Exploring new therapeutic targets and novel therapies for resistant colorectal cancer subtypes

Abstract

Colorectal cancer (CRC) represents the fourth leading cause of death by cancer in the world. CRC treatment is determined according to disease stage. 5-fluoruracil (5-FU), oxaliplatin and Irinotecan are the main chemotherapeutic compounds used in CRC treatment in different therapeutic strategies. However, in most aggressive CRCs, cells often develop resistance mechanisms leading to ineffectiveness of these therapies. Thus, it is of great importance the better understanding of molecular mechanisms underlying CRC in order to find new therapeutic targets and novel therapeutic strategies for treating advanced and resistant CRC. Deregulation of Wnt/β-catenin and Sonic hedgehog/Gli (Shh/Gli) signaling pathways, among many others, has been implicated in CRC carcinogenesis and metastasis. Excessive activation of Wnt/β-catenin signaling stimulates CRC development through activation of downstream cancer-related targets. TCF7L2 gene, encoding the main transcriptional activator of this pathway, originates different TCF7L2 isoforms that have been implicated in CRC. Moreover, defective regulation of Shh/Gli pathway have been denoted for its significant role in CRC progression, affecting the regulation of a diversity of cell processes involved in CRC carcinogenesis. During metastasis, cells develop mesenchymal characteristics, through the epithelial-to-mesenchymal transition (EMT) process. Furthermore, there is an established link between cancer stem cells (CSCs) and metastasis. Therefore, the aim of this project was to explore new therapeutic targets and novel therapies for resistant colorectal cancer subtypes. By studying TCF7L2 gene expression in a cohort of 38 CRC patients and CRC representative cell lines, we identified differential expression of specific TCF7L2 isoforms, varying in exon inclusion within exons 1-5 and exons 11-17, that appear to differ among CRC patients’ samples and between normal and tumor tissues. Therefore, this opens the door for further investigation on differential expression of TCF7L2 isoforms and its relation to CRC tumorigenesis and eventually to CRC risk. In a second phase of the project we tested a panel of 10 different compounds (cytostatic drugs used in conventional CRC treatment, epigenetic modulators, targeted therapies of specific signaling pathways and nutraceuticals) and the most promising combinations between them, for anti-proliferative and anti-migratory activities, in two CRC cell lines representative of mucinous tumors resistant to therapy (HT-29 and LS174T). The most promising combinations were evaluated for their effect in the expression of gene markers involved in cell-cycle, CRC stemness, epithelial-mesenchymal transition and Wnt/β-catenin and Sonic hedgehog/Gli (Shh/Gli) signaling pathways. With this work we were able to identify promising therapy combinations for the treatment of resistant CRC subtypes and explore the potential of new compounds as complement for conventional therapy in treatment of aggressive forms of CRC.