Biochemical modification of streptavidin and avidin: in vitro and in vivo analysis

Abstract

The high affinity streptavidin (or avidin)/biotin system is being investigated for imaging and radiotherapy procedures. Streptavidin (SA) and avidin exhibit markedly different pharmacokinetics, with avidin clearing from the blood much faster than SA. To optimize blood clearance kinetics, SA and avidin were biochemically modified and analyzed in vitro and in vivo.

Methods: Galactose moieties were covalently attached to promote binding by hepatocyte galactose receptors and hasten SA clearance. To prolong avidin clearance, avidin was deglycosylated and/or neutralized by acetylation of its lysine amino acids. In vitro, the modified proteins were analyzed by isoelectric focusing, SDS polyacrylamide electrophoresis and a biotin binding saturation assay. The modified and native proteins were radiolabeled with 131I and injected into rabbits for pharmacokinetic, redistribution and imaging analysis.

Results: For SA, the resulting increase in blood clearance and liver accumulation was correlated to the amount of galactose bound to SA. For avidin, each type of modification increased its circulation time, with the slowest clearance resulting from a combination of deglycosylation and neutralization.

Conclusion: Biochemical modification of SA and avidin resulted in altered pharmacokinetics compared to the native proteins. Modified SA or avidin, when cross-linked with a lesion-specific targeting agent, may be applicable for rapid two-step in vivo imaging techniques.