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:3.6.3.44 (P-glycoprotein)
13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have studied the effects of extracellular pH (pHo) and osmotic strength on the expression of the human multidrug resistance (MDR) protein. Both lowered pHo and hypertonic shock increase the level of hu MDR protein 5-10-fold in membranes isolated from the human colon carcinoma cell lines SW620 and HCT15 and the human kidney carcinoma line SKRC-39. Increased protein expression is dependent on the duration of acid or osmotic shock and is reversed within several days when normal growth conditions are restored. Quantitative northern blot analysis with a hu MDR 1 specific probe reveals increased MDR mRNA in the acid and hypertonically shocked cells. Interestingly, we find a greater increase in mRNA levels for hypotonically shocked colon cells, without an apparent increase in protein levels. Overexpressing cells are found to retain less [3H]vinblastine relative to cells cultured under normal conditions, and they are resistant to the cytotoxic effects of doxorubicin, vinblastine, and colchicine, but not methotrexate. This resistance appears to be reversed by treatment with verapamil. In contrast, SW620 cells previously induced to overexpress MDR protein via the administration of differentiation agents [Mickley et al. (1989) J. Biol. Chem. 264, 18031-18040] did not exhibit decreased retention of [3H]vinblastine; thus low-pHo-induced overexpression of MDR protein in these cells may provide additional factors that promote the full expression of the MDR phenotype. These data may help to explain why many solid tumors (e.g., of colon and kidney origin) develop MDR prior to chemotherapy, since they usually grow under similar acidic conditions. These data also support the contention that MDR protein may play a role in intracellular pH and volume homeostasis.
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PMID:Low external pH and osmotic shock increase the expression of human MDR protein. 791 81

Well established UCLA-P3 human lung tumor xenografts were significantly regressed by treatment with a monoclonal antibody-vinca immunoconjugate whereas no regressions were observed for the LS174T and SW948 human colon carcinoma xenografts by this therapy. Antibody and complementary DNA probes utilized for detection of the MDR1 gene product and mRNA levels, respectively, revealed that prior to drug treatment the lung tumor had virtually no detectable P-glycoprotein while both colon carcinomas displayed low and heterogeneous expression of this resistance-related protein. It was subsequently determined, however, that the low level of P-glyocoprotein expression observed for one of the colon tumors could be rapidly modulated following therapy with free or MoAb-conjugated vinca. These data indicated that elevated P-glycoprotein levels resulting from drug therapy may play a role in the lack of regression of the human colon xenografts. Most significantly, our results also indicated that the time interval between drug treatment and tissue sampling may be a critical factor to be considered in studies which attempt to correlate P-glycoprotein expression with chemotherapy.
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PMID:In vivo expression of P-glycoprotein in a human colon carcinoma xenograft is modulated by therapy with free and monoclonal antibody-conjugated vinca alkaloids. 791 8

The outcome of cancer metastasis depends on the interaction of metastatic cells with various host factors. The implantation of human cancer cells into anatomically correct (orthotopic) sites in nude mice can be used to ascertain their metastatic potential. While it is clear that vascularity and local immunity can retard or facilitate tumor growth, we have found that the organ environment also influences tumor cell functions such as production of degradative enzymes. The organ microenvironment can also influence the response of metastases to chemotherapy. It is not uncommon to observe the regression of cancer metastases in one organ and their continued growth in other sites after systemic chemotherapy. We demonstrated this effect in a series of experiments using a murine fibrosarcoma, a murine colon carcinoma, and a human colon carcinoma. The tumor cells were implanted subcutaneously or into different visceral organs. Subcutaneous tumors were sensitive to doxorubicin (DXR), whereas lung or liver metastases were not. In contrast, sensitivity to 5-FU did not differ between these sites of growth. The differences in response to DXR between s.c. tumors (sensitive) and lung or liver tumors (resistant) were not due to variations in DXR potency or DXR distribution. The expression of the multidrug resistance-associated P-glycoprotein as determined by flow cytometric analysis of tumor cells harvested from lesions in different organs correlated inversely with their sensitivity to DXR: increased P-glycoprotein was associated with overexpression of mdr1 mRNA. However, the organ-specific mechanism for upregulating mdr1 and P-glycoprotein has yet to be elucidated.
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PMID:Modulation of tumor cell response to chemotherapy by the organ environment. 792 51

