Premature senescence in human breast cancer and colon cancer cells by tamoxifen-mediated reactive oxygen species generation

Pharmacological modulation of cellular senescence: Implications for breast cancer progression and therapeutic strategies

Senescence, defined by the cessation of cell proliferation, plays a critical and multifaceted role in breast cancer progression and treatment. Senescent cells produce senescence-associated secretory phenotypes (SASP) comprising inflammatory cytokines, chemokines, and small molecules, which actively shape the tumor microenvironment, influencing cancer development, progression, and metastasis. This review provides a comprehensive analysis of the types and origins of senescent cells in breast cancer, alongside their markers and detection methods. Special focus is placed on pharmacological strategies targeting senescence, including drugs that induce or inhibit senescence, their molecular mechanisms, and their roles in therapeutic outcomes when combined with chemotherapy and radiotherapy. By exploring these pharmacological interventions and their impact on breast cancer treatment, this review underscores the potential of senescence-targeting therapies to revolutionize breast cancer management.

A Xanthine Derivative With Novel Heat Shock Protein 90-Alpha Inhibitory and Senolytic Properties

The accumulation of senescent cells contributes to aging and related diseases; therefore, discovering safe senolytic agents-compounds that selectively eliminate senescent cells-is a critical priority. Heat shock protein 90 (HSP90) inhibitors (HSP90i), traditionally investigated for cancer treatment, have shown potential as senolytic agents. However, inhibitors face formulation, toxicity, and cost challenges. To overcome these limitations, we employed a virtual screening approach combining structure-based prefiltering with a ligand-based pharmacophore model to identify novel, potentially safe HSP90 alpha isoform inhibitors exhibiting senolytic properties. This strategy identified 14 candidate molecules evaluated for senolytic activity in primary human fetal pulmonary fibroblasts. Four compounds exhibited significant HSP90i and senolytic activity, including two novel compounds, namely K4 and K5. The latter, 1-benzyl-3-(2-methylphenyl)-3,7-dihydro-1H-purine-2,6-dione, structurally related to the xanthinic family, emerged as a promising, well-tolerated senolytic agent. K5 demonstrated senolytic activity across various cellular senescence models, including human fibroblasts, mesenchymal stem cells, and breast cancer cells. It was also effective in vivo, extending lifespan in Drosophila and reducing senescence markers in geriatric mice. Additionally, the xanthinic nature of K5 implicates a multimodal action, now including the inhibition of HSP90α, that might enhance its efficacy and selectivity towards senescent cells, Senolytic index SI > 1320 for IMR90 cells, and SI > 770 for WI38 cells, underscoring its therapeutic potential. These findings advance senolytic therapy research, opening new avenues for safer interventions to combat age-related inflammaging and diseases, including cancer, and possibly extend a healthy lifespan.

Antioxidant Senotherapy by Natural Compounds: A Beneficial Partner in Cancer Treatment

Aging is a general biological process inherent in all living organisms. It is characterized by progressive cellular dysfunction. For many years, aging has been widely recognized as a highly effective mechanism for suppressing the progression of malignant neoplasms. However, in recent years, increasing evidence suggests a "double-edged" role of aging in cancer development. According to these data, aging is not only a tumor suppressor that leads to cell cycle arrest in neoplastic cells, but also a cancer promoter that ensures a chronic proinflammatory and immunosuppressive microenvironment. In this regard, in our review, we discuss recent data on the destructive role of senescent cells in the pathogenesis of cancer. We also identify for the first time correlations between the modulation of the senescence-associated secretory phenotype and the antitumor effects of naturally occurring molecules.

New Mitochondria-Targeted Fisetin Derivative Compromises Mitophagy and Limits Survival of Drug-Induced Senescent Breast Cancer Cells

Mitochondria are considered as promising targets for cancer treatment. In the present study, triphenyl phosphonium cationic group-conjugated fisetin (mito-fisetin) was synthesized, and its anticancer activity was investigated in several cellular models of estrogen receptor (ER)-positive breast cancer in vitro and in vivo in proliferating and tamoxifen-promoted senescent states. Mito-fisetin, when used at low micromolar concentrations, stimulated the dissipation of mitochondrial membrane potential and oxidative stress, and affected mitochondrial function, resulting in apoptosis induction in senescent breast cancer cells. Mito-fisetin-mediated cytotoxicity was due to increased levels of phosphorylated AMPK, decreased levels of AKT and HSP90, and impaired mitophagic response, as judged by the analysis of the markers of mitophagosome formation. Senescent breast cancer cells were found to be more sensitive to mito-fisetin treatment than proliferating ones. We postulate that mitochondrial targeting in the case of fisetin may be considered as a promising anticancer and senotherapeutic strategy to eliminate drug-resistant senescent breast cancer cells.

Modulation of tumor plasticity by senescent cells: Deciphering basic mechanisms and survival pathways to unravel therapeutic options

Senescence is a cellular state in which the cell loses its proliferative capacity, often irreversibly. Physiologically, it occurs due to a limited capacity of cell division associated with telomere shortening, the so-called replicative senescence. It can also be induced early due to DNA damage, oncogenic activation, oxidative stress, or damage to other cellular components (collectively named induced senescence). Tumor cells acquire the ability to bypass replicative senescence, thus ensuring the replicative immortality, a hallmark of cancer. Many anti-cancer therapies, however, can lead tumor cells to induced senescence. Initially, this response leads to a slowdown in tumor growth. However, the longstanding accumulation of senescent cells (SnCs) in tumors can promote neoplastic progression due to the enrichment of numerous molecules and extracellular vesicles that constitutes the senescence-associated secretory phenotype (SASP). Among other effects, SASP can potentiate or unlock the tumor plasticity and phenotypic transitions, another hallmark of cancer. This review discusses how SnCs can fuel mechanisms that underlie cancer plasticity, like cell differentiation, stemness, reprogramming, and epithelial-mesenchymal transition. We also discuss the main molecular mechanisms that make SnCs resistant to cell death, and potential strategies to target SnCs. At the end, we raise open questions and clinically relevant perspectives in the field.

Autophagy and senescence facilitate the development of antiestrogen resistance in ER positive breast cancer

Estrogen receptor positive (ER+) breast cancer is the most common breast cancer diagnosed annually in the US with endocrine-based therapy as standard-of-care for this breast cancer subtype. Endocrine therapy includes treatment with antiestrogens, such as selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators (SERDs), and aromatase inhibitors (AIs). Despite the appreciable remission achievable with these treatments, a substantial cohort of women will experience primary tumor recurrence, subsequent metastasis, and eventual death due to their disease. In these cases, the breast cancer cells have become resistant to endocrine therapy, with endocrine resistance identified as the major obstacle to the medical oncologist and patient. To combat the development of endocrine resistance, the treatment options for ER+, HER2 negative breast cancer now include CDK4/6 inhibitors used as adjuvants to antiestrogen treatment. In addition to the dysregulated activity of CDK4/6, a plethora of genetic and biochemical mechanisms have been identified that contribute to endocrine resistance. These mechanisms, which have been identified by lab-based studies utilizing appropriate cell and animal models of breast cancer, and by clinical studies in which gene expression profiles identify candidate endocrine resistance genes, are the subject of this review. In addition, we will discuss molecular targeting strategies now utilized in conjunction with endocrine therapy to combat the development of resistance or target resistant breast cancer cells. Of approaches currently being explored to improve endocrine treatment efficacy and patient outcome, two adaptive cell survival mechanisms, autophagy, and "reversible" senescence, are considered molecular targets. Autophagy and/or senescence induction have been identified in response to most antiestrogen treatments currently being used for the treatment of ER+ breast cancer and are often induced in response to CDK4/6 inhibitors. Unfortunately, effective strategies to target these cell survival pathways have not yet been successfully developed. Thus, there is an urgent need for the continued interrogation of autophagy and "reversible" senescence in clinically relevant breast cancer models with the long-term goal of identifying new molecular targets for improved treatment of ER+ breast cancer.

