Induction of Oxidative Stress and Ferroptosis in Triple-Negative Breast Cancer Cells by Niclosamide via Blockade of the Function and Expression of SLC38A5 and SLC7A11

Abstract

The amino acid transporters SLC38A5 and SLC7A11 are upregulated in triple-negative breast cancer (TNBC). SLC38A5 transports glutamine, methionine, glycine and serine, and therefore activates mTOR signaling and induces epigenetic modifications. SLC7A11 transports cystine and increases the cellular levels of glutathione, which protects against oxidative stress and lipid peroxidation via glutathione peroxidase, a seleno (Se)-enzyme. The primary source of Se is dietary Se-methionine (Se-Met). Since SLC38A5 transports methionine, we examined its role in Se-Met uptake in TNBC cells. We found that SLC38A5 interacts with methionine and Se-Met with comparable affinity. We also examined the influence of Se-Met on Nrf2 in TNBC cells. Se-Met activated Nrf2 and induced the expression of Nrf2-target genes, including SLC7A11. Our previous work discovered niclosamide, an antiparasitic drug, as a potent inhibitor of SLC38A5. Here, we found SLC7A11 to be inhibited by niclosamide with an IC50 value in the range of 0.1–0.2 μM. In addition to the direct inhibition of SLC38A5 and SLC7A11, the pretreatment of TNBC cells with niclosamide reduced the expression of both transporters. Niclosamide decreased the glutathione levels, inhibited proliferation, suppressed GPX4 expression, increased lipid peroxidation, and induced ferroptosis in TNBC cells. It also significantly reduced the growth of the TNBC cell line MB231 in mouse xenografts.

Impact of Oncogenic Changes in p53 and KRAS on Macropinocytosis and Ferroptosis in Colon Cancer Cells and Anticancer Efficacy of Niclosamide with Differential Effects on These Two Processes

“…It is also important to point out here that the potency of niclosamide as an inhibitor of SLC7A11 (IC 50 , <0.25 µM) is greater than most of the inhibitors, including erastin, reported thus far in the literature [78]. We found a similar IC 50 value in triple-negative breast cancer cells [32]. Even though derivatives of erastin have been developed recently with a much greater potency to inhibit SLC7A11 (IC 50 values in the low-nanomolar range) [79], niclosamide may have an advantage in terms of therapeutic use for cancer therapy because of its feature as an already FDA-approved drug that has been in use in humans for several decades.…”

“…Based on our previous studies with breast cancer cells [ 31 , 32 ], the ability of niclosamide to induce intracellular acidification and inhibit SLC38A5 is expected to suppress macropinocytosis. We tested this by monitoring macropinocytosis-mediated cellular entry of TMR-dextran in all four colon cancer cell lines with a 30-min preincubation with and without niclosamide (5 μM).…”

“…Recently, we published reports on macropinocytosis and ferroptosis in the triple-negative breast cancer cell lines MB231 and TXBR-100 and on the effects of the anti-helminthic drug niclosamide on these two processes [ 31 , 32 , 45 ]. In these cell lines, niclosamide caused intracellular acidification and had opposing effects on macropinocytosis (suppression) and ferroptosis (induction).…”

“…The diffusional component was calculated by measuring the uptake of [ 3 H]-glutamate in the presence of excess unlabeled glutamate (5 mM). The transport activity of SLC7A11 was determined by subtracting the diffusional component from total uptake [ 32 ].…”

Oxidative Stress in Breast Cancer: A Biochemical Map of Reactive Oxygen Species Production

“…Recently, it was shown that SLC38A5 could transport selenomethionine (Se-Met), the most common dietary source of selenium. Since the selenoenzyme GPX4 is a critical component of the antioxidant machinery in TNBC cells, the possible involvement of SLC38A5 in the delivery of selenium to cancer cells in the form of Se-Met may represent a novel function of the transporter in promoting cancer growth [109]. Fan et al showed that Se-Met is an activator of Nrf2, an important transcription factor associated with the antioxidant mechanism [110].…”