1049 TAA antibody library and novel linker/payload BLD1102 for ADC, bispecific ADC and nanobody-drug conjugate development

Background Tumor-associated antigens (TAAs) are pivotal drug targets in cancer immunotherapy, as they are highly expressed on tumor cells but less on healthy cells. Antibody-drug conjugates (ADCs) targeting TAAs have demonstrated their potential in clinical use, but still face challenges of off-target toxicity and unsatisfactory anti-tumor efficacy. Bispecific ADCs (bsADCs) and nanobody-drug conjugates offer enhanced tumor specificity, broader killing capdacity, and improved tissue penetration, potentially overcoming tumor heterogeneity. Methods Using proprietary size-unlimited precise chromosome engineering (SUPCE) technology, we developed fully human antibody discovery RenMice® platforms (RenMabTM, RenLite®, and RenNano®). RenMice® were further engineered with a specific drug target gene knocked-out (KO) to generate antibodies with increased sequence and epitope diversity. Fully human monoclonal antibodies (mAbs), common-light-chain antibodies, and heavy-chain-only antibodies (HCAbs) targeting TAAs were discovered from RenMice or RenMice KO platforms, and screened for internalization activity. We also developed a novel proprietary linker/payload system BLD1102 composed of a highly potent DNA topoisomerase I inhibitor (TOP1i) payload BCPT02 and a hydrophilic protease-cleavable linker. Novel ADC and bsADCs, including anti-CH3 ADC (BCG014) and anti-PTK7xTROP2 bsADC (BCG033) were generated using our TAA library and linker/payload system. Their internalization and in vivo anti-tumor activity were evaluated. The ability of TFR1 HCAbs to cross blood-brain barrier (BBB) and deliver payload was evaluated by HCAb or HCAb-drug conjugate concentration in the mouse parenchyma. Results Target KO RenMice® generated more antibody-secreting B cells for targets with high homology between mouse and human, including 5T4, CD39, PD-L1, CD47, and SIRPa. A library of fully human monoclonal antibodies, common light chain antibodies, and nanobodies targeting 200+ TAAs were generated by RenMice or RenMice KO platforms. BLD1102-conjugated ADCs demonstrated super hydrophilicity comparable to mAbs and superior than Deruxtecan-conjuageted ADCs. CDH3 mAb showed superior binding and internalization in NCI-H1650 lung cancer cell line compared to the benchmark antibody. BCG014-BLD1102 demonstrated superior efficacy in NSCLC PDX models compared to the benchmark ADC. BCG033-BLD1102 showed potent anti-tumor activity in a colorectal cancer PDX model where benchmark ADCs were ineffective even at a high dose. TFR1 HCAbs can cross the BBB and deliver drug payloads efficiently, demonstrating the potential to be developed into nanobody-drug conjugates. Conclusions Biocytogen has successfully established a TAA antibody library and a proprietary linker/payload BLD1102 to support the ADC drug development (table 1). The library contains RenMice-derived mAbs and HCAbs for over 200 TAAs, many of which have been screened for internalization activity. This ready-to-use resource expedites the large-scale development of ADCs across various modalities.