Development of fluorinated magnetic resonance imaging probes as alternative to gadolinium-based contrast agents

The increasing concerns about gadolinium-based contrast agents (GBCAs), including their long-term retention in tissues, nephrotoxicity in vulnerable patients and environmental accumulation, have prompted the development of safer and more sustainable alternatives for magnetic resonance imaging (MRI). Among the different strategies, fluorine-19 (19F) MRI is one of the most promising techniques, offering high specificity, quantifiability and the advantage of background-free signal due to the absence of endogenous fluorine in biological tissues. This doctoral research focuses on the development, optimization and characterization of innovative 19F-based MRI probes as potential alternatives to conventional GBCAs. The project is structured into three experimental chapters, each addressing a distinct design strategy. Chapter 2 investigates the encapsulation of hexafluorophosphate (PF6-) and fluoride (F⁻) anions into the aqueous core of liposomes and examines how compartmentalization modulates their NMR relaxation properties. By varying liposome size and internal concentration, significant alterations in 19F T1 and T2 relaxation times were observed. Moreover, the responsiveness of these systems to external stimuli, such as ultrasound-induced release, underscores their potential as theranostic agents capable of reporting payload release in real time. Chapter 3 explores a bioinspired strategy to enhance probe circulation time and immune evasion by camouflaging perfluorocarbon (PFCE)-loaded PLGA nanoparticles with red blood cell membranes (RBCMs). The resulting PFCE-PLGA-RBCM nanoparticles demonstrated enhanced stability in biological environments, reduced uptake by the mononuclear phagocyte system and improved 19F signal in tumor tissue. These results highlight the effectiveness of membrane-coating strategies for in vivo 19F MRI applications. Chapter 4 delves into the dynamic behaviour of fluoride binding to diamagnetic lanthanide complexes based on DOTAM ligands (with Lu3+ and Y3+ ions). Using advanced NMR techniques, the study revealed multiple fluorinated species in equilibrium and provided insights into their thermodynamic and kinetic parameters. These findings not only contribute to the understanding of fluoride coordination chemistry but also establish a method to detect fluorinated species present at sub-micromolar concentrations, otherwise not detectable with the standard techniques. Altogether, this thesis presents a multifaceted approach to the design of safe, effective and stimuli-responsive fluorinated MRI contrast agents. The integration of structural design, nanocarrier engineering and molecular imaging offers new opportunities for non-invasive diagnostics and real-time monitoring of physiological and pathological events. These strategies pave the way for future translation of 19F MRI probes into clinical and preclinical imaging workflows, representing a significant advancement in the field of molecular imaging.