MRI visualisation of drug delivery/release
The design of imaging procedures aimed at providing pharmacologists/ clinicians a valuable in vivo and minimally-invasive support to visualize the effective delivery and release of a drug in the diseased region is very crucial to improve the efficiency of a pharmacological therapy and to optimize the therapeutic planning on an individual base (personalized medicine). This research area, which is part of theranosis, requires the development of chemicals that have to generate an imaging response as a function of the delivered and/or released drug. In principle, imaging protocols for the visualization of drug delivery can be designed for almost all the available imaging modalities (nuclear, CT, optical, US, MRI, and hybrid technologies). However, for imaging drug release purposes, MRI is certainly the choice of election because of the widespread and successful preclinical and clinical use, the good spatio-temporal resolution, the possibility to reach deep tissues/organs without any limitations, and the rich portfolio of agents and contrast modalities available. The motivation of using nanocarriers in the pharmacological field is mainly driven by the necessity to improve the therapeutic index of a drug. The rational is to influence the biodistribution of the drug to favour (by passive or active targeting) the accumulation and availability at the target organ, thereby improving therapeutic efficacy and reducing side effects. However, to exert the effect, the drug needs to be released from the carrier. For the nanomedicines currently approved for clinical use, this fundamental step occurs spontaneously, i.e. following the natural degradability of the nanocarrier interacting with tissue components. However, a significantly better control of the release can be achieved through a specific stimulation, especially suitable for treating solid tumours. The release of a drug is dependent on many factors, including the physico-chemical properties of the nanocarrier, and therefore, the development of new drug delivery systems is still an important research area.