COMPARATIVE-EVALUATION BY SEMIQUANTITATIVE REVERSE-TRANSCRIPTASE POLYMERASE-CHAIN-REACTION OF MDR1, MRP AND GSTP GENE-EXPRESSION IN BREAST CARCINOMAS

Identification and quantitative evaluation of drug resistance markers are essential to assess the impact of multidrug resistance (MDR) in cl inical oncology. The MDR1 gene confers pleiotropic drug resistance in tumour cells, but other molecular mechanisms are also involved in drug resistance. In particular, the clinical pattern of expression of the other MDR-related genes is unclear and their interrelationships are st ill unknown. Here, we report standardization of the procedures used to determine a reliable method of semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) using a standard series of drug-se nsitive and increasingly resistant cell lines to evaluate the expressi on of three MDR-related genes, i.e. MDR1 (multidrug resistance gene 1) , MRP (multidrug resistance related protein) and GSTp (glutathione-S-t ransferase p), reported to be endogenous standard genes for normalizat ion of mRNAs, A total of 74 breast cancer surgical biopsies, obtained before any treatment, were evaluated by this method. When compared wit h classical clinical and laboratory findings, GSTp mRNA level was high er in diploid tumours, However, the main finding of our study suggests a clear relationship between two of these MDR-related gene expression s, namely GSTp and MRP. This finding provides new insight into human b reast tumours, which may possibly be linked to the glutathione conjuga te carrier function of MRP, Well defined semiquantitative RT-PCR proce dures can therefore constitute a powerful tool to investigate MDR phen otype at mRNA levels of different related genes in small and precious tumour biopsy specimens.