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Background: Colorectal carcinoma (CRC) is one of the most frequently diagnosed forms of cancer worldwide. The RAS (KRAS, NRAS) and BRAF genes encode proteins that are important therapeutic targets for the treatment of CRC and, together with the mismatch repair (MMR) system, are closely related to patient prognosis and survival in advanced CRC. Here we evaluate the mutational profile and the frequency of mutations in the KRAS, NRAS and BRAF genes, along with the expression of MMR in advanced CRC, at a tertiary hospital in southern Brazil. Methods: A cross-sectional retrospective study was carried out, where molecular analysis of mutations in the KRAS, NRAS and BRAF genes was carried out, as well as immunohistochemistry for MMR proteins. Results: Next-generation sequencing (NGS) analysis of 310 tumors revealed that 202 patients (65.2%) had mutations. The KRAS gene (53.2%) was the most frequently mutated in our sample, with G12D being the most frequent, representing 30.5% of the mutations in this gene. The most frequent mutation found in BRAF was V600E (n=25; 89.3%) and differed significantly in women and in the right colon in patients with MMR deficiency. Among the 283 patients tested for MMR, the rate of loss of expression was 8.8% (25/283). Conclusions: Deficiency in the MMR system is associated with the presence of the BRAF V600E mutation, tumors located in the right colon, and the female sex. In our case series, more than 60% of patients had at least one mutation in KRAS, NRAS, or BRAF. The presence of mutations in these genes is closely related to CRC prognosis and helps define the best therapeutic approach in patients with metastatic CRC.
RESUMO
PURPOSE: Presence of cancer stem cells (CSCs) contributes to tumor outgrowth, chemo-resistance and relapse in some cancers including colorectal carcinoma (CRC). The current characterization methods of CSCs in CRC only allows enrichment of CSCs but not their purification. Recent reports showed that ST6 beta-galactoside alpha-2,6-sialyltransferase 1 (ST6Gal-I) plays an essential role in protecting tumor cells against harsh environment like oxidative stress and nutrient deprivation. Therefore, whether ST6Gal-I may be highly expressed in CSCs or whether it may enhance resistance of tumor cells to chemotherapy deserves exploration. METHOD: ST6Gal-I levels were determined in CRC specimens, compared to paired normal colorectal tissue, and examined in CD133+ vs CD133- CRC cells, and CD44+ vs CD44- CRC cells. ST6Gal-I levels and their association with patient survival were examined. In vivo, 2 CRC cell lines Caco-2 and SW48 were transduced with two lentiviruses, one lentivirus carrying a green fluorescent protein reporter and a luciferase reporter under a cytomegalovirus promoter to allow tracing tumor cells by both fluorescence and luciferase activity, and one lentivirus carrying a nuclear red fluorescent protein under the control of ST6Gal-I promoter to allow separation of ST6Gal-I+ vs ST6Gal-I- CRC cells. Tumor sphere formation, resistance to fluorouracil-induced apoptosis, and frequency of tumor formation after serial adoptive transplantation were done on ST6Gal-I+ vs ST6Gal-I- CRC cells. RESULT: ST6Gal-I levels were significantly upregulated in clinically obtained CRC specimens, compared to paired normal colorectal tissue. Poorer patient survival was detected in ST6Gal-I-high CRC, compared to ST6Gal-I-low subjects. Higher levels of ST6Gal-I were detected in CD133+ CRC cells than CD133- CRC cells, and in CD44+ CRC cells than in CD44- CRC cells. Compared to ST6Gal-I- CRC cells, ST6Gal-I+ CRC cells generated significantly more tumor spheres in culture, were more resistant to fluorouracil-induced apoptosis likely through upregulating cell autophagy, and generated tumor more frequently after serial adoptive transplantation. CONCLUSION: ST6Gal-I may be highly expressed in the cancer stem-like cells in CRC and enhances cancer cell resistance to chemotherapy.