Investigations Of Directly Labeling Octreotide With Rhenium-188

Octreotide has numerous functions including inhibition of hormone release, immunomodulation and neurotransmission and is an endogenous inhibitor of cell proliferation and angiogenesis.Objective To establish a useful and stable method for direct labeling of bovine serum albumin (BSA) and octreotide with l88Re.Methods The "pretinning" procedure was adopted to label BSA and octreotide. The labeling conditions were changed. 1. Direct labeling BSA with l88Re. (1) Sodium gluconate or tartrate were selected as chelate agent respectively, (2) The radiochemical purity was determined every an hour from Ih to 6h after labeling, (3) the pH value of acetate buffer from 3.8 to 5.8, (4) the volume of l88Re perrhenate from 50?L to 250 ? L. (5) sodium hydroxide or acetate buffer were chosen to modulate the pH value of reaction solution, (6) the amount of SnCl2 from 100?g to 2500?g, (7) reaction keeping 5h on room temperature or 37? respectively. (8) The percentage of radiocolloid was determined by paper chromatography (PC) with 85% ethanol as a mobile phase. 2. Direct labeling octreotide with l88Re. (1) The procedures (1)⁴ of labeling BSA were repeated, (2) The amount of octreotide and the amount of SnCl2 were changed as well, the amount of SnCl2 from 100?g to 1600?g, the amount of octreotide from 20?g to 150?g, (3) the vitro stability of l88Re-octreotide was analyzed by using human serum as challenging agent, and the radiochemical purity was determined from 1h to 48 hours after labeling.Results 1. Direct labeling BSA with l88Re. (1) The reactioncondition was controlled easier with sodium gluconate as chelate agent than tartrate. (2) When the keeping time of reaction was 5h, the radiochemical purity of 188Re-BSA was (91.6 ? 3.35)%, (3) When the pH value of acetate buffer was 5.0, the radiochemical purity of l88Re-BSA was (95.2 ?.6)%, (4) When the volume of l88Re perrhenate was 100?L, the radiochemical purity of 188Re-BSA was (88.9 + 5.1)%, (5) when theI OO _amount of SnCN was SOOug, the radiochemical purity of Re-BSA was(91.7 + 4.5)%, (6) the results of this study showed there was no difference between sodium hydroxide and acetate buffer in modulating the pH value of reaction solution, and between reaction keeping 5h on room1 flBtemperature and 37癈. 2. Direct labeling octreotide with Re. (1) The reaction condition was controlled easier with sodium gluconate as chelate agent than tartrate. (2) When the keeping time of reaction was 3h, the radiochemical purity of' 88Re-octreotide was (92.6+1.9)%, (3) When the pH value of acetate buffer was 5.0, the radiochemical purity of I88Re-octreotide was (87.7 + 4.4)%, (4) When the volume of 188Reperrhenate was 100?L, the radiochemical purity of Re-octreotide was (87.7 ? 4.4)%, (5) when the amount of octreotide was 100?g and meanwhile the amount of SnCl2 was 800?g, the radiochemical purity of 188Re-octreotide was (92.4?4.0)%, (6) when the keeping time of reaction was 24h, the radiochemical purity was remained (86.6?1.8)%. 188Re-octreotide has shown good vitro stability in human serum for 24h, the radiochemical purity was remained (84.2?2.7)%.Conclusions The optimum conditions of labeling BSA were 0.1 mL sodium gluconate (0.3mol/L), 0.08mL stannous chloride (10mg/mL), 0.04mL acetate buffer (pH 5.0), 0.04mL BSA (10mg/mL), 0.1mL 188Re perrhenate, incubation on room temperation. It was found that the radiochemical purity of l88Re-BSA could reach (96.8?1.06)% and theamount of radiocolloid was less than 10%. The optimum conditions of labeling octreotide were 0.1 mL sodium gluconate (0.3mol/L), 0.04mL stannous chloride (20mg/mL), 0.04mL acetate buffer (pH 5.0), 0.05mL octreotide (2mg/mL), 0.1mL 188Re perrhenate, incubation on room temperation. The radiochemical purity of 188Re-octreotide could reach (92.6?1.9)% and the amount of radiocolloid was less than 8%. This method of directly labeling l88Re to BSA and octreotide with SnCl2 and sodium gluconate is stable and the high radiochemical purity was obtained. This...