Drug delivery using ultrasound with ultrasound contrast agents : sonophoresis and sonoporation

Abstract

Ultrasound has been used not only for diagnostic imaging modality due to character of real-time, non-invasive but as a means of therapy such as lithotripsy, hyperthermia, high intensity focused ultrasound, drug or gene delivery. The purpose of various medical applications using ultrasound generates the bio-effect in biological structures or tissues and cells. The clinical uses of ultrasound are known to have the potential to create two major types of bio-effects: thermal effect and cavitation effect. Ultrasound energy is partially absorbed into the tissue during ultrasound sonication, and therefore absorption of energy causes a local temperature increase in the tissue. Another bio-effect generated by ultrasound is cavitation. Acoustic cavitation is the term used to describe response of bubbles in acoustic field including the expansion, contraction, oscillation, and collapse of bubbles. Cavitation phenomena are involved in the safety issue of diagnostic ultrasound as well as roles of main mechanisms on therapeutic application of ultrasound. Ultrasound can be also utilized for drug or gene delivery by biological effect mentioned above. In this thesis, the studies on transdermal drug delivery and gene delivery using therapeutic ultrasound with ultrasound contrast agents (UCAs) are performed.Firstly, the study on transdermal drug delivery using ultrasound with UCAs is explored. A transdermal drug delivery (TDD) is a non-invasive and topical administration method of therapeutic agents through the skin. Although TDD represents a considerable advance compared to oral delivery, the use of TDD is limited due to barrier functions of the skin. The technique of driving molecules of drug across the skin to the target area using ultrasound perturbation is termed ‘sonophoresis’. Sonophoresis, which uses ultrasound as a physical enhancer for systemic delivery of drug,

temporally increases skin permeability such that various medications can be delivered noninvasively. The feasibility of controlled cavitation using UCAs at high frequency was evaluated through in-vitro and in-vivo experiments. Results indicated that the addition of small amounts of UCA can increase skin permeability in sonophoresis without any visible skin damage. Sonophoresis combined with UCA for TDD was verified to safe and more effective modality through these experiments.Secondly, the study on gene delivery using ultrasound with UCAs is explored. Gene therapy has been intensively investigated as an ideal modality to treat various diseases such as immunodeficiency, cancer, cardiovascular diseases. The successful gene therapy depends on transfection efficiency, transferring the genetic material into the cell. The non-viral vector technology as carrier of gene which has advantages in non-immunogenicity, low acute toxicity, and simplicity in use, is one of powerful gene therapy methods for suppressing gene expression of endogenously proteins. However, a drawback of non-viral vectors in vivo is the significantly low transfection efficiency due to the vector’s negative charge, large size, hydrophilic nature and susceptibility to nuclease attacks. Therefore, the development of an efficient and targeted gene delivery method is clearly needed. The drug(/gene) delivery technique using ultrasound with UCAs which is termed sonoporation, is designed to induce transient permeability in biological membranes by opening transient pores, thereby facilitating delivery of drugs including DNA into the cells by increased transfection efficiency. We investigated the efficacy of sonoporation with UCA in a mouse xenograft model with human breast cancer cells, and evaluated the change of transfection efficiency by ultrasound sonication on plasmid DNA prior to transfection. We found that ANT2 shRNA gene delivery via systemic administration using ultrasound with SonoVue® increased the efficiency of gene transfection in localized cancer tissue and lead to tumor regression and increased survival rate in mice. In addition, ultrasound sonication on DNA prior to transfection experiments contributes to increase the transfection efficiency of DNA into the cell. Consequently, gene therapy using ultrasound combined with microbubbles can be utilized as a reasonable gene delivery technique in clinical study.Consequently, therapeutic ultrasound combined with specific microbubble has the potential to treat a variety of diseases in clinical application. In addition, if the characteristics of ultrasound including focusing, non-invasive are made best use, drug delivery is possible to a specific and localized area in deeply located tissue.