The biological significance and clinical implication of KRAS mutant-mediated oxaliplatin chemotherapy sensitivity in metastatic colorectal cancer (mCRC)

Colorectal cancer (CRC) is one of the leading cause of cancer death worldwide. Although cutting-edge technology and intervention continuously advance, median overall survival (mOS) of metastatic colorectal cancer (mCRC), under currently state-of-art treatment with molecularly targeted therapy plus chemotherapy, remains only 20-30 months. Mutation of the KRAS gene in mCRC has been identified as a negative predictor to anti-epidermal growth factor receptor (anti-EGFR) monoclonal antibody (mAB), which is one of the currently available molecularly targeted therapy approved to be used in mCRC patients. Therefore, KRAS mutant mCRC patients have therapeutically unmet needs because they cannot use anti-EGFR mAB and have fewer treatment options than KRAS wild-type mCRC patients. To identify potentially better regimens from currently available systemic treatments or to explore newer agents for the treatment of KRAS mutant mCRC patients is thus warranted. If we primarily focus on chemotherapy alone group in the OPUS and PRIME studies, in which first-line oxaliplatin-based chemotherapy (FOLFOX, oxaliplatin/5-fluorouracil (5-FU)/leucovorin) was given in both studies, it is intriguing to find that the progression-free survival (PFS) in KRAS mutant group was longer than the PFS in KRAS wild-type group, with 8.6 versus 7.2 months in the OPUS study and 8.8 versus 8.0 months in the PRIME study. In contrast, in the CRYSTAL study, if we focused on chemotherapy alone group, in which first-line irinotecan-based chemotherapy (FOLFIRI, irinotecan/5-FU/leucovorin) was given, the median PFS was 7.7 months in KRAS mutant group and 8.4 months in the KRAS wild-type group. According to these observations, we hypothesized that oxaliplatin-based regimens may be more beneficial to KRAS mutant than wild-type mCRC patients. We conducted in vitro and clinical studies trying to prove our hypothesis. In the in vitro study, KRAS gene was knocked-down in KRAS-mutant CRC cells (DLD-1G13D and SW480G12V) and overexpressed in KRAS-wild-type CRC cells (COLO320DM) to generate paired CRC cells. In KRAS wild-type CRC cells (COLO320DM), we found KRAS overexpression caused excision repair cross-complementation group 1 (ERCC1) down regulation in protein and mRNA levels, and enhanced oxaliplatin sensitivity. In contrast, in KRAS mutant CRC cells (DLD-1G13D and SW480G12V), KRAS knocked-down by KRAS-siRNA led to ERCC1 up-regulation and increased oxaliplatin resistance. The sensitivity of irinotecan and 5FU did not change in the paired CRC cells. To validate ERCC1 as a predictor of sensitivity for oxaliplatin, ERCC1 was knocked-down by siRNA in KRAS-wild-type CRC cells, which restored oxaliplatin sensitivity. In contrast, ERCC1 was overexpressed by ERCC1-expressing vectors in KRAS-mutant CRC cells, and caused oxaliplatin resistance. Overall, our first study suggests that KRAS mutation is a predictor of oxaliplatin sensitivity in colon cancer cells by the mechanism of ERCC1 downregulation. Our second clinical study, evaluating clinicopathologic features and treatment outcome of mCRC patients including first-line PFS and overall survival (OS) in association with KRAS mutation status by using the Cox proportional hazard model, demonstrated that in patients who received first-line oxaliplatin-based regimens, the first-line PFS was significantly longer in KRAS mutant patients than that in KRAS wild-type patients. The median PFS was 8.5 months in KRAS mutant versus 5.8 months in KRAS wild-type patients (P = .008). In contrast, in patients who received first-line irinotecan-based regimens, the PFS was shorter in KRAS mutant patients (N = 15) than that in KRAS wild-type patients (N = 20). Median PFS was 3.9 months in KRAS mutant versus 6.0 months in KRAS wild-type patients (P = .23). Median OS between KRAS mutant and wild-type patients was not significantly different in both oxaliplatin-based and irinotecan-based regimens. In multivariate analyses, KRAS mutation remains an independent predictive factor for longer PFS in first-line oxaliplatin-based regimens. In our third study, clinicopathologic features and OS of KRAS mutant and wild-type mCRC patients who had used oxaliplatin-based, irinotecan-based, bevacizumab-based, as well as cetuximab-based regimens were compared to those who had never-used oxaliplatin-based, irinotecan-based, bevacizumab-based, as well as cetuximab-based regimens, respectively. We demonstrated that in KRAS mutant patients who had used oxaliplatin-based regimens (N = 131), the OS was significantly longer than that in KRAS mutant patients who had never-used oxaliplatin-based regimens (N = 38). The OS was 28.8 months in KRAS mutant patients who had used oxaliplatin-based regimens versus 17.8 months in KRAS mutant patients who had never-used oxaliplatin-based regimens (P = 0.026). Notably, OS in KRAS wild-type mCRC patients who had used oxaliplatin-based regimens (N = 185) was not significantly longer than that in KRAS wild-type mCRC patients who had never used oxaliplatin-based regimens (N = 40) (P = 0.25). Furthermore, the OS in KRAS mutant patients who had used either irinotecan-based, bevacizumab-based or cetuximab-based regimens was not significantly different than that in KRAS mutant patients who had never-used either irinotecan-based, bevacizumab-based or cetuximab-based regimens, respectively. In multivariate analyses, patients who had used oxaliplatin-based regimens remains an independent prognostic factor for longer OS in KRAS mutant mCRC patients. In conclusion, oxaliplatin-based regimens may be more beneficial in KRAS mutant than in KRAS wild-type mCRC patients.