In our study cohort WRN was found to be hypermethylated
In our study cohort, WRN was found to be hypermethylated in
23.5% of patients with metastatic CRC, and this rate was lower than the ~40% reported previously [5,13]. Although DNA hypermethy-lation in a specific gene has long been regarded to reflect decreased mRNA and protein expression in the corresponding gene, it may not be correlated with repressive gene expression in some cases because of the complex regulation of gene expression besides DNA methylation . Although we included WRN methylation as one of the potential biomarkers in this study, WRN methylation was marginally correlated with TTP, and the correlation was not maintained in a multivariate analysis. Recently, it was reported that WRN methylation was not predictive of good clinical outcomes in 93 patients with metastatic CRC treated with irinotecan and capecitabine . Remarkably, WRN mRNA and protein expression levels were independent of WRN methylation status in the study, which was also confirmed with TCGA data. We suspect that this absence of correlation between WRN methylation and mRNA or protein levels might be the main reason for the lack of correlation in WRN methylation with treatment outcome in our study.
Currently, most of the irinotecan-based systemic chemotherapy is given in combination with anti-EGFR Ibrutinib or anti-VEGF/ VEGFR antibodies because combination chemotherapy in both forms have been proven to provide survival benefit in the first-line (cetuximab, panitumumab, bevacizumab) as well as second-line (bevacizumab, ziv-aflibercept, ramucirumab) and third-line settings (cetuximab) when compared to irinotecan-based cytotoxic chemotherapy alone. In our study, we selected patients that had been treated in the era when there was limited access to combination with molecular targeted agents. In fact, most (93/102 patients, 91.2%) of the patients in our study cohort were treated with irinotecan-based systemic chemotherapy alone. Although this selection was not intended and was mainly because there were limitations to the archival tumor tissues collected after 2005 made by
154 CHFR Promoter Methylation in Metastatic Colorectal Cancer Cha et al. Neoplasia Vol. 21, No. 1, 2019
domestic legal provisions when this study was planned, we believe that this selection allowed us to better define the pure impact of irinotecan on patient outcomes.
Our study has the following limitations. First, we did not validate our findings in a separate cohort. However, the preclinical observation of our study is fully in agreement with the clinical findings, and the association of CHFR and irinotecan could be mechanistically explainable. Although our findings are not confirmative and are more likely to be hypothesis generating, we believe that these points make our study more generalizable and worthy of further investigation in a larger study cohort. Second, in the absence of another treatment arm, we could not verify that CHFR methylation was predictive or prognostic in nature. However, the changes shown after overexpression and knockdown of CHFR in the preclinical study suggest that CHFR methylation is more likely to be predictive of irinotecan treatment. Third, mainly because of tissue availability, a limited number of patients heterogeneous in their clinical characteristics, including treatment lines, were included. In our study, number of treatment lines was one of the most significant factors in univariate analyses for both TTP and OS, and the association of CHFR methylation or CIMP status with treatment outcomes was more prominent when stratified by number of prior treatment(s). Therefore, the correlation between CHFR methylation and irinotecan sensitivity might have been more evident if we had evaluated a more homogeneous population. In summary, we report that CHFR is recurrently hypermethylated in metastatic CRC and that methylated CHFR is associated with better treatment outcomes in terms of TTP in patients with metastatic CRC treated with irinotecan-based systemic chemotherapy. Interestingly, in patients with unmethylated CHFR, the CIMP status could further discriminate patient outcomes. The association of CHFR and irinotecan treatment outcomes was confirmed in a preclinical study by overexpress-ing or knocking down CHFR and investigating the changes in irinotecan sensitivity accordingly. Considering the major importance of irinotecan-based chemotherapy in patients with metastatic CRC and the absence of a biomarker to guide treatment in these patients, we believe that our findings deserve confirmation in a larger patient cohort and could facilitate patient selection for irinotecan chemotherapy.
Declarations of Interest
We sincerely acknowledge the Omics Core Lab of NCC for supporting the preclinical part of our study.