Two human colon carcinoma drug resistant clones (LoVo-IDA-1 and LoVo-IDA-2) were selected by continuous pressure of LoVo parent cell lines to idarubicin (IDA). Both cell sublines exhibited a typical multidrug resistance (MDR) phenotype but, despite IDA selection, the resistance index (RIext) was higher for daunorubicin (DAU) (RIext = 101-112) than for IDA (RIext = 20-23). A similar pattern of cross-resistance was also observed in two (DOX) doxorubicin-selected LoVo cell lines (LoVo-DOX-1 and LoVo-DOX-2). All the MDR cell lines exhibited decreased drug accumulation and increased intracellular drug tolerance as evidenced by the greater intracellular amount of drug required to cause a 50% growth inhibition (IC50int) compared to their parent cell line. The differences between DAU and IDA RIext exhibited by MDR cells were a function of intracellular resistance. DAU IC50int was 13.9 and 14.9 times higher in LoVo-IDA-1,2 and 6.4 and 6.2 in LoVo-DOX-1,2 cell lines, respectively, than in LoVo-sensitive cells, whereas IDA IC50int was only 3.6 and 3.2 times higher in LoVo-IDA-1,2 and 2.2 and 2.3 in LoVo-DOX-1,2 cell lines, respectively. Conversely, variations in IDA accumulation between resistant and sensitive cells were similar to those observed for DAU [the ratios between DAU uptake in sensitive and resistant cells were almost identical (P = NS) to those observed for IDA]. Differences between IDA and DAU intracellular distribution accounted for the relatively higher DAU intracellular resistance. In fact nuclear/cytoplasmic (N/C) DAU fluorescence ratio was higher (P < 0.01) in sensitive (N/C = 3.4 +/- 2.7) than in MDR cells (N/C ranging from 0.31 +/- 0.2 to 0.41 +/- 0.1). In contrast, no significant (P = NS) differences were observed in IDA N/C ratios between sensitive and MDR cells (N/C ranging from 0.16 +/- 0.1 to 0.20 +/- 0.1). In MDR cells, 1-hr VER (10 microM) treatment partially reverted both DAU N/C ratios and intracellular DAU resistance but neither changes in IDA N/C ratios nor variation in intracellular IDA resistance were observed following VER exposure. In conclusion, the greater intracellular drug tolerance that MDR cells show for DAU compared to IDA makes IDA more effective than DAU in MDR cells overexpressing P-glycoprotein (P-gp).
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PMID:Comparison of mechanisms responsible for resistance to idarubicin and daunorubicin in multidrug resistant LoVo cell lines. 798 98

Two drug-resistant sublines, CP2.0 and RT, were simultaneously selected by cis-diamminedichloroplatinum (CDDP) from the human colon carcinoma cell line LoVo by the conventional method of continuous drug exposure. The 2 sublines differed in morphology, growth kinetics and pattern of gene expression. Genetic signature analysis indicated that the lines were independent subclones but that both arose from LoVo. These sublines were maintained in a growth medium containing 2.0 micrograms/ml CDDP. However, CP2.0 cells were 3 times more resistant to CDDP than were RT cells. Although both were cross-resistant to mustargen and 5-fluorouracil, only CP2.0 was resistant to Adriamycin and vincristine. Western-blot analysis, immunocytochemical staining and in vitro phosphorylation experiments indicated that the level of P-glycoprotein was significantly elevated in CP2.0 but not in RT. Despite the differences between these sublines, they possess similar CDDP-resistance mechanisms, including decreased intracellular CDDP accumulation, elevated levels of glutathione and metallothionein-like proteins, increased glutathione transferase-pi mRNA, and enhanced susceptibility to CDDP cytotoxicity after treatment with DL-buthionine-[S,R]-sulfoximine. Nevertheless, our results suggest that, in certain tumor types, P-glycoprotein-mediated multi-drug resistance and CDDP-resistance phenotypes can coexist in cells with primary resistance to CDDP.
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PMID:Distinct P-glycoprotein expression in two subclones simultaneously selected from a human colon carcinoma cell line by cis-diamminedichloroplatinum (II). 809 74

