分析天然植物對苯二酚衍生物HQ17(3)對帶有t(4;11)染色體轉位急性淋巴性白血病細胞株RS4;11的影響

Abstract

急性淋巴性白血病（Acute lymphoblastic leukemia, ALL）為造血系統不正常病變導致不成熟淋巴球異常增生的疾病；佔兒童癌症發生的第一位。目前兒童ALL的藥物治療成效良好，五年無事件存活率約達76~86%，不過帶有t(9;22)或MLL基因轉位的極高危險群（Very high risk, VHR）病人經密集高劑量化學治療後尚無法達到長時間的緩解。因此，發展對VHR-ALL病患更有效的治療療程或者新藥是ALL的重要研究課題。漆樹萃取物對苯二酚衍生物 HQ17(3)於先前曾經被研究發現有抗癌能力，且低濃度即對惡性骨髓性血癌細胞株HL-60有毒殺效果。 本研究於先驅測試中確定低濃度HQ17(3)對四株ALL細胞株即具有細胞毒性，乃選定帶有MLL-AF4基因轉位的RS4;11細胞株為標的，研究HQ17(3)造成VHR ALL細胞毒性之機轉。結果顯示HQ17(3)會誘導RS4;11細胞株中活性氧（ROS）的產生，破壞粒線體膜電位，硫胱胺酸蛋白酶（Caspase）活化，多二磷酸腺苷核糖聚合酶（PARP）被切割，細胞發生凋亡（Apoptosis）。加入泛硫胱胺酸蛋白酶抑制劑（Pan-caspase inhibnitor）雖然可以抑制HQ17(3)所誘發的caspase活性，但是卻無法抑制PARP切割與細胞死亡。抗氧化劑（Antioxidants, ROS scavengers）榖胱苷肽（GSH）和維生素C可以減緩HQ17(3)所誘導的ROS產生，減少細胞粒線體膜電位的變化，挽救細胞死亡。綜合本研究的實驗結果顯示ROS是HQ17(3)誘導RS4;11細胞死亡的主要原因之一；HQ17(3)雖亦造成caspase活化，但非HQ17(3)誘導RS4;11細胞死亡的原因。此外，本研究結果指出若可選擇性誘導細胞中ROS產生，可能有潛力發展輔助治療如MLL-AF4基因轉位的VHR ALL的策略。

Acute lymphoblastic leukemia (ALL), a haematopoietic malignant disorder of lymphoid cells, is the most prevalent childhood cancer. Although the rate of success in the treatment of childhood ALL has been improved with a 5-year event-free survival of 76-88%, patients succumbing very-high- risk (VHR) ALLs (those harboring t(9;22) or MLL rearrangements chromosomal abnormalities) display poor clinical outcomes even with intensive chemotherapies. Thus, more effective treatment protocols or new drugs are beneficial for these patients. HQ17(3)(10’(Z),13’(E),15’(E)-heptadecatrienyl- hydroquinone), isolated from the sap of Rhus succedanea, had been reported to have anti-cancer activity, and low concentration of HQ17(3) showed cytotoxicity to the HL-60 myeloid leukemia cells. Our pilot screening confirmed HQ17(3) exhibited effective cytotoxic effect on four tested ALL cell lines. Thus, the RS4;11 cell line harboring MLL-AF4 gene translocation was chosen for the detailed investigation of the effects of HQ17(3) on VHR ALL cells. HQ17(3) induced reactive oxygen species (ROS) production in RS4;11 cells, and disrupted the mitochondrial membrane potential, activated caspase-3, and cleaved poly (ADP-ribose) polymerase (PARP). RS4;11 cells treated with HQ17(3) showed features of apoptotic cell death. Pan-caspase inhibitor could effectively inhibit HQ17(3)-induced caspase-3 activation, but could neither reduce HQ17(3)-induced PARP cleavage nor rescue cells from death. Antioxidants or ROS scavengers (GSH, vitamin C) attenuated HQ17(3)-induced ROS production, mitochondrial membrane potential lost, and cell death. These results indicated that oxidative stress associated with ROS production is one of the major mechanisms to cause HQ17(3)-induced RS4;11 cell death. In conclusion, HQ17(3) displayed significant anti-leukemic activity by inducing ROS and cell apoptotic death. These results further indicated that ROS-inducing agents might potentially augment the treatment for VHR ALL with t(4;11) translocation.