Integrin Binding Peptides in a Nude Mouse Model

The v 3 integrin is expressed on proliferating endothelial cells such as those present in growing tumors, as well as on tumor cells of various origin. Tumor-induced angiogenesis can be blocked in vivo by antagonizing the v 3 integrin with small peptides containing the Arg-Gly-Asp (RGD) amino acid sequence. This tripeptidic sequence, naturally present in extracellular matrix proteins, is the primary binding site of the v 3 integrin. Because of selective expression of v 3 integrin in tumors, radiolabeled RGD peptides are attractive candidates for v 3 integrin targeting in tumors. We studied the in vivo behavior of the radiolabeled dimeric RGD peptide E-[c(RGDfK)]2 in the NIH:OVCAR-3 s.c. ovarian carcinoma xenograft model in BALB/c nude mice. Conjugation of the 1,4,7,10-tetraazadodecane-N,N ,N ,N -tetraacetic acid (DOTA) and hydrazinonicotinamide (HYNIC) chelators enabled efficient radiolabeling with In/Y and Tc, respectively. The radiolabeled peptide was rapidly excreted renally. Uptake in nontarget organs such as liver and spleen was considerable. Tumor uptake peaked at 7.5% injected dose (ID)/g (In-DOTA-E-[c(RGDfK)]2) or 6.0%ID/g ( Tc-HYNIC-E[c(RGDfK)]2) at 2 and 1 h postinjection, respectively. Integrin v 3 receptor binding specificity was demonstrated by reduced tumor uptake after injection of the scrambled control peptide In-DOTA-E-[c(RDKfD)]2 (0.28%ID/g at 2 h p.i.) and after coinjection of excess nonradioactive In-DOTA-E-[c(RGDfK)]2 (0.22%ID/g at 2 h p.i.). A single injection of Y-DOTA-E-[c(RGDfK)]2 at the maximum-tolerated dose (37 MBq) in mice with small s.c. tumors caused a significant growth delay as compared with mice treated with 37 MBq Y-labeled scrambled peptide or untreated mice (median survival of 54 versus 33.5 versus 19 days, respectively). In conclusion, the radiolabeled RGD peptides In-DOTAE-[c(RGDfK)]2 and Tc-HYNIC-E-[c(RGDfK)]2 demonstrated high and specific tumor uptake in a human tumor xenograft. Injection of Y-DOTA-E-[c(RGDfK)]2 induced a significant delay in tumor growth. Potentially, these peptides can be used for peptide receptor radionuclide imaging as well as therapy.