Molecular mechanisms and mode of tamoxifen resistance in breast cancer

The anti-aromatase and anti-estrogenic activity of plant products in the treatment of estrogen receptor-positive breast cancer

Despite being the focal point of decades of research, female breast cancer (BC) continues to be one of the most lethal cancers in the world. Given that 80 % of all diagnosed BC cases are estrogen receptor-positive (ER+) with carcinogenesis driven by estrogen-ERα signalling, current standard of care (SOC) hormone therapies are geared towards modulating the function and expression levels of estrogen and its receptors, ERα and ERβ. Currently, aromatase inhibitors (AIs), selective ER modulators (SERMs) and selective ER degraders (SERDs) are clinically prescribed for the management and treatment of ER+ BC, with the anti-aromatase activity of AIs abrogating estrogen biosynthesis, while the anti-estrogenic SERMs and SERDs antagonise and degrade the ER, respectively. The use of SOC hormone therapies is, however, significantly hampered by the onset of severe side-effects and the development of resistance. Given that numerous studies have reported on the beneficial effects of plant compounds and/or extracts and the multiple pathways through which they target ER+ breast carcinogenesis, recent research has focused on the use of dietary chemopreventive agents for BC management. When combined with SOC treatments, several of these plant components and/or extracts have demonstrated improved efficacy and/or synergistic impact. Moreover, despite a lack of in vivo investigations, plant products are generally reported to have a lower side-effect profile than SOC therapies and are therefore thought to be a safer therapeutic choice. Thus, the current review summarizes the findings from the last five years regarding the anti-aromatase and anti-estrogenic activity of plant products, as well as their synergistic anti-ER+ BC effects in combination with SOC therapies.

Cholesteryl ester transfer protein knock-down in conjunction with a cholesterol-depleting agent decreases tamoxifen resistance in breast cancer cells

The cholesterogenic phenotype, encompassing de novo biosynthesis and accumulation of cholesterol, aids cancer cell proliferation and survival. Previously, the role of cholesteryl ester (CE) transfer protein (CETP) has been implicated in breast cancer aggressiveness, but the molecular basis of this observation is not clearly understood, which this study aims to elucidate. CETP knock-down resulted in a >50% decrease in cell proliferation in both 'estrogen receptor-positive' (ER+; Michigan Cancer Foundation-7 (MCF7) breast cancer cells) and 'triple-negative' breast cancer (TNBC; MDA-MB-231) cell lines. Intriguingly, the abrogation of CETP together with the combination treatment of tamoxifen (5 μM) and acetyl plumbagin (a cholesterol-depleting agent) (5 μM) resulted in twofold to threefold increase in apoptosis in both cell lines. CETP knockdown also showed decreased intracellular CE levels, lipid raft and lipid droplets in both cell lines. In addition, RT2 Profiler PCR array (Qiagen, Germany)-based gene expression analysis revealed an overall downregulation of genes associated in cholesterol biosynthesis, lipid signalling and drug resistance in MCF7 cells post-CETP knock-down. On the contrary, resistance in MDA-MB-231 cells was reduced through increased expression in cholesterol efflux genes and the expression of targetable surface receptors by endocrine therapy. The pilot xenograft mice study substantiated CETP's role as a cancer survival gene as knock-down of CETP stunted the growth of TNBC tumour by 86%. The principal findings of this study potentiate CETP as a driver in breast cancer growth and aggressiveness and thus targeting CETP could limit drug resistance via the reduction in cholesterol accumulation in breast cancer cells, thereby reducing cancer aggressiveness.

Precision therapeutics and emerging strategies for HR-positive metastatic breast cancer

Anti-oestrogen-based therapies, often combined with a CDK4/6 inhibitor, are the current standard-of-care first-line therapy for patients with advanced-stage hormone receptor-positive (HR+) breast cancer. Resistance to anti-oestrogen agents inevitably occurs, mediated by oestrogen receptor (ER)-dependent or ER-independent mechanisms that drive tumour progression. Emerging endocrine therapies include, but are not limited to, next-generation oral ER degraders and proteolysis targeting chimeras, which might be particularly effective in patients with ESR1-mutant breast cancer. Furthermore, cancers harbouring driver alterations in oncogenic signalling pathways, including AKT and PI3K, might be susceptible to novel combination strategies involving targeted inhibitors. Next-generation CDK2/4 inhibitors are an area of active clinical investigation, and efforts are ongoing to evaluate the role of sequential CDK inhibition. Approved and emerging antibody-drug conjugates exploiting novel target antigens have also demonstrated promising clinical activity. These novel agents, as well as further identification and characterization of predictive biomarkers, will hopefully continue to improve clinical outcomes, reduce the incidence of toxicities, and limit the extent of overtreatment in this population. In this Review, we describe the evolving treatment paradigm for patients with metastatic HR+ breast cancer in light of the growing armamentarium of drugs and biomarkers that will help to shape the future therapeutic landscape. These strategies are expected to involve tumour molecular profiling to enable the delivery of precision medicine.

Dexamethasone-tamoxifen combination exerts synergistic therapeutic effects in tamoxifen-resistance breast cancer cells

Tamoxifen (TAM) is a key player in estrogen receptor-positive (ER+) breast cancer (BC); however, ∼30% of patients experience relapse and a lower survival rate due to TAM resistance. TAM resistance was related to the over expression of SOX-2 gene, which is regulated by the E2F3 transcription factor in the Wnt signaling pathway. It was suggested that SOX-2 overexpression was suppressed by dexamethasone (DEX), a glucocorticoid commonly prescribed to BC patients. The aim of the present study is to explore the effect of combining DEX and TAM on the inhibition of TAM-resistant LCC-2 cells (TAMR-1) through modulating the E2F3/SOX-2-mediated Wnt signaling pathway. The effect of the combination therapy on MCF-7 and TAMR-1 cell viability was assessed. Drug interactions were analyzed using CompuSyn and SynergyFinder softwares. Cell cycle distribution, apoptotic protein expression, gene expression levels of SOX-2 and E2F3, and cell migration were also assessed. Combining DEX with TAM led to synergistic inhibition of TAMR-1 cell proliferation and migration, induced apoptosis, reduced SOX-2 and E2F3 expression and was also associated with S and G2-M phase arrest. Therefore, combining DEX with TAM may present an effective therapeutic option to overcome TAM resistance, by targeting the E2F3/SOX-2/Wnt signaling pathway, in addition to its anti-inflammatory effect.

Adverse effects of tamoxifen treatment on bone mineral density in premenopausal patients with breast cancer: a systematic review and meta-analysis

BACKGROUND

It is well known that adjuvant tamoxifen treatment for breast cancer in postmenopausal women decreased bone loss. However, the effects of adjuvant tamoxifen therapy on bone mineral density (BMD) in premenopausal patients with breast cancer remains uncertain. Tamoxifen would have a potential impact of premenopausal BMD on health. The aim of this meta-analysis was to assess this in premenopausal women with primary breast cancer.

METHODS

Through April 2020, studies reporting BMD changes of lumbar spine or hip in premenopausal women with primary breast cancer treated with adjuvant tamoxifen and tamoxifen plus chemotherapy or ovarian function suppression (OFS) were collected from EMBASE and PubMed. The meta-analysis was performed using random effects model of the standardized mean difference (SMD) of BMD in patients.

RESULTS

A total of 1432 premenopausal patients were enrolled in eight studies, involving 198 patients treated with tamoxifen alone in three studies. After a 3-year median follow-up, adjuvant tamoxifen decreased the lumbar spinal and hip BMD by as much as an SMD of -1.17 [95% confidence interval (CI); -1.58 to -0.76)] and -0.66 (95% CI, -1.55 to 0.23), respectively. In subgroup analysis in patients treated adjuvant tamoxifen and tamoxifen plus chemotherapy or OFS according to follow-up duration, the bone change of < 3 years follow-up group was -0.03 SMD (95% CI, -0.47 to 0.41) and that of ≥ 3 years follow-up group was -1.06 SMD (95% CI, -1.48 to -0.64). Compared with patients who received tamoxifen alone, patients who received combination therapy with chemotherapy or OFS showed lesser bone loss at the lumbar spine.

CONCLUSIONS

Our meta-analysis demonstrated that adjuvant tamoxifen therapy in premenopausal patients caused bone loss after 3 years of follow-up, especially at the lumbar spines. For a definite evaluation of the adverse effects of tamoxifen on bone, it is necessary to accumulate more relevant studies.

