Radionuclide Adsorption by Chlorella and Zn-InsP6

Zn-InsP6 was prepared by the method previously reported with slight modification^{9 (link)}. Zn-InsP6 (Zn : InsP6 = 2 : 1) was used for both in vitro and in vivo experiments. This in vitro adsorption experiment was performed according to our previous study^{8 (link)}. Namely, Chlorella (10, 30, or 100 mg) or Zn-InsP6 (1, 3, 10, or 30 mg) was suspended and ²²³Ra (925 Bq) was added in 1 mL of the first test solution (artificial gastric juice, pH 1.2) or the second test solution (artificial intestinal juice, pH 6.8) defined in the Japanese Pharmacopoeia. After shaking the suspension at 1,000 rpm at 37ºC for 1 h using a shaking incubator (SI-300C; AS ONE Corp., Osaka, Japan), the samples were centrifuged at 10,000 g at room temperature for 10 min. The radioactivity of the supernatant was measured using an auto-well gamma counter (ARC-7010B; Hitachi Ltd., Tokyo, Japan) and the counts were corrected for background radiation. A window from 50 to 300 keV was used for the counting. The measurement time of each sample was set to 1 min. Control experiments were performed using the same procedure but without Chlorella or Zn-InsP6. The binding ratios were determined as follows:
Binding ratio to Chlorella or Zn-InsP6 (%) = [1 − (radioactivity of the supernatant of each sample) / (radioactivity of the supernatant of the respective control)] × 100.