Background
Epidemiologic and experimental studies have shown that cyclooxygenase-2 (COX-2) inhibitors as non-steroidal anti-inflammatory drugs (NSAIDs) are effective chemopreventive agents. The mechanisms underlying the antitumor activity of COX-2 inhibitors are thought to involve inhibition of COX-2 enzyme activity and induction of apoptosis. The aim of the current work was to study the mechanisms of synergistic action noted in HeLa cervical carcinoma cells under doxorubicin (DOX) and sulindac (SUL) co-treatment.
Material and Method
Cytotoxic activity of the drugs was defined with MTT test, apoptosis was detected with TUNEL test, DOX transmembrane efflux was measured fluorometrically, expression of MDR-1 and MRP-1 was determined with quantitative real time - PCR (QRT-PCR).
Results
It was shown that SUL at non-toxic concentrations, 10 and 50 microM, is an effective enhancer of cytotoxic action for DOX in 0.5 and 1 microM, respectively; however, only for SUL concentration equal to 50 microM potentiated apoptosis induced by 1 microM of DOX. Moreover, blocking DOX efflux outside the cells was observed. The QRT - PCR analysis has shown that, when used simultaneously, DOX 1 microM and SUL 50 microM results in decreased mRNA level for MDR-1 and MRP-1.
Conclusions
It is concluded that cytotoxic action of DOX against HeLa cells is enhanced by non-toxic concentrations of SUL. The observed effect is due to quenching of MDR-1 and MRP-1 genes expression, which results in blocking of efflux of DOX outside the cells, which in turn correlates with enhanced apoptotic effects. According to obtained results the mechanisms of potentiating of DOX action by SUL are dose specific.

Keywords: Reverse Transcriptase Polymerase Chain Reaction, Multidrug Resistance-Associated Proteins - metabolism, P-Glycoprotein - metabolism, In Situ Nick-End Labeling, Hela Cells, Gene Expression Regulation, Neoplastic - drug effects, Drug Synergism, Doxorubicin - therapeutic use, Sulindac - therapeutic use, Dose-Response Relationship, Drug, DNA Primers - genetics, Cyclooxygenase Inhibitors - therapeutic use, Tetrazolium Salts, Thiazoles, Uterine Cervical Neoplasms - drug therapy