Caffeine mitigates tamoxifen-induced fatty liver in Wistar rats.

PURPOSE: Tamoxifen, a widely used drug for breast cancer treatment, is associated with adverse effects on the liver, including the development of fatty liver. This study aimed to investigate the potential protective effect of caffeine against tamoxifen-induced fatty liver in Wistar rats. METHODS: Rats were divided into normal control, tamoxifen + saline, and tamoxifen + caffeine. Plasma samples were assessed for biochemical markers related to oxidative stress, inflammation, liver function, and cell damage. Additionally, liver histopathology was examined to quantify the extent of fatty infiltration. RESULTS: In the tamoxifen + saline group, elevated levels of plasma malondialdehyde (MDA), tumor necrosis factor-alpha (TNF-α), alanine aminotransferase (ALT), cytokeratin 18, and soluble ST2 were observed compared to the normal control group, indicating increased oxidative stress, inflammation, and liver injury (p < 0.01). Moreover, histopathological examination revealed a significant increase in fatty infiltration (p < 0.001). However, in the tamoxifen + caffeine group, these markers were markedly reduced (p < 0.05, p < 0.01), and fatty infiltration was significantly mitigated (p < 0.001). CONCLUSIONS: The findings suggest that caffeine administration attenuates tamoxifen-induced fatty liver in rats by ameliorating oxidative stress, inflammation, liver injury, and cell damage. Histopathological evidence further supports the protective role of caffeine. This study highlights the potential of caffeine as a therapeutic intervention to counter tamoxifen-induced hepatic complications, contributing to the optimization of breast cancer treatment strategies.

Cystathionine-γ-lyase contributes to tamoxifen resistance, and the compound I194496 alleviates this effect by inhibiting the PPARγ/ACSL1/STAT3 signalling pathway in oestrogen receptor-positive breast cancer.

Tamoxifen (TAM) resistance is a major challenge in treating oestrogen receptor-positive (ER+) breast cancers. It is possible that the H2S synthase cystathionine-γ-lyase (CSE), which has been previously shown to promote tumour growth and metastasis in other cancer cells, is involved in this resistance. Therefore, we investigated CSE's role and potential mechanisms in TAM-resistant breast cancer cells. First, we examined the effect of CSE expression on TAM sensitivity and resistance in MCF7 (breast cancer) cells. The findings revealed that CSE was directly associated with TAM sensitivity and involved in TAM resistance in ER+ breast cancer cells, indicating that it may be useful as a biomarker. Next, we wanted to determine the molecular mechanism of CSE's role in TAM resistance. Using cell migration, co-immunoprecipitation, western blotting, and cell viability assays, we determined that the CSE/H2S system can affect the expression of PPARγ by promoting the sulfhydrylation of PPARγ, which regulates the transcriptional activity of ACSL1. ACSL1, in turn, influences STAT3 activation by affecting the phosphorylation, palmitoylation and dimerization of STAT3, ultimately leading to the development of TAM resistance in breast cancer. Finally, we examined the effect of CSE inhibitors on reducing drug resistance to determine whether CSE may be used as a biomarker of TAM resistance. We observed that the novel CSE inhibitor I194496 can reverse TAM resistance in TAM-resistant breast cancer via targeting the PPARγ/ACSL1/STAT3 signalling pathway. Overall, our data indicate that CSE may serve as a biomarker of TAM resistance and that the CSE inhibitor I194496 is a promising candidate for combating TAM resistance.

Increasing adult-born neurons protects mice from epilepsy.

