(336f) Ultrasound-Enhanced Chemotherapy and Gene Delivery for Gliosarcoma Cells

Malignant brain cancer afflicts more than 80,000 Americans and many more worldwide. In the United States, close to 18,000 new cases are diagnosed and 13,000 patients die each year [1-3]. Treatment by surgery is preferred if the tumor is accessable. If not, radiation is often used. Chemotherapy has generally been found to be less effective against brain cancer, because gliomas are relatively slow-dividing tumors and the blood brain barrier hampers delivery of chemotherapeutics to the brain. Gene therapy may provide a new way to treat cancer, including suicide gene therapy [4], downregulation of oncogenes [5] and antiangiogenic therapy [6]. In all of these treatment options, one of the critical limitations of current therapy is insufficient targeting to cancer cells [7]. In recent years, BCNU biodegradable wafers (Gliadel) implaneted locally into brain have been introduced as a targeted therapy, which has been shown to increase life expectancy [8, 9]. Despite moderate clinical success of Gliadel wafers, the prognosis for brain cancer patients generally remains poor and overall treatment of brain cancer, especially for high-grade gliomas, needs significant improvement [10]. This study addresses the hypothesis that ultrasound may be used to enhance intracellular delivery and efficacy of chemotherapeutics and genes in glioma cells. Guided by this understanding of ultrasound mechanisms and previous successes with ultrasound for enhanced drug therapy, this study sought to determine if ultrasound could enhance cytotoxicity of chemotherapeutic drugs for brain cancer. Specifically, we looked for synergistic effects between ultrasound and exposure to BCNU (carmustine), which is an established chemotherapeutic for local treatment of brain cancer [8], and bleomycin, which is not typically used for brain cancer, but its efficacy is known to be limited by poor intracellular uptake [11], which could be improved by ultrasound. We addressed these questions using a 9L rat gliosarcoma model in vitro. To our knowledge, this is the first study to examine ultrasound's effects on chemotherapy of glial cells. This study also sought to assess the ability of ultrasound to facilitate gene transfer and expression in glioma cells. Nucleic acid therapeutics offer an exciting opportunity to efficiently target therapy to cancer cells, but require intracellular delivery of genetic material, which is notoriously inefficient using nonviral methods. In a recent study, we showed that gene transfection of prostate cancer cells was increased up to 100-fold using an optimized ultrasound protocol [12]. This study builds off those observations to partially optimize transfection of gliosarcoma cells. This study assessed, for the first time, the prospects of using ultrasound to enhance treatments of brain cancer. Guided by initial experiments to identify suitable ultrasound conditions for intracellular delivery to glioma cells, we found that ultrasound synergistically increased in vitro cytotoxicity of two chemotherapeutics with very different physicochemical properties: BCNU and bleomycin. This suggests the possibility that chemotherapeutics could be administered to the brain in combination with ultrasound focused on the tumor to increase efficacy by a mechanism believed to involve increased intracellular uptake of drug. We also found that ultrasound increased in vitro glioma cell transfection with a GFP reporter DNA plasmid by 30-fold. This similarly suggests that ultrasound could facilitate gene therapy in the brain, especially for indications where the dangers of virus-based delivery are undesirable and moderate transfection efficiency is sufficient.

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