BRD4 Inhibition as a Strategy to Prolong the Response to Standard of Care in Estrogen Receptor-Positive Breast Cancer

Breast cancer is the most commonly occurring malignancy in women and the second most common cause of cancer-related deaths. ER+ breast cancer constitutes approximately 70% of all breast cancer cases. The standard of care for ER+ breast cancer involves estrogen antagonists such as tamoxifen or fulvestrant in combination with CDK4/6 inhibitors such as palbociclib. However, these treatments are often not curative, with disease recurrence and metastasis being responsible for patient mortality. Overexpression of the epigenetic regulator, BRD4, has been shown to be a negative prognostic indicator in breast cancer, and BET family inhibitors such as ARV-825 and ABBV-744 have garnered interest for their potential to improve and prolong the response to current therapeutic strategies. The current work examined the potential of utilizing ARV-825 and ABBV-744 to increase the effectiveness of tamoxifen or fulvestrant plus palbociclib. ARV-825 was effective in both p53 wild-type (WT) breast tumor cells and in cells lacking functional p53 either alone or in combination with tamoxifen, while the effectiveness of ABBV-744 was limited to fulvestrant plus palbociclib in p53 WT cells. These differential effects may be related to the capacity to suppress c-Myc, a downstream target of BRD4.

The beneficial effects of tamoxifen on arteries: a key player for cardiovascular health of breast cancer patient

Breast cancer is the most common cancer in women. Over the past few decades, advances in cancer detection and treatment have significantly improved survival rate of breast cancer patients. However, due to the cardiovascular toxicity of cancer treatments (chemotherapy, anti-HER2 antibodies and radiotherapy), cardiovascular diseases (CVD) have become an increasingly important cause of long-term morbidity and mortality in breast cancer survivors. Endocrine therapies are prescribed to reduce the risk of recurrence and specific death in estrogen receptor-positive (ER+) early breast cancer patients, but their impact on CVD is a matter of debate. Whereas aromatase inhibitors and luteinizing hormone-releasing hormone (LHRH) analogs inhibit estrogen synthesis, tamoxifen acts as a selective estrogen receptor modulator (SERM), opposing estrogen action in the breast but mimicking their actions in other tissues, including arteries. This review aims to summarize the main clinical and experimental studies reporting the effects of tamoxifen on CVD. In addition, we will discuss how recent findings on the mechanisms of action of these therapies may contribute to a better understanding and anticipation of CVD risk in breast cancer patients.

Targeting senescence as an anticancer therapy

Cellular senescence is a stress response elicited by different molecular insults. Senescence results in cell cycle exit and is characterised by multiple phenotypic changes such as the production of a bioactive secretome. Senescent cells accumulate during ageing and are present in cancerous and fibrotic lesions. Drugs that selectively kill senescent cells (senolytics) have shown great promise for the treatment of age-related diseases. Senescence plays paradoxical roles in cancer. Induction of senescence limits cancer progression and contributes to therapy success, but lingering senescent cells fuel progression, recurrence, and metastasis. In this review, we describe the intricate relation between senescence and cancer. Moreover, we enumerate how current anticancer therapies induce senescence in tumour cells and how senolytic agents could be deployed to complement anticancer therapies. "One-two punch" therapies aim to first induce senescence in the tumour followed by senolytic treatment to target newly exposed vulnerabilities in senescent tumour cells. "One-two punch" represents an emerging and promising new strategy in cancer treatment. Future challenges of "one-two punch" approaches include how to best monitor senescence in cancer patients to effectively survey their efficacy.

Targeting mitochondrial metabolism for metastatic cancer therapy

Primary tumors evolve metabolic mechanisms favoring glycolysis for adenosine triphosphate (ATP) generation and antioxidant defenses. In contrast, metastatic cells frequently depend on mitochondrial respiration and oxidative phosphorylation (OxPhos). This reliance of metastatic cells on OxPhos can be exploited using drugs that target mitochondrial metabolism. Therefore, therapeutic agents that act via diverse mechanisms, including the activation of signaling pathways that promote the production of reactive oxygen species (ROS) and/or a reduction in antioxidant defenses may elevate oxidative stress and inhibit tumor cell survival. In this review, we will provide (1) a mechanistic analysis of function-selective extracellular signal-regulated kinase-1/2 (ERK1/2) inhibitors that inhibit cancer cells through enhanced ROS, (2) a review of the role of mitochondrial ATP synthase in redox regulation and drug resistance, (3) a rationale for inhibiting ERK signaling and mitochondrial OxPhos toward the therapeutic goal of reducing tumor metastasis and treatment resistance. Recent reports from our laboratories using metastatic melanoma and breast cancer models have shown the preclinical efficacy of novel and rationally designed therapeutic agents that target ERK1/2 signaling and mitochondrial ATP synthase, which modulate ROS events that may prevent or treat metastatic cancer. These findings and those of others suggest that targeting a tumor's metabolic requirements and vulnerabilities may inhibit metastatic pathways and tumor growth. Approaches that exploit the ability of therapeutic agents to alter oxidative balance in tumor cells may be selective for cancer cells and may ultimately have an impact on clinical efficacy and safety. Elucidating the translational potential of metabolic targeting could lead to the discovery of new approaches for treatment of metastatic cancer.

Estrogen receptor inhibition mediates radiosensitization of ER-positive breast cancer models

Endocrine therapy (ET) is an effective first-line therapy for women with estrogen receptor-positive (ER + ) breast cancers. While both ionizing radiation (RT) and ET are used for the treatment of women with ER+ breast cancer, the most effective sequencing of therapy and the effect of ET on tumor radiosensitization remains unclear. Here we sought to understand the effects of inhibiting estrogen receptor (ER) signaling in combination with RT in multiple preclinical ER+ breast cancer models. Clonogenic survival assays were performed using variable pre- and post-treatment conditions to assess radiosensitization with estradiol, estrogen deprivation, tamoxifen, fulvestrant, or AZD9496 in ER+ breast cancer cell lines. Estrogen stimulation was radioprotective (radiation enhancement ratios [rER]: 0.51–0.82). Conversely, when given one hour prior to RT, ER inhibition or estrogen depletion radiosensitized ER+ MCF-7 and T47D cells (tamoxifen rER: 1.50–1.60, fulvestrant rER: 1.76–2.81, AZD9496 rER: 1.33–1.48, estrogen depletion rER: 1.47–1.51). Combination treatment resulted in an increase in double-strand DNA (dsDNA) breaks as a result of inhibition of non-homologous end joining-mediated dsDNA break repair with no effect on homologous recombination. Treatment with tamoxifen or fulvestrant in combination with RT also increased the number of senescent cells but did not affect apoptosis or cell cycle distribution. Using an MCF-7 xenograft model, concurrent treatment with tamoxifen and RT was synergistic and resulted in a significant decrease in tumor volume and a delay in time to tumor doubling without significant toxicity. These findings provide preclinical evidence that concurrent treatment with ET and RT may be an effective radiosensitization strategy.

