Metastatic disease is the primary cause of cancer mortality, but effective treatments remain elusive. Therefore, our LONG-TERM GOAL is to address the CRITICAL NEED for more targeted strategies to treat metastatic disease. The Rho family GTPases Rac and Cdc42 and their downstream effector p21-activated kinase (PAK) are pivotal regulators of metastatic cancer cell migration and invasion; and thus, represent ideal targets for prevention of metastasis. Rac and Cdc42 do not have to be overexpressed in cancer to drive metastasis, because they can be over activated by oncogenic cell surface receptor signaling pathways. Therefore, we developed MBQ-167, which inhibits Rac and Cdc42 activation by blocking GTP exchange without affecting expression. MBQ-167 is superior to other known Rac/Cdc42 inhibitors, and inhibits cell and tumor growth, metastasis and survival of metastases in breast and pancreatic cancer cell and mouse models at low physiological concentrations. Moreover, MBQ-167 has an excellent safety profile in both rodents and dogs (both non-GLP and GLP studies completed) up to 1000 mg/kg body weight and has acceptable bioavailability in rodent and dog plasma and tumor tissue (IND submitted to the US FDA). The rationale for this application stems from the PI’s SC3 GM084824 award (2008-2022), which resulted in ~25 publications, 3 patents, graduated 8 Ph.D. students, and trained numerous graduate and undergraduate students, all of whom are underrepresented minorities. During the present cycle of the SC3 award, we identified two new Rac/Cdc42 inhibitors, MBQ-168 and EHop-097, with enhanced efficacy compared to their respective parent molecules MBQ-167 and EHop-016. This SuRE proposal will test the HYPOTHSIS that Rac/Cdc42 inhibitors are viable antimetastatic cancer therapeutics in breast and pancreatic cancer. Aim 1 will demonstrate the efficacy, safety, and bioavailability of Rac/Cdc42 inhibitors MBQ-168 and EHop-097 in pre-clinical mouse models using chemiluminescence imaging of luciferase tagged breast and pancreatic cancer cells in mice from spontaneous and experimental metastasis assays. Aim 2 will demonstrate the efficacy of Rac/Cdc42 inhibitors in ex vivo cultures of patient tissues. Our innovative research design will use fresh breast and pancreatic cancer patient tissue (from biopsies and surgery), in ex vivo cultures, to test for changes in cancer cell proliferation, immune cell infiltration, and inhibitor efficacy following short-term vehicle, MBQ-167, MBQ-168, or EHop-097 treatment. Drug efficacy in cancer cells and the immune cells infiltrating the tumor microenvironment (TME) will be assessed in situ via immunohistochemistry, using specific antibodies to pharmacodynamic markers of Rac/Cdc42 efficacy, as well as immune cells in the TME. The OUTCOME of this study will delineate the complex action of Rac/Cdc42 inhibitors in experimental mouse models and patient tissues and forward the translational development of Rac/Cdc42 inhibitors in panc...