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)

5-Aminolaevulinic acid (ALA)-induced porphyrin biosynthesis and phototoxicity in vitro was investigated in five malignant and two normal cell lines. Intracellular protoporphyrin IX (PpIX) content was quantified by extraction and fluorescence spectroscopy. Cellular PpIX content did not always correlate with cell proliferation rate as measured by the doubling times of cell lines. Cellular efflux of PpIX was also investigated. In a bladder carcinoma cell line, the observed rapid efflux was not blocked by verapamil, an inhibitor of the P-glycoprotein efflux pump. These data support the view that cellular PpIX accumulation is a dynamic process that is determined by both the efflux of PpIX from the cells and enzyme activities in the haem biosynthesis pathway. Desferrioxamine (desferal), a modulator of PpIX biosynthesis, enhanced ALA-induced cellular PpIX content significantly in all carcinoma cell lines but not in non-malignant cell lines. The enhanced PpIX cellular accumulation is attributed to inhibition of ferrochelatase activity, the enzyme responsible for the conversion of PpIX to haem. PpIX-mediated cellular photodestruction following irradiation with an argon ion laser at 514.5 nm was determined by the 'MTT assay'. There appeared to be a 'threshold' effect of cellular PpIX content; cells that synthesised less than 140 ng/mg-1 protein exhibited very little phototoxic damage, while cell lines having greater than 140 ng PpIX/mg-1 protein [corrected] exhibited a consistent phototoxic response. Among the cell lines which did undergo phototoxic damage, there was not a strict correlation between PpIX cellular content and ALA-induced phototoxicity. Desferal enhanced the PpIX content and phototoxic effect in the responsive cells. Fluorescence microscopy of the ALA-treated cells revealed marked accumulation of PpIX in mitochondria (rhodamine 123 co-staining). That the primary site of phototoxic damage is also the mitochondria was confirmed by electron micrographs of cells photosensitised with ALA-induced PpIX, which showed swelling of mitochondria within minutes after irradiation while other suborganelles appeared to be unaffected. The repair or further destruction of the mitochondria was fluence and cell-type dependent. The data from this study suggest that the basis of increased ALA-induced PpIX accumulation in tumours is a combination of various aspects of the metabolic process and pharmacokinetics and that the efficacy of photodestruction of malignancy will be determined not only by the rate of PpIX synthesis but also by specific cellular and tissue characteristics.
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PMID:A mechanistic study of cellular photodestruction with 5-aminolaevulinic acid-induced porphyrin. 801 36

Although the incidence is very low, the prognosis of anaplastic carcinoma of the thyroid is very poor regardless of the results of various therapeutic trials. We found that the mechanism of anti-cancer drug resistance in anaplastic carcinoma of the thyroid was not explicable only in terms of expression of the mdr1 and its gene product, P-glycoprotein. Therefore, expression of multidrug resistance-associated protein (MRP) mRNA was examined in 11 anaplastic thyroid carcinomas and eight anaplastic thyroid carcinoma cell lines. High MRP mRNA expression was recognized in 7/11 and 8/8, respectively. Our results may contribute to elucidation of the mechanism of anti-cancer drug resistance in this neoplasm.
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PMID:Expression of multidrug resistance-associated protein (MRP) in anaplastic carcinoma of the thyroid. 805 90

Many human tumors such as bladder carcinoma that are initially responsive to chemotherapy eventually fail to respond to treatment. For most drugs, dose escalation that may be required for a cure cannot be achieved because sensitive tissues such as bone marrow limit cytotoxic therapy. Approaches to prevent or circumvent myelosuppression are therefore a high priority of research on dose intensification protocols. One such strategy is to protect bone marrow cells by virtue of expression of the multidrug-resistance (MDR1) gene encoding for P-glycoprotein. In our first set of experiments, we transplanted bone marrow cells derived from transgenic mice that constitutively express MDR1 to lethally irradiated recipients (n = 36). From 6 weeks to 10 months after the transplant, all animals contained MDR1 DNA in spleen and bone marrow specimens as indicated by Southern-blot analysis and expressed MDR1 RNA in bone marrow samples as detected by slot-blot analysis. In addition, these animals were resistant to the myelosuppressive effect of doxorubicin, daunomycin, taxol, vinblastine, vincristine, etoposide, and actinomycin D, whereas control animals that were reconstituted with normal bone marrow reacted with a significant decrease in their white blood counts. In a second set of experiments, we retrovirally transfected a construct consisting of a murine long-terminal repeat (LTR) promoter and the human MDR1 gene into CD34-positive bone marrow stem cells from rhesus monkeys using the same technique as in the ongoing clinical ADA gene-therapy protocol. Upon transplantation, high-level and long-lasting expression of the human MDR1 gene was observed in recipient monkeys.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:From laboratory expertise to clinical practice: multidrug-resistance-based gene therapy becomes available for urologists. 808 40

