METHODS::Aims: Radiotherapy is predominantly used as one of the treatment modalities to treat local tumor in colorectal cancer (CRC). Hindrance in disease treatment can be attributed to radio-tolerance of cancer stem cells (CSCs) subsistence in the tumor. Understanding the radio-resistant property of CSCs might help in the accomplishment of targeted radiotherapy treatment and increased disease-free survival. Telomeric RAP1 contributes in modulation of various transcription factors leading to aberrant cell proliferation and tumor cell migration. Therefore, we investigated the role of RAP1 in maintaining resistance phenotype and acquired stemness in radio-resistant cells.Main Methods: Characterization of HCT116 derived radio-resistant cell (HCT116RR) was performed by cell survival and DNA damage profiling. RAP1 silenced cells were investigated for DNA damage and expression of CSC markers through western blotting and Real-time PCR post-irradiation. Molecular docking and co-immunoprecipitation study were performed to investigate RAP1 and KLF4 interaction followed by RAP1 protein status profiling in CRC patient.Key findings: We established radio-resistant cells, which showed tolerance to radiotherapy and elevated expression of CSC markers along with RAP1. RAP1 silencing showed enhanced DNA damage and reduced expression of CSC markers post-irradiation. We observed strong physical interaction between RAP1 and KLF4 protein. Furthermore, higher RAP1 expression was observed in the tumor of CRC patients. Dataset analysis also revealed that high expression of RAP1 expression is associated with poor prognosis.Significance: We conclude that higher expression ofRAP1 implicates its possible role in promoting radio-resistance in CRC cells by modulating DNA damage and CSC phenotype.

METHODS::Cancer stem-like cells are rare immortal cells within tumor, which are thought to play important roles in ionizing radiation (IR) therapy-resistance. Quercetin is a natural flavonoid with potential anti-cancer properties without significant cytotoxicity in normal tissues. In this study, we demonstrated that quercetin-IR combination treatment exhibited more dramatic anti-cancer effect than either quercetin or IR treatment alone via targeting colon cancer stem cells (CSCs) and inhibiting the Notch-1 signaling. These effects were further verified by in vivo studies which showed remarkable decrease of the CSCs markers and the expression of Notch-1 signaling proteins in human colon cancer xenografts in nude mice. Co-treatment with quercetin and low dose of radiation significantly reduced the expressions of all five proteins of γ-secretase complex in HT-29 and DLD-1 cells. In addition, ectopic expression of the Notch intracellular domain (NICD) partly reversed the inhibition effects by the combination therapy. In conclusion, our results indicated that the combination of quercetin (20 μM) and IR (5Gy) might be a promising therapeutic strategy for colon cancer treatment by targeting colon cancer stem-like cells and inhibiting the Notch-1 signaling. In future studies, we intend to further explore the potential therapeutic efficacy of the quercetin-radiation combination treatment in clinical trials.

METHODS:OBJECTIVES:Long-term prevention of metastatic disease remains a challenge in locally advanced rectal cancer, and robust pretreatment prognostic factors for metastatic progression are lacking. We hypothesized that detecting circulating tumor-specific DNA (ctDNA) based on hypermethylation of the neuropeptide Y gene (meth-ctDNA) could be a prognostic marker in the neoadjuvant setting; we examined this in a secondary, explorative analysis of a prospective trial. MATERIALS AND METHODS:Serum samples were prospectively collected in a phase III trial for locally advanced rectal cancer. Positivity for and fractional abundance of meth-ctDNA in baseline samples were estimated. Overall survival (OS) and the rate of distant metastases were compared between meth-ctDNA positive and negative patients; other prognostic factors were controlled for in multivariate Cox regression. Importance of quantitative load was examined by considering the fractional abundance of meth-ctDNA relative to total circulating DNA. RESULTS:Baseline serum samples were available for 146 patients. In total, 30 patients had presence of meth-ctDNA, with no correlation with cT (P=0.8) or cN (P=0.6) stages. Median follow-up was 10.6 years for OS and 5.1 years for freedom from distant metastases. Patients with meth-ctDNA had significantly worse 5-year OS (47% vs. 69%), even when controlling for other prognostic factors (hazard ratio=2.08; 95% confidence interval, 1.23-1.51). This seemed mainly driven by disparity in the rate of distant metastases (55% vs. 72% at 5 y, P=0.01); hazard ratio=2.20 (95% confidence interval, 1.19-4.07, P=0.01) in multivariate analysis. Increased quantitative load was highly significant for worse outcomes. CONCLUSIONS:Meth-ctDNA could be a potential prognostic marker in the neoadjuvant setting and may, if validated, identify patients at increased risk of distant metastases.