Dynamics of multidrug resistance: P-glycoprotein analyses with positron emission tomography.
Multidrug resistance (MDR) is characterized by the occurrence of cross-resistance to a broad range of structurally and functionally unrelated drugs. Several mechanisms are involved in MDR. One of the most well-known mechanisms is the overexpression of P-glycoprotein (P-gp), encoded by the MDR1 gene in humans and by the mdr1a and mdr1b genes in rodents. P-gp is extensively expressed in the human body, e.g., in the blood-brain barrier and also in solid tumor tissue. Overexpression of P-gp on tumor membranes might result in MDR of human tumors. To circumvent this resistant phenotype, several P-gp modulators such as cyclosporin A (CsA) are available. Competition between P-gp drugs and modulators results in decreased transport of the drug out of tumor tissue and an increased cellular level of these drugs. For effective clinical treatment it is important to have knowledge about P-gp functionality in tumors. Therefore, we have developed a method to measure the P-gp functionality in vivo with PET and [(11)C]verapamil as a positron-emitting P-gp substrate. The results obtained in rodents and in cancer patients are described in this article.
PET Center, University Hospital Groningen, P.O. Box 30.001, 9700 RB Groningen, The Netherlands. n.h.hendrikse@pet.azg.nl
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Hendrikse
Willem
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Vaalburg
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis* / Q000378:metabolism; D000328:Adult; D000818:Animals; D018288:Carcinoma, Small Cell / Q000378:metabolism / Q000473:pathology; D018432:Drug Resistance, Multiple / Q000502:physiology*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology; D008297:Male; D008875:Middle Aged; D051381:Rats; D011923:Rats, Nude; D014018:Tissue Distribution; D014055:Tomography, Emission-Computed / Q000379:methods*; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000493:pharmacokinetics
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D014700:Verapamil