Tunicamycin potentiates paclitaxel-induced apoptosis through inhibition of PI3K/AKT and MAPK pathways in breast cancer

An EMC-Hpo-Yki axis maintains intestinal homeostasis under physiological and pathological conditions

Balanced control of stem cell proliferation and differentiation underlines tissue homeostasis. Disruption of tissue homeostasis often results in many diseases. However, how endogenous factors influence the proliferation and differentiation of intestinal stem cells (ISCs) under physiological and pathological conditions remains poorly understood. Here, we find that the evolutionarily conserved endoplasmic reticulum membrane protein complex (EMC) negatively regulates ISC proliferation and intestinal homeostasis. Compromising EMC function in progenitors leads to excessive ISC proliferation and intestinal homeostasis disruption. Mechanistically, the EMC associates with and stabilizes Hippo (Hpo) protein, the key component of the Hpo signaling pathway. In the absence of EMC, Yorkie (Yki) is activated to promote ISC proliferation due to Hpo destruction. The EMC-Hpo-Yki axis also functions in enterocytes to maintain intestinal homeostasis. Importantly, the levels of the EMC are dramatically diminished in tunicamycin-treated animals, leading to Hpo destruction, thereby resulting in intestinal homeostasis disruption due to Yki activation. Thus, our study uncovers the molecular mechanism underlying the action of the EMC in intestinal homeostasis maintenance under physiological and pathological conditions and provides new insight into the pathogenesis of tunicamycin-induced tumorigenesis.

Protein kinase B (Akt) blockade inhibits LH/hCG-mediated 17,20-lyase, but not 17α-hydroxylase activity of Cyp17a1 in mouse Leydig cell steroidogenesis

Androgens are produced by adrenal and gonadal cells thanks to the action of specific enzymes. We investigated the role of protein kinase B (Akt) in the modulation of Δ4 steroidogenic enzymes' activity, in the mouse Leydig tumor cell line mLTC1. Cells were treated for 0-24 h with the 3 × 50% effective concentration of human luteinizing hormone (LH) and choriogonadotropin (hCG), in the presence and in the absence of the specific Akt inhibitor 3CAI. Cell signaling analysis was performed by bioluminescence resonance energy transfer (BRET) and Western blotting, while the expression of key target genes was investigated by real-time PCR. The synthesis of progesterone, 17α-hydroxy (OH)-progesterone and testosterone was measured by immunoassay. Control experiments for cell viability and caspase 3 activation were performed as well. We found that both hormones activated cAMP and downstream effectors, such as extracellularly-regulated kinase 1/2 (Erk1/2) and cAMP response element-binding protein (Creb), as well as Akt, and the transcription of Stard1, Hsd3b1, Cyp17a1 and Hsd17b3 genes, boosting the Δ4 steroidogenic pathway. Interestingly, Akt blockade decreased selectively Cyp17a1 expression levels, inhibiting its 17,20-lyase, but not the 17-hydroxylase activity. This effect is consistent with lower Cyp17a1 affinity to 17α-OH-progesterone than progesterone. As a result, cell treatment with 3CAI resulted in 17α-OH-progesterone accumulation at 16-24 h and decreased testosterone levels after 24 h. In conclusion, in the mouse Leydig cell line mLTC1, we found substantial Akt dependence of the 17,20-lyase activity and testosterone synthesis. Our results indicate that different intracellular pathways modulate selectively the dual activity of Cyp17a1.

