Abstract 1781: Up284, a novel inhibitor to treat quadruple negative breast cancer

Abstract Quadruple negative breast cancer (QNBC), lacking the expression of ER (estrogen receptor), PR (progesterone receptor), HER2 (human epidermal growth factor receptor 2) and AR (androgen receptor), is the breast cancer subtype with the worst prognosis, and QNBC disproportionately afflicts African Americans. It has no standard-of-care treatment targets and thus efficacious and safe treatments are urgently sought for this unmet medical need, and to address the disparity in breast cancer outcomes. The current proposal is motivated by data showing elevated expression of proteasome subunit RPN13 is associated with both African American race and lower survival in QNBC patients, that RPN13 selectively targeted by a small molecule Up284 developed by Up Therapeutics. Both triple negative breast cancer and QNBC cell lines show evidence of greater vulnerability to proteasome inhibitors. However, licensed 20S proteasome inhibitors, e.g. bortezomib, have proven ineffective against solid tumors, with emergence of resistance, and dose limiting toxicities including thrombocytopenia and neutropenia. Up284 has a target and structure designed to overcome the limitations of the licensed drugs with respect to drug resistance. Up284 blocks substrate recognition and deubiquitination rather than just one of the three 20S catalytic activities), poor activity against solid tumors (Up284 has a novel spiro structure with evidence of improved drug access to tumor as compared to peptide-based 20S inhibitors), key toxicities of thrombocytopenia and neutropenia (unlike 20S inhibitors, Up284 does not target the immunoproteasome expressed by hematopoietic cells and does not show these toxicities). Up284 shows broad anticancer activity in vitro, including against QNBC lines with a robust therapeutic index, a promising safety profile and pharmacodynamics, and the ability to control xenograft tumor. By inhibiting proteasome ubiquitin receptor RPN13 function and its associated deubiquitinase activity, Up284 triggers more rapid accumulation and increased molecular weight polyubiquinated protein aggregates than is induced by 20S inhibitors. These toxic misfolded protein aggregates produce an unresolved ER stress, activate the canonical Unfolded Protein Response (UPR) signaling cascade and more rapidly triggers apoptosis than 20S inhibitor. The safety parameters and promising efficacy of Up284 against breast cancer lines encourages us to validate Up284 efficacy in more QNBC lines and animal models. We discuss Up284 efficacy and pharmacological analysis in our presentation. Citation Format: Balasubramanyam Karanam, Clayton Yates, Ravi Anchoori. Up284, a novel inhibitor to treat quadruple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1781.