteins, and cytosine in nucleic acids), isomerization (e.g., Asp
TABLE 1
Q1 A generic toolbox for the formulation of different modalities of biologic drugs Formulation agents/ingredients
Purpose of action
Examples
Buffers Salts
pH modulator Tonicifiers Stabilizers/destabilizers (Hofmeister series) Surface adsorption inhibitors Interfacial stabilizers Inhibitors of microbial growth (multidose formulations) Free radical scavengers Inhibitors of metal-induced degradation Tonicifiers Cryoprotectants Stabilizers (preferential hydration) Stabilizers Antioxidants Tonicifiers Rheology modulators Sustained release/extended half-life Surface adsorption inhibitor Bulking agents Condensing agents for nucleic acids Viscosity modifiers, cofactors, cell stabilizers
Citrate, acetate, histidine, phosphate, tris Sodium chloride, potassium chloride
Surfactants Preservatives Antioxidants/chelators Osmolytes/sugars
L-amino acids
Bio-/polymers
Polycations Metal ions
Polysorbate-20, pluronic-188 Phenol, m-cresol EDTA, DTPA, methionine, ascorbic acid Sucrose, trehalose, sorbitol, TMAO
Arginine, glycine, proline, lysine, methionine
HSA, PLGA, PEG, cyclodextrins
Cationic lipids, spermidine, tetra-arginine Calcium, magnesium, manganese
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in proteins), disulfide bond shuffling (e.g., strand separation and desulfurization in DNA and mRNA), and clipping of functional groups and/or linkers (e.g., payload deconjugation in ADCs), among others. The most common chemical liabilities are often mitigated via genetic engineering efforts during the discovery stage. The mechanisms of physical and chemical degradation and the variety of molecular and environmental factors impacting the stability of biologics have been extensively reviewed elsewhere. [15]. Herein, only a high-level risk-based analysis of the main degradation pathways according to the modality of the biologic is provided to aid discussions on formulation development (Table 1). In addition, computational modeling and theoretical predictions of potential liabilities (e.g., aggregation and selected chemical degradation hotspots) can further help the formulation design space [16]. Selection and optimization of appropriate formulation components that protect the biologics against potential physical and chemical degradation can be rationally conducted according to the identified routes of degradation [17,18]. Table 2 classifies some of the more common formulation excipients and their intended modes of action that are used to stabilize a range of biological modalities. These excipients should have a proper safety profile and be approved for parenteral use. Other potential considerations, such as the compatibility of the selected formulations with the intended dosage form configuration, the route of administration, and the designated device component, as applicable, might also have roles in formulation selection and optimization strategies, as discussed in the following sections. Another important consideration when utilizing pharmaceutical additives is their purity and stability profile. Impurities within pharmaceutical excipients, such as trace metal ions, hydroperoxides, and bacterial endotoxins, have been observed and can impact the stability and potency of the biologic. Regulatory guidelines often outline the type of analytical data as well as vendor manufacturing information required for pharmaceutical excipients that are intended for use in the formulation of biologics to meet quality standards [19].
