Plasma and cerebrospinal fluid pharmacokinetics of nelarabine in nonhuman primates

Introduction Nelarabine is a water-soluble prodrug of the cytotoxic deoxyguanosine analog ara-G, to which it is rapidly converted in vivo by adenosine deaminase. Nelarabine has shown activity in the treatment of T-cell malignancies, especially T-cell acute lymphoblastic leukemia. Preliminary data suggested that nelarabine might penetrate into the CSF. We therefore studied the CSF penetration of nelarabine and ara-G in a nonhuman primate model that has been highly predictive of anticancer drug distribution in humans. Methods Nelarabine (35 mg/kg, similar to 700 mg/m(2)) was administered over 1 h through a surgically implanted central venous catheter to four nonhuman primates. Blood (four animals) and ventricular CSF (three animals) samples were obtained at intervals for 24 h for determination of nelarabine concentrations, which were measured by HPLC-mass spectrometry. Results The nelarabine plasma AUC (median +/- s.d.) was 2,820 +/- 1,140 mu M min and the ara-G plasma AUC was 20,000 +/- 8,100 mu M min. The terminal half-life of nelarabine in plasma was 25 +/- 5.2 min and clearance was 42 +/- 61 ml/min/kg. The terminal half-life of ara-G in plasma was 182 +/- 45 min. In CSF the terminal half-life of nelarabine was 77 +/- 28 min and of ara-G was 232 +/- 79 min. The AUC(csf):AUC(plasma) was 29 +/- 11% for nelarabine and 23 +/- 12% for ara-G. Conclusion The excellent CSF penetration of nelarabine and ara-G supports further study of the contribution of nelarabine to the prevention and treatment of CNS leukemia.