Several novel cell lines with variable resistance to Vinca alkaloids have been derived from the Caco-2 human colorectal carcinoma cell line. Parental Caco-2 cells were found by PCR analysis and immunofluorescence studies to produce a low amount of the mdr-1 gene product (P-glycoprotein) that may well be clinically significant. These cells, which were initially highly sensitive to desacetylvinblastine sulfate (DAVLB sulfate) were selected, without mutagenesis, through continuous culture with increasing concentrations of DAVLB sulfate over a 335-day period. This selection resulted in cell lines that displayed an mdr (multiple-drug-resistance) cross-resistance profile that could be reversed with agents such as verapamil and vindoline. During the selection process the amount of mdr-1 mRNA present, the extent of gene amplification and the amount of gp170 expressed all correlated well with the level of drug resistance. However, this correlation does not hold in the absence of selective pressure for the more resistant cell lines where gene amplification and the amount of P-glycoprotein present remained constant while the level of drug resistance and the amount of mdr-1 mRNA present declined. These cell lines are potential models for studying mdr-I gene expression and drug resistance in human epithelial malignancies.
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PMID:The development and characterization of Vinca alkaloid-resistant Caco-2 human colorectal cell lines expressing mdr-1. 809 16

KB-A1 and KB-A10 are 2 multi-drug-resistant cell lines which are 100- and 1,000-fold resistant to Adriamycin, respectively. We have examined the expression of P-glycoprotein at the molecular and cellular levels in these human carcinoma cells. Both MDR cell lines, when compared to the parental KB-3-1, show characteristic increases in mdr 1 gene copy number, an increase in mdr 1 mRNA expression, a corresponding increase in transcription rate and a consequent over-expression of P-glycoprotein. However, the more highly resistant KB-A10 cells have a lower gene copy number, express less mdr 1 mRNA and contain less P-glycoprotein than the A1 cell line. To determine whether higher levels of cellular resistance were attributable to enhanced efficacy of P-glycoprotein or to other cellular regulatory mechanisms, we examined other major cellular properties known to be associated with the mdr phenotype. Both the KB-A1 and KB-A10 lines exhibit similar increases in protein kinase C activity as compared to the drug-sensitive parent. In addition, neither glutathione-S-transferase nor topoisomerase II activities account for enhanced resistance of the KB-A10 cells. The above observations are contrary to the premise that the level of drug resistance is necessarily proportional to expression of P-glycoprotein or to other common factors thought to participate in drug insensitivity; consequently, new mechanisms of resistance must be in operation in these cells.
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PMID:Anomalous expression of P-glycoprotein in highly drug-resistant human KB cells. 809 16

We previously found that human cervix carcinoma HeLa cells irradiated with multiple fractions of gamma rays (0.5 Gy daily, five times per week over 6 weeks) become resistant to cis-dichlorodiammineplatinum(II) (cis-DDP), methotrexate (MTX) and vincristine (VCR), but retain the same sensitivity to gamma rays or UV light. In the present report attempts were made to elucidate the mechanisms by which these cells have acquired resistance to cis-DDP and VCR. The sensitivity to different drugs was measured by modified MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method. Neither buthionine sulfoximine (BSO) nor ethacrinic acid were able to reverse the resistance of preirradiated cells to cis-DDP. Therefore, neither the increased levels of glutathione nor glutathione transferase seem to be involved in resistance to cis-DDP. Preirradiated cells did show resistance to cadmium, indicating the increased levels of metallothioneins in these cells. Resistance of preirradiated cells to vincristine was abolished by the addition of verapamil, indicating that resistance to this drug may depend on the increased expression of plasma membrane P-glycoprotein. It was concluded that mechanisms of resistance of preirradiated cells to cytostatics are multifactorial and involve at least the increased levels of metallothioneins and changes in the plasma membrane. Acquired resistance to cytotoxic drugs induced by preirradiation may be the reason for the reduced response to these drugs after radiation treatment of certain tumors.
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PMID:Multifactorial molecular mechanisms are involved in resistance of preirradiated human cervix carcinoma cells to cis-dichlorodiammineplatinum (II) and vincristine. 810 78

