Kim Kwang Woon, Moretti Luigi, Lu Bo
Department of Radiation Oncology, Vanderbilt Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America.
PLoS One. 2008 May 28;3(5):e2275. doi: 10.1371/journal.pone.0002275.
Lung cancer remains the leading cause of cancer death worldwide. Radioresistance of lung cancer cells results in unacceptable rate of loco-regional failure. Although radiation is known to induce apoptosis, our recent study showed that knockdown of pro-apoptotic proteins Bak and Bax resulted in an increase in autophagic cell death and lung cancer radiosensitivity in vitro. To further explore the potential of apoptosis inhibition as a way to sensitize lung cancer for therapy, we tested M867, a novel chemical and reversible caspase-3 inhibitor, in combination with ionizing radiation in vivo and in vitro.
M867 reduced clonogenic survival in H460 lung cancer cells (DER = 1.27, p = 0.007) compared to the vehicle-treated treated cells. We found that administration of M867 with ionizing radiation in an in vivo mouse hind limb lung cancer model was well tolerated, and produced a significant tumor growth delay compared to radiation alone. A dramatic decrease in tumor vasculature was observed with M867 and radiation using von Willebrand factor staining. In addition, Ki67 index showed >5-fold reduction of tumor proliferation in the combination therapy group, despite the reduced levels of apoptosis observed with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining. Radiosensitizing effect of M867 through inhibiting caspases was validated using caspase-3/-7 double-knockout (DKO) mouse embryonic fibroblasts (MEF) cell model. Consistent with our previous study, autophagy contributed to the mechanism of increased cell death, following inhibition of apoptosis. In addition, matrigel assay showed a decrease in in vitro endothelial tubule formation during the M867/radiation combination treatment.
M867 enhances the cytotoxic effects of radiation on lung cancer and its vasculature both in vitro and in vivo. M867 has the potential to prolong tumor growth delay by inhibiting tumor proliferation. Clinical trials are needed to determine the potential of this combination therapy in patients with locally advanced lung cancer.
肺癌仍然是全球癌症死亡的主要原因。肺癌细胞的放射抗性导致局部区域失败率令人难以接受。虽然已知辐射可诱导细胞凋亡，但我们最近的研究表明，敲低促凋亡蛋白Bak和Bax会导致自噬性细胞死亡增加以及体外肺癌放射敏感性增加。为了进一步探索抑制细胞凋亡作为使肺癌对治疗敏感的一种方法的潜力，我们在体内和体外测试了一种新型化学可逆性半胱天冬酶-3抑制剂M867与电离辐射联合使用的效果。
与载体处理的细胞相比，M867降低了H460肺癌细胞的克隆形成存活率（剂量增强比=1.27，p=0.007）。我们发现在体内小鼠后肢肺癌模型中，M867与电离辐射联合给药耐受性良好，与单独放疗相比，显著延迟了肿瘤生长。使用血管性血友病因子染色观察到，M867与放疗联合使用时肿瘤血管显著减少。此外，尽管通过末端脱氧核苷酸转移酶介导的dUTP缺口末端标记染色观察到凋亡水平降低，但联合治疗组的Ki67指数显示肿瘤增殖降低了5倍以上。使用半胱天冬酶-3/-7双敲除（DKO）小鼠胚胎成纤维细胞（MEF）细胞模型验证了M867通过抑制半胱天冬酶的放射增敏作用。与我们之前的研究一致，在抑制细胞凋亡后，自噬促成了细胞死亡增加的机制。此外，基质胶试验显示，在M867/放疗联合治疗期间，体外内皮小管形成减少。
M867在体外和体内均增强了辐射对肺癌及其血管的细胞毒性作用。M8具有通过抑制肿瘤增殖来延长肿瘤生长延迟的潜力。需要进行临床试验以确定这种联合治疗对局部晚期肺癌患者的潜力。