Neurogenesis occurs in the adult brain in the hippocampal dentate gyrus, an area that contains neurons which are vulnerable to insults and injury, such as severe seizures. Previous studies showed that increasing adult neurogenesis reduced neuronal damage after these seizures. Because the damage typically is followed by chronic life-long seizures (epilepsy), we asked if increasing adult-born neurons would prevent epilepsy. Adult-born neurons were selectively increased by deleting the pro-apoptotic gene Bax from Nestin-expressing progenitors. Tamoxifen was administered at 6 weeks of age to conditionally delete Bax in Nestin-CreERT2Baxfl/fl mice. Six weeks after tamoxifen administration, severe seizures (status epilepticus; SE) were induced by injection of the convulsant pilocarpine. After mice developed epilepsy, seizure frequency was quantified for 3 weeks. Mice with increased adult-born neurons exhibited fewer chronic seizures. Postictal depression was reduced also. These results were primarily in female mice, possibly because they were more affected by Bax deletion than males, consistent with sex differences in Bax. The female mice with enhanced adult-born neurons also showed less neuronal loss of hilar mossy cells and hilar somatostatin-expressing neurons than wild-type females or males, which is notable because loss of these two hilar cell types is implicated in epileptogenesis. The results suggest that selective Bax deletion to increase adult-born neurons can reduce experimental epilepsy, and the effect shows a striking sex difference. The results are surprising in light of past studies showing that suppressing adult-born neurons can also reduce chronic seizures.

Polyoxometalate inhibition of SOX2-mediated tamoxifen resistance in breast cancer.

BACKGROUND: Increased cancer stem cell (CSC) content and SOX2 overexpression are common features in the development of resistance to therapy in hormone-dependent breast cancer, which remains an important clinical challenge. SOX2 has potential as biomarker of resistance to treatment and as therapeutic target, but targeting transcription factors is also challenging. Here, we examine the potential inhibitory effect of different polyoxometalate (POM) derivatives on SOX2 transcription factor in tamoxifen-resistant breast cancer cells. METHODS: Various POM derivatives were synthesised and characterised by infrared spectra, powder X-ray diffraction pattern and nuclear magnetic resonance spectroscopy. Estrogen receptor (ER) positive breast cancer cells, and their counterparts, which have developed resistance to the hormone therapy tamoxifen, were treated with POMs and their consequences assessed by gel retardation and chromatin immunoprecipitation to determine SOX2 binding to DNA. Effects on proliferation, migration, invasion and tumorigenicity were monitored and quantified using microscopy, clone formation, transwell, wound healing assays, flow cytometry and in vivo chick chorioallantoic membrane (CAM) models. Generation of lentiviral stable gene silencing and gene knock-out using CRISPR-Cas9 genome editing were applied to validate the inhibitory effects of the selected POM. Cancer stem cell subpopulations were quantified by mammosphere formation assays, ALDEFLUOR activity and CD44/CD24 stainings. Flow cytometry and western blotting were used to measure reactive oxygen species (ROS) and apoptosis. RESULTS: POMs blocked in vitro binding activity of endogenous SOX2. [P2W18O62]6- (PW) Wells-Dawson-type anion was the most effective at inhibiting proliferation in various cell line models of tamoxifen resistance. 10 µM PW also reduced cancer cell migration and invasion, as well as SNAI2 expression levels. Treatment of tamoxifen-resistant cells with PW impaired tumour formation by reducing CSC content, in a SOX2-dependent manner, which led to stem cell depletion in vivo. Mechanistically, PW induced formation of reactive oxygen species (ROS) and inhibited Bcl-2, leading to the death of tamoxifen-resistant cells. PW-treated tamoxifen-resistant cells showed restored sensitivity to tamoxifen. CONCLUSIONS: Together, these observations highlight the potential use of PW as a SOX2 inhibitor and the therapeutic relevance of targeting SOX2 to treat tamoxifen-resistant breast cancer.

Synergistic effect of curcumin and tamoxifen loaded in pH-responsive gemini surfactant nanoparticles on breast cancer cells.