A Novel Paclitaxel Derivative for Triple-Negative Breast Cancer Chemotherapy

Paclitaxel-triethylenetetramine hexaacetic acid conjugate (PTX-TTHA), a novel semi-synthetic taxane, is designed to improve the water solubility and cosolvent toxicity of paclitaxel in several aminopolycarboxylic acid groups. In this study, the in vitro and in vivo antitumor effects and mechanisms of PTX-TTHA against triple-negative breast cancer (TNBC) and its intravenous toxicity were evaluated. Results showed the water solubility of PTX-TTHA was greater than 5 mg/mL, which was about 7140-fold higher than that of paclitaxel (<0.7 µg/mL). PTX-TTHA (10-10⁵ nmol/L) could significantly inhibit breast cancer proliferation and induce apoptosis by stabilizing microtubules and arresting the cell cycle in the G2/M phase in vitro, with its therapeutic effect and mechanism similar to paclitaxel. However, when the MDA-MB-231 cell-derived xenograft (CDX) tumor model received PTX-TTHA (13.73 mg/kg) treatment once every 3 days for 21 days, the tumor inhibition rate was up to 77.32%. Furthermore, PTX-TTHA could inhibit tumor proliferation by downregulating Ki-67, and induce apoptosis by increasing pro-apoptotic proteins (Bax, cleaved caspase-3) and TdT-mediated dUTP nick end labeling (TUNEL) positive apoptotic cells, and reducing anti-apoptotic protein (Bcl-2). Moreover, PTX-TTHA demonstrated no sign of acute toxicity on vital organs, hematological, and biochemical parameters at the limit dose (138.6 mg/kg, i.v.). Our study indicated that PTX-TTHA showed better water solubility than paclitaxel, as well as comparable in vitro and in vivo antitumor activity in TNBC models. In addition, the antitumor mechanism of PTX-TTHA was related to microtubule regulation and apoptosis signaling pathway activation.

P-Y/G@NHs sensitizes non-small cell lung cancer cells to radiotherapy via blockage of the PI3K/AKT signaling pathway

Radioresistance represents a common phenomenon found in cancer treatment. Herein, the current study sought to evaluate the effects of a nanodrug delivery system of YSAYPDSVPMMS (YSA) peptide-modified gold nanoparticles-dextran-based hydrogel loaded with paclitaxel-succinic anhydride (P-Y/G@NHs) on non-small cell lung cancer (NSCLC) cell radiosensitivity. Firstly, utilizing the coupling reaction and layer-by-layer assembly technique, P-Y/G@NHs was prepared. The therapeutic effects of the P-Y/G@NHs in NSCLC cells in relation to the PI3K/AKT signaling pathway were examined by assessing the colony formation, apoptosis, and reactive oxygen species (ROS) generation of A549 cells under 10 Gy X-rays irradiation. Moreover, A549 tumor-bearing mice were generated to further validate the therapeutic effect in vivo. We confirmed the successful conjugation of the nanocomposite. Under 10 Gy X-rays irradiation, P-Y/G@NHs reduced the number of colonies of A549 cells, while inducing both cell apoptosis and ROS production. Moreover, P-Y/G@NHs enhanced the radiosensitivity of A549 cells by inhibiting the PI3K/AKT signaling pathway. In vivo fluorescence experiments validated that P-Y/G@NHs effectively-targeted and accumulated at the tumor site in nude mice, thus augmenting the radiosensitivity of tumors without significant immune toxicity or side effects. Conclusively, our findings highlighted that P-Y/G@NHs significantly enhanced the radiosensitivity of NSCLC cells by repressing the PI3K/AKT signaling pathway.

Concise Synthesis of Tunicamycin V and Discovery of a Cytostatic DPAGT1 Inhibitor

A short total synthesis of tunicamycin V (1), a non-selective phosphotransferase inhibitor, is achieved via a Büchner-Curtius-Schlotterbeck type reaction. Tunicamycin V can be synthesized in 15 chemical steps from D-galactal with 21 % overall yield. The established synthetic scheme is operationally very simple and flexible to introduce building blocks of interest. The inhibitory activity of one of the designed analogues 28 against human dolichyl-phosphate N-acetylglucosaminephosphotransferase 1 (DPAGT1) is 12.5 times greater than 1. While tunicamycins are cytotoxic molecules with a low selectivity, the novel analogue 28 displays selective cytostatic activity against breast cancer cell lines including a triple-negative breast cancer.

Anastasis: cell recovery mechanisms and potential role in cancer

Balanced cell death and survival are among the most important cell development and homeostasis pathways that can play a critical role in the onset or progress of malignancy steps. Anastasis is a natural cell recovery pathway that rescues cells after removing the apoptosis-inducing agent or brink of death. The cells recuperate and recover to an active and stable state. So far, minimal knowledge is available about the molecular mechanisms of anastasis. Still, several involved pathways have been explained: recovery through mitochondrial outer membrane permeabilization, caspase cascade arrest, repairing DNA damage, apoptotic bodies formation, and phosphatidylserine. Anastasis can facilitate the survival of damaged or tumor cells, promote malignancy, and increase drug resistance and metastasis. Here, we noted recently known mechanisms of the anastasis process and underlying molecular mechanisms. Additionally, we summarize the consequences of anastatic mechanisms in the initiation and progress of malignancy, cancer cell metastasis, and drug resistance.