Binding of the angiogenic/senescence inducer CCN1/CYR61 to integrin α6β1 drives endocrine resistance in breast cancer cells

CCN1/CYR61 promotes angiogenesis, tumor growth and chemoresistance by binding to its integrin receptor α_vβ₃ in endothelial and breast cancer (BC) cells. CCN1 controls also tissue regeneration by engaging its integrin receptor α₆β₁ to induce fibroblast senescence. Here, we explored if the ability of CCN1 to drive an endocrine resistance phenotype in estrogen receptor-positive BC cells relies on interactions with either α_vβ₃ or α₆β₁. First, we took advantage of site-specific mutagenesis abolishing the CCN1 receptor-binding sites to α_vβ₃ and α₆β₁ to determine the integrin partner responsible for CCN1-driven endocrine resistance. Second, we explored a putative nuclear role of CCN1 in regulating ERα-driven transcriptional responses. Retroviral forced expression of a CCN1 derivative with a single amino acid change (D125A) that abrogates binding to α_vβ₃ partially phenocopied the endocrine resistance phenotype induced upon overexpression of wild-type (WT) CCN1. Forced expression of the CCN1 mutant TM, which abrogates all the T1, H1, and H2 binding sites to α₆β₁, failed to bypass the estrogen requirement for anchorage-independent growth or to promote resistance to tamoxifen. Wild-type CCN1 promoted estradiol-independent transcriptional activity of ERα and enhanced ERα agonist response to tamoxifen. The α₆β₁-binding-defective TM-CCN1 mutant lost the ERα co-activator-like behavior of WT-CCN1. Co-immunoprecipitation assays revealed a direct interaction between endogenous CCN1 and ERα, and in vitro approaches confirmed the ability of recombinant CCN1 to bind ERα. CCN1 signaling via α₆β₁, but not via α_vβ₃, drives an endocrine resistance phenotype that involves a direct binding of CCN1 to ERα to regulate its transcriptional activity in ER+ BC cells.

Cytotoxic effects of the biflavonoids isolated from Selaginella trichoclada on MCF-7 cells and its potential mechanism

A new biflavonoid, (2''S)-6''-methyl-2'',3''-dihydroochnaflavone (1), along with two known ochnaflavones (2, 3), four known amentoflavones (4-7) and two known robustaflavones (8, 9) were obtained from the 70% EtOH extract of Selaginella trichoclada. The chemical structures of isolated compounds were elucidated by extensive spectroscopic analyses. Overall, compounds 1-9 displayed moderate cytotoxic effects against human breast cancer MCF-7 cell lines. Among them, compounds 2 and 8 exhibited relatively strong cytotoxic effects against MCF-7 cells with an IC₅₀ value of 7.7 and 6.9 μΜ, respectively. The results of RNA-sequencing and KEGG functional enrichment analysis showed that 8 could induce ferroptosis in MCF-7 cells by down-regulating the expression of ferroptosis-related genes including ACSL4, NOXO1, NOXA1, ACSL5, STEAP3, LPCAT3, ATG7 and TP53. Then 8 could inhibit the expression of ACSL4 proteins through molecule docking analysis, which showed a strong interaction of - 11.89 Kcal/mol binding energy. Those results indicate that 8 could be chemotherapy agents to fight drug resistance in breast cancer by down-regulating the expression level of ACSL4 proteins via ferroptosis, which needs to be further certified in vitro.

Diabetes and Colorectal Cancer Risk: A New Look at Molecular Mechanisms and Potential Role of Novel Antidiabetic Agents

Epidemiological data have demonstrated a significant association between the presence of type 2 diabetes mellitus (T2DM) and the development of colorectal cancer (CRC). Chronic hyperglycemia, insulin resistance, oxidative stress, and inflammation, the processes inherent to T2DM, also play active roles in the onset and progression of CRC. Recently, small dense low-density lipoprotein (LDL) particles, a typical characteristic of diabetic dyslipidemia, emerged as another possible underlying link between T2DM and CRC. Growing evidence suggests that antidiabetic medications may have beneficial effects in CRC prevention. According to findings from a limited number of preclinical and clinical studies, glucagon-like peptide-1 receptor agonists (GLP-1RAs) could be a promising strategy in reducing the incidence of CRC in patients with diabetes. However, available findings are inconclusive, and further studies are required. In this review, novel evidence on molecular mechanisms linking T2DM with CRC development, progression, and survival will be discussed. In addition, the potential role of GLP-1RAs therapies in CRC prevention will also be evaluated.

Differential biological effects of aromatase inhibitors: Apoptosis, autophagy, senescence and modulation of the hormonal status in breast cancer cells

Estrogen receptor-positive (ER⁺) breast carcinomas are the most common subtype, corresponding to 60% of the cases in premenopausal and 75% in postmenopausal women. The third-generation of aromatase inhibitors (AIs), the non-steroidal Anastrozole (Ana) and Letrozole (Let) and the steroidal Exemestane (Exe), are considered a first-line endocrine therapy for postmenopausal women. Despite their clinical success, the development of resistance is the major setback in clinical practice. Nevertheless, the lack of cross-resistance between AIs hints that these drugs may act through distinct mechanisms. Therefore, this work studied the different effects induced by AIs on biological processes, such as cell proliferation, death, autophagy and senescence. Moreover, their effects on the regulation of the hormonal environment were also explored. The non-steroidal AIs induce senescence, through increased YPEL3 expression, on aromatase-overexpressing breast cancer cells (MCF-7aro), whereas Exe promotes a cytoprotective autophagy, thus blocking senescence induction. In addition, in a hormone-enriched environment, the non-steroidal AIs prevent estrogen signaling, despite up-regulating the estrogen receptor alpha (ERα), while Exe down-regulates ERα and maintains its activation. In these conditions, all AIs up-regulate the androgen receptor (AR) which blocks EGR3 transcription in Exe-treated cells. On the other hand, in hormone-depleted conditions, a crosstalk between AR and ERα occurs, enhancing the estrogenic effects of Exe. This indicates that Exe modulates both ERα and AR, while Ana and Let act as pure AIs. Thus, this study highlights the potential clinical benefit of combining AR antagonists with Exe and discourages the sequential use of Exe as second-line therapy in postmenopausal breast cancer.