BACKGROUND: Drug combination therapy is preferred over monotherapy in clinical research to improve therapeutic effects. Developing a new nanodelivery system for cancer drugs can reduce side effects and provide several advantages, including matched pharmacokinetics and potential synergistic activity. This study aimed to examine and determine the efficiency of the gemini surfactants (GSs) as a pH-sensitive polymeric carrier and cell-penetrating agent in cancer cells to achieve dual drug delivery and synergistic effects of curcumin (Cur) combined with tamoxifen citrate (TMX) in the treatment of MCF-7 and MDA-MB-231 human BC cell lines. METHODS: The synthesized NPs were self-assembled using a modified nanoprecipitation method. The functional groups and crystalline form of the nanoformulation were examined by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and dynamic light scattering (DLS) used to assess zeta potential and particle size, and the morphological analysis determined by transmission electron microscopy (TEM). The anticancer effect was evaluated through an in vitro cytotoxicity MTT assay, flow cytometry analysis, and apoptosis analysis performed for mechanism investigation. RESULTS: The tailored NPs were developed with a size of 252.3 ± 24.6 nm and zeta potential of 18.2 ± 4.4 mV capable of crossing the membrane of cancer cells. The drug loading and release efficacy assessment showed that the loading of TMX and Cur were 93.84% ± 1.95% and 90.18% ± 0.56%, respectively. In addition, the drug release was more controlled and slower than the free state. Polymeric nanocarriers improved controlled drug release 72.19 ± 2.72% of Tmx and 55.50 ± 2.86% of Cur were released from the Tmx-Cur-Gs NPs after 72 h at pH = 5.5. This confirms the positive effect of polymeric nanocarriers on the controlled drug release mechanism. moreover, the toxicity test showed that combination-drug delivery was much more greater than single-drug delivery in MCF-7 and MDA-MB-231 cell lines. Cellular imaging showed excellent internalization of TMX-Cur-GS NPs in both MCF-7 and MDA-MB-231 cells and synergistic anticancer effects, with combination indices of 0.561 and 0.353, respectively. CONCLUSION: The combined drug delivery system had a greater toxic effect on cell lines than single-drug delivery. The synergistic effect of TMX and Cur with decreasing inhibitory concentrations could be a more promising system for BC-targeted therapy using GS NPs.

Synergistic anticancer effects and reduced genotoxicity of silver nanoparticles and tamoxifen in breast cancer cells.

Nanotechnology is emerging as a promising tool to enhance traditional cancer treatments due to rising chemotherapy resistance and the severe side effects of toxic drugs. Silver nanoparticles (AgNPs) are widely acknowledged for their antimicrobial and antiproliferative properties. Given these AgNP characteristics, this research conducts a comprehensive nanotoxicological assessment of strategic combinations involving AgNPs (68 nm) commercial formulation and tamoxifen on MCF-7 and MDA-MB-231 breast tumor cells. Utilizing CompuSyn software, the combination index was determined, revealing a synergistic cytotoxic and antiproliferative effect in AgNPs and tamoxifen combinations (CI < 0.97). Furthermore, this combination impaired cell migration (the scratch zone expanded by over 270%) and significantly increased reactive oxygen species production (up to 96% for MDA-MB-231 and 52% for MCF-7 cells). Surprisingly, the genotoxic effect of these mixtures was minimal (below the allowable genotoxicity index of 1.5). Additionally, both breast tumor cell lines exhibited increased proapoptotic and oxidative stress gene expression following the combined treatment. The internalization of AgNPs into breast cancer cells was observed, enhancing their synergistic antiproliferative effect when combined with tamoxifen. These findings suggest the potential of combining AgNPs with chemotherapeutic agents for innovative studies in oncology therapy.

Low ozone concentrations do not exert cytoprotective effects on tamoxifen-treated breast cancer cells in vitro.

Medical treatment with low ozone concentrations proved to exert therapeutic effects in various diseases by inducing a cytoprotective antioxidant response through the nuclear factor erythroid derived-like 2 (Nrf2) transcription factor pathway. Low ozone doses are increasingly administered to oncological patients as a complementary treatment to mitigate some adverse side-effects of antitumor treatments. However, a widespread concern exists about the possibility that the cytoprotective effect of Nrf2 activation may confer drug resistance to cancer cells or at least reduce the efficacy of antitumor agents. In this study, the effect of low ozone concentrations on tamoxifen-treated MCF7 human breast cancer cells has been investigated in vitro by histochemical and molecular techniques. Results demonstrated that cell viability, proliferation and migration were generally similar in tamoxifen-treated cells as in cells concomitantly treated with tamoxifen and ozone. Notably, low ozone concentrations were unable to overstimulate the antioxidant response through the Nfr2 pathway, thus excluding a possible ozone-driven cytoprotective effect that would lead to increased tumor cell survival during the antineoplastic treatment. These findings, though obtained in an in vitro model, support the hypothesis that low ozone concentrations do not interfere with the tamoxifen-induced effects on breast cancer cells.

Comment on "2-methoxyestradiol sensitizes tamoxifen-resistant MCF-7 breast cancer cells via downregulating HIF-1α".