N-Glycosylation at Asn291 Stabilizes TIM-4 and Promotes the Metastasis of NSCLC

T-cell immunoglobulin domain and mucin domain 4 (TIM-4) is a transmembrane protein that promotes epithelial-mesenchymal transition (EMT), migration and invasion of non-small cell lung cancer (NSCLC) cells. Most transmembrane proteins are modified by N-glycosylation and the importance of protein N-glycosylation in cancer cell metastasis has been well appreciated. However, whether TIM-4 is modified by N-glycosylation and the role of TIM-4 N-glycosylation in NSCLC remains largely unknown. In the current study, we reported that TIM-4 was extensively N-glycosylated at Asn291. After the removal of N-glycosylation, the stability of TIM-4 protein was decreased and TIM-4 was more susceptible to degradation by ER-localized ubiquitin ligase-mediated ERAD. Thus, the expression of TIM-4 on the cell surface was decreased, which suppressed TIM-4-mediated metastasis in NSCLC. In summary, the present study identifies TIM-4 N-glycosylation and its role in NSCLS migration, which would provide a valuable biomarker for developing drugs targeting N-glycosylation at Asn291 on TIM-4.

Endoplasmic reticulum stress inhibits 3D Matrigel-induced vasculogenic mimicry of breast cancer cells via TGF-β1/Smad2/3 and β-catenin signaling

Endoplasmic reticulum (ER) stress is a cellular stress condition involving disturbance in the folding capacity of the ER caused by endogenous and exogenous factors. ER stress signaling pathways affect tumor malignant growth, angiogenesis and progression, and promote the antitumor effects of certain drugs. However, the impact of ER stress on the vasculogenic mimicry (VM) phenotype of cancer cells has not been well addressed. VM is a phenotype that mimics vasculogenesis by forming patterned tubular networks, which are related to stemness and aggressive behaviors of cancer cells. In this study, we used tunicamycin (TM), the unfolded protein response (UPR)-activating agent, to induce ER stress in aggressive triple-negative MDA-MB-231 breast cancer cells, which exhibit a VM phenotype in 3D Matrigel cultures. TM-induced ER stress was able to inhibit the VM phenotype. In addition to the tumor spheroid phenotype observed upon inhibiting the VM phenotype, we observed alterations in glycosylation of integrin β1, loss of VE-cadherin and a decrease in stem cell marker Bmi-1. Further study revealed decreased activated transforming growth factor β1, Smad2/3, Phospho-Smad2 and β-catenin. β-Catenin knockdown markedly inhibited the VM phenotype and resulted in the loss of VE-cadherin. The data suggest that the activation of ER stress inhibited VM phenotype formation of breast cancer cells via both the transforming growth factor β1/Smad2/3 and β-catenin signaling pathways. The discovery of prospective regulatory mechanisms involved in ER stress and VM in breast cancer could lead to more precisely targeted therapies that inhibit vessel formation and affect tumor progression.

2-Hydroxypropyl-β-cyclodextrin Regulates the Epithelial to Mesenchymal Transition in Breast Cancer Cells by Modulating Cholesterol Homeostasis and Endoplasmic Reticulum Stress