Potential of covalently linked tamoxifen hybrids for cancer treatment: recent update

Cancer is a complex disease and the second leading cause of death globally, and breast cancer is still a leading cause of cancer death in women. Tamoxifen is the most commonly used drug for breast cancer (ER-positive) treatment and chemoprevention, saving the lives of millions of patients every year. In addition, the tamoxifen template has been explored extensively for the development of selective estrogen receptor modulators (SERMs) applicable in breast cancer, osteoporosis, and postmenopausal symptom treatment. Numerous anticancer drugs, including tamoxifen, are in use, but the complexity and heterogeneous nature of cancer complicate the effect of conventional targeted drugs, leading to adverse reactions and resistance. One of the significant approaches to overcome these shortcomings is drug hybrids, generated by covalently linking two or more active pharmacophores. These drug hybrids are remarkably effective in acting on multiple drug targets with higher selectivity and specificity. In recent years, several tamoxifen hybrids have been discovered as potential candidates for cancer treatment. The review highlights the recent progress in developing anticancer hybrids, including organometallic, fluorescent, photocaged, and novel ligand-based tamoxifen hybrids. It also demonstrates the significance of merging various pharmacophores with tamoxifen to produce more potent, precise, and effective anticancer agents. The study offers valuable knowledge to researchers working on cancer research with the hope of enhancing drug potency and reducing drug toxicity to improve cancer patients' lives.

Influence of tumor microenvironment on the different breast cancer subtypes and applied therapies

Despite the significant improvements made in breast cancer therapy during the last decades, this disease still has increasing incidence and mortality rates. Different targets involved in general processes, like cell proliferation and survival, have become alternative therapeutic options for this disease, with some of them already used in clinic, like the CDK4/6 inhibitors for luminal A tumors treatment. Nevertheless, there is a demand for novel therapeutic strategies focused not only on tumor cells, but also on their microenvironment. Tumor microenvironment (TME) is a very complex and dynamic system that, more than surrounding and supporting tumor cells, actively participates in tumor development and progression. During the last decades, it has become clear that the cellular and acellular components of TME differ between the various breast cancer subtypes and shape the differences regarding their severity and prognosis. The pivotal role of the TME in controlling tumor growth and influencing responses to therapy represents a potential source for novel targets and therapeutic strategies. In this review, we present a description of the multiple therapeutic options used for different breast cancer subtypes, as well as the influence that the TME may exert on the development of the disease and on the response to the distinct therapies, which in some cases may explain their failure by the occurrence of relapses and resistance. Furthermore, the ongoing studies focused on the use of TME components for developing potential cancer treatments are described.

Decoding cell death signalling: Impact on the response of breast cancer cells to approved therapies

Breast cancer is a principal cause of cancer-related mortality in female worldwide. While many approved therapies have shown promising outcomes in treating breast cancer, understanding the intricate signalling pathways controlling cell death is crucial for optimizing the treatment outcome. A growing body of evidence has unveiled the aberrations in multiple cell death pathways across diverse cancer types, highlighting these pathways as appealing targets for therapeutic interventions. In this review, we provide a comprehensive overview of the current state of knowledge on the cell death signalling mechanisms with a particular focus on their impact on the response of breast cancer cells to approved therapies. Additionally, we discuss the potentials of combination therapies that exploit the synergy between approved drugs and therapeutic agents targeting modulators of cell death pathways.

Small molecule inhibitor targeting the Hsp70-Bim protein-protein interaction in estrogen receptor-positive breast cancer overcomes tamoxifen resistance

INTRODUCTION

Estrogen receptor (ER) positive patients compromise about 70% of breast cancers. Tamoxifen, an antagonist of ERα66 (the classic ER), is the most effective and the standard first-line drug. However, its efficacy is limited by the development of acquired resistance.

METHODS

A specific inhibitor of Hsp70-Bim protein-protein interaction (PPI), S1g-2, together with an inhibitor of Hsp70-Bag3 PPI, MKT-077 and an ATP-competitive inhibitor VER155008, were used as chemical tools. Cell viability assays, co-immunoprecipitation and gene knockdown were used to investigate the role of Hsp70 in tamoxifen resistance. A xenograft model was established in which tamoxifen-resistant breast cancer (MCF-7/TAM-R) cells maintained in the presence of 5 μM tamoxifen were subcutaneously inoculated. The anti-tumor efficiency of S1g-2 was measured after a daily injection of 0.8 mg/kg for 14 days.

RESULTS

It was revealed that Hsp70-Bim PPI protects ERα-positive breast cancer from tamoxifen-induced apoptosis through binding and stabilizing ERα36, rather than ERα66, resulting in sustained EGFR mRNA and protein expression. Disruption of Hsp70-Bim PPI and downregulation of ERα36 expression in tumor samples are consistent with the in vitro functions of S1g-2, resulting in about a three-fold reduction in tumor volume.

CONCLUSIONS

The in vivo activity and safety of S1g-2 illustrated that it is a potential strategy for Hsp70-Bim disruption to overcome tamoxifen-resistant ER-positive breast cancer.

Exploring the potential of tamoxifen-based copper(ii) dichloride in breast cancer therapy

For decades, tamoxifen-based hormone therapy has effectively addressed oestrogen receptor positive (ER+) luminal A breast cancer. Nonetheless, the emergence of tamoxifen resistance required innovative approaches, leading to hybrid metallodrugs with several therapeutic effects besides the inhibition of oestrogen receptor α (ERα). Drawing inspiration from tamoxifen metabolite structures (4-hydroxytamoxifen and 4,4'-dihyroxytamoxifen), a phenyl ring was replaced by a bidentate 2,2'-bipyridine donor moiety to give 4-[1,1-bis(4-methoxyphenyl)but-1-en-2-yl]-2,2'-bipyridine (L), enabling coordination of bioactive transition metal compounds such as copper(ii) dichloride, yielding [CuCl(μ-Cl)(L-κ2N,N')]2 (1). Notably, copper(ii) complex 1 exhibited remarkable activity within the low micromolar concentration range against ER+ human glioblastoma U251, as well as breast carcinomas MDA-MB-361 and MCF-7, surpassing the efficacy of previously reported palladium(ii) and platinum(ii) dichloride analogs against these cell lines. The pronounced efficacy of complex 1 against triple-negative MDA-MB-231 cells highlights its potential multitherapeutic approach, evident through induction of apoptosis and antioxidant activity. This study evaluates the potential of copper-tamoxifen hybrid complex 1 as a potent therapeutic candidate, highlighting its diverse mechanism of action against challenging breast cancer subtypes.

Involvement of RFC3 in tamoxifen resistance in ER-positive breast cancer through the cell cycle

Since the establishment of the molecular subtyping system, ER positive breast cancer was considered to be the most prevalent type of breast cancer, and endocrine therapy was a very important solution. However, numerous studies have shown that the cell cycle plays a key role in the progression and metastasis of breast cancer. The present study showed that RFC3 was involved in the cell cycle through DNA replication. Furthermore, RFC3 expression was significantly higher in breast cancer-resistant cells than in parental cells, which correlated with the cell cycle. We confirmed these results by established drug-resistant cell lines for breast cancer, raw letter analysis and immunohistochemical analysis of primary and recurrent tissues from three ER+ breast cancers. In addition, analysis of the results through an online database revealed that RFC3 expression was significantly associated with poor prognosis in ER+ breast cancer. We also demonstrated that in ER positive breast cancer-resistant cells, knockdown of RFC3 blocked the S-phase of cells and significantly attenuated cell proliferation, migration and invasion. Furthermore, RFC3 overexpression in ER positive breast cancer cells enhanced cell proliferation, migration and invasion. Taking all these findings into account, we could conclude that RFC3 was involved in endocrine resistance in breast cancer through the cell cycle. Thus, RFC3 may be a target to address endocrine therapy resistance in ER positive breast cancer and may be an independent prognostic factor in ER positive breast cancer.

Targeting autophagy with tamoxifen in breast cancer: From molecular mechanisms to targeted therapy

BACKGROUND

Tamoxifen (TAM) is often recommended as a first-line treatment for estrogen receptor-positive breast cancer (BC). However, TAM resistance continues to be a medical challenge for BC with hormone receptor positivity. The function of macro-autophagy and autophagy has recently been identified to be altered in BC, which suggests a potential mechanism for TAM resistance. Autophagy is a cellular stress-induced response to preserve cellular homeostasis. Also, therapy-induced autophagy, which is typically cytoprotective and activated in tumor cells, could sometimes be non-protective, cytostatic, or cytotoxic depending on how it is regulated.

OBJECTIVE

This review explored the literature on the connections between hormonal therapies and autophagy. We investigated how autophagy could develop drug resistance in BC cells.

METHODS

Scopus, Science Direct, PubMed, and Google Scholar were used to search articles for this study.

RESULTS

The results demonstrated that protein kinases such as pAMPK, BAX, and p-p70S6K could be a sign of autophagy in developing TAM resistance. According to the study's findings, autophagy plays an important role in BC patients' TAM resistance.

CONCLUSION

Therefore, by overcoming endocrine resistance in estrogen receptor-positive breast tumors, autophagy inhibition may improve the therapeutic efficacy of TAM.

