Evaluation of Tc-99m-labeled Photosan-3, a hematoporphyrin derivative, as a potential radiopharmaceutical for tumor scintigraphy

A quick and reproducible method for radiolabeling of Photosan-3(R), a photo sensitizer used worldwide for photodynamic therapy (PDT) of cancer, with ra dioisotope of technetium (Tc-99m) was developed. The radiotracer was evalua ted for radiochemical purity, stability, and tissue distribution in a murin e tumor model. The Tc-99m-Photosan-3, which was prepared by using Tc-99m-pe rtechnetate in place of reduced Tc-99m, demonstrated better labeling effici ency (>90%) and reproducibility. The procedure also minimized radiation exp osure to the radiochemist because handling time was considerably reduced. D ue to the commercial availability of Photosan-3, the risk of batch-to-batch variation in the in situ synthesis of hematoporphyrin derivative, which is a complex mixture of at least five compounds, was also significantly reduc ed. The biodistribution studies and tumor scintigraphy confirmed that Tc-99 m-labeled Photosan-3 was preferentially taken up by the neoplastic tissue s imilar to the parent compound. In addition to its applications in tumor ima ging, Tc-99m-Photosan-3 could also be used for estimating tumor uptake of P hotosan-3 as may be required for individualization of clinical protocols of PDT. NUCL MED BIOL 27;4:419-426, 2000. (C) 2000 Elsevier Science Inc. All rights reserved.