Cholesterol metabolism affects endoplasmic reticulum (ER) stress and modulates epithelial-mesenchymal transition (EMT). Our previous study demonstrated that 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) attenuated EMT by blocking the transforming growth factor (TGF)-β/Smad signaling pathway and activating ER stress in MDA-MB-231 cells. To further assess the detailed mechanisms between cholesterol metabolism, ER stress, and EMT, LXR-623 (an agonist of LXRα) and simvastatin were used to increase and decrease cholesterol efflux and synthesis, respectively. Here, we found that high HP-β-CD concentrations could locally increase cholesterol levels in the ER by decreasing LXRα expression and increasing Hydroxymethylglutaryl-Coenzyme A reductase (HMGCR) expression in MDA-MB-231 and BT-549 cells, which triggered ER stress and inhibited EMT. Meanwhile, tunicamycin-induced ER stress blocked the TGF-β/Smad signaling pathway. However, low HP-β-CD concentrations can decrease the level of membrane cholesterol, enhance the TGF-β receptor I levels in lipid rafts, which helped to activate TGF-β/Smad signaling pathway, inhibit ER stress and elevate EMT. Based on our findings, the use of high HP-β-CD concentration can lead to cholesterol accumulation in the ER, thereby inducing ER stress, which directly suppresses TGF-β pathway-induced EMT. However, HP-β-CD is proposed to deplete membrane cholesterol at low concentrations and concurrently inhibit ER stress and induce EMT by promoting the TGF-β signaling pathways.

Tunicamycin-induced endoplasmic reticulum stress inhibits chemoresistance of FaDu hypopharyngeal carcinoma cells in 3D collagen I cultures and in vivo

The prognosis in patients with advanced head and neck squamous cell carcinoma (HNSCC) is widely affected by the resistance to chemotherapy. As a culture scaffold, collagen I was showed to promote CSC (cancer stem cell) properties of cancer cells which could be used as in vitro models to study the chemoresistance in HNSCC. Endoplasmic reticulum (ER) stress is a cellular stress condition which could affect tumor progression and promote the anti-tumor effects of certain drugs. However, the impact of ER stress on collagen I induced CSC properties and chemoresistance of HNSCC cells has not been addressed. In this study we investigated the effects of tunicamycin (TM) induced ER stress on the stemness and sensitivity to chemotherapeutic drugs of FaDu hypopharyngeal carcinoma cells in 3D (three-dimensional) collagen I cultures and mouse xenograft models. Our study revealed that Collagen I scaffold promoted CSC properties and increased G1 population of FaDu cells in 3D cultures, accompanied by maturation of integrin β1 and enhanced activated TGF-β1 concentration. Compared to 2D (two-dimensional) cultured cells, cells in 3D Collagen I scaffold exhibited significantly increased resistance to chemotherapeutic drugs of cisplatin and paclitaxel. Further analysis revealed that TM induced ER stress preferentially attenuated chemoresistance of FaDu cells in 3D collagen I, downregulated their CSC properties and TGF-β1 concentration and resulted in deglycosylation of integrin β1. TM was further evaluated in the mouse xenograft models and showed significant tumor growth inhibition in combination with paclitaxel than either TM or paclitaxel alone. Taken together, Our findings suggest that TM-induced ER stress potentiates anticancer efficacy of FaDu cells in 3D cultures and in vivo, and highlight implications for targeting chemotherapy-resistant cancer stem cells under ER stress conditions.

Kinase shRNA screening reveals that TAOK3 enhances microtubule-targeted drug resistance of breast cancer cells via the NF-κB signaling pathway

BACKGROUND

Chemotherapy is currently one of the most effective treatments for advanced breast cancer. Anti-microtubule agents, including taxanes, eribulin and vinca-alkaloids are one of the primary major anti-breast cancer chemotherapies; however, chemoresistance remains a problem that is difficult to solve. We aimed to discover novel candidate protein targets to combat chemoresistance in breast cancer.

METHODS

A lentiviral shRNA-based high-throughput screening platform was designed and developed to screen the global kinome to find new therapeutic targets in paclitaxel-resistant breast cancer cells. The phenotypes were confirmed with alternative expression in vitro and in vivo. Molecular mechanisms were investigated using global phosphoprotein arrays and expression microarrays. Global microarray analysis was performed to determine TAOK3 and genes that induced paclitaxel resistance.

RESULTS

A serine/threonine kinase gene, TAOK3, was identified from 724 screened kinase genes. TAOK3 shRNA exhibited the most significant reduction in IC50 values in response to paclitaxel treatment. Ectopic downregulation of TAOK3 resulted in paclitaxel-resistant breast cancer cells sensitize to paclitaxel treatment in vitro and in vivo. The expression of TAOK3 also was correlated to sensitivity to two other anti-microtubule drugs, eribulin and vinorelbine. Our TAOK3-modulated microarray analysis indicated that NF-κB signaling played a major upstream regulation role. TAOK3 inhibitor, CP43, and shRNA of NF-κB both reduced the paclitaxel resistance in TAOK3 overexpressed cells. In clinical microarray databases, high TAOK3 expressed breast cancer patients had poorer prognoses after adjuvant chemotherapy.

