Imaging fibrosarcoma with Tc-99m labeled polymer pretargeted with bombesin-bispecific antibody complex

Objectives Whether murine Fibrosarcoma can be imaged with Tc-99m DTPA-polymers(Tc-DSPL) after pretargeting with Bombesin-anti-DTPA bispecific antibody complex (BABAC) was studied.

Methods 10⁵ MCA205 cells were injected sc in the shoulder of mice. After 14 days 10 μg BABAC (n = 3) or saline (n = 4) were injected iv. Then 37 MBq Tc-DSPL were injected iv 24 h later. Mice were imaged at injection, 10 -15 minutes and 24 hours. Each image was analyzed by computer planimetry for tumor, and contralateral shoulder, region activities. Tumor to contralateral pixel density ratios were correlated to time of imaging.

Results Tumors pretargeted with BABAC can be visualized in 15 min. Mean uptake ratio at 24 hours (6.7+0.84) was significantly greater than that of control mice (2.16+1.45 , p < 0.01). An increase in the uptake ratio of Tc-DSPL in tumors pre-targeted with BABAC (y = 0.86Ln(x) +4.001, R²= 0.98) was observed, whereas control mice injected showed a correlation of y = 0.13Ln(x) +1.68 (R² = 0.593).

Conclusions BABAC can be used to pre-target MCA205 Fibrosarcoma in mice with Tc-DSPL. Although Tc-DSPL localized in Fibrosacroma via “Enhanced Permeability Retention (EPR) ” effect at 24 h, uptake of Tc-DSPL in Fibrosarcoma pretargeted with BABAC was approximately 3 times greater.