Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We previously showed that combined neoadjuvant doxorubicin (DOX) treatment and orthotopic liver transplantation produced a 3-year tumor-free survival rate of 54% in stage II-IVa nonresectable hepatocellular carcinomas (HCCs). These patients received posttransplant immunosuppressive doses of cyclosporin A (CsA). CsA has been shown to modify the function of a membrane P-glycoprotein (Pgp) whose overexpression is associated with a multidrug-resistant (MDR1) phenotype. This study utilized HCC cell lines to characterize the in vitro chemomodulatory properties of CsA as found in posttransplant patient plasma to consider the hypothesis that CsA may prolong posttransplant survival by enhancing the therapeutic efficacy of DOX against multidrug-resistant hepatoma cells. We characterized Pgp expression in the HCC lines Hep3B, Hep G2, and SK-HEP-1 by immunohistochemistry and the reverse transcription-polymerase chain reaction. The combined cytotoxicity of DOX + CsA was examined by [3H]thymidine uptake and flow cytometric drug-retention assays. Pgp expression was assessed further after prolonged (10-day) treatment with CsA. Hep3B and Hep G2 cells expressed low to moderate levels of Pgp. The effective DOX dose required for inhibiting MDR1(+) Hep3B and Hep G2 cell proliferation by 50% (DOX IC50) was 44.5 ng/ml and 43.5 microgram/ml, as compared with 10.7 ng/ml for Pgp-negative SK-HEP-1 cells. Optimal concentrations of CsA (0.8 micrometer) lowered DOX IC50 for Hep3B cells and Hep G2 cells by 6-fold and 4-fold, respectively. Similarly, plasma from patients containing immunosuppressive levels of CsA lowered DOX IC50 of the MDR1(+) Hep G2 cells by up to 4-fold. Prolonged exposure to CsA did not affect its chemosensitizing capacity or Pgp expression of HCC cells. PSC-833, a nonimmunosuppressive analogue of CsA, was equally effective in reducing the DOX IC50 of MDR1(+) HCC cells. CsA and PSC-833 increased drug retention by approximately 75%, but did not significantly affect hepatoma cell viability or Pgp expression. Pharmacological concentrations of cyclosporin analogues, including one nonimmunosuppressive form, enhance DOX cytotoxicity of MDR1(+) HCC cells by modulating drug retention. CsA as found in posttransplant patient plasma enhanced DOX cytotoxicity to human MDR1(+) hepatoma cells in vitro, albeit at less than optimal chemosensitizing concentrations. Prolonged exposure to CsA did not affect its chemosensitizing properties or block Pgp expression of HCC cells. These findings support our hypothesis that in vivo immunosuppressive levels of CsA may enhance DOX chemotherapeutic efficacy on MDR1(+) HCC cells.
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PMID:Chemosensitization of human hepatocellular carcinoma cells with cyclosporin A in post-liver transplant patient plasma. 981

P-glycoprotein (Pgp), an efflux pump, was confirmed the first time to regulate the expressions of miR/gene in cells. Pgp is known to be associated with multidrug resistance. RHepG2 cells, the multidrug resistant subline of human hepatocellular carcinoma HepG2 cells, expressed higher levels of Pgp as well as miR-16, and lower level of Bcl-2 than the parental cells. In addition, RHepG2 cells were more radiation sensitive and showed more pronounced radiation-induced apoptotic cell death than the parental cells. Mechanistic analysis revealed that transfection with mdr1 specific antisense oligos suppressed radiation-induced apoptosis in HepG2 cells. On the other hand, ectopic mdr1 expression enhanced radiation-induced apoptosis in HepG2 cells, SK-HEP-1 cells, MiHa cells, and furthermore, induced miR-16 and suppressed its target gene Bcl-2 in HepG2 cells. Moreover, the enhancement effects of Pgp and miR-16 on radiation-induced apoptosis were counteracted by overexpression of Bcl-2. The Pgp effect on miR-16/Bcl-2 was suppressed by Pgp blocker verapamil indicating the importance of the efflux of Pgp substrates. The present study is the first to reveal the role of Pgp in regulation of miRNA/gene expressions. The findings may provide new perspective in understanding the biological function of Pgp.
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PMID:P-glycoprotein enhances radiation-induced apoptotic cell death through the regulation of miR-16 and Bcl-2 expressions in hepatocellular carcinoma cells. 2133 67