BIOCHEMICAL MODIFICATIONS OF AVIDIN IMPROVE PHARMACOKINETICS AND BIODISTRIBUTION, AND REDUCE IMMUNOGENICITY

Pretargeting techniques using the avidin-biotin system have shown enco uraging results in both diagnostic and therapeutic clinical trials. It has been shown that in cancer therapy the ideal agent to be used for pretargeting should have a plasma half-life longer than avidin and low er immunogenicity than streptavidin in order for these procedures to b e applied safely and repeatedly in patients. We prepared a recombinant form of avidin with no carbohydrates and avidins, biochemically modif ied either by decreasing the positive charges with succinic anhydride or by linking polyethylene glycol (PEG) at three different molar ratio s and evaluated their in vivo behaviour after i.p, administration in m ice. The succinylation and PEGylation of avidin increased the plasma h alf-life proportionally to the degree oi protein modification. The pro cedures, however, affected the biotin binding to some extent. The biod istribution studies showed that, for all six time points (ranging from 20 min to 18 h post-injection), the liver and kidney to blood ratios were lower for PEGylated avidins than native, recombinant and succinyl avidin, Recombinant and low PEGylated avidin evoked an immune respons e in all mice after at least three injections. Native, recombinant and succinyl avidins showed higher serum titres than PEGylated avidins. I n conclusion, the conjugation of avidin to PEG chains (n=7) originates a compound with a suitable blood clearance, low immunogenicity and co ncurrent low cross-reactivity with avidin.