Non-steroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase-2 (COX-2) specific inhibitors are antiinflammatory agents that have also shown to be useful in anticancer therapy. The effects of chebulagic acid (CA), a benzopyran tannin from Terminalia chebula having COX-2/5-LOX dual inhibitory properties, on the sensitivity of doxorubicin (Dox) in human hepatocellular carcinoma cell line HepG2 were studied in the present investigation. CA increased the accumulation of Dox in a concentration dependant manner and also enhanced the cytotoxicity of Dox in HepG2 cells by 20 folds. Quantitation of interaction by calculating Combination Index (CI) showed a strong synergistic interaction between CA and Dox in terms of cell growth inhibition. Calculation of dose reduction index (DRI) for CA-Dox combinations also showed a significant decrease in the dosage of Dox in the presence of CA. The induction of multidrug resistance protein-1 (MDR-1) expression by PGE2, a metabolite of COX-2, and its downregulation by COX-2 knockdown or CA implies that the enhanced sensitivity of HepG2 cells to doxorubicin by CA is mediated by the downregulation of MDR1 expression, via COX-2-dependent mechanism. Further studies reveal the inactivation of signal transduction pathways involving Akt, ERK, JNK and p38 and the transcription factor NF-κB in the CA induced down regulation of MDR1. The present study shows the efficacy of CA to overcome MDR-1 mediated drug resistance in HepG2 cells through COX-2 dependant modulation of MDR-1.
Keywords: Chebulagic acid, combination index, cyclooxygenase-2, dose reduction index, doxorubicin, HepG2, MDR-1, Non-steroidal anti-inflammatory drugs, COX-2, antiinflammatory, Terminalia chebula, dual inhibitory properties, DRI, PGE2
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