Previous studies have shown that a styrylpyrone derivative (SPD) from a local tropical plant had antiprogestin and antiestrogenic effects in early pregnant mice models (Azimahtol et al. 1991). Antiprogestins and antiestrogens can be exploited as a therapeutic approach to breast cancer treatment and thus the antitumor activity of SPD was tested in three different human breast cancer cell lines that is: MCF- 7, T47D and MDA-MB-231, employing, the antiproliferative assay of Lin and Hwang (1991) slightly modified. SPD (10(-10) - 10(-6) M) exhibited strong antiproliferative activity in estrogen and progestin-dependent MCF-7 cells (EC50 = 2.24 x 10(-7) M) and in hormone insensitive MDA-MB-231 (EC50 = 5.62 x 10(-7) M), but caused only partial inhibition of the estrogen- insensitive T47D cells (EC50 = 1.58 x 10(-6) M). However, tamoxifen showed strong inhibition of MCF-7 cells (EC50 = 1.41 x 10(-6) M) and to a lesser extent the T47D cells (EC50 = 2.5 x 10(-6) M) but did not affect the MDA-MB-231 cells. SPD at 1 microM exerted a beffer antiestrogenic activity than 1 microM tamoxifen in suppressing the growth of MCF-7 cells stimulated by 1 nM estradiol. Combined treatment of both SPD and tamoxifen at 1 microM showed additional inhibition on the growth of MCF-7 cells in culture. The antiproliferative properties of SPD are effective on both receptor positive and receptor negative mammary cancer cells, and thus appear to be neither dependent on cellular receptor status nor cellular hormone responses. This enhances in vivo approaches as tumors are heterogenous masses with varying receptor status.
Early studies reported that a styrylpyrone derivative (SPD) purified from the Goniothalamus sp. acts as a non-competitive antiestrogen in early pregnant mice (1). In the immature rat uterine wet weight test, we found that SPD markedly reduced uterine weight at doses 1 and 100 mg/kg, thus reflecting negative antiestrogenicity, probably attributed to low binding affinities towards ER. Tamoxifen (Tam) on the other hand exhibited partial antiestrogenicity at all doses (0.01-10 mg/kg BW) and dose-dependent estrogenicity. However, the estrogen antagonism: agonism ratio for SPD is much higher than Tam, which is indicative of the breast cancer antitumor activity as seen in compounds such as MER-25. Pretreatment assessment on 1 mg/kg BW SPD and Tam showed that SPD is not a very good, estrogen antagonist compared to Tam, as it was unable to revert the estrogenicity effect of estradiol benzoate (EB) on immature rat uterine weight. Antitumor activity assessment for SPD exhibited significant tumor growth retardation in 7,12-dimethyl benzanthracene (DMBA) induced rat mammary tumors at all doses employed (2, 10 and 50 mg/kg) compared to the controls (p < 0.01). This compound was found to be more potent than Tam (2 and 10 mg/kg) and displayed greater potency at a dose of 10 mg/kg. It caused complete remission of 33.3% of tumors but failed to prevent onset of new tumors. However, SPD administration at 2 mg/kg caused 16.7% complete remission and partial remission. It also prevented the onset of new tumors throughout the experiment.