Abstract 7628: Pharmacodynamic biomarkers for Rac and Cdc42 inhibitor efficacy

Abstract Metastatic disease drastically reduces clinical prognosis, and remains the primary cause of mortality from solid cancers, such as breast and pancreatic cancer. Since targeted therapeutic options are limited, we developed small molecule compounds to block activation (GTP loading) of the Rho GTPases Rac and Cdc42. Rac and Cdc42 are ideal molecular targets due to their regulation of cell migration, proliferation, invasion, and signaling in cancer and immunosuppressive cells in the tumor microenvironment. Our lead compound MBQ-167 is a dual Rac and Cdc42 inhibitor with IC50 of ~100 nM for inhibition of Rac/Cdc42 activation and the phosphorylation of their common downstream effector p21-activated kinase (PAK). MBQ-167 is highly effective in mouse models of breast cancer metastasis and is currently undergoing a Phase I clinical trial in advanced breast cancer patients. The purpose of this study is to investigate potential target molecules that can be used as biomarkers predictive of Rac/Cdc42 inhibitor efficacy. We recently published that in addition to inhibiting the growth and migration of breast and pancreatic cancer cells, MBQ-167 inhibits macrophage cell migration, immunosuppressive myeloid cell activation and release of interleukin-6 (IL-6), a pro-inflammatory cytokine associated with cancer. Transcriptomic data of tumors from mice treated with vehicle or MBQ-167 identified a number of immunomodulatory pathways downregulated by MBQ-167, including IL-6 and S100A family signaling, and Chitinase 3-like (CHI3L1/CHI4L1) genes coding for the human YKL-40 protein. We tested for the activation status of PAK (phospho (p) -PAK) as a diagnostic marker for Rac/Cdc42 inhibitor efficacy using breast cancer patient tissue in ex vivo culture treated with vehicle or MBQ-167 and found decreased p-PAK staining following immunohistochemistry of MBQ-167-treated tissue. From flow cytometry, using Alexa-488-tagged anti p-PAK antibody, we found that p-PAK was reduced from peripheral blood mononuclear cells (PBMCs) following MBQ-167. ELISA assays for YKL-40/CHI3L1 proteins after treatment of pancreatic cancer cell lines and macrophage-like cells with Rac/Cdc42 inhibitors show that MBQ-167 and the derivative MBQ-168 reduced CHI3L1 levels from conditioned media. These results demonstrate the potential of p-PAK and YKL-40/CHI3L1 from blood as biomarkers for Rac/Cdc42 inhibitor efficacy. This study impacts pharmacodynamic biomarker design for the planned Phase 2 clinical trials for MBQ-167 in breast and pancreatic cancer. Citation Format: Anamaris Torres-Sanchez, Ailed M. Cruz-Collazo, Michael Rivera-Robles, Olga Katsara, Stephanie Dorta-Estremera, Viviana Negron, Victor P. Carlo, Robert J. Schneider, Suranganie Dharmawardhane. Pharmacodynamic biomarkers for Rac and Cdc42 inhibitor efficacy 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 7628.