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)

On the basis of the overexpression of the MDR1 gene in human colorectal cancer, which may constitute a molecular basis for intrinsic drug resistance that can be reversed, and because of the limited therapeutic value of conventional cytotoxic treatment in this common disease, the present phase II study of P-glycoprotein-directed double modulation was initiated. Fifteen patients with measurable metastatic colorectal cancer, all of whom were refractory to first-line chemotherapy with 5-fluorouracil/leukovorin, were entered in this trial. Treatment consisted of 80 mg tamoxifen twice daily on days 1-9, oral dexverapamil every day on days 7-9, and 60 mg/m2 doxorubicin given by intravenous bolus injection on day 8. Courses were repeated every 4 weeks. After a median of three (between one and six) courses, none of the 14 evaluable patients had objective response, and 4 had stable disease. Adverse reactions consisted mainly of myelosuppression (WHO grade IV granulocytopenia was noted in 40%), and mild and reversible dexverapamil-related cardiovascular side-effects, specifically hypotension (47%). Our results suggest that, despite the histological demonstration of high levels of P-glycoprotein in colorectal cancer and administration of two potentially synergistic chemosensitizers, we were unsuccessful in circumventing its primary resistance to chemotherapy.
 ...
PMID:Treatment of advanced colorectal cancer with doxorubicin combined with two potential multidrug-resistance-reversing agents: high-dose oral tamoxifen and dexverapamil. 929 9

S9788 is a new triazineaminopiperidine derivate capable of reversing multidrug resistance (MDR) in cells resistant to chemotherapeutic agents such as doxorubicin. It does not belong to a known class of MDR revertants, but its action involves the binding of P-glycoprotein. Thirty-eight evaluable patients with advanced colorectal or renal cell cancer were treated with doxorubicin alone (16 patients) followed after disease progression with combination treatment of doxorubicin plus S9788 (12 patients) or upfront with the combination of doxorubicin plus S9788 (22 patients). S9788 was given i.v. as a loading dose of 56 mg m-2 over 30 min followed by doxorubicin given at 50 mg m-2 as a bolus infusion. Thereafter, a 2-h infusion of S9788 was administered at escalating doses ranging from 24 to 120 mg m-2 in subsequent cohorts of 4-10 patients. Pharmacokinetic analysis demonstrated that concentrations of S9788 that are known to reverse MDR in vitro were achieved in patients at non-toxic doses. Compared with treatment with doxorubicin alone, treatment with the combination of doxorubicin and S9788 produced a significant increase in the occurrence of WHO grade 3-4 granulocytopenia. Treatment with S9788 was cardiotoxic as it caused a dose-dependent and reversible increase in corrected QT intervals as well as clinically non-significant arrhythmias on 24- or 48-h Holter recordings. Although clinically relevant cardiac toxicities did not occur, the study was terminated as higher doses of S9788 may increase the risk of severe cardiac arrhythmias. Twenty-nine patients treated with S9788 plus doxorubicin were evaluable for response, and one patient, who progressed after treatment with doxorubicin alone, achieved a partial response. We conclude that S9788 administered at the doses and schedule used in this study results in relevant plasma concentrations in humans and can safely be administered in combination with doxorubicin.
 ...
PMID:Phase IB study of doxorubicin in combination with the multidrug resistance reversing agent S9788 in advanced colorectal and renal cell cancer. 937 86

Malignant melanoma is increasing in frequency at a rapid rate in the United States. Metastatic disease is chemoresistant with DTIC considered the most active single agent. CI-980 is a synthetic mitotic inhibitor that blocks the assembly of tubulin and microtubules. It has shown cytotoxic activity against a broad spectrum of murine and human tumor cell tines. CI-980 can cross the blood brain barrier, is effective when given orally or parenterally, and is active against multidrug resistant cell lines overexpressing P-glycoprotein. In this trial, patients with disseminated melanoma with measurable disease, SWOG performance status of 0-1, no prior chemotherapy or immunotherapy for metastatic disease, and adequate hepatic and renal function, were enrolled. Treatment with CI-980 was given by 72 h continuous i.v. infusion at a dose of 4.5 mg/m2/day, days 1-3 every 21 days. Twenty-four patients were registered on this study with no patients ineligible. They ranged in age from 33-78 with performance status of 0 in 15 patients and 1 in 9 patients. Nineteen patients had visceral disease with 12 having liver involvement. There were no confirmed responses. The overall response rate was 0% (95% CI 0%-14%). The median overall survival is eleven months (95% CI 4-14 months). The most common toxicities were hematologic and consisted of leukopenia/granulocytopenia and anemia, with nausea/vomiting and malaise/fatigue/weakness also frequent. CI-980 administered at this dose and schedule has insufficient activity in the treatment of disseminated malignant melanoma to warrant further investigation.
 ...
PMID:Phase II trial of CI-980 in patients with disseminated malignant melanoma and no prior chemotherapy. A Southwest Oncology Group study. 1156 81

