99mTc-Hydrazinonicotinic acid-Glu-{Glu-[cyclo(Arg-Gly-Asp-D-Phe-Lys)]2}2

99mTc-HYNIC-E{E[c(RGDfK)]2}2

Leung K.

Publication Details

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In vitro Rodents

Background

[PubMed]

Integrins are a family of heterodimeric glycoproteins on cell surfaces that mediate diverse biological events involving cell-cell and cell-matrix interactions (1). Integrins consist of an α and a β subunit and are important for cell adhesion and signal transduction. αvβ3 integrin is the most prominent receptor affecting tumor growth, tumor invasiveness, metastasis, tumor-induced angiogenesis, inflammation, osteoporosis, and rheumatoid arthritis (2-7). Expression of αvβ3 integrin is strong on tumor cells and activated endothelial cells, whereas expression is weak on resting endothelial cells and most normal tissues. αvβ3 antagonists are being studied as antitumor and antiangiogenic agents and the agonists as angiogenic agents for coronary angiogenesis (6, 8, 9). Extracellular matrix proteins (vitronectin, fibrinogen, laminin, and collagen) contain a tripeptide sequence consisting of Arg-Gly-Asp (RGD), which binds to a variety of integrins, including αvβ3. Various radiolabeled antagonists have been introduced for imaging of tumors and tumor angiogenesis (10).

Most of the cyclic RGD peptides are composed of five amino acids. Haubner et al. (11) reported that various cyclic RGD peptides exhibit selective inhibition of binding to αvβ3 (IC50, 7-40 nM) but not to αvβ5 (IC50, 600-4,000 nM) or αIIbβ3 (IC50, 700-5,000 nM) integrins. Various radiolabeled cyclic RGD peptides have been found to have high accumulation in tumors in nude mice (12). Hydrazinonicotinic acid (HYNIC) is a coupling agent for 99mTc labeling of peptides that can achieve high specific activities without affecting receptor-binding ability of the amino acid sequence. Liu et al. (13) reported the success of radiolabeling cylco(Arg-Gly-Asp-D-Phe-Lys) (c(RGDfK)) tetramer linked by glutamic acid that was conjugated with HYNIC. Trisodium triphenylphosphine-3,3’,3’’-trisulfonate (TPPTS) and tris(hydroxymethyl)-methylglycine (tricine) were used as coligands. 99mTc-HYNIC-E{E[c(RGDfK)]2}2(tricine)(TPPTS) showed high tumor accumulation in nude mice bearing human tumor xenografts.

Synthesis

[PubMed]

Liu et al. (13) reported the synthesis of 99mTc-HYNIC-E{E[c(RGDfK)]2}2(tricine)(TPPTS) by incubation of 20 μg HYNIC-E{E[c(RGDfK)]2}2, 6.5 mg tricine, 5 mg TPPTS, and 1.85 GBq (50 mCi ) Na[99mTcO4] for 20-25 min at 100ºC. Radiochemical purity was >95%.

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

Using a receptor-binding assay with 125I-echistatin to αvβ3 integrin receptors on cell surface of MDA-MB-435 human breast cancer cells, Liu et al. (13) reported that E{E[c(RGDfK)]2}2 and E[c(RGDfK)]2 had IC50 values of 51 ± 11 and 78 ± 27 nM, respectively. IC50 values for HYNIC-E{E[c(RGDfK)]2}2 and HYNIC-E[c(RGDfK)]2 were 55 ± 11 and 52 ± 9 nM, respectively. The in vitro solution stability of 99mTc-HYNIC-E{E[c(RGDfK)]2}2(tricine)(TPPTS) was tested by incubating the radiolabeled peptide in buffer solution that contained 1.0 mg/ml cysteine at 37ºC for up to 12 h. No significant degradation of 99Tc-HYNIC-E{E[c(RGDfK)]2}2(tricine)(TPPTS) was observed under this condition.

Animal Studies

Rodents

[PubMed]

Liu et al. (13) performed biodistribution studies of 99mTc-HYNIC-E{E[c(RGDfK)]2}2(tricine)(TPPTS) in nude mice bearing MDA-MB-435 tumors. Tumor uptake was 5.60 ± 0.87% ID/g at 5 min after injection and increased to 7.30 ± 1.32% ID/g at 120 min. The uptakes of the tetramer in the tumor were significantly higher than that of the dimer (3.50% ID/g at 5 min and 3.82% ID/g at 120 min). Tumor/blood ratios were similar at all time points with highest at 24 h with a value of 63 for both compounds. At all time points, retention of the tetramer in the kidney (33.05% ID/g at 5 min and 25.93% ID/g at 120 min) was significantly higher as compared to the dimer (24.15% ID/g at 5 min and 14.33% ID/g at 120 min). Both peptides exhibited similar accumulation in the spleen, liver and lung. The tumor/blood, tumor/liver and tumor/lung ratios were significantly better than those of the dimer at 30-120 min after injection.

Co-injection of E-[c(RGDfK)]2 (30 mg/kg) with 99mTc-HYNIC-E{E[c(RGDfK)]2}2(tricine)(TPPTS) resulted in a significant reduction of radioactivity in the tumor, lung, liver, spleen, and intestine. The radioactivity in the kidney and muscle was also slightly reduced. SPECT imaging in nude mice bearing MDA-MB-435 tumors with 15 MBq (0.41 mCi) of 99mTc-HYNIC-E{E[c(RGDfK)]2}2(tricine)(TPPTS) revealed that the tumors were clearly visualized at 1, 2, and 4 h after injection with low radioactivity levels in the liver and lungs.

Other Non-Primate Mammals

[PubMed]

No publication is currently available.

Non-Human Primates

[PubMed]

No publication is currently available.

Human Studies

[PubMed]

No publication is currently available.

NIH Support

R01 CA115883-01A2

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