A radioimmunoassay for 1-beta-D-arabinofuranosylcytosine

A rapid and reliable radioimmunoassay method for 1-beta-D-arabinofuranosylcytosine (ara-C) has been developed using antibody induced in rabbits, [3H]ara-C, and a Millipore filtration technique. The sensitivity of this assay was such that ara-C, 0.02 mug/ml, in plasma could be detected, and the assay was practically free from interference by deoxycytidine, cytidine, 1-beta-D-arabinofuranosyluracil, and other nucleosides, as well as from various antibiotics. Blood levels of ara-C in C57BL X DBA/2F1 mice were determined after injection of 1-(3-O-octanoyl-beta-D-arabinofuranosyl) cytosine. Relatively high ara-C levels could be maintained for a fairly long period. Plasmas of mouse, rat, and rabbit contained high esterase activity which hydrolyzed the 3'-octanoyl group in 1-(3-O-octanoyl-beta-D-arabinofuranosyl)cytosine, whereas this activity was relatively low in dog and human plasmas.