The interplay between apoptosis and cellular senescence: Bcl-2 family proteins as targets for cancer therapy

Cell death by apoptosis and permanent cell cycle arrest by senescence serve as barriers to the development of cancer. Chemotherapeutic agents not only induce apoptosis, they can also induce senescence known as therapy-induced senescence (TIS). There are, however, controversies whether TIS improves or worsens therapeutic outcome. Unlike apoptosis, which permanently removes cancer cells, senescent cells are metabolically active, and can contribute to tumor progression and relapse. If senescent cells are not cleared by the immune system or if cancer cells escape senescence, they may acquire resistance to apoptotic stimuli and become highly aggressive. Thus, there have been significant efforts in developing senolytics, drugs that target these pro-survival molecules to eliminate senescent cells. The anti-apoptotic Bcl-2 family proteins not only protect against cell death by apoptosis, but they also allow senescent cells to survive. While combining senolytics with chemotherapeutic drugs is an attractive approach, there are also limitations. Moreover, members of the Bcl-2 family have distinct effects on apoptosis and senescence. The purpose of this review article is to discuss recent literatures on how members of the Bcl-2 family orchestrate the interplay between apoptosis and senescence, and the challenges and progress in targeting these Bcl-2 family proteins for cancer therapy.

Autophagy and senescence in cancer therapy

Tumor cells can undergo diverse responses to cancer therapy. While apoptosis represents the most desirable outcome, tumor cells can alternatively undergo autophagy and senescence. Both autophagy and senescence have the potential to make complex contributions to tumor cell survival via both cell autonomous and cell non-autonomous pathways. The induction of autophagy and senescence in tumor cells, preclinically and clinically, either individually or concomitantly, has generated interest in the utilization of autophagy modulating and senolytic therapies to target autophagy and senescence, respectively. This chapter summarizes the current evidence for the promotion of autophagy and senescence as fundamental responses to cancer therapy and discusses the complexity of their functional contributions to cell survival and disease outcomes. We also highlight current modalities designed to exploit autophagy and senescence in efforts to improve the efficacy of cancer therapy.

Senolytics for Cancer Therapy: Is All That Glitters Really Gold?

Simple Summary

Senescence is an essential component of tumor cell biology and is a primary cell stress response to therapy. While the long-term impact of senescence in cancer therapy is not yet fully understood, the use of senolytics, drugs that selectively kill senescent cells, is an area of active investigation in cancer treatment. Several challenges and unanswered questions have arisen from the current preclinical literature, indicating the need to re-evaluate some of the basic premises and experimental approaches, as well as the potential utility for translating to the clinic the application of senolytics as adjuvants to current cancer therapy.

Abstract

Senolytics represent a group of mechanistically diverse drugs that can eliminate senescent cells, both in tumors and in several aging-related pathologies. Consequently, senolytic use has been proposed as a potential adjuvant approach to improve the response to senescence-inducing conventional and targeted cancer therapies. Despite the unequivocal promise of senolytics, issues of universality, selectivity, resistance, and toxicity remain to be further clarified. In this review, we attempt to summarize and analyze the current preclinical literature involving the use of senolytics in senescent tumor cell models, and to propose tenable solutions and future directions to improve the understanding and use of this novel class of drugs.

Targeting Redox Metabolism in Pancreatic Cancer

Cell metabolism is reprogrammed in cancer cells to meet their high bioenergetics and biosynthetic demands. This metabolic reprogramming is accompanied by alterations in redox metabolism, characterized by accumulation of reactive oxygen species (ROS). Elevated production of ROS, mostly by mitochondrial respiration, is counteracted by higher production of antioxidant defenses (mainly glutathione and antioxidant enzymes). Cancer cells are adapted to a high concentration of ROS, which contributes to tumorigenesis, metastasis formation, resistance to therapy and relapse. Frequent genetic alterations observed in pancreatic ductal adenocarcinoma (PDAC) affect KRAS and p53 proteins, which have a role in ROS production and control, respectively. These observations led to the proposal of the use of antioxidants to prevent PDAC development and relapse. In this review, we focus on the therapeutic strategies to further increase ROS level to induce PDAC cell death. Combining the promotion of ROS production and inhibition of antioxidant capacity is a promising avenue for pancreatic cancer therapy in the clinic.

Pharmacologic downregulation of protein arginine methyltransferase1 expression by adenosine dialdehyde increases cell senescence in breast cancer

We investigated the role of protein arginine methylation (PAM) in estrogen receptor (ER)-positive breast cancer cells through pharmacological intervention. Tamoxifen (TAM) or adenosine dialdehyde (ADOX), independently, triggered cell cycle arrest and down-regulated PAM, as reduced protein arginine methyltransferase1 (PRMT1) mRNA and asymmetric dimethylarginine (ADMA) levels. Synergistic effect of these compounds elicited potent anti-cancer effect. However, reduction in ADMA was not proportionate with the compound-induced down-regulation of PRMT1 mRNA. We hypothesized that the disproportionate effect is due to the influence of the compounds on other methyltransferases, which catalyze the arginine dimethylation reaction and the diversity in the degree of drug-protein interaction among these methyltransferases. In silico analyses revealed that independently, ADOX or TAM, binds with phosphatidylethanolamine-methyltransferase (PEMT) or betaine homocysteine-methyl transferase (BHMT); and that the binding affinity of ADOX with PEMT or BHMT is prominent than TAM. These observations suggest that in breast cancer, synergistic effect of ADOX + TAM elicits impressive protective function by regulating PAM; and plausibly, restoration of normal enzyme activities of methyltransferases catalyzing arginine dimethylation could have clinical benefits.

TRIM27 Functions as a Novel Oncogene in Non-Triple-Negative Breast Cancer by Blocking Cellular Senescence through p21 Ubiquitination

In the current study, we aimed to explore the correlation between TRIM27 and breast cancer prognosis, as well as the functions of TRIM27 in breast cancer and their underlying mechanisms. Bioinformatics analyses were used to examine the correlation between TRIM27 and breast cancer prognosis. Moreover, TRIM27 knockdown and overexpression in breast cancer cells were performed to investigate its functions in breast cancer. Tamoxifen (TAM) was applied to evaluate the influence of TRIM27 on chemoresistance of breast cancer cells, while co-immunoprecipitation (coIP) was performed to identify the E3 ubiquitin ligase capability of TRIM27. High expression of TRIM27 was found in non-triple-negative breast cancer (non-TNBC) tumor tissues and was positively correlated with the mortality of non-TNBC patients. Moreover, TRIM27 could suppress non-TNBC cell apoptosis and senescence, promote cell viability and tumor growth, counteract the anti-cancer effects of TAM, and mediate ubiquitination of p21. In addition, EP300 could enhance the expression of TRIM27 and its transcription promoter H3K27ac. TRIM27, through ubiquitination of p21, might serve as a prognostic biomarker for non-TNBC prognosis. TRIM27 functions as a novel oncogene in non-TNBC cellular processes, especially suppressing cell senescence and interfering with non-TNBC chemoresistance.

Targeting ferroptosis in breast cancer

Ferroptosis is a recently discovered distinct type of regulated cell death caused by the accumulation of lipid-based ROS. Metabolism and expression of specific genes affect the occurrence of ferroptosis, making it a promising therapeutic target to manage cancer. Here, we describe the current status of ferroptosis studies in breast cancer and trace the key regulators of ferroptosis back to previous studies. We also compare ferroptosis to common regulated cell death patterns and discuss the sensitivity to ferroptosis in different subtypes of breast cancer. We propose that viewing ferroptosis-related studies from a historical angle will accelerate the development of ferroptosis-based biomarkers and therapeutic strategies in breast cancer.

