Evaluation of 99mTc-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 photosensitizer used worldwide for photodynamic therapy (PDT) of cancer, with radioisotope of technetium (Tc-99m) was developed. The radiotracer was evaluated for radiochemical purity, stability, and finally tissue distribution in a murine tumor model. The Tc-99m-Photosan-3 prepared by using Tc-99m-pertechnetate in place of reduced Tc-99m demonstrated better labeling efficiency (>90%) and reproducibility. The procedure also minimized the radiation exposure to the radiochemist as handling time was considerably reduced. Due to the commercial availability of Photosan-3(R), 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 reduced. The biodistribution studies and tumor scintigraphy confirmed that Tc-99m-labeled Photosan-3(R) was preferentially taken up by the neoplastic tissue in a manner similar to the parent compound. In addition to applications in tumor imaging, Tc-99m-Photosan-3 could also be used for estimating tumor uptake of Photosan-3(R) as may be required for individualization of clinical protocols of PDT, NUCL MED BIOL 27;6:587-592, 2000. (C) 2000 Elsevier Science Inc. All rights reserved.