Radiosynthesis and bioevaluation of [68Ga]-labeled 5,10,15,20-tetra(4-methylpyridyl)-porphyrin for possible application as a PET radiotracer for tumor imaging.

PURPOSE: Porphyrins have inherent ability to localize preferentially in tumor lesions. Cationic porphyrins are readily water soluble and reported to exhibit strong DNA-binding capabilities. Therefore, attempt has been made to prepare a water soluble [(68)Ga]-labeled cationic porphyrin, viz., 5,10,15,20-tetra(4-methylpyridyl)porphyrin (TMP), and evaluate its potential as a positron emission tomography (PET) radiotracer for tumor imaging. PROCEDURES: The cationic porphyrin TMP was synthesized following a two-step procedure and subsequently radiolabeled with Ga-68, eluted from a commercial (68)Ge/(68)Ga generator. Purification of the [(68)Ga]-labeled porphyrin derivative was carried out using Sep-Pak(®) cartridges. The tumor-targeting potential of the [(68)Ga]-labeled-5,10,15,20-tetra(4-methylpyridyl)porphyrin was evaluated by biodistribution studies in Swiss mice bearing fibrosarcoma tumor.
RESULTS: Under optimized reaction conditions, [(68)Ga]-labeled TMP was obtained with ~90 % radiochemical purity which was subsequently improved to >99 % after purification through Sep-Pak(®) cartridges. Biodistribution studies revealed high tumor uptake of the radiotracer within 30-min post-injection (6.47 ± 0.87 % of injected activity) and retention until the final 2 h post-administration (4.48 ± 1.11 % of injected activity) time point. The initial uptake observed in non-target organs cleared away with time resulting in gradually improving tumor/blood and tumor/muscle ratios.
CONCLUSION: Preliminary bioevaluation studies indicated the potential of the radiolabeled porphyrin derivative for tumor imaging, and further detailed studies are warranted to evaluate the true potential of the developed radiotracer.