Abstract LB-221: Novel anti-Sialyl-Tn monoclonal antibodies and antibody-drug conjugates (ADCs) demonstrate tumor specificity, unique sequence homology and in vitro and in vivo antitumor efficacy

Abstract

Abstract Siamab Therapeutics is developing monoclonal antibodies and antibody drug conjugates (ADCs) targeting tumor-associated carbohydrate antigens such as Sialyl-Tn (STn). These antibodies are selected using a proprietary glycan microarray that enriches for candidates whose binding is protein independent, highly specific and demonstrates exceptional target affinity. STn is a cancer specific antigen that is expressed on the surface of carcinomas including ovarian, colon, prostate, and pancreatic tumors but is rarely present in normal tissue. STn expression has been linked to innate immune suppression, a chemoresistant phenotype, metastasis, and poor prognosis. Previous attempts to target this antigen in the clinic with synthetic glycan vaccines proved safe but lacked efficacy. Siamab has developed over 20 murine mAbs that bind STn with high affinity and specificity. When formatted as ADCs, anti-STn mAb-ADCs target and selectively kill STn expressing cells and also demonstrate efficacy in multiple xenograft studies. Multiple murine mAbs perform well in IHC studies with multiple solid tumor samples and tissue microarrays and demonstrate high tumor specificity. Remarkable sequence homology across all murine mAbs was observed in both heavy and light chains, and hot spots for hypermutation were identified. Humanization was successfully completed using a selection of mAbs and multiple humanized mAbs maintain their target specific binding, affinity and cytotoxicity in vitro. Our data demonstrates that high-affinity, STn-specific mAbs show promise both as therapies for solid tumors and as a potential tool for the development of biomarkers and companion diagnostics enabling selection of patients most likely to respond to therapy. Citation Format: David Eaverone, Jeff Behrens, Jillian Prendergast. Novel anti-Sialyl-Tn monoclonal antibodies and antibody-drug conjugates (ADCs) demonstrate tumor specificity, unique sequence homology and in vitro and in vivo antitumor efficacy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-221.