15-amino-4-7-10-13-tetraoxapentadecanoic-acid and Neoplasms

Radiolabeled cyclic RGD (Arg-Gly-Asp) peptides have great potential for the early tumor detection and noninvasive monitoring of tumor metastasis and therapeutic response. (18)F-labeled RGD analogs ([(18)F]-AH111585 and [(18)F]Galacto-RGD) have been investigated in clinical trials for positron emission tomography (PET) imaging of integrin expression in cancer patients. To develop new RGD radiotracers with higher tumor accumulation, improved in vivo kinetics, easy availability and low cost, we developed two new RGD peptides and labeled them with generator-eluted (68)Ga (t(1/2) = 68 min) for PET imaging of integrin alpha(v)beta(3) expression in tumor xenograft models.. The two new cyclic RGD dimers, E[PEG(4)-c(RGDfK)](2) (P(4)-RGD2, PEG(4) = 15-amino-4,7,10,13-tetraoxapentadecanoic acid) and E[Gly(3)-c(RGDfK)](2) (G(3)-RGD2, G(3) = Gly-Gly-Gly) were designed, synthesized and conjugated with 1,4,7-triazacyclononanetriacetic acid (NOTA) for (68)Ga labeling. The microPET imaging and biodistribution of the (68)Ga labeled RGD tracers were investigated in integrin alpha(v)beta(3)-positive tumor xenografts.. The new RGD dimers with the Gly(3) and PEG(4) linkers showed higher integrin alpha(v)beta(3) binding affinity than no-linker RGD dimer (RGD2). NOTA-G(3)-RGD2 and NOTA-P(4)-RGD2 could be labeled with (68)Ga within 30 min with higher purity (>98%) and specific activity (8.88-11.84 MBq/nmol). Both (68)Ga-NOTA-P(4)-RGD2 and (68)Ga-NOTA-G(3)-RGD2 exhibited significantly higher tumor uptake and tumor-to-normal tissue ratios than (68)Ga-NOTA-RGD2.. Because of their high affinity, high specificity and excellent pharmacokinetic properties, further investigation of the two novel RGD dimers for clinical PET imaging of integrin alpha(v)beta(3) expression in cancer patients is warranted.

Topics: Animals; Cell Line, Tumor; Dimerization; Female; Gallium Radioisotopes; Glycine; Humans; Integrin alphaVbeta3; Mice; Neoplasms; Peptides, Cyclic; Polyethylene Glycols; Positron-Emission Tomography; Radiochemistry; Staining and Labeling; Tissue Distribution

Radiolabeled cyclic RGD (Arg-Gly-Asp) peptides represent a new class of radiotracers with potential for early tumor detection and noninvasive monitoring of tumor metastasis and therapeutic response in cancer patients. This article describes the synthesis of two cyclic RGD peptide dimer conjugates, DOTA-PEG(4)-E[PEG(4)-c(RGDfK)](2) (DOTA-3PEG(4)-dimer: DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid; PEG(4) = 15-amino-4,7,10,13-tetraoxapentadecanoic acid) and DOTA-G(3)-E[G(3)-c(RGDfK)](2) (DOTA-3G(3)-dimer: G(3) = Gly-Gly-Gly). Integrin alpha(v)beta(3) binding affinities of cyclic RGD peptides were determined by competitive displacement of (125)I-echistatin bound to U87MG human glioma cells and follow the order of DOTA-E{E[c(RGDfK)](2)}(2) (DOTA-tetramer: IC(50) = 10 +/- 2 nM) > DOTA-3G(3)-dimer (IC(50) = 62 +/- 6 nM) approximately DOTA-3PEG(4)-dimer (IC(50) = 74 +/- 3 nM) > DOTA-E[c(RGDfK)](2) (DOTA-dimer: IC(50) = 102 +/- 5 nM). The addition of PEG(4) and G(3) linkers between two cyclic RGD motifs in DOTA-3G(3)-dimer and DOTA-3PEG(4)-dimer makes it possible for them to achieve the simultaneous integrin alpha(v)beta(3) binding in a bivalent fashion. Both (64)Cu(DOTA-3PEG(4)-dimer) and (64)Cu(DOTA-3G(3)-dimer) were prepared in high yield with specific activity being >50 Ci/mmol. Biodistribution and imaging studies were performed in athymic nude mice bearing U87MG human glioma xenografts. The results from those studies show that PEG(4) and G(3) linkers are particularly useful for improving tumor uptake and clearance kinetics of (64)Cu radiotracers from the nontumor organs, such as kidneys, liver, and lungs. There is a linear relationship between the tumor size and %ID tumor uptake, suggesting that (64)Cu(DOTA-3PEG(4)-dimer) and (64)Cu(DOTA-3PEG(4)-dimer) might be useful for noninvasive monitoring of tumor growth or shrinkage during antiangiogenic therapy. MicroPET imaging data clearly demonstrate the utility of (64)Cu(DOTA-3G(3)-dimer) as a new PET radiotracer for imaging integrin alpha(v)beta(3)-positive tumors.

Topics: Animals; Copper Radioisotopes; Dimerization; Gene Expression Regulation, Neoplastic; Glioma; Heterocyclic Compounds, 1-Ring; Humans; Integrin alphaVbeta3; Mice; Neoplasms; Oligopeptides; Peptides, Cyclic; Polyethylene Glycols; Positron-Emission Tomography; Radiochemistry; Staining and Labeling; Tissue Distribution; Transplantation, Heterologous