Targeting breast cancer metabolism with a novel inhibitor of mitochondrial ATP synthesis

Inhibitors of mitochondrial respiration and ATP synthesis may promote the selective killing of respiration-competent cancer cells that are critical for tumor progression. We previously reported that CADD522, a small molecule inhibitor of the RUNX2 transcription factor, has potential for breast cancer treatment. In the current study, we show that CADD522 inhibits mitochondrial oxidative phosphorylation by decreasing the mitochondrial oxygen consumption rate (OCR) and ATP production in human breast cancer cells in a RUNX2-independent manner. The enzyme activity of mitochondrial ATP synthase was inhibited by CADD522 treatment. Importantly, results from cellular thermal shift assays that detect drug-induced protein stabilization revealed that CADD522 interacts with both α and β subunits of the F1-ATP synthase complex. Differential scanning fluorimetry also demonstrated interaction of α subunits of the F1-ATP synthase to CADD522. These results suggest that CADD522 might target the enzymatic F1 subunits in the ATP synthase complex. CADD522 increased the levels of intracellular reactive oxygen species (ROS), which was prevented by MitoQ, a mitochondria-targeted antioxidant, suggesting that cancer cells exposed to CADD522 may elevate ROS from mitochondria. CADD522-increased mitochondrial ROS levels were enhanced by exogenously added pro-oxidants such as hydrogen peroxide or tert-butyl hydroperoxide. Conversely, CADD522-mediated cell growth inhibition was blocked by N-acetyl-l-cysteine, a general ROS scavenger. Therefore, CADD522 may exert its antitumor activity by increasing mitochondrial driven cellular ROS levels. Collectively, our data suggest in vitro proof-of-concept that supports inhibition of mitochondrial ATP synthase and ROS generation as contributors to the effectiveness of CADD522 in suppression of tumor growth.

Senescence and Cancer: A Review of Clinical Implications of Senescence and Senotherapies

Cellular senescence is a key component of human aging that can be induced by a range of stimuli, including DNA damage, cellular stress, telomere shortening, and the activation of oncogenes. Senescence is generally regarded as a tumour suppressive process, both by preventing cancer cell proliferation and suppressing malignant progression from pre-malignant to malignant disease. It may also be a key effector mechanism of many types of anticancer therapies, such as chemotherapy, radiotherapy, and endocrine therapies, both directly and via bioactive molecules released by senescent cells that may stimulate an immune response. However, senescence may contribute to reduced patient resilience to cancer therapies and may provide a pathway for disease recurrence after cancer therapy. A new group of drugs, senotherapies, (drugs which interact with senescent cells to interfere with their pro-aging impacts by either selectively destroying senescent cells (senolytic drugs) or inhibiting their function (senostatic drugs)) are under active investigation to determine whether they can enhance the efficacy of cancer therapies and improve resilience to cancer treatments. Senolytic drugs include quercetin, navitoclax, and fisetin and preclinical and early phase clinical data are emerging of their potential role in cancer treatments, although none are yet in routine use clinically. This article provides a review of these issues.

The Premature Senescence in Breast Cancer Treatment Strategy

Cellular senescence is a permanent blockade of cell proliferation. In response to therapy-induced stress, cancer cells undergo apoptosis or premature senescence. In apoptosis-resistant cancer cells or at lower doses of anticancer drugs, therapy-induced stress leads to premature senescence. The role of this senescence in cancer treatment is discussable. First of all, the senescent cells lose the ability to proliferate, migrate, and invade. In addition, the senescent cells secrete a set of proteins (inflammatory cytokines, chemokines, growth factors) known as the senescence-associated secretory phenotype (SASP), which influences non-senescent normal cells and non-senescent cancer cells in the tumor microenvironment and triggers tumor promotion and recurrence. Recently, many studies have examined senescence induction through breast cancer therapy and potentially using this phenomenon to treat this cancer. This review summarizes the recent in vitro, in vivo, and clinical studies investigating senescence in breast cancer treatments. Senescence inductors, senolytics, as well as their action mechanism are discussed herein. Potential SASP-modulating treatment strategies are also described.

Therapy-Induced Senescence: An "Old" Friend Becomes the Enemy

For the past two decades, cellular senescence has been recognized as a central component of the tumor cell response to chemotherapy and radiation. Traditionally, this form of senescence, termed Therapy-Induced Senescence (TIS), was linked to extensive nuclear damage precipitated by classical genotoxic chemotherapy. However, a number of other forms of therapy have also been shown to induce senescence in tumor cells independently of direct genomic damage. This review attempts to provide a comprehensive summary of both conventional and targeted anticancer therapeutics that have been shown to induce senescence in vitro and in vivo. Still, the utility of promoting senescence as a therapeutic endpoint remains under debate. Since senescence represents a durable form of growth arrest, it might be argued that senescence is a desirable outcome of cancer therapy. However, accumulating evidence suggesting that cells have the capacity to escape from TIS would support an alternative conclusion, that senescence provides an avenue whereby tumor cells can evade the potentially lethal action of anticancer drugs, allowing the cells to enter a temporary state of dormancy that eventually facilitates disease recurrence, often in a more aggressive state. Furthermore, TIS is now strongly connected to tumor cell remodeling, potentially to tumor dormancy, acquiring more ominous malignant phenotypes and accounts for several untoward adverse effects of cancer therapy. Here, we argue that senescence represents a barrier to effective anticancer treatment, and discuss the emerging efforts to identify and exploit agents with senolytic properties as a strategy for elimination of the persistent residual surviving tumor cell population, with the goal of mitigating the tumor-promoting influence of the senescent cells and to thereby reduce the likelihood of cancer relapse.

Germline BRCA-Associated Endometrial Carcinoma Is a Distinct Clinicopathologic Entity

PURPOSE

Whether endometrial carcinoma (EC) should be considered part of the gBRCA1/2-associated hereditary breast and ovarian cancer (HBOC) syndrome is topic of debate. We sought to assess whether ECs occurring in gBRCA carriers are enriched for clinicopathologic and molecular characteristics, thereby supporting a causal relationship.

EXPERIMENTAL DESIGN

Thirty-eight gBRCA carriers that developed EC were selected from the nationwide cohort study on hereditary breast and ovarian cancer in the Netherlands (HEBON), and these were supplemented with four institutional cases. Tumor tissue was retrieved via PALGA (Dutch Pathology Registry). Nineteen morphologic features were scored and histotype was determined by three expert gynecologic pathologists, blinded for molecular analyses (UCM-OncoPlus Assay including 1213 genes). ECs with LOH of the gBRCA-wild-type allele (gBRCA/LOHpos) were defined "gBRCA-associated," those without LOH (gBRCA/LOHneg) were defined "sporadic."

RESULTS

LOH could be assessed for 40 ECs (30 gBRCA1, 10 gBRCA2), of which 60% were gBRCA/LOHpos. gBRCA/LOHpos ECs were more frequently of nonendometrioid (58%, P = 0.001) and grade 3 histology (79%, P < 0.001). All but two were in the TP53-mutated TCGA-subgroup (91.7%, P < 0.001). In contrast, gBRCA/LOHneg ECs were mainly grade 1 endometrioid EC (94%) and showed a more heterogeneous distribution of TCGA-molecular subgroups: POLE-mutated (6.3%), MSI-high (25%), NSMP (62.5%), and TP53-mutated (6.3%).