Enhancing Tamoxifen Therapy with α-Mangostin: Synergistic Antiproliferative Effects on Breast Cancer Cells and Potential Reduced Endometrial Impact

Breast cancer is the most prevalent neoplasia among women worldwide. For the estrogen receptor-positive (ER+) phenotype, tamoxifen is the standard hormonal therapy; however, it carries the risk of promoting endometrial carcinoma. Hence, we aimed to evaluate the antiproliferative effect of the phytochemical α-mangostin (AM) as a co-adjuvant alongside tamoxifen on breast cancer cells to improve its efficacy while reducing its adverse effects on endometrium. For this, ER+ breast cancer cells (MCF-7 and T-47D) and endometrial cells (N30) were treated with AM, 4-hydroxytamoxifen (4-OH-TMX), and their combination. Cell proliferation was evaluated using sulforhodamine B assay, and the pharmacological interaction was determined through the combination index and the dose reduction index calculation. The genes KCNH1, CCDN1, MKI67, and BIRC5 were amplified by real-time PCR as indicators of oncogenesis, cell cycle progression, cell proliferation, and apoptosis, respectively. Additionally, genes involved in ER signaling were analyzed. In breast cancer cells, the combination of AM with 4-OH-TMX showed a synergistic antiproliferative effect and favorable dose reduction. AM and 4-OH-TMX decreased KCNH1, CCND1, and BIRC5 gene expression. In endometrial cells, AM decreased MKI-67 gene expression, while it reverted the 4-OH-TMX-dependent CCND1 upregulation. This study establishes the benefits of incorporating AM as a co-adjuvant for first-line ER+ breast cancer therapy.

TRP Channels: The Neglected Culprits in Breast Cancer Chemotherapy Resistance?

Breast cancer is a major health concern worldwide, and resistance to therapies remains a significant challenge in treating this disease. In breast cancer, Transient Receptor Potential (TRP) channels are well studied and constitute key players in nearly all carcinogenesis hallmarks. Recently, they have also emerged as important actors in resistance to therapy by modulating the response to various pharmaceutical agents. Targeting TRP channels may represent a promising approach to overcome resistance to therapies in breast cancer patients.

SCR-6852, an oral and highly brain-penetrating estrogen receptor degrader (SERD), effectively shrinks tumors both in intracranial and subcutaneous ER + breast cancer models

BACKGROUND

Targeted estrogen receptor degradation has been approved to effectively treat ER + breast cancers. Due to the poor bioavailability of fulvestrant, the first generation of SERD, many efforts were made to develop oral SERDs. With the approval of Elacestrant, oral SERDs demonstrated superior efficacy than fulvestrant. However, due to the poor ability of known SERDs to penetrate the blood-brain barrier (BBB), breast cancer patients with brain metastasis cannot benefit from clinical SERDs.

METHODS

The ER inhibitory effects were evaluated on ERα protein degradation, and target genes downregulation. And anti-proliferation activities were further determined in a panel of ER + breast cancer cell lines. The subcutaneous and intracranial ER + tumor models were used to evaluate the efficacy of anti-tumor effects. Brain penetrability was determined in multiple animal species.

RESULTS

SCR-6852 is a novel SERD and currently is under early clinical evaluation. In vitro studies demonstrated that it strongly induced both wildtype and mutant ERα degradation. It potently inhibited cell proliferation in a panel of ER + breast cancer cell lines, including the cell lines containing ESR1 mutations (Y537 and D538). Furthermore, SCR-6852 exhibited pure antagonistic activities on the ERɑ signal axis identified both in vitro and in vivo. Oral administration of SCR-6852 at 10 mg/kg resulted in tumor shrinkage which was superior to Fulvestrant at 250 mg/kg, notably, in the intracranial tumor model, SCR-6852 effectively inhibited tumor growth and significantly prolonged mice survival, which correlated well with the high exposure in brains. In addition to mice, SCR-6852 also exhibited high brain penetrability in rats and dogs.

CONCLUSIONS

SCR-6852 is a novel SERD with high potency in inducing ERα protein degradation and pure antagonistic activity on ERɑ signaling in vitro and in vivo. Due to the high brain penetrability, SCR-6852 could be used to treat breast patients with brain metastasis.

Emerging Role of Epigenetic Modifiers in Breast Cancer Pathogenesis and Therapeutic Response

Breast cancer pathogenesis, treatment, and patient outcomes are shaped by tumor-intrinsic genomic alterations that divide breast tumors into molecular subtypes. These molecular subtypes often dictate viable therapeutic interventions and, ultimately, patient outcomes. However, heterogeneity in therapeutic response may be a result of underlying epigenetic features that may further stratify breast cancer patient outcomes. In this review, we examine non-genetic mechanisms that drive functional changes to chromatin in breast cancer to contribute to cell and tumor fitness and highlight how epigenetic activity may inform the therapeutic response. We conclude by providing perspectives on the future of therapeutic targeting of epigenetic enzymes, an approach that holds untapped potential to improve breast cancer patient outcomes.

Shielding and nurturing: Fibronectin as a modulator of cancer drug resistance

Resistance to chemotherapy and targeted therapies constitute a common hallmark of most cancers and represent a dominant factor fostering tumor relapse and metastasis. Fibronectin, an abundant extracellular matrix glycoprotein, has long been proposed to play an important role in the pathobiology of cancer. Recent research has unraveled the role of Fibronectin in the onset of chemoresistance against a variety of antineoplastic drugs including DNA-damaging agents, hormone receptor antagonists, tyrosine kinase inhibitors, microtubule destabilizing agents, etc. The current review summarizes the role played by Fibronectin in mediating drug resistance against diverse anticancer drugs. We have also discussed how the aberrant expression of Fibronectin drives the oncogenic signaling pathways ultimately leading to drug resistance through the inhibition of apoptosis, promotion of cancer cell growth and proliferation.

Overview of Solid Lipid Nanoparticles in Breast Cancer Therapy

Lipid nanoparticles (LNPs), composed of ionized lipids, helper lipids, and cholesterol, provide general therapeutic effects by facilitating intracellular transport and avoiding endosomal compartments. LNP-based drug delivery has great potential for the development of novel gene therapies and effective vaccines. Solid lipid nanoparticles (SLNs) are derived from physiologically acceptable lipid components and remain robust at body temperature, thereby providing high structural stability and biocompatibility. By enhancing drug delivery through blood vessels, SLNs have been used to improve the efficacy of cancer treatments. Breast cancer, the most common malignancy in women, has a declining mortality rate but remains incurable. Recently, as an anticancer drug delivery system, SLNs have been widely used in breast cancer, improving the therapeutic efficacy of drugs. In this review, we discuss the latest advances of SLNs for breast cancer treatment and their potential in clinical use.

Pterostilbene-isothiocyanate reduces miR-21 level by impeding Dicer-mediated processing of pre-miR-21 in 5-fluorouracil and tamoxifen-resistant human breast cancer cell lines

Converging evidences identifies that microRNA-21 (miR-21) is responsible for drug resistance in breast cancer. This study aims to evaluate the miR-21-modulatory potential of a hybrid compound, pterostilbene-isothiocyanate (PTER-ITC), in tamoxifen-resistant MCF-7 (TR/MCF-7) and 5-fluorouracil-resistant MDA-MB 231 (5-FUR/MDA-MB 231) breast cancer cell lines, established by repeated exposure to gradually increasing the concentrations of tamoxifen and 5-fluorouracil, respectively. The outcome of this study shows that PTER-ITC effectively reduced the TR/MCF-7 (IC50: 37.21 µM) and 5-FUR/MDA-MB 231 (IC50: 47.00 µM) cell survival by inducing apoptosis, inhibiting cell migration, colony and spheroid formations in TR/MCF-7 cells, and invasiveness of 5-FUR/MDA-MB 231 cells. Most importantly, PTER-ITC significantly reduced the miR-21 expressions in these resistant cell lines. Moreover, the downstream tumor suppressor target gene of miR-21 such as PTEN, PDCD4, TIMP3, TPM1, and Fas L were upregulated after PTER-ITC treatment, as observed from transcriptional (RT-qPCR) and translational (immunoblotting) data. In silico and miR-immunoprecipitation (miR-IP) results showed reduced Dicer binding to pre-miR-21, after PTER-ITC treatment, indicating inhibition of miR-21 biogenesis. Collectively, the significance of this study is indicated by preliminary evidence for miR-21-modulatory effects of PTER-ITC that highlights the potential of this hybrid compound as an miR-21-targeting therapeutic agent.

Gold Nanoparticles Inhibit PMA-Induced MMP-9 Expression via microRNA-204-5p Upregulation and Deactivation of NF-κBp65 in Breast Cancer Cells

OBJECTIVE

Breast cancer (BC) is the most common malignancy in females globally. Matrix metalloproteinase-9 (MMP-9) is crucial to the invasion, progression and spread of BC. Gold nanoparticles (AuNPs) have an anti-tumorigenic role, but their therapeutic role in microRNAs (miRNAs) regulation has not been explored. This study determined the potential of AuNPs against MMP-9 overexpression/production and miRNA-204-5p regulation in BC cells.