CONCLUSIONS

Here we identified TAOK3 overexpression increased anti-microtubule drug resistance through upregulation of NF-κB signaling, which reduced cell death in breast cancer. Therefore, inhibition of the interaction between TAOK3 and NF-κB signaling may have therapeutic implications for breast cancer patients treated with anti-microtubule drugs. Video abstract.

Autophagy inhibition potentiates the anti-EMT effects of alteronol through TGF-β/Smad3 signaling in melanoma cells

Accumulating evidence demonstrated that alteronol, a novel compound that has a similar structure with paclitaxel, exerts anticancer effects against diversified tumors. However, whether alteronol induces autophagy and the relationship between its anticancer effects and autophagy in melanoma remains elusive. In this study, we show that alteronol induces not only anti-proliferation activity and apoptosis but also autophagy in A375 and UACC62 cells. In addition, alteronol inhibits A375 and UACC62 cells invasion and migration by preventing the epithelial–mesenchymal transition (EMT). Blocking autophagy enhances alteronol-induced apoptosis and anti-EMT effects in vitro and in vivo. Mechanistically, we find that alteronol significantly inhibits Akt/mTOR and TGFβ/Smad3 pathways, and co-treatment with autophagy inhibitor 3-MA further potentiate these effects. Our results suggest that alteronol induces cyto-protective autophagy in melanoma cells through inhibition of Akt/mTOR pathway, thus attenuates apoptosis and promotes melanoma cell EMT through TGF-β/Smad3 pathway. Combination with alteronol and autophagy inhibitor 3-MA may be a potential treatment for melanoma as it not only significantly inhibited tumor growth but also suppressed tumor invasion and migration as anti-metastasis agent.

Hydroxypropyl‑β‑cyclodextrin attenuates the epithelial‑to‑mesenchymal transition via endoplasmic reticulum stress in MDA‑MB‑231 breast cancer cells

The epithelial-to-mesenchymal transition (EMT) has been reported to serve vital roles in regulating the progress of cancer metastasis. In addition, lipid rafts enriched in sphingolipids and cholesterol serve important roles in physiological and biochemical processes as a signaling platform. The present study explored the effects of hydroxypropyl-β-cyclodextrin (HP-β-CD), a cholesterol-depleting agent of lipid rafts, on the transforming growth factor (TGF)-β/Smad signaling pathway and endoplasmic reticulum (ER) stress in mediating EMT in MDA-MB-231 breast cancer cells. HP-β-CD treatment inhibited TGF-β1-induced EMT, based on increased expression of E-cadherin and decreased expression of vimentin. HP-β-CD reduced the expression of the TGF receptor TβRI and blocked the phosphorylation of Smad2. In addition, HP-β-CD increased the expression of ER stress-related proteins (binding immunoglobulin protein and activating transcription factor 6), but TGF-β1 could reverse these changes. Sodium 4-phenylbutyrate, an inhibitor of ER stress, suppressed these effects of HP-β-CD on EMT and TGF-β/Smad signaling pathway inhibition in breast cancer cells. Thus, HP-β-CD can block the TGF-β/Smad signaling pathway via diminishing the expression of TβRI which helps to activate ER stress and attenuate EMT in MDA-MB-231 cells, highlighting a potential target of lipid rafts for breast cancer treatment.

