In vitro and in vivo anti-leukemia activity of CHR-2845, a cell-targeted HDAC inhibitor for use in monocytic leukemia

Abstract

e14579 Background: Histone deacetylase inhibitors alter gene expression and induce apoptosis in a wide range of cancer cells including those derived from human leukemias. CHR-2845 is a novel hydroxamic acid derivative histone deacetylase inhibitor (HDACi) which is a selective substrate for the intracellular carboxylesterase hCE-1, whose expression is restricted to cells of the monocyte- macrophage lineage. Methods: We studied the in vitro and in vivo anti-leukemia activity of CHR-2845 using cell proliferation assay, annexin V binding assay, cell cycle analysis, western blot and in vitro primary leukemia cell culture. Results: Both U937 and THP1 cells express high levels of hCE-1 whereas the myeloid cell line, HL60, does not. In comparison to vorinostat, CHR-2845 showed increased anti-proliferative potency (IC50) against monocytic cell lines (THP1, 30 nM vs 700 nM and U937, 30 nM vs 475 nM), compared to a myeloid cell line (HL60, 700nM vs 470 nM). In a broad panel of leukemic cell lines, the potency of CHR-2845 over vorinostat correlated completely with hCE-1 expression. In monocytic cell lines, CHR-2845 induced more apoptosis than vorinostat (THP1: 45±5% vs 11±1% and U937: 23±14% vs 6±1%), as measured by flow cytometry using Annexin V. Biochemical assessment of histone H3 and H4 protein acetylation by Western blot also indicateed that CHR-2845 is at least 10 times more potent than vorinostat in monocytic cell lines but not in HL-60 cells. This increase in histone acetylation was associated with increased phosphohistone H2AX, indicating formation of double-strand DNA breaks induced by this compound. These data for CHR-2845 and vorinostat on apoptosis and histone acetylation in THP1 and U937 versus HL60 cells, confirmed the selectivity of this novel compound for cells of the monocytic lineage. We also studied the anti-leukemia activity of CHR-2845 in primary leukemia cells from 8 patients with acute or chronic myelomonocytic leukemia. CHR-2845 decreased proliferation and induced apoptosis more than an equivalent dose of vorinostat in some of the patients we studied. Conclusions: These results indicated that CHR-2845 has potential to be efficacious in the treatment of patients with monocytic leukemia. [Table: see text]