This study investigates the potential of 2-methoxyestradiol (2-ME) to overcome tamoxifen (TAM) resistance in MCF-7 breast cancer cells by downregulating hypoxia-inducible factor 1 alpha (HIF-1α). Through a series of in vitro experiments, the authors demonstrate that combining 2-ME with TAM enhances the cytotoxic effects on resistant cells, increases apoptosis markers, and reduces cholesterol and triglyceride levels. While the findings highlight a promising therapeutic approach, the lack of in vivo or clinical data limits direct clinical application. Future research should focus on validating these results in animal models and exploring long-term efficacy and molecular mechanisms.

Mechanical Disruption by Focused Ultrasound Re-sensitizes ER+ Breast Cancer Cells to Hormone Therapy.

OBJECTIVE: Tamoxifen is the most used agent to treat estrogen receptor-positive (ER+) breast cancer (BC). While it decreases the risk of cancer recurrence by 50%, many patients develop resistance to this treatment, culminating in highly aggressive disease. Tamoxifen resistance comes from the repression of ER transcriptional activity that switches the cancer cells to proliferation via nonhormonal signaling pathways. Here, we evaluate a potential strategy to overcome tamoxifen resistance by focused ultrasound (FUS), a noninvasive approach for the mechanical excitation of cancer cells. METHODS: Resistant and nonresistant ER+ BC cells and xenografts from patients with ER+ BC were treated with tamoxifen, FUS or their combination. The apoptosis, proliferation rate, gene expression and activity of estrogen receptor, and morphological changes were measured in treated cells and tissues. RESULTS: FUS caused the mechanical disruption of tamoxifen-resistant BC cells that in turn led to the upregulation of ERα-encoding gene expression and long-term re-sensitization of the cells to tamoxifen. Patient-derived xenografts treated with Tamoxifen and FUS demonstrated a significant reduction in tumor viability and proliferation and a strong structural damage to tumor cells and extracellular matrix. CONCLUSION: FUS can improve ER+ BC treatment by re-sensitizing the cancer cells to tamoxifen.

Dehydroepiandrosterone-α-2-Deoxyglucoside Exhibits Enhanced Anticancer Effects in MCF-7 Breast Cancer Cells and Inhibits Glucose-6-Phosphate Dehydrogenase Activity.

In the pentose phosphate pathway, dehydroepiandrosterone (DHEA) uncompetitively inhibits glucose-6-phosphate dehydrogenase (G6PD), reducing NADPH production and increasing oxidative stress, which can influence the onset and/or progression of several diseases, including cancer. 2-Deoxy-D-glucose (2-DG), a glucose mimetic, competes with glucose for cellular uptake, inhibiting glycolysis and competing with glucose-6-phosphate (G-6-P) for G6PD activity. In this study, we report that DHEA-α-2-DG (5), an α-covalent conjugate of DHEA and 2-DG, exhibits better anticancer activity than DHEA, 2-DG, DHEA +2-DG, and polydatin in MCF-7 cells, and reduces NADPH/NADP+ ratio in cellular assays. In vitro enzyme kinetics and molecular docking studies showed that 5 uncompetitively inhibits human G6PD activity and binds to the structural NADP+ site but not to the catalytic NADP+ site. Further combining 5 with the FDA-approved drug tamoxifen enhanced its cytotoxicity against MCF-7 cells, suggesting that it could serve as a candidate for combination of drug strategies.

Fibroblast stromal support model for predicting human papillomavirus-associated cancer drug responses.

