954. High Intensity Focused Ultrasound (HIFU) Induced Trans-Gene Activation in Solid Tumors

Abstract

This work investigated the feasibility of HIFU-induced gene activation in sublethally injured cancer cells in a murine tumor model. 4T1 mouse mammary cancer cells were implanted subcutaneously in the hindlimbs of Balb/C mice and luciferase marker gene vectors (Ad-hsp-Luc) under the control of a heat-sensitive promoter (hsp70B) were injected intratumorly (2x108 pfu/tumor) for dissemination and gene transfection. One day following virus injection, targeted tumors (D=6 8mm) were heated to a peak temperature of 550C, 650C, 750C and 850C (measured with thermocouples), respectively, for 5s-20s at multiple sites by using a focused 1.1-MHz HIFU transducer. The time course of HIFU- induced luciferase gene expression was monitored and quantified using a Xenogen in vivo bioluminescence imaging system for one week. Inducible luciferase gene expression was found to be highly thermal dose dependent with total luminescence intensity increased by 15 – 120 fold at different HIFU exposure conditions compared to the control group. The maximum gene activation (120 fold) was induced at 650C-10s and 750C-10s one day after HIFU exposure and decayed gradually within 7 days. Histology examinations (H&E staining) of the tumor tissue one day after 750C-10s HIFU exposure revealed multiple focal areas of necrotic injury surrounded by sublethally injured and unaffected tumor tissues. Corresponding tumor growth after 750C-10s HIFU exposure was reduced by 50% from the original volume within 20 days while the tumor volume in the control group increased by 3 fold. Altogether, these results demonstrated the feasibility of HIFU-induced transgene activation presumably in sublethally injured tumor tissues. This observation opens up the possibility for the combination of HIFU-induced thermal ablation with simultaneous heat-induced gene therapy for cancer therapy. Furthermore, efforts are also underway to explore HIFU-targeted gene delivery to solid tumors.