We observed increased levels of mdr-1 mRNA and its protein product P-glycoprotein (Pgp) in the human colon carcinoma cell line, LS 180, and its drug-resistant sublines, LS 180-Ad50 and LS 180-Vb2, after treatment with the Pgp antagonists, verapamil, nifedipine, and cyclosporin A. Increases in mdr-1 RNA were observed within 8 h of the addition of the Pgp antagonists and continued to rise over time. Peak levels were attained after several weeks and were sustained for the duration of treatment up to several months, with a rapid decline in mdr-1 mRNA levels after removal of the Pgp antagonist. Corresponding changes in Pgp were demonstrated with addition and removal of the Pgp antagonists. Increased mdr-1 mRNA was also seen with two other calcium channel blockers, nicardipine and diltiazem, but not with the Pgp antagonists, quinidine and chlorpromazine. Treatment with verapamil or nifedipine was associated with electron microscopic changes consistent with increased differentiation and resulted in increased carcinoembryonic antigen expression, suggesting that the increase in mdr-1 expression was associated with the process of differentiation. Nuclear runoff experiments and inhibition of new RNA synthesis with actinomycin D treatment failed to detect an increase in mdr-1 transcription or stabilization of the mdr-1 mRNA suggesting that the effect of these agents is mediated posttranscriptionally within the nucleus.
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PMID:Increased mdr-1/P-glycoprotein expression after treatment of human colon carcinoma cells with P-glycoprotein antagonists. 809 79

In this study we report detection of mdr1 gene expression in the liver metastases of 7/11 patients with colon carcinoma and characterise the MDR phenotype associated with a panel of 19 human colon carcinoma cell lines. Within this panel, mdr1 mRNA biosynthesis and surface localisation of Pgp were assessed with respect to MDR functionality where the cell lines are representative of different clinical stages of tumour progression, metastatic potential and differentiation. The data indicates that constitutive levels of mdr1 mRNA/Pgp expression may not necessarily result in the functional expression of the MDR phenotype. While low levels of mdr1 mRNA/Pgp were detected in 5/8 well differentiated colon cell lines, only 2/8 were functionally MDR. In contrast, 10/11 moderate and poorly differentiated lines expressed mdr1 mRNA/Pgp and of these, 9/11 were functionally MDR. The phosphorylation status of the mature 170 kD P-glycoprotein and the surface localisation of this glycoprotein showed the strongest correlation with functionality. Analysis of cell lines for cross-resistance and chemosensitivity profiles against a battery of chemotherapeutic drugs suggests multiple mechanisms, in addition to Pgp, contribute to the overall resistance of colorectal cancer.
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PMID:Constitutive expression of multidrug resistance in human colorectal tumours and cell lines. 809 14

Expression of the MDR1 (P-glycoprotein) gene confers resistance to several classes of chemotherapeutic drugs (multi-drug resistance). Colon carcinomas frequently express high levels of MDR1 mRNA and P-glycoprotein, presumably reflecting the origin of these tumors from MDR1-expressing normal colonic cells. In 4 colon carcinoma cell lines (SW 620, HCT-15, DLD-1, LS 180), MDR1 expression was reported in an earlier study to be elevated after exposure to a differentiating agent, sodium butyrate (NaB). In one of these cell lines (SW 620), increased MDR1 expression reportedly was not accompanied by a decrease in the accumulation or cytotoxicity of vinblastine, a P-glycoprotein-transported drug, suggesting a possible functional abnormality of NaB-induced P-glycoprotein. We have re-examined the effect of NaB on MDR1/P-glycoprotein expression and function in the same colon carcinoma cell lines. NaB treatment induced differentiation-related changes and increased expression of MDR1 mRNA in all 4 cell lines. A major increase in MDR1 mRNA and P-glycoprotein expression was observed in only one line, SW 620. This increase, however, was accompanied by a commensurate increase in the activity of P-glycoprotein, indicating that the induced protein was fully functional. NaB treatment caused a relatively minor increase in MDR1 mRNA expressed in the other 3 cell lines. Two of these lines showed a detectable increase in the P-glycoprotein expression and function, but in the third line (LS 180) P-glycoprotein was undetectable either before or after exposure to NaB. The magnitude of MDR1 induction by NaB showed no apparent correlation with differentiation-related changes induced by this agent.
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PMID:Variable effects of sodium butyrate on the expression and function of the MDR1 (P-glycoprotein) gene in colon carcinoma cell lines. 810 60