METHODS

AuNPs were newly engineered, and their stability was analyzed using the zeta potential, polydispersity index, surface-plasmon-resonance peak and transmission electron microscopy. A bioinformatics algorithm was used to predict the pairing of miRNA in the 3'untranslated-region (3'UTR) of MMP-9 mRNA. TaqMan assays were carried out to quantify miRNA and mRNA, whereas MMP-9-specific immunoassays and gelatin zymography were used to determine protein secretion and activity. The binding of miRNA in MMP-9 mRNA 3'UTR was verified by luciferase reporter clone assays and transfection with anti-miRNAs. In addition, NF-κBp65 activity was determined and confirmed with parthenolide treatment.

RESULTS

Engineered AuNPs were highly stable and spherical in shape, with a mean size of 28.3 nm. Tested in MCF-7 BC cells, microRNA-204-5p directly regulates MMP-9. AuNPs inhibit PMA-induced MMP-9 mRNA and protein via hsa-miR-204-5p upregulation. Anti-miR-204 transfected MCF-7 cells demonstrated enhanced MMP-9 expression (p < 0.001), while AuNPs treatment attenuated MMP-9 expression in a dose-dependent manner (p < 0.05). Moreover, AuNPs also inhibit PMA-induced NF-κBp65 activation in anti-hsa-miR-204 transfected MCF-7 cells.

CONCLUSION

Engineered AuNPs were stable and non-toxic to BC cells. AuNPs inhibit PMA-induced MMP-9 expression, production and activation via NF-κBp65 deactivation and hsa-miR-204-5p upregulation. These novel therapeutic potentials of AuNPs on stimulated BC cells provide novel suggestions that AuNPs inhibit carcinogenic activity via inverse regulation of microRNAs.

Innovative Thiosemicarbazones that Induce Multi-Modal Mechanisms to Down-Regulate Estrogen-, Progesterone-, Androgen- and Prolactin-Receptors in Breast Cancer

The estrogen receptor-α (ER-α) is a key driver of breast cancer (BC) and the ER-antagonist, tamoxifen, is a central pillar of BC treatment. However, cross-talk between ER-α, other hormone and growth factor receptors enables development of de novo resistance to tamoxifen. Herein, we mechanistically dissect the activity of a new class of anti-cancer agents that inhibit multiple growth factor receptors and down-stream signaling for the treatment of ER-positive BC. Using RNA sequencing and comprehensive protein expression analysis, we examined the activity of di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT) and di-2-pyridylketone-4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), on the expression and activation of hormone and growth factor receptors, co-factors, and key resistance pathways in ER-α-positive BC. DpC differentially regulated 106 estrogen-response genes, and this was linked to decreased mRNA levels of 4 central hormone receptors involved in BC pathogenesis, namely ER, progesterone receptor (PR), androgen receptor (AR), and prolactin receptor (PRL-R). Mechanistic investigation demonstrated that due to DpC and Dp44mT binding metal ions, these agents caused a pronounced decrease in ER-α, AR, PR, and PRL-R protein expression. DpC and Dp44mT also inhibited activation and down-stream signaling of the epidermal growth factor (EGF) family receptors, and expression of co-factors that promote ER-α transcriptional activity, including SRC3, NF-κB p65, and SP1. In vivo, DpC was highly tolerable and effectively inhibited ER-α-positive BC growth. Through bespoke, non-hormonal, multi-modal mechanisms, Dp44mT and DpC decrease the expression of PR, AR, PRL-R, and tyrosine kinases that act with ER-α to promote BC, constituting an innovative therapeutic approach.

Dynamacophore model for breast cancer estrogen receptor alpha as an effective lead generation screening technique

Regardless to overwhelming quantum of cancer research worldwide, there are few drugs on the market to treat disease conditions. This is owing to multiple process inferences of drug targets in integrated pathways for invasion, growth, and metastasis. Over the past years, the death rate due to breast cancer has been increasing, that set the stage for improved better treatment. Therefore, there is a persistent and vital demand for innovative development of drugs to treat breast cancer. Many studies have reported that more than 60% of breast cancers are Estrogen receptor-α (ERα)-positive tumours and a key transcription factor, Estrogen receptor-α (ERα) was believed to promote proliferation of breast cancer cells. In this study, 150 ns of molecular dynamics was performed for protein-ligand complex to retrieve the potential stable conformations. The most populated dynamics cluster of 4-Hydroxytamoxifen intact with active site amino acid was selected to generate dynamacophore model (dynamic pharmacophore). Further, internal model validation with AU-ROC values ∼0.93 indicate the best model to screen library. The refined hits are funnelled in pharmacokinetics/dynamics, CDOCKER molecular docking, MM-GBSA and density functional theory to identify the promising ERα ligand candidates.Communicated by Ramaswamy H. Sarma.

Repositioning Cannabinoids and Terpenes as Novel EGFR-TKIs Candidates for Targeted Therapy Against Cancer: A virtual screening model using CADD and biophysical simulations

This study examines the potential of Cannabis sativa L. plants to be repurposed as therapeutic agents for cancer treatment through designing of hybrid Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs). A set of 50 phytochemicals was taken from Cannabinoids and Terpenes and subjected for screening using Semi-flexible and Flexible Molecular Docking methods, MM-GBSA free binding energy computations, and pharmacokinetic/pharmacodynamic (ADME-Tox) predictions. Nine promising phytochemicals, Cannabidiolic acid (CBDA), Cannabidiol (CBD), Tetrahydrocannabivarin (THCV), Dronabinol (Δ-9-THC), Delta-8-Tetrahydrocannabinol (Δ-8-THC), Cannabicyclol (CBL), Delta9-tetrahydrocannabinolic acid (THCA), Beta-Caryophyllene (BCP), and Gamma-Elemene (γ-Ele) were identified as potential EGFR-TKIs natural product candidates for cancer therapy. To further validate these findings, a set of Molecular Dynamics simulations were conducted over a 200 ns trajectory. This hybrid early drug discovery screening strategy has the potential to yield a new generation of EGFR-TKIs based on natural cannabis products, suitable for cancer therapy. In addition, the application of this computational strategy in the virtual screening of both natural and synthetic chemical libraries could support the discovery of a wide range of lead drug agents to address numerous diseases.

The crosstalk between ubiquitination and endocrine therapy

Endocrine therapy (ET), also known as hormone therapy, refers to the treatment of tumors by regulating and changing the endocrine environment and hormone levels. Its related mechanism is mainly through reducing hormone levels and blocking the binding of hormones to corresponding receptors, thus blocking the signal transduction pathway to stimulate tumor growth. However, with the application of ET, some patients show resistance to ET, which is attributed to abnormal accumulation of hormone receptors (HRs) and the production of multiple mutants of HRs. The targeted degradation of abnormal accumulation protein mediated by ubiquitination is an important approach that regulates the protein level and function of intracellular proteins in eukaryotes. Here, we provide a brief description of the traditional and novel drugs available for ET in this review. Then, we introduce the link between ubiquitination and ET. In the end, we elaborate the clinical application of ET combined with ubiquitination-related molecules. KEY MESSAGES: • A brief description of the traditional and novel drugs available for endocrine therapy (ET). • The link between ubiquitination and ET. • The clinical application of ET combined with ubiquitination-related molecules.

Superparamagnetic Iron-Oxide Nanoparticles Synthesized via Green Chemistry for the Potential Treatment of Breast Cancer

In the emerging field of nanomedicine, nanoparticles have been widely considered as drug carriers and are now used in various clinically approved products. Therefore, in this study, we synthesized superparamagnetic iron-oxide nanoparticles (SPIONs) via green chemistry, and the SPIONs were further coated with tamoxifen-conjugated bovine serum albumin (BSA-SPIONs-TMX). The BSA-SPIONs-TMX were within the nanometric hydrodynamic size (117 ± 4 nm), with a small poly dispersity index (0.28 ± 0.02) and zeta potential of -30.2 ± 0.09 mV. FTIR, DSC, X-RD, and elemental analysis confirmed that BSA-SPIONs-TMX were successfully prepared. The saturation magnetization (M_s) of BSA-SPIONs-TMX was found to be ~8.31 emu/g, indicating that BSA-SPIONs-TMX possess superparamagnetic properties for theragnostic applications. In addition, BSA-SPIONs-TMX were efficiently internalized into breast cancer cell lines (MCF-7 and T47D) and were effective in reducing cell proliferation of breast cancer cells, with IC₅₀ values of 4.97 ± 0.42 μM and 6.29 ± 0.21 μM in MCF-7 and T47D cells, respectively. Furthermore, an acute toxicity study on rats confirmed that these BSA-SPIONs-TMX are safe for use in drug delivery systems. In conclusion, green synthesized superparamagnetic iron-oxide nanoparticles have the potential to be used as drug delivery carriers and may also have diagnostic applications.

