Radioimmunoassay for hydroxyphosphinyl-3-hydroxybutanoic acid (SQ 33,600), a hypocholesterolemia agent

A specific and sensitive radioimmunoassay (RIA) for the measurement of SQ 33,600 in biological fluids has been developed. The assay utilizes a SQ 33,600 polyclonal antibody, [125I]iodohistamine-SQ 33,600 radiolabel, and standards in serum. Satisfactory zero binding and sensitivity were obtained after an overnight incubation at 4 degrees C. Separation of the antibody-bound and free radiolabel was achieved by employing polyethylene glycol-goat anti-rabbit gamma-globulin (PEG-GARG) separant. A quantitative recovery in serum and urine of the exogenous analyte was obtained at all concentrations of SQ 33,600 tested. Intra-assay coefficients of variation (CVs) were 6.19 and 5.57% for the low and high controls, respectively. Interassay CVs were 6.64 and 6.06% for the low and medium controls, respectively. Results from the parallelism studies were acceptable for both serum and urine samples. Comparison of results from samples which were assayed by RIA and high-performance liquid chromatography (HPLC) demonstrated a significant correlation (r = 0.994; HPLC = 1.09 RIA + 57.98; n = 45). The present RIA has been successfully used to assay clinical specimens from pharmacokinetic studies.