Experimental study for development of microbubble applicable to clinical use in oral cancer chemotherapy

在本研究中，我们开发了一种使用微泡作为一种有效的超声造影剂的微成像系统，以及一种使用微泡和超声治疗口腔癌的分子传递系统。结果表明，利用高分辨率超声微成像系统（最高频率为80MHz）可以显示直径为200nm的微泡，即流动的血管。此外，当使用直径小于200nm的纳米级气泡作为超声造影剂时，超声微成像系统也显示了增强的渗透性和滞留效应，即气泡在肿瘤组织中比在正常组织中更容易积聚。另一方面，为了测试微泡和超声联合使用是否有可能将一些治疗物质输送到癌细胞中，我们检测了5-FU和顺铂以及一种自杀基因——单纯疱疹病毒胸苷激酶（HSVtk）基因的输送效率。利用癌细胞系和实验小鼠进行的体外和体内研究结果表明，超声作用下的微泡产生了明显的细胞毒性，这是超声或药物单独作用所没有的。此外，使用微泡和超声将HSVtk基因转染到癌细胞中显示更昔洛韦可能具有细胞毒性敏感性。这些结果表明，同时使用微成像系统和分子传递系统，利用微泡和超声方法结合抗癌药物和/或自杀基因治疗，有可能治疗口腔癌。

In the present study, we have developed a micro-imaging system using microbubbles as an effective type of ultrasound contrast agent, and a molecular delivery system for oral cancer therapy using microbubbles and ultrasound. As a result, it was clarified that microbubbles of 200nm in diameter, flowing blood vessels, could be visualized by using high-resolution ultrasound micro-imaging system (the highest frequency : 80MHz). In addition, when the nanosized bubbles less than a diameter of 200nm were used as an ultrasound contrast agent, the enhanced permeability and retention effect, that is the property by which the bubbles tend to accumulate in tumor tissue much more than they do in normal tissues, was also visualized by the ultrasound micro-imaging system. On the other hand, to test whether the combined use of microbubbles and ultrasound has a potential to deliver some therapeutic materials into cancer cells, we examined the delivery efficiency of 5-FU and cisplatin, and a suicide gene, herpes simplex virus thymidine kinase (HSVtk) gene. From results of in vitro and in vivo studies using cancer cell lines and experimental mice, microbubbles with ultrasound produced significant cytotoxicity not seen with either ultrasound or drug alone. Moreover, HSVtk gene transfection to cancer cells using microbubbles and ultrasound showed a potential of cytotoxic sensitivity by ganciclovir. These results suggests that simultaneous use of the micro-imaging system and the molecular delivery system by using the microbubbles and ultrasound method combined with anti-cancer agents and/or suicide gene therapy has a potential to treat oral cancer.