Inhibition of angiogenesis by selective estrogen receptor modulators through blockade of cholesterol trafficking rather than estrogen receptor antagonism

Abstract

Selective estrogen receptor modulators (SERM) including tamoxifen are known to inhibit angiogenesis. However, the underlying mechanism, which is independent of their action on the estrogen receptor (ER), has remained largely unknown. In the present study, we found that tamoxifen and other SERM inhibited cholesterol trafficking in endothelial cells, causing a hyper-accumulation of cholesterol in late endosomes/lysosomes. Inhibition of cholesterol trafficking by tamoxifen was accompanied by abnormal subcellular distribution of vascular endothelial growth factor receptor-2 (VEGFR2) and inhibition of the terminal glycosylation of the receptor. Tamoxifen also caused perinuclear positioning of lysosomes, which in turn trapped the mammalian target of rapamycin (mTOR) in perinuclear region in endothelial cells. Abnormal distribution of VEGFR2 and mTOR and inhibition of VEGFR2 and mTOR activities by tamoxifen were significantly reversed by addition of cholesterol-cyclodextrin complex to the culture media of endothelial cells. Moreover, high concentrations of tamoxifen inhibited endothelial and breast cancer cell proliferation in a cholesterol-dependent, but ER-independent, manner. Together, these results unraveled a previously unrecognized mechanism of angiogenesis inhibition by tamoxifen and other SERM, implicating cholesterol trafficking as an attractive therapeutic target for cancer treatment.

Cholesterol Trafficking: An Emerging Therapeutic Target for Angiogenesis and Cancer

“…The cholesterol depletion influences membrane-bound, major angiogenic signaling proteins, such as mTOR and VEGFR2, inhibits angiogenic signaling in endothelial cells, and suppresses angiogenesis (Figure 3). Replenishing the endothelial cells with cholesterol rescued the inhibitory effect of the cholesterol trafficking inhibitors on mTOR, VEGFR2, and angiogenesis [37,49,56,57]. This observation not only validates the essentiality of the membrane’s cholesterol level in angiogenic signaling, but also proposes a hypothesis that cholesterol trafficking inhibitors may be less effective in hypercholesterolemic individuals when used for anticancer applications.…”

“…However, the molecular mechanism that allows SERM to inhibit angiogenesis has not been explained until recently. Our group recently found that SERM, including tamoxifen, toremifene, clomifene, and raloxifene, inhibited cholesterol trafficking in endothelial cells [49]. Treatment of HUVEC with SERM strongly induced the NPC-like phenotype in the cells and blocked VEGFR2 and mTOR signaling.…”

“…Maintaining proper levels of intracellular cholesterol is very important as the level regulates the functions of several key membrane signaling proteins. In endothelial cells, VEGFR2 and mTOR are major signaling proteins that are regulated by cholesterol levels on the cell membrane and lysosomal membrane, respectively [29,37,49,56,57]. Body or intracellular cholesterol levels can be modulated by changing cholesterol biosynthesis, cholesterol absorption from the gastrointestinal tract, cellular cholesterol efflux, and intracellular cholesterol trafficking.…”

Selective inhibition of Ebola entry with selective estrogen receptor modulators by disrupting the endolysosomal calcium

“…Moreover, several studies have showed that some of the CADs (including the SERMs) have some incidental biological activities, i.e., drug-induced phospholipidosis (DIP)1718192021, cholesterol accumulation22, steatohepatitis23242526, and functional inhibition of acid sphingomyelinase (ASM) and acid ceramidase (AC)2728. Much of the incidental biological activities of the CADs are related to their structural properties; several CADs are weak bases which are protonated after entering the low pH of the endolysosome.…”

Identification of CETP as a molecular target for estrogen positive breast cancer cell death by cholesterol depleting agents

“…Altogether a better understanding of cholesterol processes in ER+ BC is being unravelled in light of failed clinical response to selective ER modulators (SERMs) like Tamoxifen and aromatase inhibitors. Recently Shim et al found that endothelial and BC cell proliferation was inhibited in a cholesterol-dependent manner, unrelated to ER inhibition, by high concentrations of Tamoxifen [39]. Notably continued activation of ER signalling despite aromatase therapy or tamoxifen treatment has been attributed to non-aromatized molecules like 27 hydroxycholesterol (27HC) and 25 hydroxycholesterol (25HC).…”