Preclinical dosimetric estimation of [111In] 5, 10, 15, 20-tetra phenyl porphyrin complex as a possible imaging/PDT agent

Introduction: Recent studies show that porphyrin derivatives have interesting pharmacological and photodynamic properties and wide range of usage in photodynamic therapy treatment. This study describes the preparation, biodistribution and absorbed dose prediction of [111In] labeled 5, 10, 15, 20-tetra phenyl porphyrin (TPP) in human organs, based on rats' biodistribution data. Methods: Five rats were sacrificed at each exact time intervals (2, 4 and 24 h post injection) and the percentage of injected dose per gram of each organ was measured by direct counting from rats data from 12 harvested organs. The Medical Internal Radiation Dose (MIRD) formulation was applied to extrapolate from rats to human and to project the absorbed radiation dose for various organs in humans. Results: From rat data we estimated that injection of [111In] TPP into the humans would result in an estimated effective absorbed dose of 0.09 mSv/MBq in the whole body. While the highest effective absorbed dose for 111In-TPP was in the heart wall (0.22 mSv), the organs that received the next highest doses were the Kidneys (0.06 mSv), thymus (0.04 mSv) and lungs (0.03 mSv). Conclusions: The skin dose will four times higher compare to the other 111In compounds, which was due to magnificent skin uptakes. According to the fast wash-out, tumor avidity and the short half-life, [111In] can be a suitable candidate for labeling of photo dynamic therapy (PDT) agents as a tracer for accurate biological evaluation of other PDT agents such as Photofrin and its homologs.