Currently, there are no specific antiviral therapeutic approaches targeting Human papillomaviruses (HPVs), which cause around 5% of all human cancers. Specific antiviral reagents are particularly needed for HPV-related oropharyngeal cancers (HPV+OPCs) whose incidence is increasing and for which there are no early diagnostic tools available. We and others have demonstrated that the estrogen receptor alpha (ERα) is overexpressed in HPV+OPCs, compared to HPV-negative cancers in this region, and that these elevated levels are associated with an improved disease outcome. Utilizing this HPV+-specific overexpression profile, we previously demonstrated that estrogen attenuates the growth and cell viability of HPV+ keratinocytes and HPV+ cancer cells in vitro. Expansion of this work in vivo failed to replicate this sensitization. The role of stromal support from the tumor microenvironment (TME) has previously been tied to both the HPV lifecycle and in vivo therapeutic responses. Our investigations revealed that in vitro co-culture with fibroblasts attenuated HPV+-specific estrogen growth responses. Continuing to monopolize on the HPV+-specific overexpression of ERα, our co-culture models then assessed the suitability of the selective estrogen receptor modulators (SERMs), raloxifene and tamoxifen, and showed growth attenuation in a variety of our models to one or both of these drugs in vitro. Utilization of these SERMs in vivo closely resembled the sensitization predicted by our co-culture models. Therefore, the in vitro fibroblast co-culture model better predicts in vivo responses. We propose that utilization of our co-culture in vitro model can accelerate cancer therapeutic drug discovery. IMPORTANCE: Human papillomavirus-related cancers (HPV+ cancers) remain a significant public health concern, and specific clinical approaches are desperately needed. In translating drug response data from in vitro to in vivo, the fibroblasts of the adjacent stromal support network play a key role. Our study presents the utilization of a fibroblast 2D co-culture system to better predict translational drug assessments for HPV+ cancers. We also suggest that this co-culture system should be considered for other translational approaches. Predicting even a portion of treatment paradigms that may fail in vivo with a co-culture model will yield significant time, effort, resource, and cost efficiencies.

Crosstalk of methylation and tamoxifen in breast cancer (Review).

Tamoxifen is a widely used anti­estrogen drug in the endocrine therapy of breast cancer (BC). It blocks estrogen signaling by competitively binding to estrogen receptor α (ERα), thereby inhibiting the growth of BC cells. However, with the long­term application of tamoxifen, a subset of patients with BC have shown resistance to tamoxifen, which leads to low overall survival and progression­free survival. The molecular mechanism of resistance is mainly due to downregulation of ERα expression and abnormal activation of the PI3K/AKT/mTOR signaling pathway. Moreover, the downregulation of targeted gene expression mediated by DNA methylation is an important regulatory mode to control protein expression. In the present review, methylation and tamoxifen are briefly introduced, followed by a focus on the effect of methylation on tamoxifen resistance and sensitivity. Finally, the clinical application of methylation for tamoxifen is described, including its use as a prognostic indicator. Finally, it is hypothesized that when methylation is used in combination with tamoxifen, it could recover the resistance of tamoxifen.

2-methoxyestradiol sensitizes tamoxifen-resistant MCF-7 breast cancer cells via downregulating HIF-1α.

The clinical studies for breast cancer (BC) are now assessing the efficacy of 2-Methoxyestradiol (2-ME), a naturally occurring derivative of estradiol. Our study aimed to explore the potential of combining the 2-ME and tamoxifen (TAM) on sensitization of TAM-resistant cells using LCC2 the TAM-resistant cells as a model and comparing the results to the sensitive cells MCF-7. Sulphorhodamine-B (SRB) assay is used to examine the 2-ME chemo-sensitizing impact on the cytotoxicity of TAM on LCC2 cells. Colorimetric assay kits were used to assess the level of the apoptosis-related markers caspases 3, Bcl2, and Bax in cell lysate. Hypoxia-inducible factor 1 alpha (HIF-1α) expression was measured using western blotting. Total cholesterol and triglyceride (TG) levels were examined colorimetrically, using the BIOLABO kit. The use of 2-ME enhanced the cytotoxic effects of TAM and effectively reversed TAM resistance. This was achieved by inhibiting the expression of HIF-1α, while concurrently increasing the levels of apoptotic marker caspase-3, as well as the pro-apoptotic protein Bax. Additionally, there was a reduction in the levels of Bcl2, an anti-apoptotic protein. Furthermore, a reduction in TG and cholesterol levels was noted. Our findings show that HIF-1α plays an important role in TAM resistance and that suppression of HIF-1α by 2-ME-mediated sensitization of BC-resistant cells to TAM. Therefore, the concurrent administration of TAM/2-ME might potentially serve as a viable therapeutic approach to address TAM resistance and enhance the overall therapy efficacy for patients with BC.

