Intratumoral Injection of 188Re labeled Cationic Polyethylenimine Conjugates: A Preliminary Report

188Re (Rhenium) is easily obtained from an in-house 188W/188Re generator that is similar to the current 99Mo/99mTc generator, making it very convenient for clinical use. This characteristic makes this radionuclide a promising candidate as a therapeutic agent. Polyethylenimine (PEI) is a cationic polymer and has been used as a gene delivery vector. Positively charged materials interact with cellular blood components, vascular endothelium, and plasma proteins. In this study, the authors investigated whether intratumoral injection of 188Re labeled transferrin (Tf)-PEI conjugates exert the effect of radionuclide therapy against the tumor cells. When the diameters of the Ramos lymphoma (human Burkitt's lymphoma) xenografted tumors reached approximately 1 cm, 3 kinds of 188Re bound compounds (HYNIC-PEI-Tf, HYNIC-PEI, 188Re perrhenate) were injected directly into the tumors. There were increases in the retention of 188Re inside the tumor when PEI was incorporated with 188Re compared to the use of free 188Re. The 188Re HYNIC-Tf-PEI showed the most retention inside the tumor (retention rate=approximately 97%). H&E stain of isolated tumor tissues showed that 188Re labeled HYNIC-PEI-Tf caused extensive tumor necrosis. These results support 188Re HYNIC-PEI-Tf as being a useful radiopharmaceutical agent to treat tumors when delivered by intratumoral injection.