CONCLUSIONS

We provide novel evidence in favor of EC being part of the gBRCA-associated HBOC-syndrome. gBRCA-associated ECs are enriched for EC subtypes associated with unfavorable clinical outcome. These findings have profound therapeutic consequences as these patients may benefit from treatment strategies such as PARP inhibitors. In addition, it should influence counseling and surveillance of gBRCA carriers.

Multimodal network diffusion predicts future disease-gene-chemical associations

MOTIVATION

Precision medicine is an emerging field with hopes to improve patient treatment and reduce morbidity and mortality. To these ends, computational approaches have predicted associations among genes, chemicals and diseases. Such efforts, however, were often limited to using just some available association types. This lowers prediction coverage and, since prior evidence shows that integrating heterogeneous data is likely beneficial, it may limit accuracy. Therefore, we systematically tested whether using more association types improves prediction.

RESULTS

We study multimodal networks linking diseases, genes and chemicals (drugs) by applying three diffusion algorithms and varying information content. Ten-fold cross-validation shows that these networks are internally consistent, both within and across association types. Also, diffusion methods recovered missing edges, even if all the edges from an entire mode of association were removed. This suggests that information is transferable between these association types. As a realistic validation, time-stamped experiments simulated the predictions of future associations based solely on information known prior to a given date. The results show that many future published results are predictable from current associations. Moreover, in most cases, using more association types increases prediction coverage without significantly decreasing sensitivity and specificity. In case studies, literature-supported validation shows that these predictions mimic human-formulated hypotheses. Overall, this study suggests that diffusion over a more comprehensive multimodal network will generate more useful hypotheses of associations among diseases, genes and chemicals, which may guide the development of precision therapies.

AVAILABILITY AND IMPLEMENTATION

Code and data are available at https://github.com/LichtargeLab/multimodal-network-diffusion.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Sirtuin 3 silencing improves oxaliplatin efficacy through acetylation of MnSOD in colon cancer

Sirtuin 3 (SIRT3) is the major mitochondria deacetylase and regulates ROS levels by targeting several key proteins, such as those involved in mitochondrial function and antioxidant defenses. This way, SIRT3 balances ROS production and scavenging and promotes cell survival. The aim of this study was to analyze the effect of SIRT3 silencing on the antioxidant response in SW620 colon cancer cell line, and whether this intervention could improve efficacy of oxaliplatin, a common drug used to treat colon cancer. For this purpose, we obtained stable clones of SW620 with SIRT3 knockdown and determined parameters such as ROS levels and ROS production, levels of several antioxidant enzymes, cell viability, and apoptosis. Results showed that after SIRT3 silencing, both ROS levels and production were increased, and antioxidant enzymes gene expression was significantly reduced. Furthermore, manganese superoxide dismutase levels and enzymatic activity were reduced. Combination of SIRT3 knockdown with oxaliplatin treatment further increased ROS production and apoptosis, reducing cell viability. Finally, survival curves on colon cancer patients suggested that SIRT3 expression is related to a poorer prognosis. In conclusion, SIRT3 could be a target for colon cancer, since it regulates the antioxidant response and its knockdown improves the efficacy of oxaliplatin treatment.

Inducers of Senescence, Toxic Compounds, and Senolytics: The Multiple Faces of Nrf2-Activating Phytochemicals in Cancer Adjuvant Therapy

The reactivation of senescence in cancer and the subsequent clearance of senescent cells are suggested as therapeutic intervention in the eradication of cancer. Several natural compounds that activate Nrf2 (nuclear factor erythroid-derived 2-related factor 2) pathway, which is involved in complex cytoprotective responses, have been paradoxically shown to induce cell death or senescence in cancer. Promoting the cytoprotective Nrf2 pathway may be desirable for chemoprevention, but it might be detrimental in later stages and advanced cancers. However, senolytic activity shown by some Nrf2-activating compounds could be used to target senescent cancer cells (particularly in aged immune-depressed organisms) that escape immunosurveillance. We herein describe in vitro and in vivo effects of fifteen Nrf2-interacting natural compounds (tocotrienols, curcumin, epigallocatechin gallate, quercetin, genistein, resveratrol, silybin, phenethyl isothiocyanate, sulforaphane, triptolide, allicin, berberine, piperlongumine, fisetin, and phloretin) on cellular senescence and discuss their use in adjuvant cancer therapy. In light of available literature, it can be concluded that the meaning and the potential of adjuvant therapy with natural compounds in humans remain unclear, also taking into account the existence of few clinical trials mostly characterized by uncertain results. Further studies are needed to investigate the therapeutic potential of those compounds that display senolytic activity.

Redox Imbalance in the Development of Colorectal Cancer

Redox imbalance is resulted from the destruction of balance between oxidants and antioxidants. The dominant oxidants are reactive oxygen species (ROS), which are involved in multiple cellular processes by physiologically transporting signal as a second messenger or pathologically oxidizing DNA, lipids, and proteins. Generally speaking, low concentration of ROS is indispensable for cell survival and proliferation. However, high concentration of ROS is cytotoxic. Additionally, ROS are now known to induce the oxidative modification of macromolecules especially proteins. The redox modification of proteins is involved in numerous biological processes related to diseases including CRC. Herein, we attempt to afford an overview that highlights the crosstalk between redox imbalance and CRC.

Telomere-Mitochondrion Links Contribute to Induction of Senescence in MCF-7 Cells after Carbon-Ion Irradiation

The effects of carbon-ion irradiation on cancer cell telomere function have not been comprehensively studied. In our previous report cancer cells with telomere dysfunction were more sensitive to carbon-ion irradiation, but the underlying mechanisms remained unclear. Here we found that telomerase activity was suppressed by carbon-ion irradiation via hTERT down-regulation. Inhibition of telomere activity by MST-312 further increased cancer cell radiosensitivity to carbon-ion radiation. hTERT suppression caused by either carbon-ion irradiation or MST-312 impaired mitochondrial function, as indicated by decreased membrane potential, mtDNA copy number, mitochondrial mass, total ATP levels and elevated reactive oxygen species (ROS). PGC-1α expression was repressed after carbion-ion irradiation, and hTERT inhibition by MST-312 could further exacerbate this effect. Lowering the mitochondrial ROS level by MitoTEMPO could partially counteract the induction of cellular senescence induced by carbon-ion radiation and MST-312 incubation. Taken together, the current data suggest that telomere-mitochondrion links play a role in the induction of senescence in MCF-7 cells after carbon-ion irradiation.

CK2 in Cancer: Cellular and Biochemical Mechanisms and Potential Therapeutic Target

CK2 genes are overexpressed in many human cancers, and most often overexpression is associated with worse prognosis. Site-specific expression in mice leads to cancer development (e.g., breast, lymphoma) indicating the oncogenic nature of CK2. CK2 is involved in many key aspects of cancer including inhibition of apoptosis, modulation of signaling pathways, DNA damage response, and cell cycle regulation. A number of CK2 inhibitors are now available and have been shown to have activity against various cancers in vitro and in pre-clinical models. Some of these inhibitors are now undergoing exploration in clinical trials as well. In this review, we will examine some of the major cancers in which CK2 inhibition has promise based on in vitro and pre-clinical studies, the proposed cellular and signaling mechanisms of anti-cancer activity by CK2 inhibitors, and the current or recent clinical trials using CK2 inhibitors.

