Rapid Detection of the C3435T Polymorphism of Multidrug Resistance Gene 1 Using Fluorogenic Hybridization Probes

Genetic polymorphisms in drug-metabolizing enzymes, transporters, receptors, and other drug targets have been linked to interindividual differences in the efficacy and toxicity of many medications (1)(2). Knowledge of an individual’s drug metabolism characteristics can help in avoiding adverse reactions or therapeutic failure and thus enhance therapeutic efficiency. One gene of particular interest in pharmacogenetics is the human multidrug resistance-1 (MDR1) gene. The MDR1 gene encodes an integral membrane protein, P-glycoprotein (PGP), whose function is the energy-dependent export of substances from the inside of cells to the outside (3). Many drugs are substrates of PGP. Therefore, expression and functionality of the MDR1 gene product can directly affect the therapeutic effectiveness of such compounds. This is of specific importance in cancer therapy, where high expression of MDR1 makes cancer cells refractory to treatment with many agents that are PGP substrates (4).MDR1 is also expressed on nonmalignant cells in various organs, e.g., the intestine and at the blood-brain barrier. Modulation of MDR1 expression in these tissues can influence the activity and bioavailability of drugs (5). Recently, a polymorphism of the MDR1 gene has been shown to be correlated with intestinal PGP expression and activity in vivo (6). This polymorphism consists of a C-to-T exchange at cDNA position 3435 located in exon 26 of the MDR1 gene. Although this base exchange does not affect the amino acid sequence of PGP, the T allele appears to be associated with markedly lower MDR1 expression compared with the C allele. Hoffmeyer et al. (6) were able to consistently show that plasma concentrations of digoxin, which reflect PGP activity in vivo, were significantly higher in individuals harboring the T allele compared with carriers of the C/C genotype.Because of its silence on the protein level and its location in a nonregulatory region of the …