A I-125 RADIOIMMUNOASSAY FOR DIETHYLSTILBESTROL IN SERUM OF PATIENTS WITH PROSTATIC-CANCER TREATED WITH STILPHOSTROL

A new radioimmunoassay for determining diethylstilbestrol in serum usi ng dophenethyl)-6-(4-O-diethylstilbestryl)-hexanamide as a radiotracer and a double antibody as a separation reagent is described. The radio tracer is prepared by synthesizing 6-(4-0-diethylstilbestryl)-hexanoic acid and coupling its succinimidyl ester with mono-[I-125]tyramine in tetrahydrofuran (16 h, 20-22-degrees-C). The standard curve is linear (semi-log transformation) and the assay is sensitive (< 0.022 pmol/tu be), reproducible (intra- and interassay coefficient of variation valu es, 5.3 and 8.1%, respectively), and accurate (recovery values, 95-101 %), with a non-specific binding less than 3.2%. Diethylstilbestrol con centrations measured in sera of nine patients with prostatic cancer by the proposed assay ranged from 0.170 to 2.517 mumol/l, which correspo nded to an only three-fold dosage variation. In all cases tested, dosi ng was adequate to retain markers of prostatic cancer in serum within accepted limits; nevertheless, individualization of dosing may be nece ssary to minimize toxicity.