Cancer drug resistance: redox resetting renders a way

Disruption of redox homeostasis is a crucial factor in the development of drug resistance, which is a major problem facing current cancer treatment. Compared with normal cells, tumor cells generally exhibit higher levels of reactive oxygen species (ROS), which can promote tumor progression and development. Upon drug treatment, some tumor cells can undergo a process of 'Redox Resetting' to acquire a new redox balance with higher levels of ROS accumulation and stronger antioxidant systems. Evidence has accumulated showing that the 'Redox Resetting' enables cancer cells to become resistant to anticancer drugs by multiple mechanisms, including increased rates of drug efflux, altered drug metabolism and drug targets, activated prosurvival pathways and inefficient induction of cell death. In this article, we provide insight into the role of 'Redox Resetting' on the emergence of drug resistance that may contribute to pharmacological modulation of resistance.

Reflections on the role of senescence during development and aging

New and stimulating results have challenged the concept that cellular senescence might not be synonymous with aging. It is indisputable that during aging, senescent cell accumulation has an impact on organismal health. Nevertheless, senescent cells are now known to display physiological roles during embryonic development, during wound healing repair and as a cellular response to stress. The fact that senescence has been found in cells that did not attain their maximal round of replications, nor have metabolic alterations or DNA damage, also challenges the paradigm that senescence is cellular aging, and it is in favor of the idea that cellular senescence is a phenomenon that has a function by itself. Therefore, in order to understand this phenomenon it is important to analyze the relationship between senescence and other cellular responses that have many features in common, such as apoptosis, cancer and autophagy, particularly highlighting their role during development and adulthood.

Loss of the N-terminal methyltransferase NRMT1 increases sensitivity to DNA damage and promotes mammary oncogenesis

Though discovered over four decades ago, the function of N-terminal methylation has mostly remained a mystery. Our discovery of the first mammalian N-terminal methyltransferase, NRMT1, has led to the discovery of many new functions for N-terminal methylation, including regulation of DNA/protein interactions, accurate mitotic division, and nucleotide excision repair (NER). Here we test whether NRMT1 is also important for DNA double-strand break (DSB) repair, and given its previously known roles in cell cycle regulation and the DNA damage response, assay if NRMT1 is acting as a tumor suppressor. We find that NRMT1 knockdown significantly enhances the sensitivity of breast cancer cell lines to both etoposide treatment and γ-irradiation, as well as, increases proliferation rate, invasive potential, anchorage-independent growth, xenograft tumor size, and tamoxifen sensitivity. Interestingly, this positions NRMT1 as a tumor suppressor protein involved in multiple DNA repair pathways, and indicates, similar to BRCA1 and BRCA2, its loss may result in tumors with enhanced sensitivity to diverse DNA damaging chemotherapeutics.

Actin-binding doliculide causes premature senescence in p53 wild type cells

Addressing the actin cytoskeleton as future anticancer target can be an innovative chemotherapeutic approach to combat malignancies. Doliculide is a potent stabilizer of actin filaments and can be used as tool and therapeutic lead in cancer research. Though a variety of molecules are known to bind to actin and lead to either its over- or depolymerization little is known about the pharmacological consequences of these effects within the cancer cell. In this work we used p53 wild-type cells to dissect the reaction of these cells towards subtoxic doses of doliculide. We could show that doliculide leads to a transient change in actin cytoskeleton dynamics that are reversible. The cells react towards the treatment with the induction of premature senescence, an established anti-cancer mechanism, in concentrations that are not cytotoxic. Furthermore, we investigated the signaling pathways that are involved in the induction and maintenance of senescence by a pathway directed mRNA PCR-array. This analysis revealed that under doliculide treatment up to 13% of senescence related genes are altered. Taken together, our data provide evidence for an antitumoral potential of actin binding agents in p53 wild type cells and brings the strategy of targeting the actin cytoskeleton closer to clinical application.

The Tumorigenic Roles of the Cellular REDOX Regulatory Systems

The cellular REDOX regulatory systems play a central role in maintaining REDOX homeostasis that is crucial for cell integrity, survival, and proliferation. To date, a substantial amount of data has demonstrated that cancer cells typically undergo increasing oxidative stress as the tumor develops, upregulating these important antioxidant systems in order to survive, proliferate, and metastasize under these extreme oxidative stress conditions. Since a large number of chemotherapeutic agents currently used in the clinic rely on the induction of ROS overload or change of ROS quality to kill the tumor, the cancer cell REDOX adaptation represents a significant obstacle to conventional chemotherapy. In this review we will first examine the different factors that contribute to the enhanced oxidative stress generally observed within the tumor microenvironment. We will then make a comprehensive assessment of the current literature regarding the main antioxidant proteins and systems that have been shown to be positively associated with tumor progression and chemoresistance. Finally we will make an analysis of commonly used chemotherapeutic drugs that induce ROS. The current knowledge of cancer cell REDOX adaptation raises the issue of developing novel and more effective therapies for these tumors that are usually resistant to conventional ROS inducing chemotherapy.

Targeting glycolysis by 3-bromopyruvate improves tamoxifen cytotoxicity of breast cancer cell lines

Background

Tamoxifen is the standard endocrine therapy for ER+ breast cancer; however, many women still relapse after long-term therapy. 3-Bromopyruvate, a glycolytic inhibitor, has shown high selective anti-tumor activity in vitro, and in vivo. The aim of this study was to evaluate the possible augmentation of the effect of tamoxifen via reprograming cancer cell metabolism using 3-bromopyruvate.

Methods

An in vitro screening of antitumor activity as well as the apoptotic, anti-metastatic, and anti-angiogenic potentials of the combination therapy were carried out using different techniques on breast cancer cell lines MCF7and T47D. In addition the antitumor effect of the combined therapy was done on mice bearing tumor.

Results

Our results showed modulation in apoptosis, angiogenesis and metastatic potential by either drug alone; however, their combination has surpassed that of the individual one. Combination regimen enhanced activated caspases-3, 7 and 9, as well as oxidative stress, signified by increased malondialdehyde and decreased glutathione level. Additionally, the angiogenesis and metastasis markers, including hypoxia inducing factor-1α, vascular endothelia growth factor, and metaloproteinases-2 and 9 were decreased after using the combination regimen. These results were further confirmed by the in vivo study, which depicted a decrease in the tumor volume and angiogenesis and an increase in oxidative stress as well.

Conclusion

3-bromopyruvate could be a valuable compound when added with tamoxifen in breast cancer treatment.

