Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The MCF-7 doxorubicin-resistant cell line MCF-7/Dox has been used extensively for studies of the multidrug resistance phenomenon. Using fluorescence-activated cell sorting (FACS), these cells were separated into two populations on the basis of rhodamine 123 (R123) accumulation. We designated these as low P-glycoprotein (LP-gp) and high P-gp (HP-gp) cells on the basis of their P-gp content. Using the reverse transcriptase polymerase chain reaction technique controlled by homologous internal standards, we analysed levels of MDR1 and MDR2 mRNA in each cell type. LP-gp and HP-gp cells had MDR1 mRNA levels of 2.17 +/- 0.17 and 6.65 +/- 2.29 amol ng-1 total RNA respectively, compared with 0.00088 +/- 0.00005 amol ng-1 in wild-type MCF-7 cells (MCF-7/WT). MCF-7/WT cells additionally contained 0.023 +/- 0.016 amol ng-1 of MDR2 mRNA, which was unchanged in LP-gp cells, but lower than in HP-gp cells, which contained 0.42 +/- 0.08 amol ng-1. Both LP-gp and HP-gp cells contained increased copies of the MDR1 gene. However, the degree of gene amplification did not correlate with the changes in MDR1 mRNA levels, indicating further regulatory levels of gene expression. The level of P-gp detected by MRK 16 correlated with R123 accumulation. HP-gp cells expressed a 10-fold higher level of P-gp1 than LP-gp cells. However, there was only a 3-fold increase in MDR1 mRNA level in HP-gp cells compared with LP-gp cells. These data suggest that some regulation of P-gp1 expression also occurred at the post-translational level. Phosphorylation of P-gp by protein kinase C (PKC)-alpha is necessary for its activity. Our analysis of PKC-alpha, 0 and epsilon isozyme levels, and subcellular distribution, shows a co-regulation of expression with P-gp, suggesting a necessary role for PKC in P-gp regulation.
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PMID:Regulation of P-glycoprotein 1 and 2 gene expression and protein activity in two MCF-7/Dox cell line subclones. 856 35

Overexpression of the P-glycoprotein/multidrug resistance 1 (MDR1) and multidrug resistance protein 1 (MRP1) gene is closely associated with the clinical outcome of various malignancies, and it is involved in responses to some anticancer chemotherapeutic agents including doxorubicin. Six human MRP subfamily members (MRP2-7) with structural similarities to MRP1 have been identified. Recently, the relationships between MRP2 and MRP3 expression levels of some cancer cells and drug sensitivity to doxorubicin have been reported, but the relationship between the clinical samples and drug sensitivity remains unclear. We determined the expressions of the MDR1, MRP1, MRP2 and MRP3 gene in bladder cancer during the clinical course and sought to learn whether the expression was correlated with drug responses to doxorubicin. Doxorubicin, used in chemotherapeutic treatment including intravesical and systemic chemotherapy, is an important anticancer agent for the treatment of bladder cancer. We used quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for our study, and the sensitivity to doxorubicin in bladder cancer was determined using the in vitro succinate dehydrogenase inhibition test. Using 47 clinical samples of bladder cancer, we confirmed the significant correlation of MDR1, MRP1 and MRP3 mRNA levels with resistance to doxorubicin. We showed that the expression of MDR1, MRP1, MRP2 and MRP3 in recurrent tumors and residual tumors after chemotherapeutic treatment was higher than that in untreated primary tumors. In particular, the MDR1 expression in residual tumors was 5.7-fold higher than that in untreated primary tumors.
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PMID:Increased expression of multidrug resistance-associated proteins in bladder cancer during clinical course and drug resistance to doxorubicin. 1192 Jun 26

This preject is to explore the reversal efficacy of calmodulin antagonist berbamine (BBM) on multidrug resistance (MDR) and its mechanism. Human erythroleukemic cell line K562 and its adriamycin-resistant counterpart K562/A02 were used in the study. The cells were co-cultured with ADR and BBM in different concentrations. MTT assay was used to analyze the effect of BBM on cell growth inhibition. According to the MTT assay, the 50% inhibitory concentration (IC(50)), the multiples of drug resistance and increased sensitivity of ADR were calculated. The concentration of intracellular ADR and expression level of P-gp were detected by flow cytometry (FCM). The expression level of mdr1 mRNA and survivin mRNA was detected by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) with beta-actin as internal reference. The results showed that IC(50) of ADR in K562 and K562/A02 cells was 1.16 +/- 0.09 micro mol/L and 37.47 +/- 1.76 micro mol/L, respectively. The resistant multiple of K562/A02 cells to ADR was 32.30 higher than that of K562 cells. BBM increased the chemo-sensitivity of ADR in K562/A02 cells with dose-dependent relationship, i.e. when 5, 10 and 20 micro mol/L BBM was added in the culture the chemo-sensitivity of ADR was increased to 2.01-, 9.68-, and 41.18-fold (P < 0.01), respectively. After treating K562/A02 cells by 5 or 10 micro mol/L BBM for 2 hours the accumulation of intracellular ADR was increased to 1.41- and 1.52-fold (P < 0.01), respectively. Treating by BBM for 72 hours decreased 4.12% (P < 0.05) and 27.09% (P < 0.01) of P-gp expression, respectively, meanwhile down-regulated expression of mdr1 mRNA and survivin mRNA was found. In conclusion, BBM could increase intracellular concentration of ADR in K562/A02 that down-regulated expression level of mdr1 mRNA and P-gp and survivin so that the sensitivity of K562/A02 to ADR was increased significantly.
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PMID:[Reversal effect of berbamine on multidrug resistance of K562/A02 cells and its mechanism]. 1470 44

