Kidney uptake of 186/188 Re(V)‐DMSA is significantly reduced when the reducing agent is changed from stannous ion to metabisulfite

We describe the work carried out on the preparation of 186/188 Re(V)‐DMSA, which showed lower kidney retention, formulated by using metabisulfite as the reducing agent. The complex was prepared by reducing 186/188 ReO 4 − (100 μg, 0.54 μM, ∼150 MBq) in the presence of Na 2 S 2 O 5 (30 mg, 0.15 mM) and reacting with DMSA (10 mg, 0.05 mM) in saline at pH 3.5 and at 80°C for 1 h. The complex was characterized by TLC using acetone and saline as two different solvent systems. Reverse phase HPLC carried out using isocratic system with 90:10 water/acetonitrile mobile phase showed the existence of four species. Biodistribution studies were carried out in albino mice with 186/188 Re(V)‐DMSA prepared via metabisulfite reductant [ 186/188 Re(V)‐DMSA (MBS)] as well as stannous chloride reductant [ 186/188 Re(V)‐DMSA (SnCl 2 )]. The distribution patterns were similar except for kidney uptake. Kidney retention in case of 186/188 Re(V)‐DMSA (MBS) was lower [0.68 (±0.06)%/g] than that observed in case of 186/188 Re(V)‐DMSA (SnCl 2 ) [2.93(±0.93)%/g] after 24 h p.i. Though bone uptake was initially similar with both the preparations, there was substantial decrease in bone activity after 24 h p.i. with 186/188 Re(V)‐DMSA (MBS). In vitro cell uptake studies were carried out with 186/188 Re(V)‐DMSA (MBS), 186/188 Re(V)‐DMSA (SnCl 2 ) and 99m Tc(V)‐DMSA using Ehrlich Ascites Tumor Cell Lines. Approximately 15% cell uptake was observed with 186/188 Re(V)‐DMSA (MBS) as well as with 186/188 Re(V)‐DMSA (SnCl 2 ) and was comparable with that of 99m Tc(V)‐DMSA (19%). Our studies indicate that 186/188 Re(V)‐DMSA prepared by using metabisulfite as a reducing agent has potential for use in targeted radiotherapy of medullary thyroid carcinoma. Copyright © 2002 John Wiley & Sons, Ltd.