Modulation of multidrug resistance in a cancer cell line by anti-multidrug resistance-associated protein (MRP) ribozyme.

Multidrug resistance-associated protein (MRP) is the major candidate molecule responsible for non-P-glycoprotein (PGp)-mediated multidrug resistance. We used a hammerhead anti-MRP ribozyme (alpha MRP-Rz) to inactivate MRP function in a multidrug resistant cancer cell line, KB8-5. The beta-actin promoter-driven alpha MRP-Rz sequence (pH beta/alpha MRP-Rz) was introduced into KB8-5 cells (KB8-5/alpha MRP-Rz) and we evaluated growth of the cell line. The gene expression of multidrug resistance-related molecules was estimated. Drug sensitivity was estimated by MTT assay in vitro. MRP mRNA expression was decreased in KB8-5/alpha MRP-Rz cells. The MTT assay showed increased IC50 values or resistance to doxorubicin (DOX), etoposide (VP-16) and cisplatin (CDDP) in KB8-5/alpha MRP-Rz cells. No significant differences were observed in expression of multidrug resistance gene (MDR1), thymidylate synthase, glutathione S-transferase pi or topoisomerase II alpha. The hammerhead ribozyme-mediated simple suppression of MRP mRNA expression was not sufficient to reverse multidrug resistance in the cancer cell line KB8-5.