Discovery of BMS-986449: A Potent, Selective Degrader of the Transcription Factors IKZF2 (Helios) and IKZF4 (Eos) to Target Regulatory T Cells in Solid Tumors

Within the tumor microenvironment (TME), regulatory T (Treg) cells promote an immunosuppressive state with limited tumor antigen presentation and antitumor effector T (Teff) cell responses, which can drive resistance to cancer immunotherapies. IKZF2 (Helios) is a transcription factor essential for stabilizing the immunosuppressive Treg cell phenotype in tumors. Herein, we present the discovery of BMS-986449, a selective Cereblon E3 Ligase Modulatory Drug (CELMoD) degrader of IKZF2 and IKZF4 (Eos) that spares the closely related transcription factors IKZF1 (Ikaros) and IKZF3 (Aiolos). BMS-986449 is an orally available degrader that demonstrates single-agent growth inhibition of syngeneic MC38 tumors implanted in humanized Cereblon (CRBN) knock-in mice. Tumor growth inhibition was more robust when BMS-986449 was administered in combination with anti-PD-1. Nonhuman primates administered daily with BMS-986449 show sustained IKZF2 degradation in Treg cells providing confidence in human clinical doses. Collectively, these findings establish BMS-986449 as a promising clinical candidate for cancer immunotherapy.