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).

Grant Number: 5R44CA278176-02
NIH Institute/Center: NIH
Principal Investigator: RAVI ANCHOORI