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Breast cancer cells are usually sensitive to several chemotherapeutic regimens, but they can develop chemoresistance after prolonged exposure to cytotoxic drugs, acquiring a more aggressive phenotype. Drug resistance might involve the multi-drug resistance (MDR) 1 gene, encoding a transmembrane glycoprotein p-170 (P-gp), which antagonizes intracellular accumulation of cytotoxic agents, such as doxorubicin. We previously demonstrated that type 2 cyclooxygenase (COX-2) inhibitors can reverse the chemoresistance phenotype of a medullary thyroid carcinoma cell line by inhibiting P-gp expression and function. The aim of our study was to investigate the role of COX-2 inhibitors in modulating chemoresistance in a human breast cancer cell line, MCF7. MCF7 cells, expressing COX-2 but not MDR1, were treated with increasing doses of doxorubicin, and they became chemoresistant after 10 days of treatment, in association with MDR1 expression induction. This effect was reversed by doxorubicin withdrawal and prevented by co-incubation with N-[2-(cyclohexyloxy)4-nitrophenyl]-methanesulfonamide (NS-398), a selective COX-2 inhibitor. Treatment with NS-398 alone did not influence cell viability of a resistant MCF7 cell clone (rMCF7), but sensitized rMCF7 cells to the cytotoxic effects of doxorubicin. Moreover, treatment with NS-398 significantly reduced MDR1 expression in rMCF7 cells. Doxorubicin-induced membrane P-gp expression and function was also greatly impaired. Our data therefore support the hypothesis that COX-2 inhibitors can prevent or reduce the development of the chemoresistance phenotype in breast cancer cells by inhibiting P-gp expression and function.

The role of Wnt pathway in digestive endocrine tumours is debated. The aim of this work is to investigate key players in Wnt pathway by a multimodal approach. Sixty cases (49 well-differentiated and 11 poorly differentiated) were investigated for methylation of adenomatous polyposis coli (APC) and E-cadherin promoters, the loss of heterozygosity (LOH) at APC locus and β -catenin and E-cadherin expression by immunohistochemistry. Tumours showing altered β-catenin localization were tested for β -catenin and APC mutations. APC promoter methylation was restricted to gastroduodenal tumours (21 out of 59, 36%), prevalent in poorly differentiated carcinomas (P=0.042) and correlating with aggressive features (high histology grade, P<0.02; tumour death, P=0.026; high fractional allelic loss, P=0.002, in turn correlating with short survival, P=0.017). LOH at APC locus was found in 14 out of 53 cases (26%, 10 gastroduodenal and 4 colorectal), prevalent in poorly differentiated carcinomas (P=0.002) and correlating with histology grade (P=0.012). β -catenin abnormal expression was found in 41 out of 54 cases (76%), with nuclear staining correlating with APC alteration (P=0.047) and short survival (P=0.006). APC, but not β -catenin, gene mutations were found (7 out of 35 tumours), 4 of which in the midgut. E-cadherin promoter methylation was rarely detected (2 out of 52 cases), with cytoplasmic expression in 18 out of 43 cases (42%), not correlating with any clinico-pathological feature. In conclusion, Wnt pathway alterations, as represented by abnormal β-catenin localization, are common events in digestive endocrine tumours, but only nuclear expression correlates with tumour aggressiveness. Though with different alteration mechanisms according to anatomical site, APC plays a major role in Wnt pathway activation and in determining the high chromosomal instability observed in aggressive endocrine carcinomas.