Abstract 391: Molecular-based enrichment strategy for Nectin-4 targeted Bicycle toxin conjugate BT8009
Authors: Gelb Tara , Santos Sean , Dickson Amy , Campbell Carly , Rigby Mike , Mckenzie Andrew J. , Rozelle Dan , Blakemore Stephen J. 
Published: July 2021

Introduction: BT8009 consists of a bicyclic peptide targeting the tumor antigen Nectin-4, linked to the cytotoxin monomethyl auristatin E (MMAE) via a molecular spacer and cleavable linker. BT8009 is currently being investigated in a Phase 1/2 clinical trial (BT8009-100, NCT04561362) in relapsed and/or refractory solid tumor patients. Nectin-4 positive tumor tissue will be a requirement for enrolment eligibility (with the exception of bladder cancer) starting in dose escalation level 3. Nectin-4 positivity will be determined by IHC on tumor tissue, requiring either tumor membrane or tumor cytoplasmic H-score ≥ 100.

Methods: Nectin-4 is not included on commercial NGS panels or routinely screened by IHC. Therefore, the work reported here aimed to identify a routinely measured molecular surrogate of tumor Nectin-4 protein expression (i.e. somatic mutation or gene amplification) that could potentially increase patient screening frequency, yield, and likelihood of response to BT8009. Here we demonstrate that Nectin-4 copy number is associated with Nectin-4 mRNA expression in 9 cancer indications in TCGA including breast, bladder, and lung cancer. In addition, across &gt;30 cancer indications in TCGA, copy number of Nectin-4 is highly correlated with SDHC copy number (these two genes are ~225 kb apart on 1q23), which is included on multiple commercially available NGS panels. Taken together, these results suggest that the existence of an SDHC amplification could be used as an enrichment tool to identify patients with Nectin-4 positive tumors. To test this hypothesis, we obtained 100 TNBC human tumor samples and generated data to determine Nectin-4 and SDHC copy number as well as Nectin-4 protein expression status by IHC.

Results: SDHC and Nectin-4 copy number were observed to be highly positively correlated (Spearman's Rho=0.93). Furthermore, all (N = 22) TNBC tumors with a Nectin-4 copy number ≥ 3 were identified as positive for Nectin-4 protein expression and were at or above the H-score threshold required for enrolment to BT8009-100. In contrast, within the subset of tumors that were diploid for Nectin-4/SDHC (n=30), there were both Nectin-4 positive and negative tumors. This suggests that the presence of SDHC/Nectin-4 amplification can be used to increase the probability of identifying Nectin-4 expressing tumors.

Conclusions: We demonstrate the potential utility of using pre-existing patient NGS data with SDHC amplifications to increase the frequency of identifying patients with high Nectin-4 expressing tumors via IHC. The use of this strategy is ongoing at all current sites enrolling patients to BT8009-100.

Citation Format: Tara Gelb, Sean Santos, Amy Dickson, Carly Campbell, Mike Rigby, Andrew J. Mckenzie, Dan Rozelle, Stephen J. Blakemore. Molecular-based enrichment strategy for Nectin-4 targeted Bicycle toxin conjugate BT8009 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 391.