Epigenetic-Metabolic Interplay in the DNA Damage Response and Therapeutic Resistance of Breast Cancer

Therapy resistance is imposing a daunting challenge on effective clinical management of breast cancer. Although the development of resistance to drugs is multifaceted, reprogramming of energy metabolism pathways is emerging as a central but heterogenous regulator of this therapeutic challenge. Metabolic heterogeneity in cancer cells is intricately associated with alterations of different signaling networks and activation of DNA damage response pathways. Here we consider how the dynamic metabolic milieu of cancer cells regulates their DNA damage repair ability to ultimately contribute to development of therapy resistance. Diverse epigenetic regulators are crucial in remodeling the metabolic landscape of cancer. This epigenetic-metabolic interplay profoundly affects genomic stability of the cancer cells as well as their resistance to genotoxic therapies. These observations identify defining mechanisms of cancer epigenetics-metabolism-DNA repair axis that can be critical for devising novel, targeted therapeutic approaches that could sensitize cancer cells to conventional treatment strategies.

GDNF-RET signaling and EGR1 form a positive feedback loop that promotes tamoxifen resistance via cyclin D1

BACKGROUND

Rearranged during transfection (RET) tyrosine kinase signaling has been previously implicated in endocrine resistant breast cancer, however the mechanism by which this signaling cascade promotes resistance is currently not well described. We recently reported that glial cell-derived neurotrophic factor (GDNF)-RET signaling appears to promote a positive feedback loop with the transcription factor early growth response 1 (EGR1). Here we investigate the mechanism behind this feedback loop and test the hypothesis that GDNF-RET signaling forms a regulatory loop with EGR1 to upregulate cyclin D1 (CCND1) transcription, leading to cell cycle progression and tamoxifen resistance.

METHODS

To gain a better understanding of the GDNF-RET-EGR1 resistance mechanism, we studied the GDNF-EGR1 positive feedback loop and the role of GDNF and EGR1 in endocrine resistance by modulating their transcription levels using CRISPR-dCAS9 in tamoxifen sensitive (TamS) and tamoxifen resistant (TamR) MCF-7 cells. Additionally, we performed kinetic studies using recombinant GDNF (rGDNF) treatment of TamS cells. Finally, we performed cell proliferation assays using rGDNF, tamoxifen (TAM), and Palbociclib treatments in TamS cells. Statistical significance for qPCR and chromatin immunoprecipitation (ChIP)-qPCR experiments were determined using a student's paired t-test and statistical significance for the cell viability assay was a one-way ANOVA.

RESULTS

GDNF-RET signaling formed a positive feedback loop with EGR1 and also downregulated estrogen receptor 1 (ESR1) transcription. Upregulation of GDNF and EGR1 promoted tamoxifen resistance in TamS cells and downregulation of GDNF promoted tamoxifen sensitivity in TamR cells. Additionally, we show that rGDNF treatment activated GDNF-RET signaling in TamS cells, leading to recruitment of phospho-ELK-1 to the EGR1 promoter, upregulation of EGR1 mRNA and protein, binding of EGR1 to the GDNF and CCND1 promoters, increased GDNF protein expression, and subsequent upregulation of CCND1 mRNA levels. We also show that inhibition of cyclin D1 with Palbociclib, in the presence of rGDNF, decreases cell proliferation and resensitizes cells to TAM.

CONCLUSION

Outcomes from these studies support the hypotheses that GDNF-RET signaling forms a positive feedback loop with the transcription factor EGR1, and that GDNF-RET-EGR1 signaling promotes endocrine resistance via signaling to cyclin D1. Inhibition of components of this signaling pathway could lead to therapeutic insights into the treatment of endocrine resistant breast cancer.

Targeting hormone-resistant breast cancer cells with docetaxel: a look inside the resistance

Aim: The study aims to analyze the effect of long-term incubation of ERα-positive MCF7 breast cancer cells with 4-hydroxytamoxifen (HT) on their sensitivity to tubulin polymerization inhibitor docetaxel. Methods: The analysis of cell viability was performed by the MTT method. The expression of signaling proteins was analyzed by immunoblotting and flow cytometry. ERα activity was evaluated by gene reporter assay. To establish hormone-resistant subline MCF7, breast cancer cells were treated with 4-hydroxytamoxifen for 12 months. Results: The developed MCF7/HT subline has lost sensitivity to 4-hydroxytamoxifen, and the resistance index was 2. Increased Akt activity (2.2-fold) and decreased ERα expression (1.5-fold) were revealed in MCF7/HT cells. The activity of the estrogen receptor α was reduced (1.5-fold) in MCF7/HT. Evaluation of class III β-tubulin expression (TUBB3), a marker associated with metastasis, revealed the following trends: higher expression of TUBB3 was detected in triple-negative breast cancer MDA-MB-231 cells compared to hormone-responsive MCF7 cells (P < 0.05). The lowest expression of TUBB3 was found in hormone-resistant MCF7/HT cells (MCF7/HT < MCF7 < MDA-MB-231, approximately 1:2:4). High TUBB3 expression strongly correlated with docetaxel resistance: IC₅₀ value of docetaxel for MDA-MB-231 cells was greater than that for MCF7 cells, whereas resistant MCF7/HT cells were the most sensitive to the drug. The accumulation of cleaved PARP (a 1.6-fold increase) and Bcl-2 downregulation (1.8-fold) were more pronounced in docetaxel-treated resistant cells (P < 0.05). The expression of cyclin D1 decreased (2.8-fold) only in resistant cells after 4 nM docetaxel treatment, while this marker was unchanged in parental MCF7 breast cancer cells. Conclusion: Further development of taxane-based chemotherapy for hormone-resistant cancer looks highly promising, especially for cancers with low TUBB3 expression.

The landscape of exosomal non-coding RNAs in breast cancer drug resistance, focusing on underlying molecular mechanisms

Breast cancer (BC) is the most common malignancy among women worldwide. Like many other cancers, BC therapy is challenging and sometimes frustrating. In spite of the various therapeutic modalities applied to treat the cancer, drug resistance, also known as, chemoresistance, is very common in almost all BCs. Undesirably, a breast tumor might be resistant to different curative approaches (e.g., chemo- and immunotherapy) at the same period of time. Exosomes, as double membrane-bound extracellular vesicles 1) secreted from different cell species, can considerably transfer cell products and components through the bloodstream. In this context, non-coding RNAs (ncRNAs), including miRNAs, long ncRNAs (lncRNAs), and circular RNAs (circRNAs), are a chief group of exosomal constituents with amazing abilities to regulate the underlying pathogenic mechanisms of BC, such as cell proliferation, angiogenesis, invasion, metastasis, migration, and particularly drug resistance. Thereby, exosomal ncRNAs can be considered potential mediators of BC progression and drug resistance. Moreover, as the corresponding exosomal ncRNAs circulate in the bloodstream and are found in different body fluids, they can serve as foremost prognostic/diagnostic biomarkers. The current study aims to comprehensively review the most recent findings on BC-related molecular mechanisms and signaling pathways affected by exosomal miRNAs, lncRNAs, and circRNAs, with a focus on drug resistance. Also, the potential of the same exosomal ncRNAs in the diagnosis and prognosis of BC will be discussed in detail.

Evaluation of Drug Resistance in the Tamoxifen-treated MKN-45 Gastric Cancer Cell Line via the Epithelial-mesenchymal Transition Signaling Pathway

One of the major challenges in gastric cancer (GC) chemotherapy is the phenomenon of multi-drug resistance (MDR). The epithelial-mesenchymal transition (EMT) and its key molecules, transforming growth factor-β (TGFβ) and SMAD2, play a central role in MDR occurrence. Tamoxifen (TAM), a triphenylethylene derivative, can overcome MDR in human gastric cancers. The aim of this study was to investigate the effect of TAM on 5-FU resistance of GC by suppressing the TGFβ1/SMAD2 signaling pathway and EMT. The MKN-45 cell line was subjected to treatment with 5-FU, TAM and a combination of both. The MTT assay was used to investigate the cytotoxic effects of 5-FU and TAM, and the DNA laddering technique was used to assess DNA fragmentation and apoptosis. Real-time RT-PCR examined the change in gene expression in EMT-related genes (SNAI2, VIM, TGFβ1 and SMAD2). The results of the present study indicated that not only TAM treatment significantly decreased the IC50 of 5-FU (P≤0.05), but also the addition of TAM to 5-FU induced apoptosis in the MKN-45 cell line. Treatment with TAM and 5-FU significantly inhibited TGFβ1 and TGFβ1-induced expression of EMT markers (VIM and SNAI2) in MKN-45 cells (P≤0.05). The reduction of TGFβ1 targets downstream of the SMAD2 signaling pathway reversed the process of EMT and significantly increased the sensitivity of MKN-45 cells to 5-FU. The results of the present study suggested that reversal of EMT-mediated MDR via the TGFβ1/SMAD signaling pathway using TAM may be a potential new therapeutic strategy to overcome chemoresistance to 5-FU during GC chemotherapy.