N-Glycoproteomic Profiling Reveals Alteration In Extracellular Matrix Organization In Non-Type Bladder Carcinoma

Treatment of advanced and metastatic bladder carcinoma is often ineffective and displays variable clinical outcomes. Studying this aggressive molecular subtype of bladder carcinoma will lead to better understanding of the pathogenesis which may lead to the identification of new therapeutic strategies. The non-type bladder subtype is phenotypically mesenchymal and has mesenchymal features with a high metastatic ability. Post-translational addition of oligosaccharide residues is an important modification that influences cellular functions and contributes to disease pathology. Here, we report the comparative analysis of N-linked glycosylation across bladder cancer subtypes. To analyze the glycosite-containing peptides, we carried out LC-MS/MS-based quantitative proteomic and glycoproteomic profiling. We identified 1299 unique N-linked glycopeptides corresponding to 460 proteins. Additionally, we identified 118 unique N-linked glycopeptides corresponding to 84 proteins to be differentially glycosylated only in non-type subtypes as compared to luminal/basal subtypes. Most of the altered glycoproteins were also observed with changes in their global protein expression levels. However, alterations in 55 differentially expressed glycoproteins showed no significant change at the protein abundance level, representing that the glycosylation site occupancy was changed between the non-type subtype and luminal/basal subtypes. Importantly, the extracellular matrix organization pathway was dysregulated in the non-type subtype of bladder carcinoma. N-glycosylation modifications in the extracellular matrix organization proteins may be a contributing factor for the mesenchymal aggressive phenotype in non-type subtype. These aberrant protein glycosylation would provide additional avenues to employ glycan-based therapies and may lead to the identification of novel therapeutic targets.

Zinc promotes prostate cancer cell chemosensitivity to paclitaxel by inhibiting epithelial-mesenchymal transition and inducing apoptosis

BACKGROUND

Paclitaxel (PTX) is a first-line chemotherapeutic drug for the treatment of prostate cancer. However, most patients develop resistance and metastasis, and thus new therapeutic approaches are urgently required. Recent studies have identified widespread anti-tumor effects of zinc (Zn) in various tumor cell lines, especially prostate cancer cells. In this study, we examined the effects of Zn as an adjuvant to PTX in prostate cancer cells.

METHODS

PC3 and DU145 cells were treated with different concentrations of Zn and/or PTX. MTT assay was used to detect cell viability. Real-time cell analysis (RTCA) and microscopy were used to observe morphological changes in cells. Western blotting was used to detect the expression of epithelial-mesenchymal transition (EMT)-related proteins. qPCR (reverse transcription-polymerase chain reaction) was used to examine changes in TWIST1 mRNA levels. Cell invasion and migration were detected by scratch and transwell assays. shRNA against TWIST1 was used to knockdown TWIST1. Colony formation assay was used to detect cell proliferation, while Annexin V and propidium iodide (PI) staining was used to detect cell apoptosis.

RESULTS

Zn and PTX increased proliferation inhibition in a dose- and time-dependent manner in prostate cancer cells, while Zn increased prostate cancer cell chemosensitivity to PTX. Combined Zn and PTX inhibited prostate cancer cell invasion and migration by downregulating the expression of TWIST1. Furthermore, knockdown of TWIST1 increased the sensitivity of prostate cancer cells to PTX. In addition, Zn and PTX reduced cell proliferation and induced apoptosis in prostate cancer cells.

CONCLUSIONS

Our results demonstrated that Zn and PTX combined therapy inhibits EMT by reducing the expression of TWIST1, which reduces the invasion and migration of prostate cancer cells. SiTWIST1 increased the sensitivity of prostate cancer cells to PTX. In addition, with prolonged treatment, Zn and PTX inhibited proliferation and led to prostate cancer cell apoptosis. Therefore, Zn may be a potential adjuvant of PTX in treating prostate cancer and combined treatment may offer a promising therapeutic strategy for prostate cancer.

Dynamic analysis of proteomic alterations in response to N-linked glycosylation inhibition in a drug-resistant ovarian carcinoma cell line

Glycosylation inhibition can improve the efficacy of antitumor drugs and enhance the apoptosis of cancer cells, thus holding great potential for cancer treatment. Inhibition of N-glycosylation induces endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), and eventually triggers ER stress-related apoptosis. Unfortunately, the detailed timeline of these cell responses and protein expression alterations related to N-glycosylation inhibition is not explicit yet, and the pathways involved in different stages of N-glycosylation inhibition still need to be characterized. In this study, the dynamic proteome alterations related to N-glycosylation inhibition were investigated by further analyzing our previously published quantitative proteomics data from tunicamycin (TM)-treated ovarian carcinoma (OVCAR-3) cells. The results revealed that N-glycosylation inhibition not only directly affects the expression of glycosylated proteins but also alters an extended scale of proteins. Functional annotation of these altered proteins demonstrated that proteins related to ER stress start changing within 6 h, followed by UPR within 24 h, and eventually ER stress-related apoptosis is triggered after 48 h, indicating the conversion of cellular response from positive to negative. The dynamic proteome data presented here provide important information for better understanding of the significance of N-glycosylation to cell survival and TM-related cancer treatment.

