Synthesis and Evaluation of Derivatives of the Proteasome Deubiquitinase Inhibitor b‐AP15

Xin Wang, Pádraig D'Arcy, Thomas R. Caulfield, Aneel Paulus, Kasyapa Chitta, Chitralekha Mohanty, Joachim Gullbo, Asher Chanan‐Khan, Stig Linder

The ubiquitin-proteasome system (UPS) is increasingly recognized as a therapeutic target for the development of anti-cancer 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 structural 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 proteasomal 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-proteasomal 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. This article is protected by copyright. All rights reserved.