Up-regulation of FXR isoforms is not required for stimulation of the expression of genes involved in the lack of response of colon cancer to chemotherapy.

Several mechanisms are involved in the poor response of colorectal adenocarcinoma (CRAC) to pharmacological treatment. Since preliminary evidences have suggested that the enhanced expression of farnesoid X receptor (FXR) results in the stimulation of chemoresistance, we investigated whether FXR up-regulation is required for the expression of genes that characterize the multidrug resistance (MDR) phenotype of CRAC. Samples of tumours and adjacent healthy tissues were collected from naive patients. Using Taqman Low-Density Arrays, the abundance of mRNA of 87 genes involved in MDR was determined. Relevant changes were re-evaluated by conventional RT-QPCR. In healthy tissue the major FXR isoforms were FXRα2(+/-) (80%). In tumours this predominance persisted (91%) but was accompanied by a consistent reduction (3-fold) in total FXR mRNA. A lower FXR expression was confirmed by immunostaining, in spite of which there was a significant change in the expression of MDR genes. Pharmacological challenge was simulated "in vitro" using human CRAC cells (LS174T cells). Short-term (72h) treatment with cisplatin slightly increased the almost negligible expression of FXR in wild-type LS174T cells, whereas long-term (months) treatment induced a cisplatin-resistant phenotype (LS174T/R cells), which was accompanied by a 350-fold up-regulation of FXR, mainly FXRα1(+/-). However, the changed expression of MDR genes in LS174T/R cells was not markedly affected by incubation with the FXR antagonist Z-guggulsterone. In conclusion, although the enhanced expression of FXR may be involved in the stimulation of chemoresistance that occurs during pharmacological treatment, FXR up-regulation is not required for the presence of the MDR phenotype characteristic of CRAC.

No correlation between the expression of FXR and genes involved in multidrug resistance phenotype of primary liver tumors.

Farnesoid X receptor (FXR) has been recently reported to enhance chemoresistance through bile acid-independent mechanisms. Thus, FXR transfection plus activation with GW4064 resulted in reduced sensitivity to cisplatin-induced toxicity. This is interesting because primary tumors of the liver, an organ where FXR is expressed, exhibit marked refractoriness to pharmacological treatment. Here we have determined whether FXR is upregulated in hepatocellular carcinoma (HCC), cholangiocarcinoma (CGC) and hepatoblastoma (HPB) and whether this is related with the expression of genes involved in mechanisms of chemoresistance. Using RT-QPCR and Taqman low density arrays we have analyzed biopsies from healthy livers or surgically removed tumors from naive patients and cell lines derived from HCC (SK-HEP-1, Alexander and Huh7), CGC (TFK1) and HPB (HepG2), before and after exposure to cisplatin at IC50 for 72 h. In liver tumors FXR expression was not enhanced but significantly decreased (healthy liver > HCC > HPB ≈ CGC). Except for CGC, this was not accompanied by changes in the proportions of FXR isoforms. Changes in 36 genes involved in drug uptake/efflux and metabolism, expression/function of molecular targets, and survival/apoptosis balance were found. Changes affecting SLC22A1, CYP2A1 and BIRC5 were shared by HCC, CGC and HPB. Similarity in gene expression profiles between cell lines and parent tumors was found. Pharmacological challenge with cisplatin induced changes that increased this resemblance. This was not dependent upon FXR expression. Thus, although FXR may play a role in inducing chemoresistance under certain circumstances, its upregulation does not seem to be involved in the multidrug resistance phenotype characteristic of HCC, CGC and HPB.