A bioassay for antiestrogenic activity — potential utility in drug development and monitoring effectivein vivo dosing

Abstract

Monitoring effective antiestrogenic activity of the triphenylethylenes in patients with breast cancer is usually determined by the duration of response. The pharmacokinetics of toremifene and tamoxifen have been shown to be highly variable but patient specific. In the present study, we developed a method to accurately assess the antiestrogenic activity of these agents using plasma specimens, cell culture, and cell cycle measurements. Plasma specimens (4-5mls) obtained from patients receiving toremifene (360mg/day for 5 days in a phase I trial) or tamoxifen (20mg/day) were extracted and reconstituted in tissue culture media (4-5mls), and growth inhibition was determined in estrogen responsive MCF-7 cells. Additionally, plasma specimens were quantified for toremifene or tamoxifen concentrations using HPLC. Growth inhibition of plasma specimens containing either toremifene or tamoxifen and their metabolites was also examined. Cell cycle measurements were determined following in vitro exposure with flow cytometric techniques. Our results show that a dose-response relationship exists between cell growth inhibition and cell cycle measurements for human plasma with added toremifene or tamoxifen, and also for human plasma specimens containing drug and its metabolites after treatment. Our antiestrogenic bioassay can address clinical research problems such as patient-specific pharmacokinetics, dosing compliance, and acquired antiestrogen resistance.

A recombinant cell bioassay for measurement of overall estrogenic activity of serum: preliminary results in women with breast cancer

“…DeGregorio et al proposed a bioassay for breast cancer patients receiving either tamoxifen or toremifen (4). DeGregorio et al proposed a bioassay for breast cancer patients receiving either tamoxifen or toremifen (4).…”

“…First of all, very little serum is needed (20 ml) and, unlike most of the previously described bioassays (4,8), no serum extraction is required. Using the MELN system is very easy and convenient.…”

“…They use direct binding to the ER, proliferation of MCF-7, or reporter gene expression in yeast or human tumor cells (1,(3)(4)(5)(6). They use direct binding to the ER, proliferation of MCF-7, or reporter gene expression in yeast or human tumor cells (1,(3)(4)(5)(6).…”