Okamoto Koichi, Zaanan Aziz, Kawakami Hisato, Huang Shengbing, Sinicrope Frank A
Department of Medicine, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota. Department of Oncology, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota.
Mol Cancer Res. 2015 Apr;13(4):659-69. doi: 10.1158/1541-7786.MCR-14-0476. Epub 2014 Dec 29.
KRAS mutations are frequently detected in human colorectal cancer and contribute to de novo apoptosis resistance and ultimately therapeutic failure. To overcome KRAS-mediated apoptosis resistance, the irreversible proteasome inhibitor, carfilzomib, was evaluated and found to potently induce Noxa, which was dependent upon c-Myc, and Bik. Isogenic mutant versus wild-type KRAS carcinoma cells showed elevated Bcl-xL, confirmed by KRAS siRNA or ectopic expression. Upregulated Bcl-xL by mutant KRAS was mediated by ERK as indicated by ERK knockdown. Bcl-xL expression was regulated at the level of mRNA and protein as shown using actinomycin D and cyclohexamide, respectively. Suppression of Bcl-xL by shRNA sensitized mutant KRAS cells to carfilzomib. Concurrent Bcl-xL antagonism by the BH3 mimetic ABT-263 combined with carfilzomib synergistically enhanced apoptosis that was dependent on Bax or p53, and was attenuated by Noxa or Bik shRNA. In support of this strategy, ectopically expressed Noxa enhanced apoptosis by ABT-263. Carfilzomib-induced Noxa and Bik sequestered Mcl-1 and ABT-263 released Bik and Bak from Bcl-xL, suggesting a mechanism for drug synergy. These preclinical findings establish mutant KRAS-mediated Bcl-xL upregulation as a key mechanism of apoptosis resistance in KRAS-mutant colorectal cancer. Furthermore, antagonizing Bcl-xL enabled carfilzomib-induced Noxa and Bik to induce synergistic apoptosis that reversed KRAS-mediated resistance.
This novel study reveals a promising treatment strategy to overcome apoptosis resistance in KRAS-mutant colorectal cancer by concurrent upregulation of Noxa/Bik and antagonism of Bcl-xL.
KRAS突变在人类结直肠癌中经常被检测到，并导致细胞凋亡抗性的产生，最终导致治疗失败。为了克服KRAS介导的细胞凋亡抗性，对不可逆蛋白酶体抑制剂卡非佐米进行了评估，发现它能有效诱导Noxa，这依赖于c-Myc和Bik。同基因的KRAS突变型与野生型癌细胞显示出Bcl-xL升高，这通过KRAS siRNA或异位表达得到证实。如ERK敲低所示，突变型KRAS上调的Bcl-xL是由ERK介导的。分别使用放线菌素D和环己酰亚胺表明，Bcl-xL的表达在mRNA和蛋白质水平上受到调节。shRNA对Bcl-xL的抑制使突变型KRAS细胞对卡非佐米敏感。BH3模拟物ABT-263与卡非佐米同时进行的Bcl-xL拮抗作用协同增强了依赖于Bax或p53的细胞凋亡，并且被Noxa或Bik shRNA减弱。为支持该策略，异位表达的Noxa增强了ABT-263诱导的细胞凋亡。卡非佐米诱导的Noxa和Bik隔离了Mcl-1，而ABT-263从Bcl-xL中释放了Bik和Bak，这提示了药物协同作用的机制。这些临床前研究结果表明，突变型KRAS介导的Bcl-xL上调是KRAS突变型结直肠癌细胞凋亡抗性的关键机制。此外，拮抗Bcl-xL可使卡非佐米诱导的Noxa和Bik诱导协同细胞凋亡，从而逆转KRAS介导的抗性。
这项新研究揭示了一种有前景的治疗策略，即通过同时上调Noxa/Bik和拮抗Bcl-xL来克服KRAS突变型结直肠癌中的细胞凋亡抗性。
