AR-42 (also known as OSU-HDAC42), a derivative of hydroxamate-tethered phenylbutyrate is a broad-spectrum deacetylase inhibitor of both histone and non-histone proteins. AR-42 treatment induces histone hyperacetylation and p21WAF/CIP1 overexpression, inhibits gp130/Stat3 pathway and induces apoptosis and cell cycle arrest in multiple myeloma cells.