Drug repositioning is an efficient strategy to search for new treatment alternatives that is especially valuable for neglected parasitic diseases such as leishmaniasis. Tamoxifen and raloxifene are selective estrogen receptor modulators (SERM) that have shown antileishmanial activity. Clomiphene is a SERM structurally similar to tamoxifen whose antileishmanial potential is unknown. That is why the objective of the present work was to evaluate its antileishmanial activity in vitro and in vivo, in comparison with tamoxifen. The inhibitory effect against promastigotes of L. amazonensis, L. major and L. mexicana was evaluated for both compounds; as well as the cytotoxicity against mouse peritoneal macrophages, the growth inhibitory activity in intracellular amastigotes of L. mexicana, and the in vivo activity in mice experimentally infected with L. mexicana. Clomiphene was about twice as active as tamoxifen against both promastigotes and intracellular amastigotes, with IC50 values of 1.7-3.3 µM for clomiphene and 2.9-6.4 µM for tamoxifen against all three species promastigotes; and 2.8 ± 0.2 µM and 3.7 ± 0.3 µM, respectively, against L. mexicana amastigotes. Clomiphene structurally affected several parasite organelles in a concentration-dependent fashion, leading to the death of both promastigotes and intracellular amastigotes. Interestingly, the macrophage host cell did not appear damaged with any of the clomiphene concentrations tested. By oral administration at 20 mg/kg for 14 days, both compounds showed similar effects in terms of reducing the growth of the lesions, as well as the weight of the lesions and the parasite load at the end of the follow-up period. The results showed the potential of SERM as antileishmanial drugs and support further testing of clomiphene and other compounds of this pharmacological group.

Aberrant estrogen receptor (ER) signaling is a major driver of breast tumor growth and progression. Sigma 2 receptor has long been implicated in breast carcinogenesis based on pharmacological studies, but its molecular identity had been elusive until TMEM97 was identified as the receptor. Herein we report that TMEM97/sigma 2 receptor is highly expressed in ER positive breast tumors and its expression is strongly correlated with ER and progesterone receptor (PR) but not with HER2 status. High expression levels of TMEM97 are associated with reduced overall survival of patients. Breast cancer cells with increased expression of TMEM97 had growth advantage over the control cells under both nutrition limiting and sufficient conditions, while knockdown of TMEM97 expression reduced tumor cell proliferations. When compared to their vector control cells, MCF7 and T47D cells with increased TMEM97 expression presented increased resistance to tamoxifen treatment and also grew better under estrogen depleted conditions. TMEM97/sigma 2 receptor enhanced ERα transcriptional activities and increased the level of transactivated ERα, especially the nuclear soluble and chromatin bounded ERα. Increased TMEM97 also stimulated mTOR/S6K1 signaling pathways in MCF7 and T47D cells. The increased level of active, phosphorylated ERα, and the enhanced resistance to tamoxifen treatment with increased TMEM97 could be blocked by an mTOR inhibitor. Knockdown of TMEM97 expression reduced ERα and mTOR/S6K1 signaling activities, rendering the cells with increased sensitivity to tamoxifen. The observations suggest that TMEM97/sigma 2 receptor is a novel regulator of ERα activities in breast tumor cell growth.

Endoplasmic reticulum (ER) stress perturbs cell homeostasis and induces the unfolded protein response (UPR). In breast cancer, this process is activated by oestrogen deprivation and is associated with tamoxifen resistance. We present evidence that the transcription factor SOX2 and the long noncoding RNA SOX2 overlapping transcript (SOX2OT) are up-regulated in oestrogen receptor-positive (ER+) breast cancer and in response to oestrogen deprivation. We examined the effect of the UPR on SOX2 and SOX2OT expression, and the effect of SOX2OT on UPR pathways in breast cancer cell lines. The induction of the UPR by thapsigargin or glucose deprivation up-regulates SOX2OT expression. This up-regulation is also shown with the anti-oestrogen 4OH-tamoxifen and mTOR inhibitor everolimus in ER + breast cancer cells that are sensitive to oestrogen deprivation or everolimus treatment. SOX2OT overexpression decreased BiP and PERK expression. This effect of SOX2OT overexpression was confirmed on BiP and PERK pathway by q-PCR. Our results show that a long noncoding RNA regulates the UPR and evince a new function of SOX2OT as a participant of ER stress reprogramming of breast cancer cells.