Abstract C169: AVA3996, a novel pre|CISION™ medicine, targets a warhead to the tumor microenvironment via Fibroblast Activation Protein (FAP) mediated cleavage to elicit tumor cell kill

Abstract

Abstract AVA3996 is a therapeutic product based on proprietary pre|CISION™ technology which incorporates a substrate that is sensitive to cleavage by FAP. The pre|CISION™ substrate can be utilized in a drug conjugate linker or to generate chemotherapeutics that are only activated in the tumor microenvironment. AVA3996 consists of a proteasome inhibitor (PI) warhead covalently bonded to a peptide containing a cleaving sequence (D-Ala-L-Pro), which is designed to be susceptible to hydrolysis by Fibroblast Activation Protein α (FAP) but is resistant to hydrolysis by both closely related and wider mammalian peptidases. FAP, a post-prolyl endopeptidase, is overexpressed on the surface of activated fibroblastic cells which are abundant in the supporting stroma of over 90% of malignant epithelial cancers. Proteasome inhibitors are a first line of treatment for certain hematologic indications such as multiple myeloma. However, clinical utility of proteasome inhibitors is limited by severe dose-limiting toxicities, including peripheral neuropathy. We have demonstrated that the pre|CISION™ substrate is exquisitely sensitive to FAP and is not cleaved by related proteases. The active PI warhead is released from AVA3996 following FAP cleavage in the tumor microenvironment, reducing systemic exposure and hence associated toxicities. Here we show that exposure of tumor cell line/fibroblast cell co-cultures to AVA3996 results in tumor cell death which is dependent on the presence of FAP on the fibroblasts. AVA3996 also shows potent tumor growth inhibition in vivo with the active warhead accumulating at high levels in the tumor with little in the plasma relative to parent drug AVA3996. A DRF/MTD study established that the maximum tolerated dose in rats was around 6-fold higher for AVA3996 compared to warhead alone. This provides further evidence that AVA3996 can be dosed at higher levels than proteasome inhibitor alone, with the potential for greater tumor targeting and improved therapeutic index. This disease positioning data presented here, including in vivo models, immunohistochemical analysis of clinical material and ongoing safety studies, further validate the efficacy and tolerability profile of AVA3996 and supports further development of this drug. Overall, the data supports wider utility of the pre|CISION™ platform to target warheads to the tumor while reducing systemic dose-limiting toxicities. Citation Format: David Jones, Curtis Rink, Sergi Marco, Marine Houee, Hanna Buist, Folake Orafidiya, Francis Wilson, Chiara Braconi, Fiona McLaughlin. AVA3996, a novel pre|CISION™ medicine, targets a warhead to the tumor microenvironment via Fibroblast Activation Protein (FAP) mediated cleavage to elicit tumor cell kill [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C169.