Targeting Snail2 improve sensitivity to parthenolide in T-cell acute lymphoblastic leukemia through PUMA activation

Background and Objective: Current therapies for childhood T-cell acute lymphoblastic leukemia (T-ALL) have increased survival rates to about 85%. The standard of care is chemotherapy, but approximately 20% patients exhibit primary or secondary resistance to current therapies. Parthenolide (PTL) has been shown to have excellent anti-cancer activity in pediatric leukemia xenografts, with minimal effects on normal hemopoietic cells. Some leukemia initiating cell populations remain resistant to PTL. This study examined mechanisms for this resistance and how to overcome the resistance. Methods: Snail2 protein expression was detected in 9 T-ALL patients, 9 normal bone marrow (NBM) cells and 4 T-ALL cell lines. We investigated the effects of loss of-function and gain-of-function of Snail2 or P53 up-regulated modulator of apoptosis on survival, colony formation, apoptosis and chemosensitivity of T-ALL cells to PTL in vitro and in vivo . Results: Snail2 protein expression was elevated in primary T-ALL patients and cell lines. CEM cells with rich Snail2 expression is resistant to PTL. JURKAT cells with poor Snail2 expression sensitizes to PTL. In vitro, Snail2 inhibition by siRNA, sensitized CEM cells to apoptosis by PTL, resulting in PUMA upregulation and caspase-3 cleavage. Inhibition of PUMA by RNA interference in Snail2-knockdown CEM cells rescued the resistance of CEM cells to PTL treatment. Snail2 re-expression in JURKAT cells is resistant to PTL. The pro-survival effect of Snail2 was found to be caused by direct repression of PTL-induced PUMA expression by Snail2 in JURKAT cells. Additionally, an orthotopic allograft in vivo model demonstrated that the Snail2 inhibitor enhanced responses to PTL in CEM cells by inducing PUMA-dependent cell apoptosis. Conclusion: This study demonstrates a pivotal role for Snail2/PUMA signals in T-ALL cell survival. It may be possible to achieve greater toxicity to childhood T-ALL by combining PTL with Snail2 knockdown.