The atypical antipsychotic, clozapine, exerts superior efficacy in therapy-resistant schizophrenia, but unfortunately induces agranulocytosis with an incidence of 0.8 - 1 %. In this study, we investigated the cellular uptake of clozapine into human promyelocytic leukaemia HL-60 cells using HPLC with electrochemical detection. On incubation with 1.25 to 40 microM clozapine for 30 min, a saturable, energy- and temperature-dependent uptake process takes place (K m = 18.8 microM, k cat = 1.36 nmol/5 min/mg protein at 37 degrees C). This suggests membrane passage of clozapine by a carrier mechanism. 10 microM Indatraline, an inhibitor of dopamine, noradrenaline and serotonin (5-HT) reuptake, but not the selective 5-HT reuptake inhibitor fluvoxamine, markedly reduced the transport of clozapine by 62 %, whereas addition of 10 mM glucose to the incubation medium increased intracellular clozapine concentrations by 28 %. Since cyclosporine A, vinblastine or verapamil up to a final concentration of 10 microM did not alter the intracellular accumulation of clozapine, an involvement of P-glycoprotein seems to be unlikely. In summary, clozapine uptake into HL-60 cells meets criteria of an active unidirectional transport. Its molecular correlates remain to be established.
 ...
PMID:Uptake of clozapine into HL-60 promyelocytic leukaemia cells. 1210 52

Doxorubicin/vinblastine combined with the P-glycoprotein inhibitors trifluoperazine and verapamil was evaluated in the treatment of patients with metastatic renal carcinoma. Patients were treated with starting doses of doxorubicin/vinblastine of 30 mg/m(2) (doxorubicin) and 3 mg/m(2) (vinblastine) intravenously every 2 weeks, combined with 4 days of oral trifluoperazine/verapamil at 2 mg tid (trifluoperazine) and 160 mg tid (verapamil) administered I day before the chemotherapy was initiated. Response was assessed every three cycles of treatment. Of 26 evaluable patients, there were no responders. Six patients had stable disease for greater than 6 months on treatment. Therapy was generally well tolerated but 7 of 26 patients developed grade 4 granulocytopenia, including one patient who died due to sepsis. The possible reasons for the failure of P-glycoprotein inhibitors to enhance the effect of chemotherapy are discussed.
 ...
PMID:Phase II evaluation of doxorubicin/vinblastine combined with inhibitors trifluoperazine/verapamil of P-glycoprotein in patients with advanced renal carcinoma. 2122 92

Clozapine use is associated with leukopenia and more rarely agranulocytosis, which may be lethal. The drug and its metabolites are proposed to interact with the multidrug resistance transporter (ABCB1/MDR1) gene product, P-glycoprotein (P-gp). Among various P-glycoprotein genetic polymorphisms, nucleotide changes in exons 26 (C3435T), 21 (G2677T), and 12 (C1236T) have been implicated for changes in pharmacokinetics and pharmacodynamics of many substrate drugs. In this study, we aimed to investigate the association between these specific ABCB1 polymorphisms and clozapine-associated agranulocytosis (CAA). Ten patients with a history of CAA and 91 control patients without a history of CAA, despite 10 years of continuous clozapine use, were included. Patient recruitment and blood sample collection were conducted at the Hacettepe University Faculty of Medicine, Department of Psychiatry, in collaboration with the members of the Schizophrenia and Other Psychotic Disorders Section of the Psychiatric Association of Turkey, working in various psychiatry clinics. After DNA extraction from peripheral blood lymphocytes, genotyping was performed using polymerase chain reaction and endonuclease digestion. Patients with CAA had shorter duration of clozapine use but did not show any significant difference in other clinical, sociodemographic characteristics and in genotypic or allelic distributions of ABCB1 variants and haplotypes compared with control patients. Among the 10 patients with CAA, none carried the ABCB1 all-variant haplotype (TT-TT-TT), whereas the frequency of this haplotype was approximately 12% among the controls. Larger sample size studies and thorough genetic analyses may reveal both genetic risk and protective factors for this serious adverse event.
...
PMID:Relation of the Allelic Variants of Multidrug Resistance Gene to Agranulocytosis Associated With Clozapine. 2735 96