Specific tumor α vβ 3 integrin binding of glucosamino-Tc-99m-RGD with favorable imaging properties

As α vβ 3 integrin is involved in tumor angiogenesis and metastasis. Monitoring of their expression with radiolabeled RGD imaging is being pursued. Since glycosylated RGD peptides have in vivo biokinetics more favorable for imaging, we synthesized a 99mTc labeled RGD compound containing a glucosamino group and investigated its in vitro and in vivo biologic characteristics. Glucosamino-[99mTc]-DKRGDf was synthesized and cell binding assays were performed using HUVECs by 1 hr incubation with varying concentration of cold cRGDyV. Biodistribution studies were done using Lewis Lung Carcinoma (LLC) tumor bearing C57BL6 mice. Specificity of α vβ 3 integrin binding was verified by preinjection in mice with 12 mg/kg of cold cRGDyV. Scintigraphic imagings were performed in LLC tumor bearing mice and RR1022 fibrosarcoma bearing nude mice. For the latter model, blocking experiments were done by preinjection of 9 mg/kg cRGDyV. Glucosamino-[99mTc]-DKRGDf binding to HUVECs were inhibited by cold cRGDyV in a dose dependent manner (IC50 = 306 nM). LLC tumor accumulation of glucosamino-[99mTc]-DKRGDf at 1 and 17 hr p.i. was 1.18 ± 0.26 %ID/g and 0.64 ± 0.26 %ID/g, respectively. At 17 hr the tumor/muscle ratio was 7.35 ± 2.24 %ID/g. At 4 hr, inhibition with 12 mg/kg cold cRGDyV resulted in a significant decrease of LLC tumor uptake from 0.92 ± 0.25 %ID/g to 0.27 ± 0.12 %ID/g, indicating specific tumor binding. Scintigraphy at 4 and 17 hr demonstrated clear visualization of both LLC and RR1022 tumors with high contrast and low biliary or intestinal activity. Blocking with cold cRGDyV significantly reduced accumulation in the RR1022 tumors. Thus, glucosamino-[99mTc]-DKRGDf allows α vβ 3 integrin specific tumor scintigraphy with favorable imaging properties, which makes it a promising radioprobe for noninvasive angiogenesis monitoring