Multifunctional hybrid nanoparticles in diagnosis and therapy of breast cancer

Breast cancer is the most prevalent non-cutaneous malignancy in women, with greater than a million new cases every year. In the last decennium, numerous diagnostic and treatment approaches have been enormously studied for Breast cancer. Among the different approaches, nanotechnology has appeared as a promising approach in preclinical and clinical studies for early diagnosis of primary tumors and metastases and eradicating tumor cells. Each of these nanocarriers has its particular advantages and drawbacks. Combining two or more than two constituents in a single nanocarrier system leads to the generation of novel multifunctional Hybrid Nanocarriers with improved structural and biological properties. These novel Hybrid Nanocarriers have the capability to overcome the drawbacks of individual constituents while having the advantages of those components. Various hybrid nanocarriers such as lipid polymer hybrid nanoparticles, inorganic hybrid nanoparticles, metal-organic hybrid nanoparticles, and hybrid carbon nanocarriers are utilized for the diagnosis and treatment of various cancers. Certainly, Hybrid Nanocarriers have the capability to encapsulate multiple cargos, targeting agents, enhancement in encapsulation, stability, circulation time, and structural disintegration compared to non-hybrid nanocarriers. Many studies have been conducted to investigate the utilization of Hybrid nanocarriers in breast cancer for imaging platforms, photothermal and photodynamic therapy, chemotherapy, gene therapy, and combinational therapy. In this review, we mainly discussed in detailed about of preparation techniques and toxicological considerations of hybrid nanoparticles. This review also discussed the role of hybrid nanocarriers as a diagnostic and therapeutic agent for the treatment of breast cancer along with alternative treatment approaches apart from chemotherapy including photothermal and photodynamic therapy, gene therapy, and combinational therapy.

Mesoporous Silica Nanoparticles Enhance the Anticancer Efficacy of Platinum(IV)-Phenolate Conjugates in Breast Cancer Cell Lines

The main reasons for the limited clinical efficacy of the platinum(II)-based agent cisplatin include drug resistance and significant side effects. Due to their better stability, as well as the possibility to introduce biologically active ligands in their axial positions constructing multifunctional prodrugs, creating platinum(IV) complexes is a tempting strategy for addressing these limitations. Another strategy for developing chemotherapeutics with lower toxicity relies on the ability of nanoparticles to accumulate in greater quantities in tumor tissues through passive targeting. To combine the two approaches, three platinum(IV) conjugates based on a cisplatin scaffold containing in the axial positions derivatives of caffeic and ferulic acid were prepared and loaded into SBA-15 to produce the corresponding mesoporous silica nanoparticles (MSNs). The free platinum(IV) conjugates demonstrated higher or comparable activity with respect to cisplatin against different human breast cancer cell lines, while upon immobilization, superior antiproliferative activity with markedly increased cytotoxicity (more than 1000-fold lower IC50 values) compared to cisplatin was observed. Mechanistic investigations with the most potent conjugate, cisplatin-diacetyl caffeate (1), and the corresponding MSNs (SBA-15|1) in a 4T1 mouse breast cancer cell line showed that these compounds induce apoptotic cell death causing strong caspase activation. In vivo, in BALB/c mice, 1 and SBA-15|1 inhibited the tumor growth while decreasing the necrotic area and lowering the mitotic rate.

Combinatorial treatments of tamoxifen and SM6Met, an extract from Cyclopia subternata Vogel, are superior to either treatment alone in MCF-7 cells

Synergistic drug combinations are not only popular in antibiotic, anti-microbial, immune disease (i.e., AIDS) and viral infection studies, but has also gained traction in the field of cancer research as a multi-targeted approach. It has the potential to lower the doses needed of standard of care (SOC) therapeutic agents, whilst maintaining an effective therapeutic level. Lower dosages could ameliorate the fundamental problems such as drug resistance and metastasis associated with current SOC therapies. In the current study, we show that the combination of SM6Met with (2)-4-hydroxytamoxifen (4-OH-Tam, the active metabolite of tamoxifen) produces a strong synergistic effect in terms of inhibiting MCF7 ER-positive (ER⁺) breast cancer cell proliferation and that a 20 times lower dose of 4-OH-Tam in combination with SM6Met is required to produce the same inhibitory effect on cell proliferation as 4-OH-Tam on its own. Cell cycle analyses of the best combination ratios of SM6Met and 4-OH-Tam also suggests that the combination results in increased accumulation of cells in the S-phase and in the apoptotic phase. Moreover, the best combination ratio (20:1) of SM6Met with 4-OH-Tam displayed greater anti-metastatic potential in terms of inhibiting ER⁺ breast cancer cell migration, invasion, and colony formation than the SOC therapy alone, suggesting that SM6Met together with 4-OH-Tam could be a viable drug combination for not only delaying resistance and ameliorating the negative side-effects associated with current SOC therapies, like tamoxifen, but could also provide a novel, more affordable therapeutic alternative for treating or preventing ER⁺ breast cancer metastasis.

Ferrocene-appended anthraquinone and coumarin as redox-active cytotoxins

Appending of ferrocene (Fc) to biologically-active organic backbones can generate novel multi-functional species for targeting bacteria and cancer. In this work Fc was linked to coumarin and anthraquinone with the goal of harnessing the redox-active Fc centre to generate new compounds that exhibit cytoxicity through the generation of toxic reactive oxygen species (ROS). A Cu(I)-catalyzed azide-alkyne cycloaddition "click" reaction was used to connect the organic and Fc components via a triazole linker. Cyclic voltammetry shows that the Fc potentials are suitable for oxidation by biological hydrogen peroxide to give reactive ferrocenium (Fc⁺) species, which can then generate hydroxyl radicals. The ability of the compounds to generate hydroxyl radicals in the presence of hydrogen peroxide was shown directly using EPR spin-trapping experiments. Furthermore, in vitro studies in MCF-7 breast cancer cells show significant increases in ROS following incubation with the Fc-functionalized compounds. Screening for antibacterial activity produced negative results for all of the Fc compounds, consitent with low levels of hydrogen peroxide typically found in bacteria. By contrast, Fc-coumarin showed cytotoxicity against A549 lung cancer and SKOV3 ovarian cancer cell lines, whereas the parent compound was inactive. This is consistent both with the cytoxic potential of the Fc group and the elevated hydrogen peroxide levels found in many cancers. Interestingly, the anthraquinone compounds showed the opposite effect with the parent compounds showing modest activity against A549 cells, but the Fc compounds being inactive. This demonstrates other potential negative impacts of including Fc, such as significantly increased lipophilicity.

Neurospora crassa is a potential source of anti-cancer agents against breast cancer

Fungi are an excellent source of pharmaceuticals including anti-tumor agents. Neurospora crassa generates metabolites with diverse structural classes, however, its potential as an anti-tumor agent source has not been explored. The purpose of this study aimed to investigate the potential of Neurospora crassa mixture against breast cancer. The in vitro T-47D and MDA-MB-231 experiments showed that N. crassa mixture at the concentrations of both 1.7 and 0.85 µg/ml significantly inhibited tumor cell proliferation, migration and invasion, and 3D spheroid formation. However, the inhibition rates of MCF-10A ranged 10-20% at concentrations of 0.85 and 1.7 µg/ml. The mixture at the concentration of 0.85 µg/ml could significantly downregulate the expressions of transcription factors of E2F1 and E2F3, cancer stem cell-related genes of LIN28, HIWI, and CD133, and onco-lncRNA HOTAIR, and increase CASP3 activity in either T-47D or MDA-MD-231 breast cancer cell lines. In vivo breast cancer C3H mouse model results showed that N. crassa mixture significantly inhibited tumor growth. These findings suggest that N. crassa contains an antitumor component(s) against breast cancer invasiveness, which may inhibit the self-renewal and differentiation of breast cancer stem cells possibly by downregulating cancer stem cell-associated and/or transcription factor genes and oncogenes, and promoting apoptosis.

Interactions Between Natural Products and Tamoxifen in Breast Cancer: A Comprehensive Literature Review

Introduction: Tamoxifen (TAM) is the most commonly used hormone therapeutic drug for the treatment of estrogen receptor-positive (ER+) breast cancer. 30%–70% of clinical breast cancer patients use natural products, which may increase the likelihood of drug interactions.

Objective: To evaluate the evidence for the interactions between natural products and TAM in breast cancer.

Methods: Electronic databases, including PubMed, CINAHL Plus (via EbscoHost), European PMC, Medline, and Google Scholar, were searched for relevant publications. The search terms include complementary and alternative medicine, natural products, plant products, herbs, interactions, tamoxifen, breast cancer, and their combinations.

