Abstract 1540: A click chemistry-activated auristatin protodrug (TCO-MMAE) demonstrates potency and safety with antibody and intratumoral tumor-targeting agents

Abstract Click chemistry encompasses chemical reactions that are highly efficient, rapid and proceed in complex environments. The 2022 Nobel prize in Chemistry was awarded to Sharpless, Meldal and Bertozzi in recognition of the transformative effect click chemistry has had in research and drug development. Using click chemistry to precisely control the activation of drugs at tumors, Shasqi has developed the Click Activated Protodrugs Against Cancer (CAPAC™) platform. In essence, a click chemistry activator is localized to tumors, which subsequently activates protodrug(s) bearing the companion click chemistry reaction partner. Shasqi is pioneering the use of click chemistry in the clinic. The lead candidate SQ3370 consists of an intratumorally (IT) injected tetrazine (Tz)-modified biopolymer and an intravenously (IV) administered trans-cyclooctene (TCO)-modified doxorubicin (Dox) protodrug. SQ3370 provides enhanced safety and efficacy in preclinical models compared to conventional Dox and is being evaluated in a Phase 2a study in soft tissue sarcomas (NCT04106492). We will present our research on an MMAE-based protodrug (TCO-MMAE), which is stable in plasma with dramatically attenuated activity in vitro and in vivo without the Tz activator. When treated with an activator in vitro, the potent cytotoxic activity of MMAE is restored. When paired with the Tz-biopolymer (IT), testing in the Karpas299 model of human non-Hodgkin’s lymphoma led to 6 of 8 (75%) complete responses in the test group. Treatment with TCO-MMAE (IV) + Tz-biopolymer (IT) also elicited significant tumor growth inhibition (p-value <0.01) in the RENCA model of murine renal adenocarcinoma. Modest body weight loss and transient cytopenia support the tolerability of the treatment. To enable systemic delivery of the click chemistry activator, we are developing a series of antigen-targeted conjugates to pair with the TCO-MMAE protodrug. We designed and generated a Fab-Tz conjugate that binds HER2. The conjugate had an average of 2.2 Tz per Fab and efficiently bound HER2-positive NCI-N87 cells. In a xenograft model of gastric cancer (NCI-N87), the Fab-Tz was dosed IV, followed by the TCO-MMAE protodrug (IV). Treatment with HER2 Fab-Tz + TCO-MMAE induced significant tumor regression compared to vehicle while a negative control Fab-Tz + TCO-MMAE treatment did not (p-value <0.05). To date, we have demonstrated the versatility and modularity of the CAPAC platform. Anti-tumor activity was observed in multiple preclinical models for the TCO-MMAE protodrug in combination with both biopolymer and Fab targeting agents. These results highlight the power of click chemistry to activate a protodrug at the tumor site, independent of tumor biology, the molecular format or delivery method of the targeting agent. Citation Format: Jesse M. McFarland, Masa Aleckovic, George Coricor, Sangeetha Srinivasan, Leslie Priddy, Matthew Tso, Tri-Hung Nguyen, John Lee, José M. Mejía Oneto. A click chemistry-activated auristatin protodrug (TCO-MMAE) demonstrates potency and safety with antibody and intratumoral tumor-targeting agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1540.