To better understand the cleavage efficiency of muhiribozyme system on its RNA substrate in the presence and absence of divalent magnesium and monovalent sodium ions.we constructed pGEM-Coat'A,pGEM-Coat'A196Rz plasmids and pGEM-MDRl target plasmid.They were applied to transcribe RNAs with SP6/T7 transcription kit.Cleavage reactions were carried out in cell-free system and reaction products were analyzed by electrophoresis on 6% denaturing polyacrylamide gels in TBS buffer.The gels were dried and exposed to X-ray films for autoradiography.The Image J software was employed to analyze the dried gels.The results indicated that the cleavage efficiency of the muhiribozyme was dependent on the concentration of divalent Mg2+.The cleavage products increased with the concentrations of divalent Mg2+ and were Mg2+ concentration and time dependent.No cleavage product was obtained in the presence of lower than 200 mmol/L Na+ alone.On the contrary,monovalent Na+ inhibited the Mg2+ -induced cleavage reaction in Na+ and Mg2+ coexistance.The cleavage rate was significantly lower than that observed with divalent Mg2+ alone.These results suggested that divalent Mg2+ was required for muhiribozyme on substrate cleavage reaction in the physical condition,whereas monovalent Na+ was not.

OBJECTIVETo evaluate the effect of adenovirus-mediated transfer of anti-MDR1 ribozyme on restoring drug sensitivity of multidrug-resistant human lymphoma both in vitro and in SCID mice.

METHODSA recombinant adenovirus expressing ribozyme against codon 196 of MDR1 mRNA (Ad-196MDR1-Rz) was developed through cotransfection of shuttle vector pCA14 containing 196MDR1-Rz and rescue vector pJM17 into human embryonic kidney cell line 293. In vitro Daudi/MDR20, a MDR1-mediated drug-resistant human lymphoma cell line, was transduced by Ad-196MDR1-Rz at MOI of 400 pfu/cell. RT-PCR and FACS analyses were used to evaluate the MDR1 expression in both transcriptional and translational levels. MTT assay was used for analysis of drug resistance. In vivo, SCID mice were inoculated subcutaneously by 5 x 10(6) Daudi/MDR20 or parental Daudi/wt cells. Adenovirus was injected locally. Vincristine (VCR) was given intraperitoneally.

RESULTSIn vitro transduction of Ad-196MDR1-Rz to Daudi/MDR20 cells was able to interrupt MDR1 transcription, inhibit P-gp expression and restore drug sensitivity to VCR. Of SCID mice bearing Daudi/MDR20 cells, tumor free rate and long term survival were 66.7% (6/9) and > 120 days in the therapeutic group of Ad-196MDR1 + VCR vs 12.5% (7/8) and none survived > 120 days in the control groups of Ad-Mock + VCR or VCR alone. The difference was very statistically significant.

CONCLUSIONAd-mediated transfer of 196MDR1-Rz can revert drug resistance of MDR tumor cells both in vitro and in vivo. Ad-196MDR1-Rz may be helpful as an adjuvant in the chemotherapy of P-gp mediated MDR human tumor.

ATP-Binding Cassette, Sub-Family B, Member 1 ; antagonists & inhibitors ; genetics ; Adenoviridae ; genetics ; Animals ; Antineoplastic Agents, Phytogenic ; therapeutic use ; Disease Models, Animal ; Drug Resistance, Neoplasm ; Gene Transfer Techniques ; Genetic Therapy ; Genetic Vectors ; genetics ; Humans ; Lymphoma ; drug therapy ; Mice ; Mice, SCID ; Neoplasm Transplantation ; Neoplasms, Experimental ; therapy ; RNA, Catalytic ; genetics ; metabolism ; therapeutic use ; Treatment Outcome ; Tumor Cells, Cultured ; Vincristine ; therapeutic use