Results: Various in vitro and in vivo studies demonstrated that the combined use of natural products with TAM produced synergistic anti-cancer effects, including improved inhibition of tumor cell growth and TAM sensitivity and reduced side effects or toxicity of TAM. In contrast, some natural products, including Angelica sinensis (Oliv.) Diels [Apiaceae], Paeonia lactiflora Pall., Rehmannia glutinosa (Gaertn.) DC., Astragalus mongholicus Bunge, and Glycyrrhiza glabra L. [Fabaceae], showed estrogen-like activity, which may reduce the anti-cancer effect of TAM. Some natural products, including morin, silybin, epigallocatechin gallate (EGCG), myricetin, baicalein, curcumin, kaempferol, or quercetin, were found to increase the bioavailability of TAM and its metabolites in vivo. However, three are limited clinical studies on the combination of natural products and TAM.

Conclusion: There is evidence for potential interactions of various natural products with TAM in pre-clinical studies, although the relevant clinical evidence is still lacking. Further studies are warranted to evaluate the potential interactions of natural products with TAM in clinical settings.

In vitro breast cancer models for studying mechanisms of resistance to endocrine therapy

The development of endocrine resistance is a common reason for the failure of endocrine therapies in hormone receptor-positive breast cancer. This review provides an overview of the different types of in vitro models that have been developed as tools for studying endocrine resistance. In vitro models include cell lines that have been rendered endocrine-resistant by ex vivo treatment; cell lines with de novo resistance mechanisms, including genetic alterations; three-dimensional (3D) spheroid, co-culture, and mammosphere techniques; and patient-derived organoid models. In each case, the key discoveries, different analysis strategies that are suitable, and strengths and weaknesses are discussed. Certain recently developed methodologies that can be used to further characterize the biological changes involved in endocrine resistance are then emphasized, along with a commentary on the types of research outcomes that using these techniques can support. Finally, a discussion anticipates how these recent developments will shape future trends in the field. We hope this overview will serve as a useful resource for investigators that are interested in understanding and testing hypotheses related to mechanisms of endocrine therapy resistance.

Dynamics of estrogen-induced ROS and DNA strand break generation in estrogen receptor α-positive breast cancer

DNA repair machinery is involved in estrogen-dependent transactivation. Mounting evidence suggests that mechanisms underlying estrogen-induced DNA damage are complicated. To date estrogen-induced DNA oxidation and its impact on ERα-mediated transaction remains ambiguous. Herein, we found that the process of 17β-estradiol (E2)-induced ROS production can be approximately divided into two phases according to responding time and generation mechanisms. The intracellular Ca²⁺ fluctuation and ERα-dependent transcription lead to temporospatially different oxidative DNA damage. Further, we demonstrate that DNA oxidation is dispensable for estrogen-responsive gene expression. Dynamics of estrogen-induced DNA strand break generation also show two-phase pattern and topoisomerase-mediated DNA stand breaks are essential in estrogen signaling. Collectively, our findings have provided new insights into oxidative DNA damage in estrogen signaling.

Functional network analysis of p85 and PI3K as potential gene targets and mechanism of oleanolic acid in overcoming breast cancer resistance to tamoxifen

Background

Tamoxifen resistance in estrogen receptor positive (ER+) breast cancer therapy increases, which is the leading cause of cancer treatment failure, as it can impair patients’ prognoses, cause cancer recurrence, metastasis, and death. Combination therapy with compounds is needed to overcome tamoxifen resistance. Oleanolic acid (OA) was known to increase tamoxifen sensitivity in tamoxifen-resistant breast cancer; however, the molecular mechanism of OA and its involvement in overcoming tamoxifen resistance remain unknown and need further investigation. This study was conducted to identify the potential gene targets and molecular mechanisms of OA in overcoming tamoxifen resistance.

Results

A bioinformatic approach for functional network analysis was used in silico by utilizing secondary data in the Gene Expression Omnibus (GEO) database and analyzing them with GEO2R to obtain data on differentially expressed genes (DEGs). The DEG data were further examined with Database for Annotation, Visualization, and Integrated Discovery (DAVID), STRING, cBioPortal website, and Cytoscape with its plugin CytoHubba. Molecular docking was performed to predict the binding properties of OA on the protein encoded by the potential gene. CD44, FGFR2, PIK3R1, and MDM2 were designated as potential target genes (PTGs), and PIK3R1 was suspected as the potential gene for OA to overcome tamoxifen resistance. Molecular docking confirms that OA can inhibit p85 activation. PIK3R1 is suggested to be the potential gene for OA in overcoming tamoxifen resistance in breast cancer therapy.

Conclusion

The predicted molecular mechanism of OA in overcoming tamoxifen resistance involves inhibiting p85 activation, leading to the inhibition of the downstream activity of the PI3K signaling pathway, causing breast cancer to respond to tamoxifen therapy once again. Results of this study need to be validated by further studies, including in vitro and in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00341-4.

G, Kathryn M. T. The importance of targeting signalling mechanisms of the SLC39A family of zinc transporters to inhibit endocrine resistant breast cancer

Aim:

Zinc is a key secondary messenger that can regulate multiple signalling pathways within cancer cells, thus its levels need to be strictly controlled. The Zrt, Irt-like protein (ZIP, SLC39A) family of zinc transporters increase cytosolic zinc from either extracellular or intracellular stores. This study examines the relevance of zinc transporters ZIP7 and ZIP6 as therapeutic targets in tamoxifen resistant (TAMR) breast cancer.

Methods:

A series of in vitro assays, including immunohistochemistry, immunofluorescence, flow cytometry, and western blotting were used to evaluate levels and activity of ZIP7 and ZIP6 in models of TAMR and sensitive (MCF-7) breast cancer. Analyses of these transporters in the clinical setting were performed using publicly available online resources: Gene Expression Profiling Interactive Analysis (GEPIA)2 and Kaplan-Meier Plotter (KmPlot).

Results:

Both total and activated levels of ZIP7 were significantly elevated in TAMR cells versus responsive MCF-7 cells. This was accompanied by an associated increase in free cytoplasmic zinc leading to amplification of downstream signals. Consistent with our proposed model, activated ZIP6 levels correlated with mitotic cells, which could be efficiently inhibited through use of our anti-ZIP6 monoclonal antibody. Mitotic inhibition translated to impaired proliferation in both models, with TAMR cells displaying increased sensitivity. Analysis of matched tumour and normal breast samples from patients revealed significant increases in both ZIP7 and ZIP6 in tumours, as well as family member ZIP4. Kaplan-Meier analysis revealed that high ZIP7 levels correlated with decreased overall and relapse-free survival (RFS) of patients, including patient groups who had received systemic endocrine therapy or tamoxifen only. In contrast, high ZIP6 levels were significantly linked to improved overall and RFS in all patients, as well as RFS in patients that received systemic endocrine therapy.

Conclusions:

TAMR cells displayed increased activity of both ZIP7 and ZIP6 transporters compared to anti-hormone responsive cells, suggesting their potential as novel therapeutic targets following development of resistant disease.

Discovery of Proteins Responsible for Resistance to Three Chemotherapy Drugs in Breast Cancer Cells Using Proteomics and Bioinformatics Analysis

Chemoresistance is a daunting obstacle to the effective treatment of breast cancer patients receiving chemotherapy. Although the mechanism of chemotherapy drug resistance has been explored broadly, the precise mechanism at the proteome level remains unclear. Especially, comparative studies between widely used anticancer drugs in breast cancer are very limited. In this study, we employed proteomics and bioinformatics approaches on chemoresistant breast cancer cell lines to understand the underlying resistance mechanisms that resulted from doxorubicin (DR), paclitaxel (PR), and tamoxifen (TAR). In total, 10,385 proteins were identified and quantified from three TMT 6-plex and one TMT 10-plex experiments. Bioinformatics analysis showed that Notch signaling, immune response, and protein re-localization processes were uniquely associated with DR, PR, and TAR resistance, respectively. In addition, proteomic signatures related to drug resistance were identified as potential targets of many FDA-approved drugs. Furthermore, we identified potential prognostic proteins with significant effects on overall survival. Representatively, PLXNB2 expression was associated with a highly significant increase in risk, and downregulation of ACOX3 was correlated with a worse overall survival rate. Consequently, our study provides new insights into the proteomic aspects of the distinct mechanisms underlying chemoresistance in breast cancer.

