Anti-angiogenesis is a promising strategy for the treatment of cancer. Integrins, consisting of two noncovalently bound transmembrane α and β subunits, are an important molecular family involved in tumor angiogenesis.

This report describes the synthesis of two cyclic RGD (Arg-Gly-Asp) conjugates, HYNIC-2PEG 4 -dimer (HYNIC = 6-hydrazinonicotinyl; 2PEG 4 -dimer = E[PEG 4 -c(RGDfK)] 2 ; and PEG 4 = 15-amino-4,7,10,13-tetraoxapentadecanoic acid) and HYNIC-3PEG 4 -dimer (3PEG 4 -dimer = PEG 4 -E [PEG 4 -c(RGDfK)] 2 ), and evaluation of their 99m Tc complexes [ 99m Tc(HYNIC-2PEG 4 -dimer) (tricine)(TPPTS)] ( 99m Tc-2PEG 4 -dimer: TPPTS = trisodium triphenylphosphine-3,3′,3″-trisulfonate) and [ 99m Tc(HYNIC-3PEG 4 -dimer)(tricine)(TPPTS)] ( 99m Tc-3PEG 4 -dimer) as novel radiotracers for imaging integrin α v β 3 expression in athymic nude mice bearing U87MG glioma and MDA-MB-435 breast cancer xenografts. The integrin α v β 3 binding affinities of RGD peptides were determined by competitive displacement of 125 I-c(RGDyK) on U87MG glioma cells. It was found that the two PEG 4 linkers between RGD motifs in HYNIC-2PEG 4 -dimer (IC 50 = 2.8 ± 0.5 nM) and HYNIC-3PEG 4 -dimer (IC 50 = 2.4 ± 0.7 nM) are responsible for their higher integrin α v β 3 binding affinity than that of HYNIC-PEG 4 -dimer (PEG 4 -dimer = PEG 4 -E[c(RGDfK)] 2 ; IC 50 = 7.5 ± 2.3 nM). Addition of extra PEG 4 linker in HYNIC-3PEG 4 -dimer has little impact on integrin α v β 3 binding affinity. 99m Tc-2PEG 4 -dimer and 99m Tc-3PEG 4 -dimer were prepared in high yield with >95% radiochemical purity and the specific activity of > 10 Ci/μmol. Biodistribution studies clearly demonstrated that PEG 4 linkers are particularly useful for improving the tumor uptake and clearance kinetics of 99m Tc-2PEG 4 -dimer and 99m Tc-3PEG 4 -dimer from non-cancerous organs. It was also found that there was a linear relationship between the tumor size and radiotracer tumor uptake expressed as %ID (percentage of the injected dose) in U87MG glioma and MDA-MB-435 breast tumor models. The blocking experiment showed that the tumor uptake of 99m Tc-2PEG 4 -dimer is integrin α v β 3 -mediated. In the metabolism study, 99m Tc-2PEG 4 -dimer had high metabolic stability during its excretion from renal and hepatobiliary routes. 99m Tc-3PEG 4 -dimer also remained intact during thee excretion from the renal route, but, had ~30% metabolism during the excretion from the hepatobiliary route. Planar imaging studies in U87MG glioma and MDA-MB-435 breast tumor models showed that the tumors of ~5 mm in diameter could be readily visualized with excellent contrast. Thus, 99m Tc-3PEG 4 -dimer is a very promising radiotracer for the early detection of integrin α v β 3 -positive tumors, and may have the potential for non-invasive monitoring of tumor growth or treatment efficacy.

Differently sized NaGdF(4) nanocrystals with narrow particle size distributions were synthesized by a high temperature approach. Upon ligand exchange, the as-prepared hydrophobic NaGdF(4) nanocrystals were transferred into water by using asymmetric PEGs simultaneously bearing phosphate and maleimide groups. Further investigations demonstrated that the water-soluble NaGdF(4) nanocrystals, coated by PEG bearing two phosphate groups on the same side, exhibit not only excellent colloidal stability in water and PBS buffer, but also higher T1 relaxivity than Gd-DTPA (Magnevist). Through "click" reaction between the maleimide residue on particle surface and thiol group from the partly reduced anti-EGFR monoclonal antibody (mAb), NaGdF(4)-PEG-mAb nanoprobes were constructed, and their biocompatibility and binding specificity were evaluated through in vitro experiments. A series of in vivo experiments were then carried out for detecting intraperitoneal tumor xenografts in nude mice by using magnetic resonance (MR) imaging technique. The results revealed that the NaGdF(4)-PEG-mAb probes possessed satisfying tumor-specific targeting ability and strong MR contrast enhancement effects.