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Despite commonalities in the mechanisms of physical and chemical degradation as well as the stabilizing effect of formulation additives, the development of a generalized universal approach to stabilize all biologics has proven unsuccessful thus far. One example includes the formulation of nucleic acids, in which their large size, highly charged nature, and high susceptibility to nuclease degradation often result in their poor uptake and suboptimal in vivo stability, demanding delivery-focused formulation and stabilization strategies that facilitate the transfection efficiency of the molecule [20]. Such strategies can include nucleic acid condensation using polycationic agents (e.g., lipids, polyamino acids, and polymers), conjugation (e.g., cholesterol), and encapsulation (e.g., liposomes, lipoplex, chitosan, and dendrimers) methods [21]. In terms of chemical stability, cytosines can spontaneously deamidate into uracil and the process is >100-fold faster in single-stranded nucleic acids. Sequence-independent depurination is also observed at higher temperatures and above neutral pH. Reactive metals, such as Hg, Zn, Co, and Ni, are known to form metal-base pairs by chelating between strands through connecting two adenines, cytosines, or mixtures thereof, thereby destabilizing and/or initializing strand separation and/or breakage [22,23]. Another example includes antibody–drug conjugates (ADCs), a hybrid of small and large molecules, with wide therapeutic applications, particularly as oncolytic agents [24,25]. ADCs combine the superior target specificity of mAbs and target-killing ability of small cytotoxic drugs (known as payloads), which are covalently conjugated to mAbs via a linker [26]. In addition to the formulation challenges associated with mAbs, the physicochemical properties of the payloads and linkers, conjugation chemistry, drug: antibody ratio, and location of the conjugation sites can all impact the overall conformational, colloidal, and in vivo stability of the ADC, which introduces unique challenges to formulation [26–29]. Finally, cell and gene-based therapies offer unique formulation development challenges because of various compounding factors, including multiple reporter genes, multiple and complex antigen epitopes, membrane fluidity and permeability, and vector heterogeneity, all of which have key roles in the stability and function of
TABLE 2
Associated formulation development risks for the most common macromolecular modalitiesa
a The risk classification of low (green), medium (yellow), and high (red) is a qualitative interpretation of the degree of formulation development challenges recognized based on authors’ experience and literature data. The list of modalities and their corresponding degradations represents a collection of the most common categories currently in biopharmaceutical development. In vitro degradations refer to those observed during drug product development, storage, and distribution life cycle. The in vivo pathways occur post administration and directly reflect the serum stability and half-life of the molecule. b* , desulfurization; **, adhesion.
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Route of administration Other parenteral 5.9%
Intramuscular 18.8%
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(a)
Intravenous 42.7% Subcutaneous 32.6%
Drug product presentation
(b)
Solid dose (other) 19.0% Liquid (not dried) 51.5% Lyophilized 29.5%
Drug Discovery Today
FIGURE 4
Two major considerations in the formulation and development of biological drugs. (a) The route of administration is mainly driven by mechanism of action of the drug and patient convenience. (b) Liquid dosage forms are the preferred configuration because of the low cost of manufacturing and ease of administration. Nonliquid dosage forms (lyophilized, spray dried, or frozen) are dictated by, but not limited to, product instability, scale of manufacturing, transportation, and storage concerns.
the cells and/or viruses [30]. Although detailed mechanisms of instability in cell-based therapeutics are generally not well understood, the substantial loss of transplanted cells has been observed upon delivery [31]. Extreme sensitivity and apoptosis to freeze-thaw and mechanical shear have been well documented during the thawing of frozen cells and their subsequent administering using various needle sizes and flow rates [31,32]. Specific classes of additive, such as polyhydric alcohols (e.g., glycerol), sugars (e.g., trehalose), and carrier proteins (e.g., gelatin and human serum albumin; HSA), have been proven effective cryoprotectants, although their mechanisms of stabilization of cells are not well understood. Cryoconcentration cells and excipients have been shown to occur for viruses during freezing and cell adhesion and/or agglomeration during diafiltration potentially impacting the viability and/or integrity of surface antigens [33]. Viscus carriers (e.g., sodium alginate or PEGs) and carrier proteins (e.g., gelatin and HSA) have been used to
overcome shear stress during administration of low cell density (104–106) dosage forms [31]. As the field evolves further, an industry consortium working with regulatory agencies would be useful to put together guidelines to accelerate the development and manufacturing of cell and gene therapy products.
