Abstract 7514: Tumor intrinsic CDC42BPB confers resistance to anti-PD-1 immune checkpoint blockade in breast cancer

Abstract Immune checkpoint blockade has been used to treat breast cancer, but the clinical responses remain relatively poor, especially for the triple-negative subtype. The weak responsiveness is attributed to tumor intrinsic as well as tumor extrinsic factors, suggesting a need for novel approaches. We have used the CRISPR Cas9 kinome knockout library consisting of 763 kinase genes to identify tumor intrinsic kinase conferring resistance to anti-PD-1 immune checkpoint blockade and identified the CDC42BPB kinase as a potential target to overcome the resistance to anti-PD-1 immunotherapy. We found that CDC42BPB is highly expressed in breast cancer patients who are non-responsive to immunotherapy. Importantly, a small molecule pharmacological inhibitor, BDP5290, which targets CDC42BPB synergized with anti-PD-1 and enhanced tumor cell killing by promoting T-cell proliferation in both in vitro and in vivo assays. Moreover, anti-PD-1 resistant breast cancer cells showed higher expression of CDC42BPB, and its inhibition rendered the resistant cells more susceptible to T cell killing in the presence of anti-PD-1. We also found that CDC42BPB phosphorylated AURKA which in turn upregulated PD-L1 through cMYC. Our results have revealed a robust link between tumor intrinsic kinase and immunotherapy resistance and provided a rationale for a novel combination therapy of CDC42BPB inhibition and anti-PD-1 immunotherapy for breast cancer. Citation Format: Ravindra Pramod Deshpande, Kerui Wu, Shih-Ying Wu, Abhishek Tyagi, John Hunting, Jimmy Ruiz, Wencheng Li, Kounosuke Watabe. Tumor intrinsic CDC42BPB confers resistance to anti-PD-1 immune checkpoint blockade in breast cancer [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(6_Suppl):Abstract nr 7514.