P53 Status Influences the Anti-proliferative Effect Induced by IFITM1 Inhibition in Estrogen Receptor-positive Breast Cancer Cells.

BACKGROUND/AIM: Interferon-induced trans-membrane protein 1 (IFITM1) is known to be involved in breast cancer progression. We aimed to investigate its role in estrogen receptor (ER)-positive breast cancer cells with wild-type p53 and tamoxifen-resistant breast cancer cells. MATERIALS AND METHODS: The ER-positive breast cancer cell lines, MCF-7 with wild-type p53 and T47D with mutant p53, were used. We established an MCF-7-derived tamoxifen-resistant cell line (TamR) by long-term culture of MCF-7 cells with 4-hydroxytamoxifen. RESULTS: IFITM1 inhibition in MCF-7 cells significantly decreased cell growth and migration. MCF-7 cells with suppression of IFITM1 using siRNA or ruxolitinib showed reduced cell viability after tamoxifen treatment compared with that in the control MCF-7 cells. Unexpectedly, mRNA and protein levels of IFITM1 were decreased in TamR cells compared with those in MCF-7 cells. TamR cells with suppression of IFITM1 using siRNA or ruxolitinib showed no change in cell viability after treatment with tamoxifen. P53 knockdown using siRNA reduced the mRNA levels of IRF9 and increased mRNA and protein levels of SOCS3 in MCF-7 cells, suggesting that loss or mutation of p53 can affect the induction of IFITM1 via the JAK/STAT signaling pathway in breast cancer. Furthermore, MCF-7 cells with p53 knockdown using siRNA showed no decrease in cell viability after tamoxifen treatment or IFITM1 inhibition, indicating that p53 status may be important for cell death after tamoxifen treatment or IFITM1 inhibition. CONCLUSION: IFITM1 inhibition may enhance the sensitivity to tamoxifen based on p53-dependent enhancement of IFN signaling in wild-type p53, ER-positive breast cancer cells.

The GPR30 Receptor Is Involved in IL-6-Induced Metastatic Properties of MCF-7 Luminal Breast Cancer Cells.

Luminal breast cancer has a high incidence worldwide and poses a severe health threat. Estrogen receptor alpha (ER-α) is activated by 17ß-estradiol (E2), and its overexpression promotes cancerous characteristics. Luminal breast cancer is an epithelial type; however, the cytokine IL-6, secreted by cells within the tumor microenvironment, stimulates the epithelial-to-mesenchymal transition (EMT) and promotes metastasis. Also, IL-6 decreases ER-α levels, favoring the tamoxifen (TMX) resistance development. However, genes under E2 regulation continue to be expressed even though this receptor is absent. GPR30 is an alternative E2 receptor present in both luminal and aggressive triple-negative breast cancer and is related to TMX resistance and cancer progression. The roles of GPR30 and IL-6 in metastasis have been individually established; however, their interplay remains unexplored. This study aims to elucidate the role of GPR30 in IL-6-induced metastatic properties of MCF-7 luminal breast cancer cells. Results showed that GPR30 contributes to the E2-induced MCF-7 proliferation because its inhibition with the antagonist G15 and the Pertussis toxin (PTX) reduced it. Besides, GPR30 upregulated vimentin and downregulated E-cadherin levels in MCF-7 and TMX-resistant (R-TMX) cells and is also involved in the IL-6-induced migration, invasion, and TMX resistance in MCF-7 cells. In addition, in MDA-MB-231 triple-negative cells, both basal and IL-6-induced metastatic properties were related to GPR30 activity. These results indicate that the GPR30 receptor regulates the EMT induced by IL-6 in breast cancer cells.

USP36 promotes tumorigenesis and tamoxifen resistance in breast cancer by deubiquitinating and stabilizing ERα.

