TransCon IL-2 β/γ: a novel long-acting prodrug with sustained release of an IL-2Rβ/γ-selective IL-2 variant with improved pharmacokinetics and potent activation of cytotoxic immune cells for the treatment of cancer

BACKGROUND: Recombinant interleukin-2 (IL-2, aldesleukin) is an approved cancer immunotherapy but causes severe toxicities including cytokine storm and vascular leak syndrome (VLS). IL-2 promotes antitumor function of IL-2Rβ/γ(+) natural killer (NK) cells and CD8(+), CD4(+) and gamma delta (γδ) T cells. However, IL-2 also potently activates immunosuppressive IL-2Rα(+) regulatory T cells (Tregs) and IL-2Rα(+) eosinophils and endothelial cells, which may promote VLS. Aldesleukin is rapidly cleared requiring frequent dosing, resulting in high C(max) likely potentiating toxicity. Thus, IL-2 cancer immunotherapy has two critical drawbacks: potent activation of undesired IL-2Rα(+) cells and suboptimal pharmacokinetics with high C(max) and short half-life. METHODS: TransCon IL-2 β/γ was designed to optimally address these drawbacks. To abolish IL-2Rα binding yet retain strong IL-2Rβ/γ activity, IL-2 β/γ was created by permanently attaching a small methoxy polyethylene glycol (mPEG) moiety in the IL-2Rα binding site. To improve pharmacokinetics, IL-2 β/γ was transiently attached to a 40 kDa mPEG carrier via a TransCon (transient conjugation) linker creating a prodrug, TransCon IL-2 β/γ, with sustained release of IL-2 β/γ. IL-2 β/γ was characterized in binding and primary cell assays while TransCon IL-2 β/γ was studied in tumor-bearing mice and cynomolgus monkeys. RESULTS: IL-2 β/γ demonstrated selective and potent human IL-2Rβ/γ binding and activation without IL-2Rα interactions. TransCon IL-2 β/γ showed slow-release pharmacokinetics with a low C(max) and a long (>30 hours) effective half-life for IL-2 β/γ in monkeys. In mouse tumor models, TransCon IL-2 β/γ promoted CD8(+) T cell and NK cell activation and antitumor activity. In monkeys, TransCon IL-2 β/γ induced robust activation and expansion of CD8(+) T cells, NK cells and γδ T cells, relative to CD4(+) T cells, Tregs and eosinophils, with no evidence of cytokine storm or VLS. Similarly, IL-2 β/γ enhanced proliferation and cytotoxicity of primary human CD8(+) T cells, NK cells and γδ T cells. SUMMARY: TransCon IL-2 β/γ is a novel long-acting prodrug with sustained release of an IL-2Rβ/γ-selective IL-2. It has remarkable and durable pharmacodynamic effects in monkeys and potential for improved clinical efficacy and tolerability compared with aldesleukin. TransCon IL-2 β/γ is currently being evaluated in a Phase 1/2 clinical trial (NCT05081609).