In vivo neutralization of colchicine toxicity by a PASylated anticalin in a rat model

We have investigated the pharmacokinetics (PK) and in vivo activity of an Anticalin exhibiting picomolar affinity towards colchicine, a plant toxin with low tolerable dose in humans. PK analysis of the 20-kDa "Colchicalin" protein in male Sprague Dawley rats (n = 3) revealed a very short plasma half-life (3.5 min), which was prolonged 21-fold via genetic fusion with a 200-residue Pro/Ala sequence (PASylation). The scavenging activity of the PASylated Colchicalin was investigated over 3.5 h via stoichiometric application following a sub-toxic i.v. dose of colchicine on anesthetized rats (n = 2) leading to a rapid rise in total plasma colchicine concentration. We then established a 14-day intoxication model in rats (n = 3) at a 30 mg/kg p.o. colchicine dose which was characterized by severe weight loss, elevated neutrophil-to-lymphocyte ratio and shortened survival. PASylated Colchicalin administration at 4.2% of the neutralizing dose (125 mg/kg/day daily for 12 consecutive days) resulted in faster relief of the symptoms in 2/3 of animals (n = 6) compared to the control group without Colchicalin treatment (n = 5). Nevertheless, 1/3 of the rats died suddenly after the first Colchicalin injection, probably due to a steep rise in the total colchicine plasma concentration, which suggests further improvement of the dosing scheme prior to potential application in acute human colchicine poisoning.