Apart from fusion inhibitors, 'conventional' antiretrovirals such as nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs) act on intracellular targets. Intracellular concentrations of these agents may be an important determinant of antiviral activity, and the pharmacokinetics of intracellular drug accumulation (including binding to cytosolic proteins, intracellular-free fraction, influx and efflux kinetics and intracellular drug metabolism) are likely to impact upon efficacy and toxicity. To date, intracellular drug accumulation has been poorly studied in vivo, due to methodological difficulties and the relatively large volumes of blood required. NRTIs require intracellular conversion to their active phosphorylated metabolites: interactions between these agents, or with other drugs may impact upon efficacy. PIs are metabolised by cytochrome P450 enzymes in gut and liver; some intracellular metabolism by P450 isoforms is also possible. PIs are also substrates for drug efflux transporters such as P-gp and MRP1. We have previously observed a hierarchy of intracellular accumulation of PIs, most probably related to physiochemical characteristics of these drugs such as lipophilicity and plasma protein binding. Comparatively, little is known about the intracellular pharmacokinetics of NNRTIs. These drugs probably do not accumulate inside cells to any significant degree. The study of intracellular pharmacokinetics of HIV drugs is central to investigating putative sanctuary sites where HIV may replicate with little selective pressure. However, stringent methodological procedures need to be applied, and techniques for measuring intracellular drug are in their infancy. Moreover, failure to differentiate between truly intracellular drug and drug bound to cell membranes render results difficult to interpret.
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PMID:Intracellular pharmacokinetics of antiretroviral agents. 1573 42

Treatment of HIV-1-infected patients with anti-retroviral agents is not always successful due to the emergence of resistant HIV-1 mutants with reduced susceptibility to the agents. However, factors other than viral mutation may also contribute to treatment failure. It has been demonstrated that the ATP-binding cassette (ABC) transporter P-glycoprotein (P-gp/ABCB1) is a key determinant of oral bioavailability of HIV-1 protease inhibitors and their penetration of the central nervous system. More recently, we have found that the expression of breast cancer resistance protein (BCRP/ABCG2) in a CD4+ T-cell line confers cellular resistance to nucleoside reverse transcriptase inhibitors (NRTIs). The anti-HIV-1 activity of the NRTI zidovudine (AZT) was significantly diminished through the reduction of its metabolite levels in MT-4 cells which express high levels of BCRP. Moreover, the BCRP-specific inhibitor fumitremorgin C could completely restore the cytotoxicity of AZT and intracellular levels of its metabolites in BCRP-expressing cells. Thus, BCRP is considered to be a cellular factor that modulates the anti-HIV-1 activity of NRTIs.
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PMID:The role of breast cancer resistance protein (BCRP/ABCG2) in cellular resistance to HIV-1 nucleoside reverse transcriptase inhibitors. 1613 May 19

The clinical efficacy of some standardized St. John's Wort extracts (SWEs) such as WS((R)) 5570, WS((R)) 5572 or LI 160 in the treatment of mild, moderate and severe major depression has been demonstrated in 38 controlled clinical trials and two recent meta-analyses. Sixteen post-marketing surveillance studies with such preparations, based on a total of 34,804 patients, recorded an incidence of adverse events (AEs) among patients between 0% and 6%. Of these studies, the four large-scale surveillance studies with a total of 14,245 patients recorded a rate of AEs ranging from 0.1% to 2.4% and a drop-out rate due to AEs of 0.1-0.9%. This is at least ten-fold lower than that recorded with synthetic antidepressants. AEs associated with SWE treatment were mild and transient in nearly all cases. As with synthetic antidepressants, pharmacokinetic interactions may occur occasionally as a result of activity changes of drug-metabolising and drug-transporting proteins, especially CYP 3A4 and P-gp. Risks to the patient are not caused by SWE but by drugs with a narrow therapeutic range. Consequently, SWE preparations should not be taken concurrently with other antidepressants, with coumarin-type anticoagulants, the immunosuppressants cyclosporine and tacrolimus, protease and reverse transcriptase inhibitors used in anti-HIV treatment or with certain antineoplastic agents. However, such cases are extremely rare and, with medical supervision, easily avoided. In conclusion, the safety of SWE must be considered more favourable than that of synthetic antidepressants.
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PMID:Safety of St. John's Wort extract compared to synthetic antidepressants. 1642 30

