Novel p97/<scp>VCP</scp> inhibitor induces endoplasmic reticulum stress and apoptosis in both bortezomib‐sensitive and ‐resistant multiple myeloma cells

Abstract

Abstract p97/ VCP is an endoplasmic reticulum ( ER )‐associated protein that belongs to the AAA ( ATP ases associated with diverse cellular activities) ATP ase family. It has a variety of cellular functions including ER ‐associated protein degradation, autophagy, and aggresome formation. Recent studies have shown emerging roles of p97/ VCP and its potential as a therapeutic target in several cancer subtypes including multiple myeloma ( MM ). We conducted a cell‐based compound screen to exploit novel small compounds that have cytotoxic activity in myeloma cells. Among approximately 2000 compounds, OSSL _325096 showed relatively strong antiproliferative activity in MM cell lines ( IC 50 , 100‐500 nmol/L). OSSL _325096 induced apoptosis in myeloma cell lines, including a bortezomib‐resistant cell line and primary myeloma cells purified from patients. Accumulation of poly‐ubiquitinated proteins, PERK , CHOP , and IRE α, was observed in MM cell lines treated with OSSL _325096, suggesting that it induces ER stress in MM cells. OSSL _325096 has a similar chemical structure to DB eQ, a known p97/ VCP inhibitor. Knockdown of the gene encoding p97/ VCP induced apoptosis in myeloma cells, accompanied by accumulation of poly‐ubiquitinated protein. IC 50 of OSSL _325096 to myeloma cell lines were found to be lower (0.1‐0.8 μmol/L) than those of DB eQ (2‐5 μmol/L). In silico protein–drug‐binding simulation suggested possible binding of OSSL _325096 to the ATP binding site in the D2 domain of p97/ VCP . In cell‐free ATP ase assays, OSSL _325096 showed dose‐dependent inhibition of p97/ VCP ATP ase activity. Finally, OSSL _325096 inhibited the growth of subcutaneous myeloma cell tumors in vivo. The present data suggest that OSSL _325096 exerts anti‐myeloma activity, at least in part through p97/ VCP inhibition.