Venetoclax (ABT-199) is a selective inhibitor of BCL2 that was introduced in clinical practice for patients with acute myeloid leukemia (AML) and the results of clinical trials are encouraging, especially in groups with very limited effective therapeutic options. In most studies, venetoclax was used in therapeutic regimens containing epigenetic modulators. Histone deacetylases (HDAC) are important epigenetic modulators, as they alter the accessibility of chromatin to transcription factors, reducing the expression of genes with tumor suppressor functions. Higher levels of HDAC have been observed in leukemia patients and associated with poor outcomes. The present study aimed to evaluate the cellular effects of a novel HDAC inhibitor in combination with venetoclax in AML models.

NB4-R2 and HEL cell lines, which are resistant to venetoclax, were used. The purine-derived phenylhydroxamate with potential HDAC inhibitor activity (compound 82) (0, 0.37, 0.5, 0.75, 1, 1.5 μM) was used in combination with venetoclax (0, 0.4, 0.8, 1.6, 3.2, 6.4 μM). Vorinostat (0, 0.37, 0.5, 0.75, 1, 1.5 μM) was used as a reference drug for all assays. Cell viability was assessed by MTT assay and apoptosis by annexin V/propidium iodide labeling and flow cytometry. Statistical analysis was performed by ANOVA and Bonferroni post-test. A p < 0.05 was considered significant.

In HEL and NB4-R2 cells, a synergic effect was observed in the combination of compound 82 plus venetoclax (all p < 0.05). Similar results, at less extension, were observed for the vorinostat plus venetoclax combination (all p < 0.05), indicating that compound 82 is more potent in this context. Apoptosis assays confirm these findings, the levels of apoptosis in NB4 cells treated with vehicle, 1.6 μM venetoclax, 1 μM compound 82, 1 μM vorinostat, 1.6 μM venetoclax plus 1 μM compound 82, 1.6 μM venetoclax plus 1 μM vorinostat were 9 ± 1%, 17 ± 1%, 29 ± 4%, 22 ± 2%, 78 ± 1% and 57±4%, respectively (all p < 0.05). Similarly, the levels of apoptotic HEL cells treated with vehicle, 6.4 μM venetoclax, 1 μM compound 82, 1 μM vorinostat, 6.4 μM venetoclax plus 1 μM compound 82, 6.4 μM venetoclax plus 1 μM vorinostat were 12 ± 2%, 47 ± 2%, 73 ± 4%, 39 ± 3%, 88 ± 1% and 76 ± 5%, respectively (all p < 0.05).

Pharmacological inhibition of HDAC sensitizes venetoclax-resistant cells. A novel HDAC inhibitor identified by our research group showed greater potency and efficacy than vorinostat in increasing venetoclax-induced apoptosis in cellular models of AML. Future studies are needed to elucidate the molecular mechanisms involved.

CNPq, CAPES, and FAPESP.