Department of Surgery, School of Medicine, Shinshu University, Matsumoto, Nagano 390‑8621, Japan.
Anaeropharma Science, Inc., Matsumoto, Nagano 390‑8621, Japan.
Int J Oncol. 2020 Nov;57(5):1179-1191. doi: 10.3892/ijo.2020.5117. Epub 2020 Sep 2.
KRAS‑mutant colorectal cancer (CRC) is a highly malignant cancer with a poor prognosis, however specific therapies targeting KRAS mutations do not yet exist. Anti‑epidermal growth factor receptor (EGFR) agents, including cetuximab and panitumumab, are effective for the treatment of certain patients with CRC. However, these anti‑EGFR treatments have no effect on KRAS‑mutant CRC. Therefore, new therapeutic strategies targeting KRAS‑mutant CRC are urgently needed. To clarify the direct effect of KRAS gene mutations, the present study transduced mutant forms of the KRAS gene (G12D, G12V and G13D) into CACO‑2 cells. A drug‑screening system (Mix Culture assay) was then applied, revealing that the cells were most sensitive to the MEK inhibitor trametinib among tested drugs, Cetuximab, Panitumumab, Regorafenib, Vemurafenib, BEZ‑235 and Palbociclib. Trametinib suppressed phosphorylated ERK (p‑ERK) expression and inhibited the proliferation of KRAS‑mutant CACO‑2 cells. However, low‑dose treatment with trametinib also increased the expression of the anti‑apoptotic protein Bcl‑xL in a dose‑dependent manner, leading to drug resistance. To overcome the resistance of KRAS‑mutant CRC to apoptosis, the combination of trametinib and the Bcl‑xL antagonist ABT263 was assessed by in vitro and in vivo experiments. Compared with the effects of low‑dose trametinib monotherapy, combination treatment with ABT263 had a synergistic effect on apoptosis in mutant KRAS transductants in vitro. Furthermore, in vivo combination therapy using low‑dose trametinib and ABT263 against a KRAS‑mutant (G12V) xenograft synergistically suppressed growth, with an increase in apoptosis compared with the effects of trametinib monotherapy. These data suggest that a low dose of trametinib (10 nM), rather than the usual dose of 100 nM, in combination with ABT263 can overcome the resistance to apoptosis induced by Bcl‑xL expression, which occurs concurrently with p‑ERK suppression in KRAS‑mutant cells. This strategy may represent a promising new approach for treating KRAS‑mutant CRC.
KRAS 突变型结直肠癌（CRC）是一种恶性程度高、预后差的癌症，但目前尚无针对 KRAS 突变的特异性治疗方法。抗表皮生长因子受体（EGFR）药物，包括西妥昔单抗和帕尼单抗，对某些 CRC 患者的治疗有效。然而，这些抗 EGFR 治疗对 KRAS 突变型 CRC 无效。因此，迫切需要针对 KRAS 突变型 CRC 的新治疗策略。为了阐明 KRAS 基因突变的直接作用，本研究将突变型 KRAS 基因（G12D、G12V 和 G13D）转导至 CACO-2 细胞。然后应用药物筛选系统（混合培养测定法），结果显示在测试的药物中，MEK 抑制剂曲美替尼对细胞的敏感性最高，其次是西妥昔单抗、帕尼单抗、regorafenib、vemurafenib、BEZ-235 和 palbociclib。曲美替尼抑制磷酸化 ERK（p-ERK）表达，并抑制 KRAS 突变型 CACO-2 细胞的增殖。然而，低剂量曲美替尼处理也呈剂量依赖性地增加抗凋亡蛋白 Bcl-xL 的表达，从而导致耐药性。为了克服 KRAS 突变型 CRC 对细胞凋亡的耐药性，通过体外和体内实验评估了曲美替尼与 Bcl-xL 拮抗剂 ABT263 的联合用药。与低剂量曲美替尼单药治疗的效果相比，ABT263 联合治疗在体外对突变型 KRAS 转染物的凋亡具有协同作用。此外，与曲美替尼单药治疗相比，低剂量曲美替尼和 ABT263 联合治疗 KRAS 突变（G12V）异种移植在体内协同抑制肿瘤生长，同时增加细胞凋亡。这些数据表明，与常规剂量 100 nM 相比，低剂量（10 nM）的曲美替尼联合 ABT263 可以克服 Bcl-xL 表达诱导的凋亡耐药性，同时抑制 KRAS 突变细胞中 p-ERK 的表达。这种策略可能为治疗 KRAS 突变型 CRC 提供一种有前途的新方法。
