D’Arcy, Pádraig

Abstract Inhibitors of the proteasome-ubiquitin system have been found to be effective in the clinical management of multiple myeloma. We here describe the compound VLX1570, an optimized lead of the 19S deubiquitinase inhibitor b- AP15. VLX1570 was shown to inhibit the enzymatic activities of both USP14 and UCHL5 in vitro, and was shown to induce accumulation of high molecular weight polyubiquitinated proteins in multiple myeloma cells. The compound showed limited inhibitory activity of a panel of kinases. VLX1570 induces apoptosis and cell death of multiple myeloma cell lines at submicromolar concentrations. Importantly, a multiple myeloma cell line selected for bortezomib resistance was found to be sensitive to VLX1570. VLX1570 was found to be able to overcome apoptosis resistance by these cells. Induction of the phosphorylation of stress-activated kinases (JNK and p38) and inhibition of ERK phosphorylation was observed in multiple myeloma cells. We finally showed that VLX1570 confers antineoplastic activity in two different myeloma xenograft models and conclude that VLX1570 is a candidate agent for treatment of multiple myeloma. Citation Format: Xin Wang, Chitralehka Mohanty, Padraig D'Arcy, Maria Hägg Olofsson, Felicitas Bossler, Asher Chanan-Khan, Stig Linder. Development of the proteasome deubiquitinase inhibitor VLX1570 for treatment of multiple myeloma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4557A. doi:10.1158/1538-7445.AM2015-4557A

The ubiquitin–proteasome system (UPS) is increasingly recognized as a therapeutic target for the development of anticancer therapies. The success of the 20S proteasome core particle (20S CP) inhibitor bortezomib in the clinical management of multiple myeloma has raised the possibility of identifying other UPS components for therapeutic intervention. We previously identified the small molecule b‐AP15 as an inhibitor of 19S proteasome deubiquitinase (DUB) activity. Building upon our previous data, we performed a structure–activity relationship (SAR) study on b‐AP15 and identified VLX1570 as an analog with promising properties, including enhanced potency and improved solubility in aqueous solution. In silico modeling was consistent with interaction of VLX1570 with key cysteine residues located at the active sites of the proteasome DUBs USP14 and UCHL5. VLX1570 was found to inhibit proteasome deubiquitinase activity in vitro in a manner consistent with competitive inhibition. Furthermore, using active‐site‐directed probes, VLX1570 also inhibited proteasome DUB activity in exposed cells. Importantly, VLX1570 did not show inhibitory activity on a panel of recombinant non‐proteasome DUBs, on recombinant kinases, or on caspase‐3 activity, suggesting that VLX1570 is not an overtly reactive general enzyme inhibitor. Taken together, our data shows the chemical and biological properties of VLX1570 as an optimized proteasome DUB inhibitor.