Monitoring glioma growth and tumor necrosis with the U-SPECT-II/CT scanner by targeting integrin αvβ3.

The purpose of this study was to validate 99m Tc-3P-RGD2 single-photon emission computed tomography/computed tomography (SPECT/CT) as an imaging tool to monitor avb3 expression and tumor necrosis. The animal model was established by subcutaneous injection of 5 3 10 6 U87MG cells into the shoulder flank of each mouse. Imaging was performed using the U-SPECT-II/CT scanner (Milabs, Utrecht, the Netherlands). Tumor volumes were determined, and the tumor uptake of 99m Tc-3P-RGD2 was calculated on the basis of SPECT/CT and compared to that from biodistribution. Immunohistochemistry was performed to determine CD31 and avb3 expression levels. We found that the tumor detection limit was < 0.5 mm 3 by 99m Tc-3P-RGD2 SPECT/CT. The tumor uptake of 99m Tc3P-RGD2 from SPECT/CT was almost identical to that from biodistribution. The avb3 was expressed mainly on blood vessels for the tumors of 0.2 to 0.5 cm 3 . In larger tumors, tumor avb3 expression increased due to more contribution from glioma cells. When tumors were . 0.5 cm 3 , the %ID/cm 3 uptake of 99m Tc-3P-RGD2 decreased because of necrosis. The overall relationship between the tumor size and %ID of 99m Tc-3P-RGD2 was modeled as a quadratic polynomial fitting curve, with R 2 being . .95. 99m Tc-3P-RGD2 SPECT/CT is excellent for monitoring avb3 expression and tumor necrosis during tumor growth and may become a screening tool for patient selection before anti-avb3 therapy.