The histone acetylation process is the best-studied type of post-translational modification, playing a key role in chromatin remodeling regulated by the activity of two enzymes: histone acetyltransferases and histone deacetylases (HDAC). High levels of HDAC have been observed in patients with hematological and solid cancers and are associated with poor prognosis. The present study aimed to evaluate the cellular effects of three novel potential HDAC inhibitors in hematological neoplasm models.

A panel containing myeloid (OCI-AML3, Kasumi 1, HL60, THP1, MOLM13, MV4-11, U937, NB4, NB4-R2, K562, KU812, SET2, and HEL) and lymphoid (Jurkat, CEM, Namalwa, NALM6, Daudi, Raji, SUP-B15, REH, U266, MM1.S, MM1.R, and Karpas 422) neoplasm cells were used. Peripheral blood mononuclear cells (normal leukocytes) from healthy donors were used for toxicity evaluation (n = 4). Three novel purine-derived phenylhydroxamate with potential HDAC inhibitor activity (named here as 82, 83, and 84) were used. Vorinostat was used as a reference drug. Cell viability was assessed by MTT assay, apoptosis by annexin V/propidium iodide labeling and flow cytometry (FC), clonogenicity by autonomous colony formation, cell cycle by propidium iodide and FC, and protein expression by Western Blot. IC50 values were obtained by non-linear regression. Statistical analysis was performed by ANOVA and Bonferroni post-test. A p < 0.05 was considered significant.

All compounds tested reduced cell viability at submicromolar concentrations being compound 82 more potent than the others exhibiting less concentration necessary to reduce cell viability by 50% (IC50 ranged from 0.09 to 2.04 μM). THP1, MOLM13, NB4-R2, and HEL leukemia cells were more sensitive to these compounds and were selected for the next experiments. In normal leukocytes, vorinostat and compound 82 did not reduce cell viability at the same extension as observed for leukemia cells, indicating a selective antineoplastic activity. All compounds induced time- and dose-dependent manner apoptosis in THP1, MOLM13, NB4-R2, and HEL cells (all p < 0.05). Vorinostat and compound 82 strongly reduced colony formation, being compound 82 more efficient, especially in MOLM13 and NB4-R2 cells (all p < 0.05). Low concentration of vorinostat and compound 82 lead to reduced cell cycle progression (all p < 0.05). THP1, MOLM13, NB4-R2, and HEL cells were exposed to vorinostat or compound 82 and the expression of proteins involved in apoptosis and HDAC activity was modulated.

Our results indicate that the three purine-derived phenylhydroxamate tested presented antineoplastic effects being a future candidate to compose the list of HDAC inhibitors in the antineoplastic arsenal.

CNPq, CAPES, and FAPESP.