Synthesis of Pyrrole-Based Macrocycles as Molecular Probes for Multimodal Imaging Techniques: Recent Trends

Background: Multimodal imaging is a tool that may allow visualization, by using a single multifunctional compound, of early stage tumors and pharmacokinetic processes, drug action mechanisms and tumor growth processes, taking advantage of the strengths of each modality. Closely related, the emergence of "noninvasive" in vivo imaging revealed several "tip of the spear" contrast agent based technologies, e.g. Positron Emission Tomography/Single-Photon Emission Computed Tomography and Magnetic Resonance Imaging. Objective: This review aims to give an insight on the state of the art regarding the application of pyrrole-based macrocycles as contrast agents in multimodal imaging techniques, asserting on the synthesis, with careful selection of influential milestones over the last decade on this field. Conclusion: Of the possible contrast agents required, pyrrole-based macrocycles constitute an important family, many groups have been devoting a considerable effort over last years to develop suitable pyrrole-based molecules that can act as contrast agents for more than one modality at the same time. While nuclear medicine uses radiolabeled tracers that produce signals by means of radioactive decay only, other molecular imaging means may use imaging agents that function by means of magnetism, (magnetic resonance imaging), or light (optical techniques of fluorescence), to name a few. In other words, in order to exploit the potential synergic advantages of each molecular imaging technique, the development of multimodal probes is considered a crucial area to validate in vivo molecular imaging experiments and allow the detection of cancer at early stages, and should be the future focus of molecular imaging in further years.