Preclinical evaluation of the effects of a novel antisense compound targeting C-raf kinase in mice and monkeys

CGP 69846A (ISIS 5132) is an antisense phosphorothioate oligodeoxynucleotid e which targets human C-raf kinase and is currently being developed as an a ntineoplastic agent. The toxicity of this compound was evaluated in mice an d monkeys following repeated iv injections or infusions for 4 weeks at dose s up to 100 mg/kg. Because CGP 69846A is inactive in the mouse, ISIS 11061, the murine-specific homologue targeting C-raf kinase mRNA was evaluated co ncurrently with CGP 69846A to assess the potential toxicity associated with reduced C-raf expression. There were no toxicities that differentiated ISI S 11061 from CGP 69846A in mice. Effects in mice included hepatomegaly and hepatocellular degeneration at the high dose of 100 mg/kg CGP 69846A that p otentially resulted in lethality. Other effects which were observed at 20 a nd 100 mg/kg included mononuclear cell infiltrates in multiple organs, extr amedullary hematopoiesis in the spleen and liver, an increase in bone marro w cellularity, an increase in white blood cells, a decrease in platelet cou nts, and Kupffer cell hyperplasia. These alterations were reversible follow ing a recovery period. No adverse effects in mice were observed with doses less than or equal to 10 mg/kg. In monkeys, administration of 10 mg/kg of C GP 69846A was associated with effects observed with other P=S ODNs, namely, prolongation of activated partial thromboplastin time (APTT) and activatio n of complement. These effects were transient and correlated with plasma co ncentrations of CGP 69846A; Below a concentration of 35 mu g/ml of intact C GP 69846A the prolongation of APTT was less than 50% and levels of compleme nt split products were not increased. All monkeys tolerated complement acti vation with no evidence of treatment-related clinical signs. Complement and coagulation were not affected by the lower doses of 1 and 3 mg/kg. No hist opathology or alteration in hematology or serum chemistry was induced by do ses up to 10 mg/kg in monkeys. The plasma and tissue deposition of CGP 6984 6A were characterized in mice and monkeys and toxicity was dependent on dos e of CGP 69846A. In the present preclinical evaluation of toxicity in mice and monkeys, CGP 69846A is well tolerated at doses targeted for clinical tr ials. Toxicities induced by CGP 69846A in monkeys and mice occurred at dose s of 10 mg/kg and greater. Effects induced by CGP 69846A were not unique an d have been observed previously with other phosphorothioate oligodeoxynucle otides. (C) 1998 Society of Toxicology.