Multimerisation of c(RGDfK) resulted in enhanced affinity for alpha(v)beta(3) as determined in vitro. Tumour uptake of a tetrameric RGD peptide was significantly higher than that of the monomeric and dimeric analogues, presumably owing to the enhanced statistical likelihood for rebinding to alpha(v)beta(3).

This report describes the design and synthesis of a series of a V b 3 integrin-directed monomeric, dimeric and tetrameric cyclo [Arg-Gly-Asp-D-Phe-Lys] dendrimers using "click chemistry". It was found that the unprotected N-e-azido derivative of cyclo[Arg-Gly-Asp-D-Phe-Lys] underwent a highly chemoselective conjugation to amino acid-based dendrimers bearing terminal alkynes using a microwave-assisted Cu(I)-catalyzed 1,3-dipolar cycloaddition. The a V b 3 binding characteristics of the dendrimers were determined in vitro and their in vivo a V b 3 targeting properties were assessed in nude mice with subcutaneously growing human SK-RC-52 tumors. The multivalent RGD-dendrimers were found to have enhanced affinity toward the a V b 3 integrin receptor as compared to the monomeric derivative as determined in an in vitro binding assay. In case of the DOTA-conjugated 111 In-labeled RGD-dendrimers, it was found that the radiolabeled multimeric dendrimers showed specifically enhanced uptake in a V b 3 integrin expressing tumors in vivo. These studies showed that the tetrameric RGD-dendrimer had better tumor targeting properties than its dimeric and monomeric congeners.

The alpha v beta 3 integrin, a transmembrane heterodimeric protein expressed on sprouting endothelial cells, binds to the arginine-glycine-aspartic acid (RGD) amino acid sequence of extracellular matrix proteins such as vitronectin. Growing malignant tumors continuously require angiogenesis. As a result, alpha v beta 3 is preferentially expressed in growing tumors and is a potential target for radiolabeled RGD-peptides. In this study we compared the tumor targeting characteristics of a monomeric radiolabeled RGD-peptide with those of a dimeric analogue. Both peptides were radiolabeled with 99mTc via the hydrazinoni-cotinamid (= HYNIC) moiety to form 99mTc-HYNIC-c(RGDfK) and 99mTc-HYNIC-E-[c(RGDfK)]2. In vitro, the IC50 showed a 10-fold higher affinity of the dimer for the alpha v beta 3 integrin as compared to the monomer (0.1 vs. 1.0 nM). In athymic female BALB/c mice with subcutaneously growing OVCAR-3 ovarian carcinoma xenografts, tumor uptake peaked at 5.8 +/- 0.7% ID/g and 5.2 +/- 0.6% ID/g for the dimer and the monomer, respectively. At 1, 2, and 4 h postinjection (p.i.) uptake of the dimer in the tumor was significantly higher than that of the monomeric analogue. Tumor-to-blood ratios were highest at 24 h p.i. at a value of 63 for both compounds. At all timepoints kidney retention of the dimer was significantly higher as compared to kidney retention of the monomer. In conclusion, in this mouse model the dimeric RGD-peptide showed better retention in the tumor than the monomeric analogue, most likely due to the bivalent interaction with the target cell. Furthermore, kidney retention of the dimeric peptide was higher than that of the monomeric peptide.

PURPOSE Pharmacokinetics, biodistribution, immunogenicity, and imaging characteristics of iodine 131 (131I)-labeled chimeric monoclonal antibody (mAb) G250 (cG250) were studied in patients with renal cell carcinoma (RCC) to determine the therapeutic potential of this antibody. PATIENTS AND METHODS Sixteen patients with RCC received a single intravenous (IV) infusion of 6 mCi 131I-labeled cG250. Five protein dose levels were investigated (2 to 50 mg). Planar scintigraphic images were acquired, and normal tissue biopsies and tumor samples were obtained of surgery (7 days postinjection). The immunogenicity of cG250 was investigated using a sandwich enzyme-linked immunosorbent assay (ELISA) and dosimetric analysis was performed. RESULTS In all patients with antigen-positive tumors (n = 13), the primary tumors and all known metastases were clearly visualized. Overall uptake, expressed as the percentage of the injected dose (%ID), in the primary tumors ranged from 2.4 to 9.0. Focally, 131I-cG250 uptake as high as 0.52% ID/g was observed. However, intratumoral uptake was highly heterogeneous. 131I-cG250 uptake in nontumorous tissues remained low. Dosimetric analysis showed that up to .48 Gy/mCi was guided to the primary tumors. Selected "hot areas" within these tumors received up to .72 Gy/mCi. A bone metastasis received .23 Gy/mCi and regional lymph node metastases received .20 Gy/mCi. Minimal human antichimeric antibody (HACA) levels were detected in two of 16 patients. CONCLUSION 131I-cG250 tumor uptake is among the highest reported in clinical studies with antitumor antibodies in solid tumors. Since tumor-sterilizing levels may be guided to the tumor when high doses 131I-cG250 are administered (> 100 mCi) and cG250 appears to be immunosilent, cG250 is a promising vehicle for radioimmunotherapy in RCC.

Fever of unknown origin (FUO) and suspected focal infection or inflammation are challenging medical problems. The aim of this study was to assess the value of fluorine-18 fluorodeoxyglucose positron emission tomography (FDG PET) in patients with FUO and patients with suspected focal infection or inflammation. All FDG PET scans ordered because of FUO or suspected focal infection or inflammation in the last 4 years were reviewed. These results were compared with the final diagnosis. Thirty-five FDG PET scans were performed in 35 patients with FUO. A final diagnosis was established in 19 patients (54%). Of the total number of scans, 37% were clinically helpful. The positive predictive value of FDG PET in these patients was 87% and the negative predictive value was 95%. Fifty-five FDG PET scans were performed in 48 patients with suspected focal infection or inflammation. A final diagnosis was established in 38 patients (82%). Of the total number of scans, 65% were clinically helpful. The positive predictive value of FDG PET in these 55 episodes of suspected infection or inflammation was 95% and the negative predictive value was 100%. It is concluded that FDG PET appears to be a valuable imaging technique in the evaluation of FUO and suspected focal infection or inflammation. Furthermore, FDG PET could become a useful tool for evaluating the effect of treatment of infectious and inflammatory processes that cannot reliably be visualised by conventional techniques. However, to assess the additional diagnostic value of this technique, prospective studies of FDG PET as part of a structured diagnostic protocol are warranted.