Low dose triptolide reverses chemoresistance in adult acute lymphoblastic leukemia cells via reactive oxygen species generation and DNA damage response disruption

// Haijun Zhao 1, 5, * , Pengcheng Shi 1, * , Manman Deng 2, * , Zhiwu Jiang 3 , Yin Li 1 , Vinodh Kannappan 4 , Weiguang Wang 4 , Peng Li 3 , Bing Xu 1, 2 1 Department of Hematology, Nanfang Hospital, Southern Medical University, Guangzhou, P. R. China 2 Department of Hematology, The First Affiliated Hospital of Xiamen University, Xiamen, P. R. China 3 Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, P. R. China 4 Research Institute in Healthcare Science, Faculty of Science and Engineering, University of Wolverhampton, Wolverhampton, UK 5 Department of Hematology, Anqing Municipal Hospital of Anhui Medical University, Anqing, P. R. China * These authors have contributed equally to this work Correspondence to: Bing Xu, email: xubingzhangjian@126.com Peng Li, email: li_peng@gibh.ac.cn Weiguang Wang, email: w.wang2@wlv.ac.uk Keywords: triptolide, chemotherapy, drug resistance, DNA damage, acute lymphoblastic leukemia Received: June 30, 2016 Accepted: October 19, 2016 Published: November 19, 2016 ABSTRACT Chemoresistance represents a major challenge for treatment of acute lymphoblastic leukemia (ALL). Thus, new drugs to overcome chemoresistance in ALL are urgently needed. To this end, we established a cytarabine (araC)-resistant ALL cell line (NALM-6/R), which interestingly displayed cross-resistance towards doxorubicin (ADM). Here we report that low dose of triptolide (TPL), a natural product used for treating inflammatory diseases such as arthritis, could reverse araC and ADM resistance and in NALM-6/R cells as well as primary cells from patients with relapsed or refractory (R/R) ALL, reflected by inhibition of cell proliferation and induction of apoptosis in vitro , and repression of tumor growth in vivo in a mouse xenograft model. Mechanistically, these events were associated with impaired mitochondrial membrane potential and increased reactive oxygen species (ROS) production. Co-treatment with TPL and araC or ADM upregulated pro-apoptotic caspase-9 protein, inhibited checkpoint kinase 1 (Chk1) and 2 (Chk2) phosphorylation, and induced γH2A.X (a DNA damage marker). Notably, the combination regimen of TPL and conventional chemotherapeutics also rapidly diminished tumor burden in a patient with R/R ALL. Together, these findings provide preclinical evidence for repurposing use of TPL in combination with chemotherapeutic agents to treat R/R ALL as an alternative salvage regimen.