Two (90)Y-Labeled Multimeric RGD Peptides RGD4 and 3PRGD2 for Integrin Targeted Radionuclide Therapy

We have recently developed a series of new Arg-Gly-Asp (RGD) dimeric peptides for specific targeting of integrin alpha(v)beta(3) with enhanced tumor uptake and improved pharmacokinetics. In this study, we investigated Y-90-labeled RGD tetramer (RGD4) and the new type of RGD dimer (3PRGD2), for the radionuclide therapy of integrin alpha(v)beta(3)-positive tumors. Biodistribution and gamma imaging studies of In-111 labeled RGD4 and 3PRGD2 were performed. Groups of nude mice were used to determine maximum tolerated dose (MTD) of Y-90-DOTA-RGD4 and Y-90-DOTA-3PRGD2. The radionuclide therapeutic efficacy of Y-90-DOTA-RGD4 and 90Y-DOTA-3PRGD2 was evaluated in U87MG tumor-bearing nude mice. The U87MG tumor uptake of In-111-DOTA-3PRGD2 was slightly lower than that of the In-111-DOTA-RGD4 (e.g., 6.13 +/- 0.82%ID/g vs 6.43 +/- 1.6%ID/g at 4 h post-injection), but the uptake of In-111-DOTA-3PRGD2 in normal organs, such as liver and kidneys, was much lower than that of In-111-DOTA-RGD4, which resulted in much higher tumor-to-nontumor ratios and lower toxicity. The MTD of Y-90-DOTA-RGD4 in nude mice is less than 44.4 MBq, while the MTD of Y-90-DOTA-3PRGD2 in mice is more than 55.5 MBq. Y-90-DOTA-3PRGD2 administration exhibited a similar tumor inhibition effect as compared with Y-90-DOTA-RGD4 at the same dose. The tumor vasculature in the Y-90-DOTA-3PRGD2 treatment group was much less than the control groups. Radionuclide therapy studies exhibited that both Y-90-DOTA-RGD4 and Y-90-DOTA-3PRGD2 caused significant tumor growth delay in the U87MG tumor model. Compared to Y-90-DOTA-RGD4, the low accumulation of Y-90-DOTA-3PRGD2 in normal organs led to lower toxicity and higher MTD in nude mice, which would make it more suitable for high dose or multiple-dose regimens, in order to achieve maximum therapeutic efficacy.