Abstract C061: BT8009, a Bicycle Toxin Conjugate targeting Nectin-4, shows target selectivity, and efficacy in preclinical large and small tumor models (2019)

Abstract Small molecule toxin conjugates offer a novel approach to tumor antigen specific targeting, allowing reduced systemic exposures and efficient tumor penetration of cytotoxic payloads, compared to large antibody toxin conjugates. BT8009 is a Bicycle Toxin Conjugate (BTC®) in which a Nectin-4 binding Bicycle® (bicyclic peptide) is conjugated through an inert sarcosine spacer chain, and a cleavable linker, to the antimitotic toxin MMAE. Increased Nectin-4 expression has been reported in multiple tumor types (including bladder, breast, esophageal, colorectal, lung, ovarian and pancreatic cancers) and so represents an appropriate tumor binding target. Bicycles are small (1.5KDa) fully synthetic, structurally constrained peptides with the specificities and affinities akin to antibodies, and pharmacokinetic properties more like small molecules. These features make Bicycles very attractive novel drug modalities for therapeutic approaches in which low systemic exposures coupled with high local drug concentrations are desired. We have previously described the identification and optimization process leading to selection of BT8009 as a candidate for IND enabling studies. BT8009 has low nanomolar (3nM) affinity for Nectin-4 and high selectivity (&amp;gt;1000 fold) over Nectins 1-3 and the 5 nectin-like family members (Necl1-5). BT8009 is active in a broad range of Nectin-4 positive cell line and patient derived xenograft tumors in vivo, leading to stable diseases and tumor regressions with durable responses. This abstract describes recent work characterizing this molecule. Selectivity of the Bicycle has been further demonstrated by assessing the binding of the biotinylated version of the Nectin-4 Bicycle on a human, plasma membrane protein cell array expressing 5528 full length human plasma membrane and secreted proteins. In this assay the Bicycle bound only Nectin-4 itself, again demonstrating the excellent target specificity. Efficacy data for BT8009 has now been extended to demonstrate the anti-tumor activity of BT8009 in large (1000mm3) xenograft tumors, in which rapid and near complete responses are observed. We have further characterized the efficacy profile of BT8009 in a panel of patient-derived non-small cell lung cancer (NSCLC) xenograft models, as well as in a panel of patient-derived pancreatic ductal (PDAC) xenograft models demonstrating a high frequency of stable diseases and partial responses. We will also describe the ongoing work for identification and validation of biomarkers for treatment response. BT8009 shows excellent efficacy in xenograft models expressing Nectin-4 target and its pharmacokinetic profile enables it to provide a rapid attainment of high tumor exposure levels with reduced systemic exposure. IND-enabling studies are currently ongoing with BT8009. Citation Format: Michael Rigby, Gavin Bennett, Liuhong Chen, Gemma Mudd, Paul Beswick, Helen Harrison, Sophie Watcham, Heather Allen, Amy Brown, Katerine Van Rietschoten, Philip Jeffrey, Peter U Park, Eric Haines, Nicholas Keen, Johanna Lahdenranta. BT8009, a Bicycle Toxin Conjugate targeting Nectin-4, shows target selectivity, and efficacy in preclinical large and small tumor models [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C061. doi:10.1158/1535-7163.TARG-19-C061