Development of a novel small molecule RPN13 inhibitor and therapeutic for advanced ovarian cancer patients

Epithelial ovarian cancer (EOC) is the most lethal gynecological malignancy despite aggressive surgery and toxic chemotherapies. More effective and safer targeted drugs are urgently needed to address this unmet medical need. Compared to normal tissues, EOC exhibits aberrant proteasome function that triggers accumulation of high molecular weight polyubiqutinated and misfolded protein aggregates. Because of this unresolved proteotoxic stress, EOC cell lines are highly susceptible to proteasome inhibitors. While highly effective against liquid cancers like multiple myeloma, unfortunately the licensed 20S proteasome inhibitors, such as bortezomib, have proven ineffective against solid tumors, including EOC. This reflects limited tissue access for these peptide-based drugs and dose-limiting toxicities, notably peripheral neuropathy, thrombocytopenia and neutropenia. Up284 is a proprietary upstream (19S) proteasome inhibitor with a novel target and mechanism, RPN13 inhibition, and a structure designed to overcome the limitations of the licensed drugs with respect to limited potency (Up284 blocks substrate recognition and deubiquitination by the 19S rather than just one of the three 20S catalytic activities), poor activity against solid tumors (Up284 has a novel spiro structure with improved drug-like properties compared to peptide-based 20S inhibitors, and promotes antigen-representation by tumor cells), key toxicities of peripheral neuropathy (Not clinically apparent with Up284 in initial murine studies) and thrombocytopenia and neutropenia (Up284 spares the immunoproteasome and lacks these side effects). Up284 shows broad anticancer activity in vitro, including against EOC lines selected for platinum resistance, with a robust therapeutic index and a promising safety profile, and the ability to control xenograft tumor in an orthotopic mouse model of EOC. This promising data reflects our extensive medicinal chemistry effort to achieve drug-like properties and a patent has been awarded in US (pending in other countries) to cover the novel backbone and lead compounds. Murine data indicate Up284 has favorable pharmacodynamics and confirm the novel mechanism of action in vivo. By inhibiting proteasome ubiquitin receptor RPN13 function and its associated deubiquitinase activity, Up284 produces more rapid accumulation of larger molecular weight polyubiquinated protein aggregates than the 20S inhibitors. These toxic misfolded protein aggregates produce an unresolved ER stress, activate the canonical Unfolded Protein Response (UPR) and thus Up284 more rapidly triggers p53-independent apoptosis than 20S inhibitor. To support an IND application to FDA, we propose: Aim 1: Assessing toxicity & Peripheral Neuropathy (PN) in mice treated IP vs IV with Up284 vs. bortezomib (months 1-3). Aim 2: Mouse clinical trial: Testing therapeutic efficacy of Up284 delivered IP vs IV against 13 ovarian PDX models (months 3-7); Aim 3: Process development, GLP manufacture, formulation stability & GLP bioanalytical method development of Up284 (months 7-24); Aims 4 & 5: GLP toxicology and safety studies of Up284 in rats & dogs (months 15-24).