The treatment of advanced metastatic prostate cancer by hormone manipulation or orchiectomy is frequently followed by the appearance of hormone-insensitive and highly chemoresistant tumor cells. In this study we have investigated the contribution of the P-glycoprotein-mediated drug efflux (multidrug-resistance; MDR) to the cellular resistance of prostate carcinoma-derived cell lines to diverse cytotoxic drugs by detection of P-glycoprotein (P-gp) measurement of P-gp-mediated drug transport and reversal of MDR by chemosensitizers. The in vitro chemosensitivity of three prostate cancer cell lines (PC-3, DU-145 and LNCaP) to doxorubicin was measured in a thymidine incorporation proliferation assay. Growth of the partially hormone-sensitive cell line LNCaP is inhibited by low doses of doxorubicin (IC50:27 ng./ml.), but PC-3 and DU-145 are highly resistant to the drug, with IC50 values of 10 micrograms./ml. and 7.5 micrograms./ml., respectively. The chemosensitivity of the PC-3 and DU-145 cells is increased in response to 1 microM. verapamil, 1 micrograms./ml. cyclosporine A and 2 microM. tamoxifen, which are known to partially reverse the MDR phenotype in other resistant tumors. A verapamil-sensitive drug efflux has been demonstrated for the PC-3 and Du-145, but not for the LNCaP, cell lines, using flow cytometric measurements of the P-gp substrate rhodamine 123 efflux from preloaded cells. In agreement with the functional measurements, the expression of the P-glycoprotein was detected in the PC-3 and Du-145 cell lines in Western blots using the monoclonal C 219 antibody. In conclusion, the chemoresistant and hormone-insensitive PC-3 and Du-145 cell lines express P-gp and exhibit verapamil-sensitive drug efflux, indicative of MDR. However, the low MDR-reversal rates observed in these cell lines in response to chemosensitizers in clinically achievable concentrations (approximately 2- to 3-fold reversal), point to non-MDR-associated cellular mechanisms as dominant factors of chemoresistance in prostate cancer.
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PMID:Role of the MDR-1-encoded multiple drug resistance phenotype in prostate cancer cell lines. 810 10

Anti-P-glycoprotein (P-gp) monoclonal antibody, MRK16, and its F(ab')2 fragment were evaluated for its therapeutic efficacy to P-gp-mediated multidrug resistant human colorectal carcinoma cell lines in a nude mouse model. In a blood clearance experiment, 125I-labeled MRK16 had a half-life (16 h) 7 times longer than its F(ab')2 fragment (half-life of 1.8 h) in circulation in nude mice, and approximately 16 and 5% of MRK16 were retained on days 10 and 20 after injection, respectively. In biodistribution experiments using nude mice bearing HCT-15, an intrinsically resistant cell line, 125I-labeled MRK16 accumulated at the tumor site significantly higher than its F(ab')2 fragment as revealed by the percentage of injected dose/g of tissue values (7.4 versus 0.6%) on day 3 after injection. In contrast, the tissue to blood ratio at the tumor site of the MRK16 was significantly lower than that of its F(ab')2 fragment (1.2 versus 10.5). Specific targeting of the MRK16 F(ab')2 fragment to the P-gp-positive tumor (HCT-15) but not to the P-gp-negative tumor (COLO 205) was observed in the nude mice bearing both tumors. In the therapeutic efficacy tests, when administered i.v. 3 times on days 1, 4, and 7 after tumor s.c. inoculation, MRK16 alone showed the significant inhibition of tumor growth of P-gp-positive cell lines, HCT-15, DLD-1, SW480, and SW1417 in contrast to cases of P-gp-negative cell lines, COLO 205 and KM20L2. This inhibitory effect of MRK16 was enhanced in combination with Adriamycin, which alone hardly inhibited the tumor growth. However, MRK16 F(ab')2 fragment alone, even at 1 mg/mouse, had little inhibitory effect on the growth of HCT-15 in the same treatment schedule. When administered at early palpable stage, the degree of HCT-15 tumor growth suppression depended on the number of MRK16 injections. At more progressed stages, treatment with MRK16 alone showed little antitumor activity but when combined with Adriamycin resulted in significant suppression of tumor growth. The present results suggest that MRK16 may be useful for in vivo immunoscintigraphy and immunotherapy of multidrug-resistant colorectal carcinoma.
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PMID:Specific targeting and killing activities of anti-P-glycoprotein monoclonal antibody MRK16 directed against intrinsically multidrug-resistant human colorectal carcinoma cell lines in the nude mouse model. 810 47