Dosage form configuration The designation of the optimal dosage form configuration of a biological drug product depends on a variety of factors, including the efficacy, intended dose, dosage regimen, stability of the macromolecule, material compatibility, designated therapeutic area, route of administration, patient compliance, and cost-of-goods analysis from a commercialization perspective. Liquid and lyophilized formulations constitute the most common dosage form configurations for biologics development, comprising 52% and 30% of all biologic dosage forms, respectively (Fig. 4). Frozen www.drugdiscoverytoday.com
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formulations, although not common for protein and nucleic acid drug products, have wide utility in the formulation of cell therapeutics, and the three are discussed herein. Spray-dried [34] and protein microcrystal dosage forms are being developed to reduce developmental costs and to achieve high concentration doses for subcutaneous delivery, respectively. Liquid dosage forms, when feasible, are the most preferred because they provide the highest level of compliance for clinicians and patients by simplifying the dose preparation procedures (e.g., elimination of reconstitution or thawing steps with lyophilized or frozen forms). In addition, they allow self or at-home administration with prefilled syringes and auto-injectors, particularly for the treatment of chronic diseases that require frequent dosing (e.g., diabetes and arthritis). Despite such advantages, there are significant challenges to their development, including the higher instability and risks involving a variety of physical and chemical forms of degradation, greater need for cold-chain storage, and more stringent transportation criteria [35–37]. In addition, in cases where high-concentration liquid formulations are needed for subcutaneous delivery because of injection volume restrictions (e.g., mAb formulations in prefilled syringes at >100 mg/ml and <1.5 ml), issues such as induced viscosity, phase separation, opalescence, or self-association can be observed from molecular crowding effects. This introduces significant processing, formulation, and delivery challenges, which impact the product quality as well as patient comfort and convenience. When the shelf-life stability, handling, or distribution become development risks (e.g., in the case of ADCs and nucleic acids) for liquid-dosage forms, lyophilized formulations present a viable alternative by improving the formulation stability based on a general phenomenon of reduced molecular mobility and degradation kinetics in the dried state [38,39]. Recent advances in lyophilization technologies, including ‘SMART’ freeze-drying based on manometric temperature measurements (MTM) and process analytical technologies (PAT) to monitor critical freeze-drying process parameters, have paved the way for more systematic and less empirically designed lyophilization processes, enhancing the freeze-drying capabilities of biologics [39,40]. Despite such advantages, from a commercial perspective, lyophilized formulations can introduce certain challenges because of the more complex dosing preparation procedures with additional reconstitution steps and also the limitations of device usability in self and/or at home set-ups. Incompatibility of certain formulation additives (e.g., salts) with the freeze-drying process can further restrain the formulation space design. Lyophilization process also adds to costof-goods, which might be reflected in the market pricing [41,42]. In addition to conventional freeze-drying, referred to as lyophilization, alternative approaches, such as spray freeze-drying, have also been utilized in the formulation of biologics to, for example, generate particles of a specific size and morphology for pulmonary delivery of aerosol powders deep into the lungs (i.e., inhaled insulin or interferons). In such cases, formulation optimization efforts via the use of appropriate excipients, such as sugars, surfactants, and, in some cases, polymeric compounds, have to be implemented to avoid macromolecular denaturation and aggregation, which are common during these processes [43]. Frozen formulations offer another alternative to their liquid counterparts and, although less desirable in the field of protein 6
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therapeutics, they are widely utilized in the formulation of cell therapeutics for which achieving liquid or lyophilized shelf-life stability is currently a significant challenge. Although they provide enhanced long-term stability compared with their liquid counterparts, the development of frozen formulations can present with unique challenges, including denaturation at the ice–water interfaces during freeze-thaw [44,45], potential buffer and/or excipient crystallization [46],and precipitation upon freezing [47], resulting in aggregation or pH shifts that might impact product quality and efficacy [48]. Additionally, heterogeneous freezing profiles, particularly at large scales because of cryoconcentration effects, can be a major issue for cell therapeutic formulations, especially given their high sensitivity to osmotic stress [49]. The higher costs associated with storage, shipping, and handling of frozen formulations can further complicate their utility from the cost of goods and compliance perspective [14].