Prediction of human tumor response based on preclinical data could reduce the failure rates of subsequent new anticancer drugs clinical development. Human small-cell lung carcinomas (SCLC) are characterized by high initial sensitivity to chemotherapy but a low median survival time because of drug resistance. The aim of this study was to evaluate the therapeutic relevance of a panel of human SCLC xenografts established in our laboratory using one compromising drug in SCLC, topotecan (TPT). Six SCLC xenografts derived from six patients were used: three were sensitive to a combination of etoposide (VP16), cisplatin (CDDP), and ifosfamide (IFO), and three were resistant, as published earlier. Growth inhibition was greater than 84% for five xenografts at doses of 1-2 mg/kg/day. TPT was combined with IFO, etoposide (VP16), and CDDP. IFO improved the efficacy of TPT in three of the five xenografts and complete responses were obtained even with the less TPT-sensitive xenograft. VP16 increased the efficacy of two of four xenografts and complete responses were obtained. The combination of TPT and CDDP did not improve TPT responses for any of the xenografts tested. Semiquantitative reverse transcriptase-PCR of genes involved in drug response, such as topoisomerase I, topoisomerase IIalpha, multidrug resistance 1 (MDR1), multidrug resistance-associated protein (MRP), lung resistance-related protein (LRP), and glutathione S-transferase pi (GSTpi), did not explain the variability in drug sensitivity between SCLC xenografts. In conclusion, these preclinical data mirror those from published clinical studies suggesting that our panel of SCLC xenografts represents a useful tool for preclinical assessment of new treatments.
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PMID:Clinical relevance of human cancer xenografts as a tool for preclinical assessment: example of in-vivo evaluation of topotecan-based chemotherapy in a panel of human small-cell lung cancer xenografts. 1982 76

ATP-binding cassette (ABC)-transporters, such as P-glycoprotein (P-gp/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs) and breast cancer resistance protein (BCRP/ABCG2) transport numerous drugs thus regulating their absorption, distribution and excretion. Angiotensin receptor type 1 blockers (ARBs), used to treat hypertension and heart failure, are commonly administered in combination therapy. However, their interaction potential is not well studied and their effect on ABC-transporters remains elusive. The study therefore aimed to elucidate the effect of various ARBs (telmisartan, candesartan, candesartan-cilexetil, irbesartan, losartan, olmesartan, olmesartan-medoxomil, eprosartan) on ABC-transporter activity in vitro. P-gp inhibition was assessed by calcein assay, BCRP inhibition by pheophorbide A efflux assay, and MRP2 inhibition by a MRP2 PREDIVEZ Kit. Induction of P-gp, BCRP and MRP2 was assessed by real time reverse transcriptase polymerase chain reaction and for P-gp also in a functional assay. Telmisartan was identified as one of the most potent inhibitors of P-gp currently known (IC(50)=0.38+/-0.2 microM for murine P-gp) and it also inhibited human BCRP (IC(50)=16.9+/-8.1 microM) and human MRP2 (IC(50)=25.4+/-0.6 microM). Moreover, the prodrug candesartan-cilexetil, but not candesartan itself, significantly inhibited P-gp and BCRP activity. None of the compounds tested induced mRNA transcription of P-gp or BCRP but eprosartan and olmesartan induced MRP2 mRNA expression. In conclusion, telmisartan substantially differed from other ARBs with respect to its potential to inhibit ABC-transporters relevant for drug pharmacokinetics and tissue defense. These findings may explain the known interaction of telmisartan with digoxin and suggest that it may modulate the bioavailability of drugs whose absorption is restricted by P-gp and possibly also by BCRP or MRP2.
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PMID:Interaction of angiotensin receptor type 1 blockers with ATP-binding cassette transporters. 2022 53

Etravirine is a novel nonnucleoside reverse transcriptase inhibitor (NNRTI) for the treatment of HIV-1 infections. ABC transporters potentially mediate clinically relevant drug-drug interactions. We assessed substrate characteristics and the inhibitory and inductive potential of etravirine on ABC transporters. Etravirine did not inhibit P-gp/ABCB1 and was not transported by the tested ABC transporters but was a potent inhibitor of BCRP/ABCG2. Etravirine induced several ABC transporters, especially BCRP/ABCG2. These data demonstrate that etravirine has the potential for drug-drug interactions by modulation of expression and function of several ABC transporters.
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PMID:Interaction potential of etravirine with drug transporters assessed in vitro. 2118 39

We examined the relationship between chemosensitivity and the expression of mdr-1 and P-gp in ten human HCC cell lines. Expression of P-gp was detected immunohistochemically and the expression of mdr-1 mRNA by the reverse transcriptase polymerase chain reaction (RT-PCR). Chemosensitivity was determined by the MTT assay. P-gp was positive in nine of the ten lines. mdr-1 mRNA expression was found in five. All cells lines positive for mdr-1 mRNA expression expressed P-gp. We could not demonstrate a correlation between mdr-1 or P-gp expression and drug resistance. We conclude that drug-resistance in HCC cells depends not only on mdr-1 but also on other factor(s).
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PMID:Relationship between mdr-1 messenger-RNA expression and anticancer drug-sensitivity in human hepatocellular-carcinoma cell-lines. 2159 33


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