In vitro evaluation of a tetrahydroisoquinoline derivative as a steroid sulfatase inhibitor and a selective estrogen receptor modulator.

Selective estrogen receptor modulators (SERMs) are currently in use in the hormonal therapy of breast cancer. In that respect, a new hormone-related approach is the therapeutical inhibition of steroid sulfatase (STS), which converts inactive, sulfated steroids into active hormones. We investigated the potential of 6-EO-14, a non-steroidal STS inhibitor with SERM potential. The latter compound, which exhibits a sulfamate moiety, releases the phenol derivative 8-EO-14 after the irreversible inhibition of STS. STS was inhibited by 6-EO-14 (IC50 = 0.3 μM), but not 8-EO-14, in HEK-293 cells transfected with an STS expression vector. The SERM potential of 8-EO-14 was assessed in osteoblast-like Saos-2 cells by investigating its effect on cell proliferation and on the activity of alkaline phosphatase (ALP), a specific differentiation marker. Saos-2 cell proliferation was increased by 21 % following 8-EO-14 addition (1 μM), and 8-EO-14 induced ALP activity (31 % increase at 0.1 nM) via estrogen receptor alpha (ERα) similarly to the SERM raloxifene. As compared to estradiol (E2) (100 %), the relative binding affinity of 6-EO-14 and 8-EO-14) for ERα was found to be weak (0.09 and 0.01 %, respectively). When assessed in two estrogen-dependent human breast cancer cell lines (MCF-7 and T-47D), 8-EO-14 did not support MCF-7 cell proliferation, whereas both 8-EO-14 and 6-EO-14 exhibited estrogen-like growth stimulation in T-47D cells. These two compounds were also unable to block E2-induced cell proliferation, suggesting their lack of antiestrogenic activity. Despite the known potency of 6-EO-14 as an STS inhibitor, the observed trophic activity of this new scaffold towards ERα-positive cells needs to be carefully considered prior to its potential utilization as a therapeutic agent.