Electroporation-enhanced gene delivery in mammary tumors

Electroporation was applied to enhance gene transfer into subcutaneous MC2 murine breast tumors. Cultured MC2 cells were also transfected by electropo ration or by cationic liposomes in the presence of serum using pSV-luc plas mids. Electroporation parameters and liposome formulation were optimized to achieve the highest relative levels of transfection. An electric field thr eshold for successful electrotransfection in cultured cells appeared around 800-900 V/cm. The liposomes used contained the cationic lipid dioleoyl-3-t rime-thylammonium propane (DOTAP). Multilamellar vesicles (MLV) had a 10-fo ld advantage over small unilamellar vesicles (SUV) in cell culture transfec tion. For in vivo gene delivery, the plasmids were injected either alone, o r in complex with MLV or SUV DOTAP liposomes. A series of six electric puls es 1 ms long were applied across tumors, using caliper electrodes on the sk in surface. Electric field strengths ranged from 400-2300 V/cm. Luciferase expression was approximately two orders of magnitude higher than controls i n tumors treated with pulses greater than or equal to 800 V/cm. Differences between enhanced relative levels of transfection using uncomplexed plasmid and lipoplexes were not statistically significant. Distribution of DNA int o tumor tissues was monitored by fluorescence in situ PCR. The highest numb ers of fluorescent cells were found in tumors electroporated following the injection of plasmid. The significant transfection improvement shows that i n vivo electroporation is a powerful tool for local gene delivery to tumors .