HDAC inhibitors potentiate the apoptotic effect of enzastaurin in lymphoma cells.

Enzastaurin is an investigational PKCβ inhibitor that has growth inhibitory and pro-apoptotic effects in both B and T-cell lymphomas. We investigated the cytotoxicity and mechanisms of cell death of the combination of enzastaurin and low concentrations of histone deacetylase (HDAC) inhibitors in B-cell and T-cell lymphoma cell lines and primary lymphoma/leukemia cells. Combined enzastaurin/suberoylanilide hydroxamic acid treatment synergistically induced apoptosis in diffuse large B-cell lymphoma and T-cell lymphoma cell lines, and primary lymphoma/leukemia samples. Similarly, combined treatment of B-cell-like lymphoma cells with enzastaurin and two different HDAC inhibitors, valproic acid and (2E,4E)-6-(4-chlorophenylsulfanyl)-2,4-hexadienoic acid hydroxyamide synergistically induced apoptosis, suggesting the synergy is generalizable to other HDAC inhibitors. Our data indicate that enzastaurin/HDAC inhibitors therapy can synergistically inhibit growth and induce apoptosis in lymphoid malignancies and may be an effective therapeutic strategy. Potential mechanisms including enzastaurin mediated inhibition of HDAC inhibitor-induced compensatory survival pathways are discussed.