Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A polymerase chain reaction (PCR)-based method was used to quantitate the expression levels of low abundance genes relevant to cancer drug activity. RNA from tumor samples as small as 20 mg was isolated and converted to cDNA using random hexamers. The 5' primers for the PCR contained a T7 polymerase promoter sequence, allowing the PCR-amplified DNA to be transcribed to RNA fragments. In each sample, the linear ranges of amplification of each cDNA of interest were established. Relative gene expressions were calculated by extrapolating the amounts of PCR products generated within the linear amplification regions of each gene to equal volumes of the cDNA solution. The method was accurate to less than a 2-fold difference in expression levels. Using beta 2-microglobulin and beta-actin gene expressions as internal reference standards and cDNA from HT-29 cells as an external linearity standard, we measured the relative expressions of thymidylate synthase, dihydrofolate reductase, and DT-diaphorase in a number of clinical tumor samples. The expressions of these genes varied from 50- to 100-fold among different tumors, although most of the values were grouped within about a 10-fold range. The amount of thymidylate synthase gene expression in tumor tissues was directly proportional to the content of thymidylate synthase protein. Those tumors with the lowest thymidylate synthase expression had the best response to both the 5-fluorouracil-leucovorin and 5-fluorouracil-cisplatin combinations.
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PMID:Quantitation of thymidylate synthase, dihydrofolate reductase, and DT-diaphorase gene expression in human tumors using the polymerase chain reaction. 172 69

Chemotherapeutic drug resistance is a major clinical problem and cause for failure in the therapy of human cancer. One of the goals of molecular oncology is to identify the underlying mechanisms, with the hope that more effective therapies can be developed. Several mechanisms have been suggested to contribute to chemoresistance: 1) amplification or overexpression of the P-glycoprotein family of membrane transporters (eg, MDR1, MRP, LRP) which decrease the intracellular accumulation of chemotherapy; 2) changes in cellular proteins involved in detoxification (eg, glutathione S-transferase pi, metallothioneins, human MutT homologue, bleomycin hydrolase, dihydrofolate reductase) or activation of the chemotherapeutic drugs (DT-diaphorase, nicotinamide adenine dinucleotide phosphate:cytochrome P-450 reductase); 3) changes in molecules involved in DNA repair (eg, O6-methylguanine-DNA methyltransferase, DNA topoisomerase II, hMLH1, p21WAF1/CIP1; 4) activation of oncogenes such as Her-2/neu, bcl-2, bcl-XL, c-myc, ras, c-jun, c-fos, MDM2, p210 BCR-abl, or mutant p53. An overview of these resistance mechanisms is presented, with a particular focus on the role of oncogenes. Some current strategies attempting to reverse their effects are discussed.
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PMID:Role of oncogenes in resistance and killing by cancer therapeutic agents. 909 Apr 98