A sensitive and specific radioimmunoassay for 1-beta-D-arabino-furanosylcytosine.

In order to determine the blood level of 1-beta-D-arabinofuranosylcytosine (Ara-C), an antileukemic agent, a sensitive and specific radioimmunoassay (RIA) system using anti-Ara-C serum, [5-3H] Ara-C and a dextran-coated charcoal method has been developed. The anti-Ara-C serum obtained from a guinea pig was hardly cross-reactive with 1-beta-D-arabinofuranosyluracil (Ara-U), tetrahydrouridine (THU) and other Ara-C analogues. The RIA system for Ara-C could detect concentrations as low as 60 pg/ml in plasma. Average of the intra- and inter-assay variancies at 5, 10, 20 ng/ml were 4.3% and 5.6%, respectively. Ara-C in blood samples obtained from human patients who orally received N4-palmitoyl-1-beta-D-arabinofuranosyl-cytosine (PL-AC) was determined by the present RIA system.