Abstract 4061: Preclinical characterization of MBS309, a conditionally active PD-1-dependent IL-2 mutation with significantly superior anti-tumor efficacy with safety

Abstract Although PD-1/PD-L1 therapies have shown significant benefit among a range of tumor types, the majority of malignancy patients do not respond or develop resistance after initial tumor regression. Development of new modality to overcome primary and acquired resistance to anti-PD-1/PD-L1 therapy is a huge unmet medical need, and IL-2 is believed a potentially powerful approach for that. However, the current clinical application of IL-2 in cancer immunotherapy has been limited by its severe toxicity. Herein, we developed MBS309 (PD1/IL2m), a novel PD-1-targeted IL-2 mutation with significantly enhanced therapeutic window. MBS309 has the similar high affinity and blockade efficacy with monoclonal antibody to PD-1, and its IL-2 mutation has reduced binding to IL-2Rβγ and abolished binding to IL-2Rα. Our in vitro assays, including HEK-blue assay and CD3+ T cell assay, both indicated that the IL-2 receptor agonist activity of MBS309 was conditionally induced only the antibody cis-binding to both PD-1 and IL-2 Rβγ. And the maximal agonist activities of MBS309 in HEK-blue assay and CD3+ T cell assay were much lower than wild-type IL-2 and RG6279 analog enabling its high tolerated drug doses in vivo. In our in vivo tumor murine models, 1mg/kg MBS309 showed much better suppression effect in MC38/hPD-L1 tumor than 1mg/kg RG6279 analog and Pembrolizumab (1mg/kg) combination with wild type IL-2 (0. 1mg/kg) ; And MBS309 at the dosage of 5mg/kg can significantly inhibit tumor growth in PD-1 resistant Pan-02 xenograft models without any side-effects observed, while RG6279 analog at the dosage of 5mg/kg induced severe body reduction of the mice and resulted in 80% (4/5) mice death after two dosages. MBS309 showed similar PK profile with anti-PD-1 monoclonal antibody and much better than RG6279 analog in mouse model. 20mg/kg of MBS309 was well tolerated in mouse, while 10mg/kg of RG6279 analog or PF-07209960 analog show severe toxicity and resulted in death of all the mice. Pharmacodynamic studies in murine models showed that MBS309 prioritized active tumor infiltrated PD-1+ CD8 T cells rather than other organs. Taken together, MBS309 effectively expands tumor infiltrated T-cells, and avoids system immune cytokine side effects compared to other PD-1-targeted 2nd generation IL-2Rβγ agonist modalities currently in clinical development. And it shows much higher anti-tumor effect compared to anti-PD-1/-L1 antibodies alone in both PD-1 sensitive and resistant tumor models. MBS309 has demonstrated a favorable safety profile and highly anti-tumor activities in vivo, which has the potential to supporting its clinical development for the treatment of cancer. Citation Format: Jiangmei Li, Guangzhong Lin, Lunfeng Zhang, Feng Li. Preclinical characterization of MBS309, a conditionally active PD-1-dependent IL-2 mutation with significantly superior anti-tumor efficacy with safety abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 4061.