In vivo toxicity and pharmacokinetic features of B43 (anti-CD19)-genistein immunoconjugate in nonhuman primates.

B43 (anti-CD19)-genistein immunoconjugate targets genistein, a naturally occurring protein tyrosine kinase-inhibitory isoflavone to the membrane-associated antiapoptotic CD19-LYN complexes and triggers apoptotic cell death. In this preclinical study, the toxicity profiles of B43-genistein as well as unconjugated genistein were evaluated in cynomolgus monkeys. B43-genistein and genistein were administered either as single bolus injections or daily injections for 5-10 consecutive days via the i.v. route to monkeys. Neither genistein nor B43-genistein was toxic to cynomolgus monkeys, and no test article-related histopathological lesions were found in any of the two genistein-treated or five B43-genistein-treated cynomolgus monkeys. B43-genistein showed a favorable pharmacokinetics in monkeys, with a plasma half-life of 10-23 h. Plasma samples from B43-genistein-treated monkeys elicited potent and CD19 antigenspecific antileukemic activity against human CD19+ leukemia cells in vitro. To our knowledge, this is the first preclinical toxicity and pharmacokinetic study of a tyrosine kinase inhibitor-containing immunoconjugate in nonhuman primates.