Cancer Immunotherapy has established itself as the fourth pillar of cancer treatment thanks to the clinical success of checkpoint inhibitors. Despite the durable responses achieved by some patients using these new therapies, the proportion of responders remains low and restricted to some cancer types. Preclinical and clinical studies have demonstrated the promise of cytokine therapy to increase antitumor immunity, however systemic toxicity and poor pharmacokinetic profiles have limited their clinical application. One of these key cytokines, interleukin-2 (IL-2), is approved for clinical use in metastatic melanoma and renal cell carcinoma. Unfortunately, this treatment is linked to serious toxicities which limits its utility. To address these limitations, our approach takes advantage of the dysregulated protease tumor microenvironment (TME) to activate an IL-2 pro-drug (IL-2 INDUKINETM) only at the desired site of activity. Peripheral inactivation is achieved by linking the cytokine to an inactivation domain using a tumor protease-sensitive linker. The INDUKINE is also engineered with a half-life extension element to improve tumor exposure. Once the IL-2 INDUKINETM reaches the tumor, tumor-associated proteases cleave the linker and release the active cytokine. This work presents data summarizing the discovery, biochemical, cellular, and in vivo activity of our lead IL-2 INDUKINETM WTX-124 and reviews the mechanism of action of these molecules. Treatment with WTX-124 results in complete regression of tumors driven by the expansion and activation of CD8+ T cells and NK cells which increases the production of effector cytokines in the tumor. Activity is dependent on the proteolytic processing of the INDUKINE as a non-cleavable control INDUKINE lacks efficacy. PK analysis in mouse models demonstrates a favorable accumulation of free IL-2 in tumors compared to plasma. The animals that rejected the tumors upon IL-2 INDUKINETM treatment were protected against follow up re-challenge with the same tumor cell line. In vitro proteolytic activation by human tumor samples will also be presented. The tumor-selective activation of WTX-124 with reduced peripheral toxicities supports its further clinical development.

Citation Format: Andres Salmeron, Heather Brodkin, Daniel Hicklin, Nesreen Ismail, Kristin Morris, Christopher Nirschl, Cynthia Seidel-Dugan, Philipp Steiner, Zoe Steuert, Jenna Sullivan, William Winston. WTX-124 is an IL-2 pro-drug conditionally activated in tumors and able to induce complete regressions in mouse tumor models [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 1723.