Molecular mechanisms targeting drug-resistance and metastasis in colorectal cancer:Updates and beyond

Colorectal cancer(CRC)is the third most diagnosed malignancy and a major leading cause of cancer-related deaths worldwide.Despite advances in therapeutic regimens,the number of patients presenting with metastatic CRC(mCRC)is increasing due to resistance to therapy,conferred by a small population of cancer cells,known as cancer stem cells.Targeted therapies have been highly successful in prolonging the overall survival of patients with mCRC.Agents are being developed to target key molecules involved in drug-resistance and metastasis of CRC,and these include vascular endothelial growth factor,epidermal growth factor receptor,human epidermal growth factor receptor-2,mitogen-activated extracellular signal-regulated kinase,in addition to immune checkpoints.Currently,there are several ongoing clinical trials of newly developed targeted agents,which have shown considerable clinical efficacy and have improved the prognosis of patients who do not benefit from conventional chemotherapy.In this review,we highlight recent developments in the use of existing and novel targeted agents against drug-resistant CRC and mCRC.Furthermore,we discuss limitations and challenges associated with targeted therapy and strategies to combat intrinsic and acquired resistance to these therapies,in addition to the importance of implementing better preclinical models and the application of personalized therapy based on predictive biomarkers for treatment selection.

Expression of the methylcytosine dioxygenase ten-eleven translocation-2 and connexin 43 in inflammatory bowel disease and colorectal cancer

BACKGROUND Inflammatory bowel disease(IBD)constitutes a substantial risk factor for colorectal cancer.Connexin 43(Cx43)is a protein that forms gap junction(GJ)complexes involved in intercellular communication,and its expression is altered under pathological conditions,such as IBD and cancer.Recent studies have implicated epigenetic processes modulating DNA methylation in the pathogenesis of diverse inflammatory and malignant diseases.The ten-eleven translocation-2(TET-2)enzyme catalyzes the demethylation,hence,regulating the activity of various cancer-promoting and tumor-suppressor genes.AIM To investigate Cx43 and TET-2 expression levels and presence of 5-hydroxymethylcytosine(5-hmC)marks under inflammatory conditions both in vitro and in vivo.METHODS TET-2 expression was evaluated in parental HT-29 cells and in HT-29 cells expressing low or high levels of Cx43,a putative tumor-suppressor gene whose expression varies in IBD and colorectal cancer,and which has been implicated in the inflammatory process and in tumor onset.The dextran sulfate sodium-induced colitis model was reproduced in BALB/c mice to evaluate the expression of TET-2 and Cx43 under inflammatory conditions in vivo.In addition,archived colon tissue sections from normal,IBD(ulcerative colitis),and sporadic colon adenocarcinoma patients were obtained and evaluated for the expression of TET-2 and Cx43.Expression levels were reported at the transcriptional level by quantitative real-time polymerase chain reaction,and at the translational level by Western blotting and immunofluorescence.RESULTS Under inflammatory conditions,Cx43 and TET-2 expression levels increased compared to noninflammatory conditions.TET-2 upregulation was more pronounced in Cx43-deficient cells.Moreover,colon tissue sections from normal,ulcerative colitis,and sporadic colon adenocarcinoma patients corroborated that Cx43 expression increased in IBD and decreased in adenocarcinoma,compared to tissues from non-IBD subjects.However,TET-2 expression and 5-hmC mark levels decreased in samples from patients with ulcerative colitis or cancer.Cx43 and TET-2 expression levels were also investigated in an experimental colitis mouse model.Interestingly,mice exposed to carbenoxolone(CBX),a GJ inhibitor,had upregulated TET-2 levels.Collectively,these results show that TET-2 levels and activity increased under inflammatory conditions,in cells downregulating gap junctional protein Cx43,and in colon tissues from mice exposed to CBX.CONCLUSION These results suggest that TET-2 expression levels,as well as Cx43 expression levels,are modulated in models of intestinal inflammation.We hypothesize that TET-2 may demethylate genes involved in inflammation and tumorigenesis,such as Cx43,potentially contributing to intestinal inflammation and associated carcinogenesis.