Pregnane × Receptor (PXR) expression in colorectal cancer cells restricts irinotecan chemosensitivity through enhanced SN-38 glucuronidation

Abstract

BackgroundClinical efficacy of chemotherapy in colorectal cancer is subjected to broad inter-individual variations leading to the inability to predict outcome and toxicity. The topoisomerase I inhibitor irinotecan (CPT-11) is worldwide approved for the treatment of metastatic colorectal cancer and undergoes extensive peripheral and tumoral metabolism. PXR is a xenoreceptor activated by many drugs and environmental compounds regulating the expression of drug metabolism and transport genes in detoxification organs such as liver and gastrointestinal tract. Considering the metabolic pathway of irinotecan and the tissue distribution of Pregnane × Receptor (PXR), we hypothesized that PXR could play a key role in colon cancer cell response to irinotecan.ResultsPXR mRNA expression was quantified by RT-quantitative PCR in a panel of 14 colon tumor samples and their matched normal tissues. PXR expression was modulated in human colorectal cancer cells LS174T, SW480 and SW620 by transfection and siRNA strategies. Cellular response to irinotecan and its active metabolic SN38 was assessed by cell viability assays, HPLC metabolic profiles and mRNA quantification of PXR target genes. We showed that PXR was strongly expressed in colon tumor samples and displayed a great variability of expression. Expression of hPXR in human colorectal cancer cells led to a marked chemoresistance to the active metabolite SN38 correlated with PXR expression level. Metabolic profiles of SN38 showed a strong enhancement of SN38 glucuronidation to the inactive SN38G metabolite in PXR-expressing cells, correlated with an increase of UDPglucuronosyl transferases UGT1A1, UGT1A9 and UGT1A10 mRNAs. Inhibition of PXR expression by lentivirus-mediated shRNA, led to SN38 chemoresistance reversion concomitantly to a decrease of UGT1A1 expression and SN38 glucuronidation. Similarly, PXR mRNA expression levels correlated to UGT1A subfamily expression in human colon tumor biopsies.ConclusionOur results demonstrate that tumoral metabolism of SN38 is affected by PXR and point to potential therapeutic significance of PXR quantification in the prediction of irinotecan response. Furthermore, our observations are pharmacologically relevant since many patients suffering from cancer diseases are often exposed to co-medications, food additives or herbal supplements able to activate PXR. A substantial part of the variability observed among patients might be caused by such interactions

Clinical Observations on Associations Between the UGT1A1 Genotype and Severe Toxicity of Irinotecan

“…2009). Our study shows that the usage of dosages adjusted by UGT1A1 genotype and patients' clinic charatcters caused the lower incidence of severe toxicity compared with 20%-30% showed in some studies (Negoro et al, 1991;Rothenberg et al, 1993;Rougier et al, 1998;Saltz et al, 2000;Rothenberg et al, 2001;Vanhoefer et al, 2001;Fuchs et al, 2003). It illustrates that pharmacogenetic testing of UGT1A1 is meaningful in clinic.…”

“…But its usage always be limited by its severe side effects especially diarrhea and myelosuppression which are doselimiting toxicities (Negoro et al, 1991;Rothenberg et al, 1993;Rougier et al, 1998;Saltz et al, 2000;Rothenberg et al, 2001;Vanhoefer et al, 2001;Fuchs et al, 2003). Clinical administration dosage is generally calculated according to the body surface area or weight presently which is the group average dose (Reilly and Workman, 1993).…”

“…There are many researches detecting the relationship and increased the risk of diarrhea (Innocenti et al, 2004;Raynal et al, 2010;Ma Dong et al, 2011). While some other suggest that UGT1A1*28 polymorphism is of some relevance to toxicity, however, it is less important than discussed in some trials (Rouits et al, 2004;Toffoli et al, 2006).…”

“…Because CPT-11 causes severe diarrhea and neutropenia in 20% to 35% of patients treated (Negoro et al, 1991;Rothenberg, et al, 1993;Rougier et al, 1998;Saltz et al, 2000;Rothenberg et al, 2001;Vanhoefer et al, 2001;Fuchs et al, 2003), and fatal events (up to 5.3% prevalence) during single-agent irinotecan treatment have been reported (Vanhoefer et al, 2001). We associated these two kind side effects with UGT1A1 genotypes, clinic characters and each other to detect the relationship between them by multivariate logistic analysis We took the sex, age, KPS, number of metastasis, history of chemotherapy, UGT1A1 genotype, dosage, leucopenia, neutropenia, primary cancer and pathological type into risk factors.…”

Anticancer Drug Metabolism: Chemotherapy Resistance and New Therapeutic Approaches

“…After its activation, PXR translocates into the nucleus to regulate gene transcription (Squires et al, 2004). PXR recognizes a wide variety of ligands including dexamethasone, rifampicin, spironolactone and pregnenolone 16 -carbonitrile being among the best characterized (Timsit and Negishi, 2007) as well as many anticancer drugs such as microtubule-binding drugs (Raynal et al, 2010). Targets genes of PXR are CYP3A4, MDR1, CYP2B6, members of UGTs superfamily and MRP3 and OATP2 transporters (Klaassen and Slitt, 2005;Tolson and Wang, 2010).…”