MRI Monitoring of Tumor-Selective Anticancer Drug Delivery with Stable Thermosensitive Liposomes Triggered by High-Intensity Focused Ultrasound.

Monitoring of drug release from a heat-activated liposome carrier provides an opportunity for real-time control of drug delivery and allows prediction of the therapeutic effect. We have developed short-chain elastin-like polypeptide-incorporating thermosensitive liposomes (STLs). Here, we report the development of STL encapsulating gadobenate dimeglumine (Gd-BOPTA), a MRI contrast agent, and doxorubicin (Dox) (Gd-Dox-STL). The Dox release profile from Gd-Dox-STL was comparable to Gd-Dox-LTSL; however, the serum stability of Gd-Dox-STL was much higher than Gd-Dox-LTSL. MRI studies showed that the difference in T1 relaxation time between 37 and 42 °C for Gd-Dox-STL was larger than the difference for Gd-Dox-LTSL. Although relaxivity for both liposomes at 42 °C was similar, the relaxivity of Gd-Dox-STL at 37 °C was 2.5-fold lower than that of Gd-Dox-LTSL. This was likely due to Gd-BOPTA leakage from the LTSL because of low stability at 37 °C. Pharmacokinetic studies showed plasma half-lives of 4.85 and 1.95 h for Gd-Dox-STL and Gd-Dox-LTSL, respectively, consistent with in vitro stability data. In vivo MRI experiments demonstrated corelease of Dox and Gd-BOPTA from STL under mild hyperthermia induced by high-intensity focused ultrasound (HIFU), which suggests STL is a promising tumor selective formulation when coupled with MR-guided HIFU.