A RAPID AND SIMPLE ASSAY TO DETERMINE THE BLOOD AND URINE CONCENTRATIONS OF 1-(5-[I-123 25]IODO-5-DEOXYARABINOFURANOSYL)-2-NITROIMIDAZOLE, A HYPOXIC CELL MARKER/

Pharmacokinetic and dosimetric parameters of the hypoxic tissue imagin g agent iodoazomycin arabinoside (I-123-IAZA) have been investigated i n human volunteers. In conjunction with this study it was necessary to develop an assay for low levels of the radiolabelled compound in bloo d and urine. A combination of high-performance liquid chromatography ( HPLC) and gamma counting produced a highly selective, sensitive and ra pid assay for the analysis of I-123/125-IAZA in human and animal blood and urine samples. Conventional HPLC assays for the tracer quantities of this radioactive agent in blood have not been reported previously. The addition of non-radiolabelled IAZA to the blood and urine samples containing radiolabelled IAZA allowed the pharmaceutical to serve as its own internal standard. This reverse isotope dilution approach perm itted identification of the appropriate HPLC peak by UV detection, fol lowed by highly sensitive quantification of the radiolabelled species by gamma counting. Blood samples were prepared for HPLC by a solid-pha se extraction without the loss of IAZA from serum, with an extraction efficiency of 99.7 +/- 7.1% from human serum. Urine samples could be a nalyzed directly by HPLC, without the solid-phase extraction step. The detection limit in biological fluids depends on the specific activity of radiolabelled I-123/125-IAZA. I, this study it was possible to det ect serum concentrations of I-I23-IAZA as low as 7.46 pg (21 fmol) per mi. The radiometric detection limit for I-123-IAZA in this assay was 10.8 Bq ml(-1) of serum. (C) 1998 Elsevier Science B.V. All rights res erved.