Enhancement of localized drug and gene delivery to murine tumors by temperature-sensitive liposomes, cationic liposomes, and electroporation

The purpose of these studies was to develop protocols for gene and drug delivery to solid tumors in vivo. First, electroporation was applied to enhance gene transfer to MC2 murine breast tumors. Cultured cells were transfected by electroporation or cationic liposome-DNA complexes using pSV-luciferase plasmids. An electrotransfection electric field threshold in vitro ∼800--900 V/cm. Multilamellar vesicles (MLV) had a tenfold advantage over small unilamellar vesicles (SUV) in vitro . In vivo, plasmids were injected alone, or complexed with liposomes. Six, 1 msec electric pulses were applied across tumors. Electric field strengths ranged from 400--2300 V/cm. Tumor samples treated with pulses ≥800 V/cm had two orders of magnitude higher luciferase expression than controls. In situ PCR monitored DNA distribution in tumors. Nearly all fluorescence appeared along the needle track. The significant transfection improvement demonstrates that in vivo electroporation is a powerful tool for local gene delivery to tumors.; A better way was sought for distributing genes throughout tumors. Consequently, a heat-sensitive liposomal delivery system, was optimized for dye release in vitro and in vivo. Upon heating, the poloxamer, F127, disrupts liposomal membranes. Many poloxamers were screened for heat sensitivity. Only F127 showed efficient heat-sensitive dye release. Liposomes heated 30 min showed temperature dependent lucifer yellow iodoacetamide (LY) release between 20° and 45°C. LY release began at 33°C, with 90% LY released at 45°C. Heat treated liposomes were added to Colon 26 cells at 20°C to measure binding of released LY to cells. 43% as much LY bound to cells after treatment with liposomes heated to 36°C and 93% as much at 44°C. Triggered delivery of LY to tumors was tested in vivo. Tumors received heat-sensitive liposomes, non-sensitive liposomes, or no liposomes. For 30 minutes, tumors were maintained at either 42°C, or cooled. Tumor autofluorescence was greater than LY fluorescence for all other treatment groups. Heated tumors receiving heat-sensitive liposomes showed 2.5 fold greater fluorescence than background. Tumors cooled or receiving heat-sensitive liposomes showed little difference in fluorescence from control groups. This study demonstrates the efficacy of using liposomes containing poloxamers as a heat-sensitive drug delivery system in vivo.