Thrombocytopenia induced by the histone deacetylase inhibitor abexinostat involves p53-dependent and -independent mechanisms

Abstract

Abexinostat is a pan histone deacetylase inhibitor (HDACi) that demonstrates efficacy in malignancy treatment. Like other HDACi, this drug induces a profound thrombocytopenia whose mechanism is only partially understood. We have analyzed its effect at doses reached in patient plasma on in vitro megakaryopoiesis derived from human CD34+ cells. When added at day 0 in culture, abexinostat inhibited CFU-MK growth, megakaryocyte (MK) proliferation and differentiation. These effects required only a short incubation period. Decreased proliferation was due to induction of apoptosis and was not related to a defect in TPO/MPL/JAK2/STAT signaling. When added later (day 8), the compound induced a dose-dependent decrease (up to 10-fold) in proplatelet (PPT) formation. Gene profiling from MK revealed a silencing in the expression of DNA repair genes with a marked RAD51 decrease at protein level. DNA double-strand breaks were increased as attested by elevated γH2AX phosphorylation level. Moreover, ATM was phosphorylated leading to p53 stabilization and increased BAX and p21 expression. The use of a p53 shRNA rescued apoptosis, and only partially the defect in PPT formation. These results suggest that HDACi induces a thrombocytopenia by a p53-dependent mechanism along MK differentiation and a p53-dependent and -independent mechanism for PPT formation.

An incomplete trafficking defect to the cell-surface leads to paradoxical thrombocytosis for human and murine MPL P106L

“…5,29 CD34 1 cells isolated from adult bone marrow (hip surgery) were grown in serum-free medium, as previously described, 28 in the presence of THPO (10 ng/mL) and stem cell factor (SCF; 25 ng/mL), and transduced on the fourth day of culture.…”

“…CD34 1 cells were isolated using an immunomagnetic cell sorting system (Automacs; Miltenyi Biotec) and cultured in plasma clot. 28 Plasma THPO levels were measured according to the manufacturer's instructions (Human Thrombopoietin Quantikine ELISA Kit; R&D Systems).…”

Phase 1 dose-escalation study of oral abexinostat for the treatment of patients with relapsed/refractory higher-risk myelodysplastic syndromes, acute myeloid leukemia, or acute lymphoblastic leukemia

“…[37] A more recent study showed that in addition to a defect in proplatelet formation which was mainly p53-independent, abexinostat also inhibited megakaryocyte differentiation by inducing progenitor and precursor apoptosis through the induction of p53. [38] ECG changes including QTc prolongation have been reported with other HDAC inhibitors and a potential class effect has been suggested. [39,40] However, in this study and others of abexinostat, [31,32,41] treatment with abexinostat did not result in clinically relevant ECG changes.…”

Targeting epigenetic regulations in cancer

“…However, there were a lot of concerns regarding toxic side effects of HDACs, typically including fatigue, thrombocytopenia, gastrointestinal toxicity, and cardiotoxicity. However, most clinical trials showed that these side effects are manageable [77,78].…”