UCP2 inhibition sensitizes breast cancer cells to therapeutic agents by increasing oxidative stress

Modulation of oxidative stress in cancer cells plays an important role in the study of the resistance to anticancer therapies. Uncoupling protein 2 (UCP2) may play a dual role in cancer, acting as a protective mechanism in normal cells, while its overexpression in cancer cells could confer resistance to chemotherapy and a higher survival through downregulation of ROS production. Thus, our aim was to check whether the inhibition of UCP2 expression and function increases oxidative stress and could render breast cancer cells more sensitive to cisplatin (CDDP) or tamoxifen (TAM). For this purpose, we studied clonogenicity, mitochondrial membrane potential (ΔΨm), cell viability, ROS production, apoptosis, and autophagy in MCF-7 and T47D (only the last four determinations) breast cancer cells treated with CDDP or TAM, in combination or without a UCP2 knockdown (siRNA or genipin). Furthermore, survival curves were performed in order to check the impact of UCP2 expression in breast cancer patients. UCP2 inhibition and cytotoxic treatments produced a decrease in cell viability and clonogenicity, in addition to an increase in ΔΨm, ROS production, apoptosis, and autophagy. It is important to note that CDDP decreased UCP2 protein levels, so that the greatest effects produced by the UCP2 inhibition in combination with a cytotoxic treatment, with regard to treatment alone, were observed in TAM+UCP2siRNA-treated cells. Moreover, this UCP2 inhibition caused autophagic cell death, since apoptosis parameters barely increased after UCP2 knockdown. Finally, survival curves revealed that higher UCP2 expression corresponded with a poorer prognosis. In conclusion, UCP2 could be a therapeutic target in breast cancer, especially in those patients treated with tamoxifen.

Protein kinase CK2 in breast cancer: the CK2β regulatory subunit takes center stage in epithelial plasticity

Structurally, protein kinase CK2 consists of two catalytic subunits (α and α') and two regulatory subunits (β), which play a critical role in targeting specific CK2 substrates. Compelling evidence shows the complexity of the CK2 cellular signaling network and supports the view that this enzyme is a key component of regulatory protein kinase networks that are involved in several aspects of cancer. CK2 both activates and suppresses the expression of a number of essential oncogenes and tumor suppressors, and its expression and activity are upregulated in blood tumors and virtually all solid tumors. The prognostic significance of CK2α expression in association with various clinicopathological parameters highlighted this kinase as an adverse prognostic marker in breast cancer. In addition, several recent studies reported its implication in the regulation of the epithelial-to-mesenchymal transition (EMT), an early step in cancer invasion and metastasis. In this review, we briefly overview the contribution of CK2 to several aspects of cancer and discuss how in mammary epithelial cells, the expression of its CK2β regulatory subunit plays a critical role in maintaining an epithelial phenotype through CK2-mediated control of key EMT-related transcription factors. Importantly, decreased CK2β expression in breast tumors is correlated with inefficient phosphorylation and nuclear translocation of Snail1 and Foxc2, ultimately leading to EMT induction. This review highlights the pivotal role played by CK2β in the mammary epithelial phenotype and discusses how a modest alteration in its expression may be sufficient to induce dramatic effects facilitating the early steps in tumor cell dissemination through the coordinated regulation of two key transcription factors.

The presence of Estrogen Receptor β modulates the response of breast cancer cells to therapeutic agents

Breast cancer is a leading cause of death for women. The estrogen receptors (ERs) ratio is important in the maintenance of mitochondrial redox status, and higher levels of ERβ increases mitochondrial functionality, decreasing ROS production. Our aim was to determine the interaction between the ERα/ERβ ratio and the response to cytotoxic treatments such as cisplatin (CDDP), paclitaxel (PTX) and tamoxifen (TAM). Cell viability, apoptosis, autophagy, ROS production, mitochondrial membrane potential, mitochondrial mass and mitochondrial functionality were analyzed in MCF-7 (high ERα/ERβ ratio) and T47D (low ERα/ERβ ratio) breast cancer cell lines. Cell viability decreased more in MCF-7 when treated with CDDP and PTX. Apoptosis was less activated after cytotoxic treatments in T47D than in MCF-7 cells. Nevertheless, autophagy was increased more in CDDP-treated MCF-7, but less in TAM-treated cells than in T47D. CDDP treatment produced a raise in mitochondrial mass in MCF-7, as well as the citochrome c oxidase (COX) and ATP synthase protein levels, however significantly reduced COX activity. In CDDP-treated cells, the overexpression of ERβ in MCF-7 caused a reduction in apoptosis, autophagy and ROS production, leading to higher cell survival; and the silencing of ERβ in T47D cells promoted the opposite effects. In TAM-treated cells, ERβ-overexpression led to less cell viability by an increment in autophagy; and the partial knockdown of ERβ in T47D triggered an increase in ROS production and apoptosis, leading to cell death. In conclusion, ERβ expression plays an important role in the response of cancer cells to cytotoxic agents, especially for cisplatin treatment.

Critical roles for nitric oxide and ERK in the completion of prosurvival autophagy in 4OHTAM-treated estrogen receptor-positive breast cancer cells

Autophagy is a mechanism of tamoxifen (TAM) resistance in ER-positive (ER+) breast cancer cells. In this study, we showed in ER+ MCF7 cells that 4-hydroxytamoxifen (4OHTAM) induced cellular nitric oxide (NO) that negatively regulates cellular superoxide (O2-) and cytotoxicity. 4OHTAM stimulated LC3 lipidation and formation of monodansylcadaverine (MDC)-labeled autophagic vesicles dependent on O2-. Depletion of NO increased O2- and LC3 lipidation, yet reduced formation of MDC-labeled autophagic vesicles. Instead, NO-depleted cells formed remarkably large vacuoles with rims decorated by LC3. The vacuoles were not labeled by MDC or the acidic lysosome-specific fluorescence dye acridine orange (AO). The vacuoles were increased by the late stage autophagy inhibitor chloroquine, which also increased LC3 lipidation. These results suggest NO is required for proper autophagic vesicle formation or maturation at a step after LC3 lipidation. In addition, 4OHTAM induced O2--dependent activation of ERK, inhibition of which destabilized lysosomes/autolysosomes upon 4OHTAM treatment and together with depletion of NO led to necrotic cell death. These results suggest an essential role for endogenous NO and ERK activation in the completion of pro-survival autophagy.

Upregulation of miR-760 and miR-186 is associated with replicative senescence in human lung fibroblast cells

We have previously shown that microRNAs (miRNAs) miR-760, miR-186, miR-337-3p, and miR-216b stimulate premature senescence through protein kinase CK2 (CK2) down-regulation in human colon cancer cells. Here, we examined whether these four miRNAs are involved in the replicative senescence of human lung fibroblast IMR-90 cells. miR-760 and miR-186 were significantly upregulated in replicatively senescent IMR-90 cells, and their joint action with both miR-337-3p and miR-216b was necessary for efficient downregulation of the α subunit of CK2 (CK2α) in IMR-90 cells. A mutation in any of the four miRNA-binding sequences within the CK2α 3'-untranslated region (UTR) indicated that all four miRNAs should simultaneously bind to the target sites for CK2α downregulation. The four miRNAs increased senescence-associated β-galactosidase (SA-β-gal) staining, p53 and p21(Cip1/WAF1) expression, and reactive oxygen species (ROS) production in proliferating IMR-90 cells. CK2α over-expression almost abolished this event. Taken together, the present results suggest that the upregulation of miR-760 and miR-186 is associated with replicative senescence in human lung fibroblast cells, and their cooperative action with miR-337-3p and miR-216b may induce replicative senescence through CK2α downregulation-dependent ROS generation.