Route of administration Biologics are often difficult to deliver via nonparenteral routes (e. g., oral) of administration because of issues such as enzymatic degradation, poor permeation, variable pharmacokinetics/pharmacodynamics (PK/PD) profiles, and low bioavailability [50]. Therefore, substantial attention has been paid to the parenteral routes of administration, which currently comprise 85% of all biological deliveries (Figure 5). There are a few recent clinical Q8 studies advancing the intratumoral delivery of oncology drugs. Within the parenteral portfolio, intravenous and subcutaneous administrations, at 37% and 28%, respectively, constitute the most common categories and, therefore, are the main focus of the discussions herein. The regulatory guidelines require demonstration of the compatibility of the biological drug product with the intended route of administration and associated material components to ensure patient safety and compliance. In recent years, the study of ‘human factors’ has been mandated to evaluate the advantages and compliance with patients where a device is implemented to deliver a drug. These are called combination products. ICH-M4Q Common Technical Document, Quality Section 3.2. P.2.6 states that ‘the compatibility of the drug product with reconstitution diluents or dosage devices should be addressed to provide appropriate and supportive information for the labeling.’ A set of formulation studies, often referred to as ‘clinical compatibility,’ is then executed to support drug product compatibility claims and must be included in regulatory submissions, such as the Investigational New Drug (IND) and Biologics License Application (BLA). Depending on the route of administration, a unique set of incompatibility issues can arise. For example, in intravenous (IV) delivery, incompatibility of the drug product (formulation) with the construction materials used in the bag or components of the infusion sets (e.g., polyvinylchloride or polyolefin) as well as with the bag diluent (e.g., saline or dextrose) has been observed to impact the stability and activity of the drug. Common incompatibility issues often include adsorption of the active pharmaceutical ingredient (API) to the surface of the IV bags and infusion sets as well as the formation of aggregates, subvisible, and visible particulates [51], which are of concern from the product immunogenicity perspective. Although the former can often be mitigated via the use of an optimal surfactant type and concentration (in some
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importantly, the choice of the delivery system involving excipients and delivery mechanisms (i.e., electroporation), impacting the targeting and transfection efficiency [58,59]. Although systemic delivery mainly in the form of intravenous administration is used in some cases, susceptibility to nuclease-induced degradation as well as high clearance rates often demand local delivery in the form of intratumoral, intraocular, and intravaginal routes of administration. Some of the unique formulation challenges associated with these administration routes include the limited volume of injection, high viscosity, photosensitivity, and high sensitivity of leachable metal ions and shear stress [30,32]. In the case of other nonparenteral routes of administration, such as transdermal, nasal, buccal, rectal, vaginal, and oral deliveries, one commonly faced challenge is the issue of poor tissue permeation, which mainly results from the large size and charged nature of the biologics. The utilization of penetration enhancers has traditionally been explored as a potentially effective formulation strategy; however, observed induced toxicities associated with the use of enhancers have limited their applications and therefore the use of these delivery routes in humans.
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cases used as an IV bag stabilizing solution), the latter might require more drastic changes in the formulation as well as more careful selection of IV administration sets with more compatible construction materials [51,52]. In the treatment of chronic diseases with a higher frequency of dosing, subcutaneous administrations with prefilled syringes, auto-injectors, pens, and so on, can enhance patient compliance by allowing self and/or at-home administration. However, the use of such devices can introduce formulation and/or incompatibility challenges, mainly because of the interaction of the API with device components, such as silicone oil and/or tungsten, causing aggregation and particulate formation [53–56]. Optimized formulations that are designed to minimize such interactions are then needed to provide the required shelf-life stability (e.g., optimization of the surfactant type and concentration). In addition to the incompatibility issues, because of the low volumes of injections associated with subcutaneous administration, high-concentration formulations might be needed to deliver the required clinical doses. Suboptimal solution properties, such as induced viscosity with an impact on pain upon injection, irritation, or injection site erythema, opalescence, and phase separation can jeopardize patient confidence in the drug. Reversible self-association with potential immunogenicity risks might arise, demanding formulation optimization strategies, including modulation of the pH, ionic strength, and excipients. Extensive details of the high-concentration formulation development challenges and strategies are detailed elsewhere [37]. To further enhance patient compliance during the treatment of chronic diseases, sustained controlled-release formulations can offer real advantages by reducing the frequency of dosing. Historically, biologic instability and degradation within the delivery system over the long designated release periods (days to months) have posed significant formulation development challenges, limiting the utility of this approach. In such cases, formulation strategies involving sustained controlled-release methods with the use of, for example, PEGylation or carrier protein fusion (e.g., somatropin, FC fusion, or HSA fusion), can offer distinct advantages. Compared with protein-based therapeutics, nucleic acids rely more heavily on the route of administration and, more
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Concluding remarks Formulation/stability/shelf-life are interlinked and have direct impact on the cost-of-goods (COGs) of parenteral biologic therapies. There are numerous efforts to develop parenteral dosage forms to minimize or eliminate cold-chain (refrigerated/frozen) using lyophilization, spray-drying or immobilization technologies. In the coming years its critical to integrate the advanced computational methods for the development of patient-centric dosage forms and devices with connected/remote monitoring and Q9 data transfer capabilities.
Uncited reference
Q10 Q11
[57].
Acknowledgements Authors would like to thank Reza Esfandairy of Biopharmaceutical Development, AstraZeneca LLC for the critical reading of the manuscript.
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