Analysis of the Effect of the Novel Histone Deacetylase Inhibitor, Depsipeptide (FK228/FR901228) on Mantle Cell Lymphoma.

Background: Mantle cell lymphoma (MCL) comprises approximately 3–5% of the non-Hodgkin’s lymphomas and the vast majority of these patients are incurable. Histone deacetylases (HDAC) inhibitors are a new class of chemotherapeutic drugs that have been shown to inhibit cell proliferation and induce apoptosis in a variety of malignancies. Depsipeptide (FK228/FR901228) is a novel inhibitor of class I HDAC and was shown to be effective in patients with cutaneous T-cell lymphoma.

Design: A MCL cell line, JeKo-1 was treated with varying concentrations of depsipeptide and analyzed for evidence of apoptosis. Apoptosis was analyzed by flow cytometry (Annexin and 7AAD staining) and by microscopic examination. The effect on the status of H3 histone acetylation and changes in the expression of the Bcl-2 family proteins (Bcl-2, Bcl-xl and Mcl-1) following treatment with depsipeptide were investigated by flow cytometric evaluation. Requirement for de novo protein synthesis and activation of JNK in depsipeptide-induced apoptosis was analyzed by treatment with cycloheximide (CHX) and JNK inhibitor (SP600125) prior to addition of depsipeptide respectively. The effect of depsipeptide in 5 primary MCL patient samples was then analyzed for morphologic evidence of apoptosis.

Results: Depsipeptide (0.25 mM/L; 80%apoptosis) induced marked apoptosis in JeKo-1 cells and this was shown to be a dose dependent fashion following 12 hours incubation. There was increase in H3 acetylation, after treatment with depsipeptide. Bcl-2, Bcl-xl and Mcl-1 showed decreased expression in the depsipeptide treated samples. Treatment with CHX (100ng/ml and 500ng/ml) and SP600125 (20ml/L) had no effect to the ability of depsipeptide-induced apoptosis. Primary MCL cells of 5 patients also showed marked apoptosis with depsipeptide treatment.

Conclusion: Depsipeptide causes increased H3 acetylation and induces apoptosis in MCL cell line and primary MCL cells. The mitochondrial apoptotic pathway is possibly altered by the depsipeptide treatment causing apoptosis, by down-regulation of Bcl-2, Bcl-xl and Mcl-1 proteins. Based on the recent phase I clinical trial demonstrating clinical response in cutaneous T cell lymphoma, our study supports the potential clinical utilization of depsipeptide in patients with MCL.