Hyaluronic acid-coated chitosan nanoparticles as targeted-carrier of tamoxifen against MCF7 and TMX-resistant MCF7 cells

Tamoxifen (TMX) is used to treat hormone-receptor-positive breast cancers at early stages. This research aimed to assess the potential of NPs in targeted delivery of TMX against MCF7 and TMX-resistant MCF7 breast cancer cell lines. For this purpose, a targeted delivery system including chitosan NPs coated with hyaluronic acid (HA-CS NPs) was created and examined in vitro. Chitosan NPs were first fabricated and loaded with TMX using the ionic-gelation method to prepare a drug-delivery system. Then, TMX-loaded CS NPs were coated by crosslinking the amino groups of chitosan to the carboxylic group of hyaluronic acid. The developed TMX delivery system was then optimized and characterized for particle fabrication, drug release, and targeting against cancer cells. The HA-CS particle size was 210 nm and its zeta potential was +25 mv. The encapsulation efficiency of TMX in NPs was 55%. TMX released from the NPs in acidic pH (5-6) was higher than the physiological pH (7.4). The cytotoxic effect of TMX-loaded HA-CS NPs on MCF7 and TMX-resistant MCF7 cells was significantly higher than TMX-loaded CS NPs and free drug. The findings confirmed the significant suppressive impact of TMX-loaded HA-CS NPs on MCF7 and TMX-resistant MCF7 cancer cells compared to the TMX-loaded CS NPs and free TMX. Graphical abstract.

Paeoniflorin Enhances the Sensitivity of ER-Positive Breast Cancer Cells to Tamoxifen through Promoting Sirtuin 4

Tamoxifen is an effective drug for treating patients with advanced estrogen receptor-positive (ER+) breast cancer (BC), but not for all ER + BC patients. Drug tolerance is the biggest obstacle. In this study, we designed an experiment to investigate whether paeoniflorin affects the ER + BC cell's sensitivity to tamoxifen in the T47D and MCF-7 cell lines. Herein, we found that paeoniflorin inhibited cell proliferation without inducing apoptosis. However, it enhanced tamoxifen-induced apoptosis in both cell lines. Immunoblotting revealed that paeoniflorin significantly increased the already elevated Bax/Bcl2 protein expression ratio and the caspase 3 activity levels, both induced by tamoxifen. Paeoniflorin was also found to increase SIRT4 expression, and deletion of SIRT4 could significantly reverse the inhibition of cell proliferation induced by paeoniflorin and significantly decrease paeoniflorin-enhanced apoptosis induced by tamoxifen. Moreover, protein expression detection revealed that paeoniflorin enhanced the tamoxifen-induced inhibition of STAT3 activation. Besides, the deletion of SIRT4 could significantly increase STAT3 activation in the T47D and MCF-7 cells. In conclusion, paeoniflorin suppressed STAT3 activation to enhance the sensitivity of ER-positive breast cancer cells to tamoxifen through promoting SIRT4 expression.

FoxO3a Inhibits Tamoxifen-Resistant Breast Cancer Progression by Inducing Integrin α5 Expression

Resistance to endocrine therapy is still a major clinical challenge in the management of estrogen receptor α-positive (ERα+) breast cancer (BC). Here, the role of the Forkhead box class O (FoxO)3a transcription factor in tumor progression has been evaluated in tamoxifen-resistant BC cells (TamR), expressing lower levels of FoxO3a compared to sensitive ones. FoxO3a re-expression reduces TamR motility (wound-healing and transmigration assays) and invasiveness (matrigel transwell invasion assays) through the mRNA (qRT-PCR) and protein (Western blot) induction of the integrin α5 subunit of the α5β1 fibronectin receptor, a well-known membrane heterodimer controlling cell adhesion and signaling. The induction occurs through FoxO3a binding to a specific Forkhead responsive core sequence located on the integrin α5 promoter (cloning, luciferase, and ChIP assays). Moreover, FoxO3a failed to inhibit migration and invasion in integrin α5 silenced (siRNA) cells, demonstrating integrin α5 involvement in both processes. Finally, using large-scale gene expression data sets, a strong positive correlation between FoxO3a and integrin α5 in ERα+, but not in ER-negative (ERα-), BC patients emerged. Altogether, our data show how the oncosuppressor FoxO3a, by increasing the expression of its novel transcriptional target integrin α5, reverts the phenotype of endocrine-resistant BC toward a lower aggressiveness.

Cisplatin-cyclooxygenase inhibitor conjugates, free and immobilised in mesoporous silica SBA-15, prove highly potent against triple-negative MDA-MB-468 breast cancer cell line

For the development of anticancer drugs with higher activity and reduced toxicity, two approaches were combined: preparation of platinum(IV) complexes exhibiting higher stability compared to their platinum(II) counterparts and loading them into mesoporous silica SBA-15 with the aim to utilise the passive enhanced permeability and retention (EPR) effect of nanoparticles for accumulation in tumour tissues. Three conjugates based on a cisplatin scaffold bearing the anti-inflammatory drugs naproxen, ibuprofen or flurbiprofen in the axial positions (1, 2 and 3, respectively) were synthesised and loaded into SBA-15 to afford the mesoporous silica nanoparticles (MSNs) SBA-15|1, SBA-15|2 and SBA-15|3. Superior antiproliferative activity of both free and immobilised conjugates in a panel of four breast cancer cell lines (MDA-MB-468, HCC1937, MCF-7 and BT-474) with markedly increased cytotoxicity with respect to cisplatin was demonstrated. All compounds exhibit highest activity against the triple-negative cell line MDA-MB-468, with conjugate 1 being the most potent. However, against MCF-7 and BT-474 cell lines, the most notable improvement was found, with IC₅₀ values up to 240-fold lower than cisplatin. Flow cytometry assays clearly show that all compounds induce apoptotic cell death elevating the levels of both early and late apoptotic cells. Furthermore, autophagy as well as formation of reactive oxygen species (ROS) and nitric oxide (NO) were elevated to a similar or greater extent than with cisplatin.

Hesperidin and its aglycone hesperetin in breast cancer therapy: A review of recent developments and future prospects

Breast cancer (BC) has high incidence and mortality rates, making it a major global health issue. BC treatment has been challenging due to the presence of drug resistance and the limited availability of therapeutic options for triple-negative and metastatic BC, thereby urging the exploration of more effective anti-cancer agents. Hesperidin and its aglycone hesperetin, two flavonoids from citrus species, have been extensively evaluated for their anti-cancer potentials. In this review, available literatures on the chemotherapeutic and chemosensitising activities of hesperidin and hesperetin in preclinical BC models are reported. The safety and bioavailability of hesperidin and hesperetin as well as the strategies to enhance their bioavailability are also discussed. Overall, hesperidin and hesperetin can inhibit cell proliferation, migration and BC stem cells as well as induce apoptosis and cell cycle arrest in vitro. They can also inhibit tumour growth, metastasis and neoplastic changes in tissue architecture in vivo. Moreover, the co-administration of hesperidin or hesperetin with doxorubicin, letrozole or tamoxifen can enhance the efficacies of these clinically available agents. These chemotherapeutic and chemosensitising activities of hesperidin and hesperetin have been linked to several mechanisms, including the modulation of signalling pathways, glucose uptake, enzymes, miRNA expression, oxidative status, cell cycle regulatory proteins, tumour suppressor p53, plasma and liver lipid profiles as well as DNA repair mechanisms. However, poor water solubility, extensive phase II metabolism and apical efflux have posed limitations to the bioavailability of hesperidin and hesperetin. Various strategies for bioavailability enhancement have been studied, including the utilisation of nano-based drug delivery systems and the co-administration of hesperetin with other flavonoids. In particular, nanoformulated hesperidin and hesperetin possess greater chemotherapeutic and chemosensitising activities than free compounds. Despite promising preclinical results, further safety and efficacy evaluation of hesperidin and hesperetin as well as their nanoformulations in clinical trials is required to ascertain their potentials to be developed as clinically useful agents for BC treatment.

Antiproliferative activity of Tamoxifen, Vitamin D3 and their concomitant treatment

Breast cancer stands out as the most common cancer type among women throughout the world. Especially for the estrogen receptor alpha (ER α +) positive breast cancer cells Tamoxifen has been widely used as an anti-cancer agent. Tamoxifen's mechanism of action is through ER. It binds to the receptor and leads to a conformational change which eventually prevents cancer cells proliferation and survival. In our current study, we aimed to investigate the combination of Tamoxifen with Vitamin D₃ to test whether this combination will enhance the anti-cancer effect of Tamoxifen on breast cancer cells in vitro. Vitamin D₃ has sterol structure and this property enables it to act similar to hormones. Vitamin D Receptor (VDR) has been commonly found in different types of cancer cells including but not limited to breast and prostate cancer cells. Through this receptor Vitamin D₃ acts as an anti-proliferative agent. We examined the proliferation rate, apoptosis and necrosis levels as well as cell cycle progression in MCF-7 breast cancer cell line in the presence of Vitamin D₃ and Tamoxifen to compare the changes with the Tamoxifen treated group. Our results suggest that Tamoxifen was a more potent anti-cancer agent than Vitamin D₃ or its combination with Vitamin D₃ based on cell cycle arrest, apoptosis and cell proliferation levels. This effect in the apoptosis rate and cell cycle stage of the MCF-7 cells were in line with the changes in gene expression profile of P53, BAX and BCL-2. Our results suggest that Tamoxifen by itself is adequate enough and more potent than Vitamin D₃ or its combination with Vitamin D₃ as anti-cancer agent for the breast cancer cells in vitro.