In Pursuit of Stability Enhancement of a Prostate Cancer Targeting Antibody Derived from a Transgenic Animal Platform

Abstract

Accelerated timelines necessitate the discovery of fully human antibodies as biotherapeutics using transgenic animals with a notion that such mAbs bypass humanization. A transgenic animal derived mAb (PCa75) targeted against a prostate cancer antigen had several 'unusual residues' (rare somatic hypermutations, rSHM, with positional frequency of <1%) that resulted in compromised biophysical properties (tm = 61 °C and intrinsic stability ΔGu = 24.3 kJ/mol) and a sub-optimal immunogenicity profile. In our quest for quality medicine, we pursued antibody engineering strategies to enhance the stability of PCa75. PCa62, an engineered variant of PCa75, retained function while significantly improving the drug-like attributes of the molecule (Tm = 75 °C and intrinsic stability ΔGu = 63.5 kJ/ mol). rSHM is rather prevalent, 18 out the 21 approved transgenic animal-derived antibodies have at least one 'unusual residue'. Thus, engineering of rSHM remains critical to enhance the stability and minimize immunogenicity risk of biotherapeutics. Monoclonal antibodies (mAbs) have fundamentally transformed the treatment of complex diseases like autoimmune disorders, cancer, and others over the last two decades 1. The complex physicochemical makeup of these biologics compared to traditional small molecule drugs is manifested in development challenges associated with immunogenicity, aggregation, chemical stability, and physical stability during drug production and delivery. These challenges are outweighed by the unmatched specificity, potency, and safety of these molecules such that mAbs remain a growing source of therapeutic molecules, particularly in Oncology applications, with over 100 new mAbs entering clinical trials yearly 2. With over 570 mAbs currently being tested in clinical trials with overlapping targets, mechanisms, and disease indications, optimization of a drug's physical attributes can result in a significant competitive advantage while also providing better value to patients. Humanized antibodies represent ~43% (i.e. 38 mAbs) of the 89 FDA approved antibodies 2. Although once tedious and time consuming, synthetic biology breakthroughs, sequencing technologies, and worldwide services for high-throughput antibody engineering have drastically reduced the time required for humanization. More recently several transgenic animal platforms have been developed to discover fully human therapeutic antibodies in rodents, circumventing the iterative process of humanization 3,4. Indeed, 21 biotherapeutics derived from four different transgenic animal platforms such as UltimAb, Xenomouse, VelocImmune and TransChromo platforms have been approved and marketed while antibodies from other transgenic animals' platforms like Merus, Harbour Biomed, Ablexis, Wuxi Pharma, Open Monoclonal Technology among others are currently in clinical trials 5. Recreating the human immune system in transgenic animals is challenging as antibody genes are assembled by V-D-J recombination and further diversified by somatic hyper-mutations to enhance specificit...

Discovery-stage identification of drug-like antibodies using emerging experimental and computational methods

“…136 However, a recent study found that mAbs from such mice are prone to rare mutations in framework regions due to somatic hypermutation that compromise their biophysical properties and immunogenicity profiles. 138 Antibody display methods, such as phage and yeast display, are also important for generating and screening of fully human synthetic libraries, thus eliminating the need for antibody humanization. 139,140 Most recently, there is great interest in using human-derived B-cells in conjunction with next-generation sequencing technologies for rapid and efficient generation of fully human mAbs.…”

Regulatory Approved Monoclonal Antibodies Contain Framework Mutations Predicted From Human Antibody Repertoires

“…Other research groups have published the effects of FR mutations on stability and heterologous expression yields (Table 2) (48)(49)(50)(51). Across these four studies, thermodynamic stability was measured (as DDG, DT 50 , DT m ) for nine point mutants.…”

“…‡Mean DT m was calculated over all genotypes presented in Table3in ref(48). *Yield is calculated as a relative percentage to the original antibody sequence.…”

Regulatory approved monoclonal antibodies contain framework mutations predicted from human antibody repertoires

“…Other research groups have published the effects of FR mutations on stability and heterologous expression yields (Table 2) (46)(47)(48)(49). Across these four studies, thermodynamic stability was measured (as ΔΔG, ΔT50, ΔTm) for 13 point mutants.…”