Page 131 - Cellular Imaging in Regenerative Medicine, Cancer and Osteoarthritis

Albutate-1, a novel long-circulating radiotracer
2. Results
2.1. Stability study
After radiolabeling [111In]In-Albutate-1 is stable up to 3 days (day 1 93.1% - day 3 88.9%) in the labeling buffer. Stability of [111In]In-Albutate-1 was found very stable in mouse serum (between 90-94% within 24h).
2.2. Binding affinity of Albutate-1
[111In]In-DOTA-TATE was displaced from somatostatin binding sites in H69 tumor sections by Albutate-1 in a monophasic, dose-dependent manner. The IC50 value calculated for Albutate-1 was 1.2 nM (95% CI: 0,21nM to 6.99nM) (Figure 2).
Figure 2 Displacement curve of [111In]In-DOTA-TATE from somatostatin binding sites on H69 tumor sections by increasing concentrations of Albutate-1.
2.3. Cell-uptake and internalization of [111In]In-Albutate-1 and [111In] In-DOTA-TATE
The internalization rate of [111In]In-Albutate-1 was assessed in comparison to that of [111In]In-DOTA-TATE (Figure 3). The total uptake was respectively 15.97 ± 0.58% AA and 12.81 ± 1.1% AA (p<0.05). We also distinguished between the internalized (intracellular fraction) and the membrane-bound fraction (membrane fraction). Most radioactivity was found to be internalized: 88.25 ± 0.87% for [111In]In-DOTA-TATE and 88.3 ± 0.99% for [111In]In-Albutate-1 (p=0.97). Both Albutate-1 and DOTA-TATE could be blocked by co-incubation with an excess of unlabeled peptide.
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