Figure 2.

Drug release imaging. (A) Nanoformulations entrapping MRI or OI agents can generate different signals when the contrast agent is in entrapped vs. in free form, allowing for non-invasive monitoring of drug release. (B) Liposomes loaded with ProHance^®, an MRI contrast agent, show low MRI contrast while being intact at physiological temperature. Upon hyperthermia, low and traditional temperature-sensitive liposomes (LTSL and TTSL) re-order their lipid biolayer, resulting in ProHance^® release and in an increase in MRI signal. This does not occur for non-temperature-sensitive liposomes (NTSL). (C) MRI signal enhancement upon hyperthermia treatment of temperature-sensitive liposomes (TSL) shows a good correlation with doxorubicin release, exemplifying the usefulness of such setups for non-invasive release monitoring. (D) MRI scan of 9L gliosarcoma rat tumors demonstrating MRI contrast agent (and drug) release from temperature-sensitive liposomes (TSL) upon focused ultrasound-based hyperthermia treatment. (E) PLGA nanoparticles co-loaded with Cy-5.5 as a FRET donor and Cy-7 as FRET acceptor enable the visualization and quantification of nanocarrier-drug association and dissociation (i.e. drug release) in MDA-MB-231 breast cancer xenograft tumors. Images reproduced, with permission, from ⁴⁸,⁴⁹,⁵³,⁵⁷.