Ultrasonic enhancement of gene transfection in murine melanoma tumors

The enhancement of gene transfection by ultrasound (US) was evaluated in vi tro and in vivo using the B16 mouse melanoma model. Cultured. cells were ei ther exposed in suspensions in vitro or implanted subcutaneously in female C57BL/6 mice for 10-14 days and, subsequently exposed, in vivo, For compari son to results with a luciferase plasmid, a reporter plasmid for green fluo rescent protein (GFP) was used to evaluate transfection efficiency. US was supplied by a system, similar to a Dornier HM-3 lithotripter, that produced shock waves (SW) of 24.4 MPa peak positive and 5.2 MPa peak negative press ure amplitudes at the focus. The plasmids were mixed with the suspensions t o achieve 20 mu L mL(-1), or were injected intratumorally to provide 0.2 mg DNA per mt of tumor. Acoustic cavitation was promoted by retaining 0.2 mL of air in the 1.2-mL exposure chambers in vitro and by injecting air at 10% of tumor volume in vivo, In vitro, cell counts declined to 5.3% of shams a fter 800 SW exposure, with 1.4% of the cells expressing GFP after 2 days of culture. In vivo, 2 days after 400 SW exposure, viable-cell recovery from excised tumors was reduced to 4.2% of shams and cell transfection was enhan ced by a factor of about 8, reaching 2.5% of cell counts (p < 0.005 in t-te st), These results show that strong tumor ablation induced by US shock wave treatment can be coupled with simultaneous enhancement of gene transfectio n. (C) 1999 World Federation for Ultrasound in Medicine & Biology.