Iodinated porphyrins in contrast media agentssynthesis, bioactivity and toxicity

Resumo

The work described in this paper, presents the literature review of porphyrins and contrast media fields and reports the preparation and assessment of porphyrin derivatives with potential application as iodinated multimodal contrast media, used in imaging diagnosis. Literature review showed that contrast agents are essential to enhance diagnosis since they increase pathologies detection and enhance pathologies staging and follow-up. Even that importance, some drawbacks are associated to actual clinical contrast media. Those pitfalls led to increasing contrast media development research. On the past five years this research was mostly directed to supramolecular systems, namely nanoparticles, and few works were pointed to molecular order. On the other hand, literature review showed that porphyrin derivatives gained in recent years special attention regarding biomedical application, namely in Photodynamic Therapy and Magnetic Resonance Imaging, but also in radiotherapy, nuclear medicine, and fluorescence imaging. Concerning literature review, in the first part of this work were synthesized several iodinated symmetric and asymmetric meso-substituted porphyrin derivatives. Those compounds were prepared through three distinct approaches: direct condensation of pyrrole and the adequate aldehyde in acid condition and using nitrobenzene as oxidant; through electrophilic aromatic iodination of porphyrin derivatives; and by coupling of a tetraiodophthalic anhydride to aminoporphyrin derivatives through a nucleophilic carbonyl substitution reaction. The manganese(II) and gadolinium(III) metalloporphyrin derivatives were also prepared from a symmetric porphyrin derivative. From these synthetic procedures resulted a total of thirteen porphyrin derivatives candidates to be used as contrast agents in imaging. In the second part of this work, were assessed some photophysical properties of the compounds such as their photostability. All porphyrin derivatives showed to be stable and photostable, with exception of porphyrin 1 that was only stable in the dark. The X-ray beam attenuation ability was evaluated by measuring the Hounsfield Units, after image acquisition by Computed Tomography. All the synthesized derivatives showed adequate ability to attenuate the X-ray beam, with results closer commercial contrast agent iomeprol®. In the third part of this work, was assessed the cytotoxicity of the synthesized derivatives. Toxicity evaluation was assessed to in vitro and in vivo models. In vitro toxicity was evaluated in a non-neoplastic cell line – Primary Mammary Epithelial Cells (HMEC-1) – and two neoplastic cell lines – Human prostate cancer cell line (PC3) and Human breast carcinoma cells (MCF-7) – assessing cellular viability through MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. Half-minimal inhibitory concentration (IC50) was calculated according to cellular viability results. Results showed decreased toxicity of several synthesized derivatives when compared with a clinical used contrast agent. In vivo toxicity was evaluated in Caenorhabditis elegans model through a developmental and reproductive toxicity (DART) assay. C. elegans is a well stablished and easy to use model to apply in drug discovery and development. Results showed same trend as in vitro model with several synthesized derivatives presenting decreased toxicity when compared with a clinical used contrast agent. All the performed worked showed the potential of iodinated porphyrin derivatives application as contrast media to solve some pitfalls observed in the actual clinical contrast media.