Intratumoral injection of 188Re labeled cationic polyethylenimine conjugates:: A preliminary report

Re-188 (Rhenium) is easily obtained from an in-house W-188/Re-188 generator that is similar to the current Mo-99/Tc-99m 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 Re-188 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 Re-188 bound compounds (HYNIC-PEI-Tf, HYNIC-PEI, Re-188 perrhenate) were injected directly into the tumors. There were increases in the retention of Re-188 inside the tumor when PEI was incorporated with Re-188 compared to the use of free Re-188. The Re-188 HYNIC-Tf-PEI showed the most retention inside the tumor (retention rate=approximately 97%). H&E stain of isolated tumor tissues showed that Re-188 labeled HYNIC-PEI-Tf caused extensive tumor necrosis. These results support Re-188 HYNIC-PEI-Tf as being a useful radiopharmaceutical agent to treat tumors when delievered by intratumoral injection.