Previously we reported the synthesis and partial characterization of 21 N10-substituted phenoxazines in reversing Vinca alkaloid resistance. Here we report on a subset of these compounds; we have compared their activities in increasing Vinca alkaloid accumulation and reversing drug resistance in KB-ChR8-5 and GC3/c1 (human colon carcinoma) cell lines. Results demonstrated that 1) N-substituted phenoxazines increase accumulation of vinblastine; 2) within this series, there is little correlation or ranking of activity between the two cell lines when Vinca alkaloid accumulation is compared at equal concentrations of modulator; 3) N-substituted phenoxazines demonstrate both quantitative and qualitative differences, compared with verapamil, a standard modulator; and 4) the series includes at least two compounds, 10-[3'-[N-bis(hydroxyethyl)amino]propyl]phenoxazine and 10-(N-piperidinoacetyl)phenoxazine, which increase Vinca alkaloid accumulation but do not significantly inhibit efflux. Additionally, certain of these multidrug resistance modulators significantly enhance accumulation (8-50-fold) of Vinca alkaloids in cell lines with very low or undetectable P-glycoprotein levels, where verapamil has little activity. It is concluded that at least part of the activity of some of these N-substituted phenoxazine modulators may be mediated through a P-glycoprotein-independent mechanism.
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PMID:Pharmacological characterization of N-substituted phenoxazines directed toward reversing Vinca alkaloid resistance in multidrug-resistant cancer cells. 810 11

Previous reports from this laboratory have demonstrated that novobiocin produces supraadditive cytotoxicity and increases the formation of drug-stabilized topoisomerase II-DNA covalent complexes in WEHI-3B myelomonocytic leukemia and A549 lung carcinoma cells when combined with etoposide (VP-16). Inhibition of the efflux of VP-16 by novobiocin is responsible for the increase in VP-16 accumulation, which in turn leads to increased formation of VP-16-stabilized topoisomerase II-DNA covalent complexes and increased cytotoxicity. We now report that novobiocin synergistically enhanced the sensitivity of the multidrug resistant variants, WEHI-3B/NOVO and A549(VP)28, to VP-16, causing almost complete reversal of the resistance to the epipodophyllotoxin. These two tumor cell variants are resistant to several topoisomerase II-targeted drugs, particularly VP-16, but not to Vinca alkaloids; this finding corresponds to the fact that they do not overexpress the P-glycoprotein. The effects of novobiocin in these resistant sublines are mediated through the intracellular accumulation of VP-16, resulting in an increase in the formation of lethal VP-16-induced topoisomerase II-DNA covalent complexes. In the P-glycoprotein expressing multidrug resistant HCT116(VM)34 colon carcinoma and L1210/VMDRC0.06 leukemia cell lines, the latter being transfected with the human mdr-1 gene, novobiocin did not potentiate the cytotoxic activity of VP-16 nor increase the intracellular accumulation of VP-16 and the formation of covalent complexes, whereas their normal counterparts were sensitive to the potentiating activity of novobiocin when used in combination with VP-16. These results indicate that the action of novobiocin on the intracellular transport of VP-16 is not directed at the level of the P-glycoprotein, but that the action of novobiocin is antagonized by the presence of the P-glycoprotein. Since novobiocin is a clinically available antibiotic, has numerous structural analogues available for comparative studies, and has a relatively low toxicity profile, this drug, as well as structurally related agents, would appear to have significant clinical potential in combination with an epipodophyllotoxin for the treatment of non-P-glycoprotein expressing multidrug resistant tumors.
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PMID:Reversal of etoposide resistance in non-P-glycoprotein expressing multidrug resistant tumor cell lines by novobiocin. 810 48


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