Porphyrins occur naturally in plants and animals. All porphyrin molecules feature an aromatic macrocycle ring with a central binding site. This site accommodates transition metals, which are held in place by inward-facing nitrogen atoms. Metalloporphyrins have usually a low toxicity and a potential of a selective uptake in tumors or necrosis. These properties are advantageous for a use as MRI tumor specific agents with positive enhancement. These contrast agents enhance tumors on T1 weighted sequences, which are isointense to surrounding tissues. Porphyrin-based compounds have also necrosis avid properties; they can depict the extent of myocardial infarction as defined by histopathology.
Metalloporphyrins are also used in photodynamic therapy of tumors. The compounds contain a 'lone star' metal atom at the center of the ring and are 'bigger than the average porphyrin'. They contain five N atoms in the central chelating core and this allows them to form complexes with large trivalent lanthanide metals, which have useful cancer therapy properties.

See also Classifications, Characteristics, etc., Gadophrin, MnIIITPPS4, Necrosis Avid Contrast Agent.

Short name: Gd-DTPA mesoporphyrin, generic name: gadophrin, central moiety: Gd2+
Gadophrin is a substance under development (Bayer Schering Pharma AG) as a positive enhancing myocardium- and necrosis- targeted MRI contrast agent.

See also Metalloporphyrins and Necrosis Avid Contrast Agent.

Short name: Gd-DTPA mesoporphyrin, generic name: gadophrin, central moiety: Gd2+
Gd-DTPA mesoporphyrin is a substance under development (Bayer Schering Pharma AG) as a positive enhancing myocardium- and necrosis- targeted MRI contrast agent.

See also Metalloporphyrins and Necrosis Avid Contrast Agent.

Short name: Gd-TPPS, central moiety: Gd2+
Gd-tetraphenyl-porphyrin sulfonate is a MRI contrast agent under development (preclin.) with tumor selective uptake for tumor detection and control.

See also Metalloporphyrins.

Short name: Mn(III)TPPS4, chemical compound: manganese(III) tetra-[4- sulfanatophenyl] porphyrin, central moiety: Mn2+, relaxivity: r1=7.5, r2=8.6
Manganese(III) TPPS4 is an agent under development (preclin. for MRI contrast medium) with tumor selective uptake for tumor detection and control.

See also Metalloporphyrins.