An orally available inhibitor of the beta-isoform of protein kinase C (PKC), with potential immunosuppressive and antineoplastic activities. Upon oral administration, PKC-beta inhibitor MS-553 selectively binds to and inhibits PKC-beta, which prevents the activation of PKC-beta-mediated signaling pathways. This may lead to the induction of cell cycle arrest and apoptosis in susceptible tumor cells. PKC-beta, a serine/threonine protein kinase overexpressed in certain types of cancer cells, is involved in tumor cell differentiation, proliferation, invasion and survival.