Abstract 3258: THOR-707, a novel not-alpha IL-2, elicits durable pharmacodynamic responses in non-human primates and efficacy as single agent and in combination with anti PD-1 in multiple syngeneic mouse models

Current landscape and future prospects of interleukin-2 receptor (IL-2R) agonists in cancer immunotherapy

Immune checkpoint blockade (ICB) has significantly improved the survival for many patients with advanced malignancy. However, fewer than 50% of patients benefit from ICB, highlighting the need for more effective immunotherapy options. High-dose interleukin-2 (HD IL-2) immunotherapy, which is approved for patients with metastatic melanoma and renal cell carcinoma, stimulates CD8+ T cells and NK cells and can generate durable responses in a subset of patients. Moreover, HD IL-2 may have potential efficacy in patients whose disease has progressed following ICB and plays a vital role in expanding tumor-infiltrating lymphocyte (TIL) in TIL therapy. Despite its potential, the use of HD IL-2 is limited by severe toxicities such as hypotension and vascular leak syndrome. Additionally, only a few patients achieve a good outcome after HD IL-2 therapy. To address these challenges, numerous next-generation IL-2 receptor (IL-2 R) agonists have been developed to exhibit treatment effects while minimizing adverse events. This review will explore IL-2 biology, the clinical application of HD IL-2 therapy, and the development of novel IL-2 R agonists for cancer immunotherapy.

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).