Arsenic trioxide exhibits anti-leukemic effect and induces autophagy in T-cell acute lymphoblastic leukemia cell lines

Abstract

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy resulting from clonal mutations in lymphoid progenitors. Although significant improvements in the outcome for pediatric patients with an overall survival (OS) of 80% have been made, the prognosis for adult patients still remains dismal (OS＜40%). Early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) is a distinct subtype of T-ALL with dismal prognosis, and refractory/relapsed disease is common for this subtype of T-ALL. Therefore, developing more effective treatment regimens is urgently needed to improve outcomes for T-ALL. Arsenic trioxide (ATO), initially approved for the treatment of acute promyelocytic leukemia (APL) by the US Food and Drug Administration, has also shown big potential in treating non-APL malignancies. However, the effectiveness of ATO in treating T-ALL is not well defined. Furthermore, evidence showed that ATO can induce autophagy in acute myeloid leukemia and chronic myeloid leukemia, which may either promote cell survival or cause cell death depending on the specific cell type and circumstance. Nevertheless, whether ATO can also induce autophagy in T-ALL or not is still unknown.

The first objective of this study is to determine the effectiveness of ATO in T-ALL using KE-37, CCRF-CEM, LOUCY and MOLT-16 cell lines. The other two objectives are to demonstrate the induction of autophagy upon ATO treatment in these four cell lines and to investigate the role of the induced autophagy in T-ALL.

Results obtained from this study suggested that ATO exhibits promising anti-leukemic efficacy against T-ALL cell lines, especially LOUCY cell line which displays ETP-ALL phenotype. Furthermore, it was proved that ATO is capable of inducing autophagy in T-ALL as detected by the increased level of LC3-II (autophagy marker) and the overexpression of autophagy-related genes upon ATO treatment. In addition, inhibition of autophagy by pharmacological inhibitors (NH4Cl, bafilomycin A1) or genetic silencing (LC3B knockdown) could not discernibly alter the sensitivity to ATO in KE-37, CCRF-CEM, LOUCY and MOLT-16 cells as evidenced by the almost unchanged cell viability and apoptotic cell percentage, indicating that the form of ATO-induced autophagy is nonprotective. Interestingly, results of this study also uncovered that bafilomycin A1 exerts potent anti-tumor activity against T-ALL and that the combination of ATO and p38 MAPK inhibitor (SB203580) shows synergistic anti-neoplastic effect in treating T-ALL.

Findings obtained from this study reveal that ATO is a promising therapeutic agent for treating T-ALL. They also provide new insights into the role of ATO-induced autophagy in T-ALL. Moreover, they offer valuable information for theoretical prediction of whether therapeutic advantages can be achieved by incorporating autophagy inhibitors into ATO treatment.