99mTc-3PRGD2

The main purpose of the study was to evaluate the activity and selectivity of 99mTc‐3PRGD2 SPECT/CT and 18F‐FDG PET‐CT in order to detect the neovascularization of A549 cell subcutaneously transplanted tumors, and clarify the relationship among tumor vasculature, hypoxia and cell proliferation in the tumor microenvironment.

We established a subcutaneous tumor model, and used 99mTc‐3PRGD2 SPECT/CT and 18F‐FDG PET‐CT when the average tumor size reached 0.3–0.5 cm3. The mice were anesthetized and sacrificed and the tumors were completely removed for frozen section analysis. We subsequently evaluated the status of neovascularization, hypoxia, as well as cell proliferation via immunofluorescence staining (IF) by detecting CD31, pimonidazole and EdU, respectively.

There was a significant positive correlation (r = 0.88, p < 0.05) between the microvascular density (41.20 ± 18.60) and tumor to nontumor ratio (T/M), which was based on the value of 99mTc‐3PRGD2 (4.20 ± 1.33); meanwhile, no significance (r = −0.16, p > 0.05) was found between the T/M and hypoxic area (116.71 ± 9.36). Neovascular proliferation was particularly vigorous in the parenchymal region of the tumor, while the cells around the cavity were generally hypoxic. 99mTC‐3PRGD2 SPECT/CT was more specific than 18F‐FDG PET‐CT in detecting malignant tumors.

Both 99mTC‐3PRGD2 and 18F‐FDG PET‐CT can be used for the detection of malignant tumors, but the specificity and accuracy of 99mTC‐3PRGD2 are better. The subcutaneous tumors showed a heterogeneous microenvironment as a result of neovascularization, a high proliferation rate of cancer cells as well as subsequent hypoxia, while most of the hypoxic areas appeared around the cavities of the vessels.

The present study evaluated interstitial alterations in doxorubicin-induced cardiomyopathy using a radiolabeled RGD peptide 99mTc-3PRGD2 specific for integrin αvβ3 that targets myofibroblasts.Cardiomyopathy was induced in 20 Sprague-Dawley rats by intraperitoneal doxorubicin injections (2.5 mg/kg/week) for up to six weeks. 99mTc-3PRGD2 scintigraphy was performed in control rats (n = 6) at baseline and three, six, and nine weeks after first doxorubicin administration (n = 6, 6, and 5 for each time point). For another three rats of 6-week modeling, cold c(RGDyK) was co-injected with 99mTc-3PRGD2 to evaluate specific radiotracer binding. Semi-quantitative parameters were acquired to compare radiotracer uptake among all groups. The biodistribution of 99mTc-3PRGD2 was evaluated by a γ-counter after scintigraphy. Haematoxylin and eosin, and Masson’s staining were used to evaluate myocardial injury and fibrosis, while western blotting and immunofluorescence co-localization were used to analyze integrin αvβ3 expression in the myocardium.The 99mTc-3PRGD2 half-life in the cardiac region (Heartt 1/2) of the 9-week model and heart radioactivity percentage (%Heart20 min, %Heart40 min and %Heart60 min) of the 6 and 9-week models were significantly increased compared to the control. Heart-to-background ratio (HBR20 min, HBR40 min and HBR60 min) increase began in the third week, continued until the sixth week, and was reversed in the ninth week, which paralleled the changing trend of cardiac integrin αvβ3 expression. The myocardial biodistribution of 99mTc-3PRGD2 was significantly correlated with integrin β3 expression.The 99mTc-3PRGD2 scintigraphy allows for non-invasive visualization of interstitial alterations during doxorubicin-induced cardiomyopathy.