BACKGROUND: Breast cancer is the most prevalent cancer in women globally. Over-activated estrogen receptor (ER) α signaling is considered the main factor in luminal breast cancers, which can be effectively managed with selective estrogen receptor modulators (SERMs) like tamoxifen. However, approximately 30-40% of ER + breast cancer cases are recurrent after tamoxifen therapy. This implies that the treatment of breast cancer is still hindered by resistance to tamoxifen. Recent studies have suggested that post-translational modifications of ERα play a significant role in endocrine resistance. The stability of both ERα protein and its transcriptome is regulated by a balance between E3 ubiquitin ligases and deubiquitinases. According to the current knowledge, approximately 100 deubiquitinases are encoded in the human genome, but it remains unclear which deubiquitinases play a critical role in estrogen signaling and endocrine resistance. Thus, decoding the key deubiquitinases that significantly impact estrogen signaling, including the control of ERα expression and stability, is critical for the improvement of breast cancer therapeutics. METHODS: We used several ER positive breast cancer cell lines, DUB siRNA library screening, xenograft models, endocrine-resistant (ERα-Y537S) model and performed immunoblotting, real time PCR, RNA sequencing, immunofluorescence, and luciferase activity assay to investigate the function of USP36 in breast cancer progression and tamoxifen resistance. RESULTS: In this study, we identify Ubiquitin-specific peptidase 36 (USP36) as a key deubiquitinase involved in ERα signaling and the advancement of breast cancer by deubiquitinases siRNA library screening. In vitro and in vivo studies showed that USP36, but not its catalytically inactive mutant (C131A), could promote breast cancer progression through ERα signaling. Conversely, silencing USP36 inhibited tumorigenesis. In models resistant to endocrine therapy, silencing USP36 destabilized the resistant form of ERα (Y537S) and restored sensitivity to tamoxifen. Molecular studies indicated that USP36 inhibited K48-linked polyubiquitination of ERα and enhanced the ERα transcriptome. It is interesting to note that our results suggest USP36 as a novel biomarker for treatment of breast cancer. CONCLUSION: Our study revealed the possibility that inhibiting USP36 combined with tamoxifen could provide a potential therapy for breast cancer.

MitoTam induces ferroptosis and increases radiosensitivity in head and neck cancer cells.

BACKGROUND AND PURPOSE: Radiotherapy (RT) is an integral treatment part for patients with head and neck squamous cell carcinoma (HNSCC), but radioresistance remains a major issue. Here, we use MitoTam, a mitochondrially targeted analogue of tamoxifen, which we aim to stimulate ferroptotic cell death with, and sensitize radioresistant cells to RT. MATERIALS AND METHODS: We assessed viability, reactive oxygen species (ROS) production, disruption of mitochondrial membrane potential, and lipid peroxidation in radiosensitive (UT-SCC-40) and radioresistant (UT-SCC-5) HNSCC cells following MitoTam treatment. To assess ferroptosis specificity, we used the ferroptosis inhibitor ferrostatin-1 (fer-1). Also, total antioxidant capacity and sensitivity to tert-butyl hydroperoxide were evaluated to assess ROS-responses. 53BP1 staining was used to assess radiosensitivity after MitoTam treatment. RESULTS: Our data revealed increased ROS, cell death, disruption of mitochondrial membrane potential, and lipid peroxidation following MitoTam treatment in both cell lines. Adverse effects of MitoTam on cell death, membrane potential and lipid peroxidation were prevented by fer-1, indicating induction of ferroptosis. Radioresistant HNSCC cells were less sensitive to the effects of MitoTam due to intrinsic higher antioxidant capacity. MitoTam treatment prior to RT led to superadditive residual DNA damage expressed by 53BP1 foci compared to RT or MitoTam alone. CONCLUSION: MitoTam induced ferroptosis in HNSCC cells, which could be used to overcome the elevated antioxidant capacity of radioresistant cells and sensitize such cells to RT. Treatment with MitoTam followed by RT could therefore present a promising effective therapy of radioresistant cancers. STATEMENT OF SIGNIFICANCE: Radiotherapy is applied in the treatment of a majority of cancer patients. Radioresistance due to elevated antioxidant levels can be overcome by promoting ferroptotic cell death combining ROS-inducing drug MitoTam with radiotherapy.

Adipocyte-conditioned medium induces tamoxifen resistance by activating PI3K/Akt/mTOR pathway in estrogen receptor-positive breast cancer cells.