Lung cancer is the leading cause of cancer death in the United States. Small cell lung cancer (SCLC) accounts for 20% to 25% of all bronchogenic carcinoma and is associated with the poorest 5-year survival of all histologic types. SCLC differs in its etiologic, pathologic, biologic, and clinical features from non-SCLC, and these differences have translated to distinct approaches to its prevention and treatment. Compared with other histologic types of lung cancer, exposures to tobacco smoke, ionizing radiation, and chloromethyl ethers pose a substantially greater risk for development of SCLC. The histologic classification of SCLC has been revised to include three categories: (1) small cell carcinoma, (2) mixed small cell/large cell, and (3) combined small cell carcinoma. Ultrastructurally, SCLC displays a number of neuroendocrine features in common with pulmonary neuroendocrine cells, including dense core vesicles or neurosecretory granules. These dense core vesicles are associated with a variety of secretory products, cell surface antigens, and enzymes. The biology of SCLC is complex. The activation of a number of dominant proto-oncogenes and the inactivation of tumor suppressor genes in SCLC have been described. Dominant proto-oncogenes that have been found to be amplified or overexpressed in SCLC include the myc family, c-myb, c-kit, c-jun, and c-src. Altered expression of two tumor suppressor genes in SCLC, p53 and the retinoblastoma gene product, has been demonstrated. Cytogenetic and molecular evidence for chromosomal loss of 3p, 5q, 9p, 11p, 13q, and 17p in SCLC has intensified the search for other tumor suppressor genes with potential import in this malignancy. Bombesin/gastrin-releasing peptide, insulin-like growth factor I, and transferrin have been identified as autocrine growth factors in SCLC, with a number of other peptides under active investigation. Several mechanisms of drug resistance in SCLC have been described, including gene amplification, the recently described overexpression of multi-drug resistance-related protein (MRP), and the expression of P-glycoprotein. The classic SCLC staging system has been supplanted by a revised TNM staging system where limited disease and extensive disease are equivalent to the TNM stages I through III and stage IV, respectively. Therapeutically, recent strategies have attained small improvements in survival but significant reductions in the toxicities of chemotherapeutic regimens. Presently, the overall 5-year survival for SCLC is 5% to 10%, with limited disease associated with a significantly higher survival rate.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Small cell lung cancer: etiology, biology, clinical features, staging, and treatment. 839 98

Using renal carcinoma and prostate carcinoma cell lines, we investigated the concept of targeting and killing multidrug resistant cells in urogenital cancers. Renal carcinoma lines HTB44, 45, 46, and 47 expressed a relatively low, but detectable level of multidrug resistance (MDR)1 mRNA as indicated by Northern blot analysis, whereas prostate lines LNCaP and DU145 were found to be MDR1-negative. Anti-P-glycoprotein monoclonal antibody MRK16 was conjugated to Pseudomonas exotoxin (PE) by a stable thioether bond. Treatment with MRK16-PE resulted in a dose-dependent killing of multidrug resistant renal carcinoma cells, while non-MDR expressing prostate carcinoma cells were not affected. Addition of excess MRK16 blocked the effect of MRK16-PE. Furthermore, MOPC-PE, a non-MDR associated monoclonal antibody control conjugate, did not target and kill multidrug resistant renal carcinoma cells. Having established that MRK16-PE was active against and specific for multidrug resistant cells in culture, we also tested bioactivity in MDR-transgenic mice, whose bone marrow cells express the human MDR1 gene at a level approximately equal to that found in many human cancers. Again, MRK16-PE killed multidrug resistant bone marrow cells with high efficiency in an intact animal, and killing was blocked by unconjugated MRK16.
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PMID:Pseudomonas exotoxin conjugated to monoclonal antibody MRK16 specifically kills multidrug resistant cells in cultured renal carcinomas and in MDR-transgenic mice. 841 4


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