Improved Tumor Targeting of Radiolabeled RGD Peptides Using Rapid Dose Fractionation.

Arginine-glycine-aspartic acid (RGD) peptides preferentially bind to ?v?3 integrin, an integrin expressedon newly formed endothelial cells and on various tumor cells. When labeled with ?-emitting radionuclides,these peptides can be used for peptide-receptor radionuclide therapy of malignant tumors. Thesestudies aimed to investigate whether tumor targeting and tumor therapy could be optimized by dose fractionation.The RGD-peptide DOTA-E-[c(RGDfK)]2 was labeled with 111In for biodistribution experiments andwith 90Y for therapy experiments. In mice with NIH:OVCAR-3 ovarian carcinoma xenografts, optimal tumoruptake was obtained at peptide doses up to 1.0 mg (4.8 %ID/g). A peptide dose of 5 mg, required toadminister the maximum tolerable dose (MTD) 90Y-DOTA-E-[c(RGDfK)]2, was administered as 5 portionsof 1.0 mg. Tumor uptake of the fifth portion was significantly higher than that of the single 5.0 mgportion (3.3 %ID/g versus 2.1 %ID/g). The therapeutic efficacy of 37 MBq 90Y-DOTA-E-[c(RGDfK)]2(1 × 5.0 mg) was compared with that of 37 MBq administered in five equal portions (5 × 1.0 mg). Nodifference in tumor growth between the fractionated and the nonfractionated therapy was observed. Inconclusion, dose fractionation resulted in higher radiation doses. However, therapeutic efficacy of the radiolabeledpeptide was not significantly improved by dose fractionation. [ABSTRACT FROM AUTHOR]