Resistance to endocrine therapy is a major clinical challenge in estrogen receptor (ER)-positive breast cancer. Obesity is associated with the clinical response to ER-positive breast cancers; however, the mechanism underlying obesity-induced resistance to endocrine therapy in ER-positive breast cancers remains unclear. In this study, we investigated the molecular mechanisms underlying obesity-induced resistance to tamoxifen (TAM), an anti-estrogen agent, in the ER-positive breast cancer cell line MCF-7 using differentiated adipocyte-conditioned medium (D-CM). Treatment of the cells with D-CM promoted TAM resistance by reducing TAM-induced apoptosis. The expression levels of the ERα target genes were higher in D-CM-treated cells than those in untreated ones. In contrast, when the cells were cultured in the presence of TAM, the expression levels were decreased, with or without D-CM. Moreover, the expression of the markers for cancer stem-like cells (CSCs) and mammosphere formation was enhanced by co-treating with D-CM and TAM, compared with TAM alone. The phosphatidylinositol-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway was activated in MCF-7 cells by D-CM treatment, even in the presence of TAM. Inhibition of the PI3K/Akt/mTOR pathway decreased the expression levels of the CSC markers, suppressed mammosphere formation, and resensitized to TAM via inducing apoptosis in D-CM-treated cells. These results indicate that the conditioned medium of differentiated adipocytes promoted TAM resistance by inducing the CSC phenotype through activation of the PI3K/Akt/mTOR pathway in ER-positive breast cancer cells. Thus, the PI3K/Akt/mTOR pathway may be a therapeutic target in obese patients with ER-positive breast cancers.

Alternative splicing of ALDOA confers tamoxifen resistance in breast cancer.

The cancer-associated alternative splicing (AS) events generate cancer-related transcripts which are involved in uncontrolled cell proliferation and drug resistance. However, the key AS variants implicated in tamoxifen (TAM) resistance in breast cancer remain elusive. In the current study, we investigated the landscape of AS events in nine pairs of primary and relapse breast tumors from patients receiving TAM-based therapy. We unrevealed a notable association between the inclusion of exon 7.2 in the 5'untranslated region (5'UTR) of ALDOA mRNA and TAM resistance. Mechanistically, the inclusion of ALDOA exon 7.2 enhances the translation efficiency of the transcript, resulting in increased ALDOA protein expression, mTOR pathway activity, and the promotion of TAM resistance in breast cancer cells. Moreover, the inclusion of exon 7.2 in ALDOA mRNA is mediated by MSI1 via direct interaction. In addition, elevated inclusion of ALDOA exon 7.2 or expression of MSI1 is associated with an unfavorable prognosis in patients undergoing endocrine therapy. Notably, treatment with Aldometanib, an ALDOA inhibitor, effectively restrains the growth of TAM-resistant breast cancer cells in vitro and in vivo. The present study unveils the pivotal role of an AS event in ALDOA, under the regulation of MSI1, in driving TAM resistance in breast cancer. Therefore, this study provides a promising therapeutic avenue targeting ALDOA to combat TAM resistance.

EZH2 PROTACs target EZH2- and FOXM1-associated oncogenic nodes, suppressing breast cancer cell growth.

Breast cancer (BC) remains the second leading cause of cancer-related mortalities in women. Resistance to hormone therapies such as tamoxifen, an estrogen receptor (ER) inhibitor, is a major hurdle in the treatment of BC. Enhancer of zeste homolog 2 (EZH2), the methyltransferase component of the Polycomb repressive complex 2 (PRC2), has been implicated in tamoxifen resistance. Evidence suggests that EZH2 often functions noncanonically, in a methyltransferase-independent manner, as a transcription coactivator through interacting with oncogenic transcription factors. Unlike methyltransferase inhibitors, proteolysis targeting chimeras (PROTAC) can suppress both activating and repressive functions of EZH2. Here, we find that EZH2 PROTACs, MS177 and MS8815, effectively inhibited the growth of BC cells, including those with acquired tamoxifen resistance, to a much greater degree when compared to methyltransferase inhibitors. Mechanistically, EZH2 associates with forkhead box M1 (FOXM1) and binds to the promoters of FOXM1 target genes. EZH2 PROTACs induce degradation of both EZH2 and FOXM1, leading to reduced expression of target genes involved in cell cycle progression and tamoxifen resistance. Together, this study supports that EZH2-targeted PROTACs represent a promising avenue of research for the future treatment of BC, including in the setting of tamoxifen resistance.