Thermosensitive liposomes have been suggested for local drug

release in combination with local hyperthermia more than 25 years ago. Microbubbles may be designed specifically to enhance cavitation effects. Real-time imaging methods, such as magnetic resonance, optical and ultrasound imaging, have led to novel insights and methods for ultrasound triggered drug delivery. Image guidance of ultrasound can be used for: (1) target identification and characterization; (2) spatiotemporal Inhibitors,research,lifescience,medical guidance of actions to release or activate the drugs and/or permeabilize membranes; (3) evaluation of biodistribution, pharmacokinetics and pharmacodynamics; and (4) physiological read-outs to evaluate the therapeutic efficacy. 3.2. FUS Induced Increase in Temperature for Tissue Specific Drug Release from Thermosensitive Carriers Liposomes show significant advantages for drug delivery in tumours. The enhanced permeability and retention effect has served as a basic rationale for using liposomes and other nanoparticles to treat solid tumors. Inhibitors,research,lifescience,medical However, it has been recently noticed that the enhanced permeation and retention effect does not guarantee a uniform delivery. This heterogeneous distribution of therapeutics is a result of physiological barriers presented by the abnormal tumor vasculature Inhibitors,research,lifescience,medical and interstitial matrix. In a recent review by Jain and Stylianopoulos, the barriers of tumour nanoparticle delivery were

summarised. First, the abnormal structure of tumor vessels results in heterogeneous tumor perfusion and extravasation, and a hostile tumor microenvironment that supports drug resistance and tumor progression. Second, in highly fibrotic tumors, Inhibitors,research,lifescience,medical the extracellular matrix blocks penetration of large nanoparticles leaving them concentrated in perivascular region. To overcome these barriers the authors suggest normalization of the vascular network and the extracellular matrix as well as development of nanoparticles that release therapeutic agents in response to the tumor microenvironment or an external stimulus (such as heat light and HIFU)

[23]. Thermosensitive carriers have a long presence in research Inhibitors,research,lifescience,medical and development. Yatvin et al. first described the effect of hyperthermia on liposomal carriers in 1978 [24]. However, development of thermosensitive liposomal carriers for cancer was only introduced as recently as 1999 when Needham’s group evaluated phase transition enhanced liposomal permeability [25]. In vivo data using cancer models were presented one year later when the authors Dichloromethane dehalogenase described a new lipid formulation containing doxorubicin optimized for mild hyperthermic temperatures (39°C to 40°C) that are readily achievable in the clinic leading to very rapid release times of the drugs. This new liposome, in combination with mild hyperthermia, was found to be significantly more effective than free drug or current liposome MK518 formulations at reducing tumour growth in a human squamous cell carcinoma xenograft [26].