Selective, ATP-competitive p38 inhibitor (IC50 = 9 nM for p38α in vitro). Displays approximately 10-fold selectivity for p38α over p38β and 2000-fold selectivity for p38α over 20 other kinases. Reduces p38α phosphorylation in multiple myeloma cells in vitro and in vivo; activity results in decreased tumor burden and angiogenesis in murine models of multiple myeloma. Also enhances bortezomib-induced cytotoxicity against multiple myeloma cells.