Project Summary This proposal aims to develop QNBC as the lead indication for our ADRM1 inhibitor, Up284, and support biomarker development to select QNBC patients for ADRM1 inhibitor therapy. It addresses critical questions for the development of effective and safe treatments for QNBC and the reduction of the disparity in breast cancer outcomes. Quadruple negative breast cancer (QNBC) is a subtype of breast cancer that does not express the hormone receptors ER and PR, the growth factor receptor HER2, and the androgen receptor AR. QNBC has the poorest prognosis among breast cancer subtypes and disproportionately affects African Americans. Currently, there is no standard-of-care treatment for QNBC, and there is an urgent need to develop effective and safe treatments and biomarkers to address this unmet medical need and the disparity in breast cancer outcomes. Our research team has recently found that elevated expression of proteasome subunit ADRM1 is associated with both African American race and lower survival in QNBC patients. Our collaborator Up Therapeutics developed an inhibitor called Up284 that targets ADRM1. While QNBC and triple negative breast cancer (TNBC) cell lines show evidence of greater vulnerability to proteasome inhibitors, approved 20S proteasome inhibitors like bortezomib have proven ineffective against solid tumors due to their partial proteasome inhibition, inability to achieve therapeutic doses, and poor pharmacokinetic properties. Up284 is a novel small molecule designed to overcome these limitations. Its structure is a non-peptide spiro compound with improved drug access and favorable pharmacokinetic properties to solid tumors compared to peptide-based 20S inhibitors. Up284 also blocks substrate recognition and deubiquitination, providing full proteasome inhibition and avoiding key toxicities like thrombocytopenia and neutropenia. In vitro studies show that Up284 has broad anticancer activity, including against QNBC lines and patient-derived organoids. It has a promising safety profile and pharmacodynamics and can control syngeneic and xenograft tumors. By inhibiting proteasome ubiquitin receptor ADRM1 function and its associated deubiquitinase activity, Up284 triggers more rapid accumulation and increased molecular weight polyubiquitinated protein aggregates than 20S inhibitors. These toxic misfolded protein aggregates produce unresolved ER stress and activate the canonical Unfolded Protein Response (UPR) signaling cascade, leading to more rapid apoptosis than 20S inhibitors. We plan to examine ADRM1 and ER stress markers' expression in diverse QNBC patient samples and validate sensitivity to Up284 to develop a biomarker for selecting patients for better therapeutic efficacy and safety. We also will validate the synergy of Up284 efficacy in combination with in-clinic chemotherapeutic agents used to treat TNBC to improve therapeutic response and block the emergence of resistance. Finally, we will assess Up284's potential t...