Figure 1.
Radioiodination does not affect binding of PGN635 F(ab’)2 to PS.
A) Competition ELISA shows 125I- PGN635 F(ab’)2 and unlabeled PGN635 F(ab’)2 have similar ability to compete with PGN635-biotin for binding to immobilized PS. B) Binding of 124I-PGN635 F(ab’)2 to PS-expressing cells. PS-exposure on ABAE and PC3-luc cells was induced by irradiation with 5 Gy 24 h before the binding assay. Non-irradiated cells served as controls. The cells were incubated with 124I-PGN635 F(ab’)2 or 124I-control F(ab’)2 for 1 h. The cells were then washed and dissolved in NaOH (1N) and 124I was quantified by gamma counting (CPM = counts/min.). Points and histograms, means; bars, + S.D.
Figure 2.
125I-PGN635 F(ab’)2 biodistribution.
Mice (n =3) bearing s.c. PC3-luc tumors were injected with 1.85 MBq (50 µg) of 125I-PGN635 F(ab’)2 or 125I-control F(ab’)2. Antibody distribution to the indicated organs was determined after 48 h by counting the radioactivity with a gamma counter. A) Biodistribution by percent injected dose per gram (%ID/g) of tissue. B) Biodistribution by percent injected dose per organ (%ID/organ). The % ID in the blood was calculated assuming a blood volume of 2.18ml/25 g body weight.
Figure 3.
PET imaging of subcutaneous PC3 tumors with 124I-PGN635 F(ab’)2.
Mice bearing s.c. PC3-luc tumors were injected with 124I-PGN635 F(ab’)2 or 124I-control F(ab’)2. The animals were imaged by PET/CT 48 h later. Reconstructed PET and CT images were fused and analyzed. The images clearly show preferential labeling of the tumor by PET (arrow). Signal from the heart is due to 124I-PGN635 F(ab’)2 in the blood. 124I-control F(ab’)2 did not label tumors and was rapidly cleared from the circulation. Representative mice from groups of 4 mice are shown.
Figure 4.
PET imaging of orthotopic PC3-luc tumors with 124I-PGN635 F(ab’)2.
Mice bearing orthotopic PC3-luc tumors were injected with 124I-PGN635 F(ab’)2 or 124I-control F(ab’)2. PET and BLI imaging were performed 48 h later. The PET images clearly show preferential labeling of the orthotopic prostate tumor. The PET images of the tumors were coincident with the BLI images. 124I-control F(ab’)2 did not label the tumors. Representative mice from groups of 4 mice are shown.
Figure 5.
124I-PGN635 F(ab’)2 localization predicts tumor response to therapy.
A) Mice bearing PC3-luc tumors were treated with 10 mg/kg docetaxel (CTx) or their tumors were irradiated with 15 Gy (RTx). After 24 h, the mice were injected with 124I-PGN635 F(ab’)2 and imaged by PET 48 h later. B) CTx and RTx significantly inhibited tumor growth (one-way ANOVA, P < 0.01). C) 124I-PGN635 F(ab’)2 uptake was significantly higher in treated tumors (one-way ANOVA, P < 0.05). D) The tumor-to-normal (T/N) ratio inversely correlated with the tumor growth over the next 28 days (Pearson’s r = -0.85, P < 0.01). The tumor volume on day 28 was divided by the volume on the day of treatment to calculate the fold change in tumor volume. The T/N ratio at the time of imaging was predictive of the tumor response.