Antagonistic anticancer effect of paclitaxel and digoxin combination

Despite the growing interest in the antitumor effect of cardiotonic steroids, combination treatments with well-established chemotherapy drugs like paclitaxel have been rarely investigated. Moreover, paclitaxel has been suggested as a Na⁺ /K⁺ -ATPase inhibitor. Here we investigated the effect of paclitaxel and digoxin alone or in combination on the viability of human lung (A549) and cervical cancer (HeLa) cell lines and the inhibitory effect of paclitaxel on several mammalian Na⁺ /K⁺ -ATPases. Although the viability of both tumor cell lines was concentration-dependently affected by digoxin treatment after 48 hours (A549 IC₅₀  = 31 nM and HeLa IC₅₀  = 151 nM), a partial effect was observed for paclitaxel, with a maximal inhibitory effect of 45% at 1000 nM with A549 and around 70% with HeLa cells (IC₅₀  = 1 nM). Although the two drugs were cytotoxic, their combined effect in HeLa cells was revealed to be antagonistic, as estimated by the combination index. No direct inhibitory effect of paclitaxel was detected in human, pig, rat, and mouse Na⁺ /K⁺ -ATPase enzymes, but high concentrations of paclitaxel decreased the Na⁺ /K⁺ -ATPase activity in HeLa cells after 48 hours without affecting protein expression. Our findings demonstrate that, under our conditions, paclitaxel and digoxin cotreatment produce antagonistic cytotoxic effects in HeLa cells, and the mechanism of action of paclitaxel does not involve a direct inhibition of Na⁺ /K⁺ -ATPase. More studies shall be designed to evaluate the consequences of the interaction of cardiotonic steroids and chemotherapy drugs.

Role of autophagy in breast cancer and breast cancer stem cells (Review)

Autophagy is a key catabolic process, in which cytosolic cargo is engulfed by the formation of a double membrane and then degraded through the fusing of autophagosomes with lysosomes. Autophagy is a constitutively active, evolutionarily conserved, catabolic process important for the maintenance of homeostasis in cellular stress responses and cell survival. Although the mechanisms of autophagy have not yet been fully elucidated, emerging evidence suggests that it plays a dual role in breast cancer and in maintaining the activity of breast cancer stem cells (CSCs). However, it may play a complex role in breast CSC therapy. Breast CSCs, a population of cells with the ability to self-renew, differentiate, and initiate and sustain tumor growth, play an essential role in cancer recurrence, anticancer resistance and metastasis. In addition, the elucidation of the association between autophagy and apoptosis in the tumor context is crucial in order to better address appropriate therapy strategies. In the present review, a summary of the mechanisms and roles of autophagy in breast cancer and CSCs is presented. The potential value of such autophagy modulators in the development of novel breast cancer therapies is discussed.

Protein Kinase Targets in Breast Cancer

With 1.67 million new cases and 522,000 deaths in the year 2012, breast cancer is the most common type of diagnosed malignancy and the second leading cause of cancer death in women around the world. Despite the success of screening programs and the development of adjuvant therapies, a significant percentage of breast cancer patients will suffer a metastatic disease that, to this day, remains incurable and justifies the research of new therapies to improve their life expectancy. Among the new therapies that have been developed in recent years, the emergence of targeted therapies has been a milestone in the fight against cancer. Over the past decade, many studies have shown a causal role of protein kinase dysregulations or mutations in different human diseases, including cancer. Along these lines, cancer research has demonstrated a key role of many protein kinases during human tumorigenesis and cancer progression, turning these molecules into valid candidates for new targeted therapies. The subsequent discovery and introduction in 2001 of the kinase inhibitor imatinib, as a targeted treatment for chronic myelogenous leukemia, revolutionized cancer genetic pathways research, and lead to the development of multiple small-molecule kinase inhibitors against various malignancies, including breast cancer. In this review, we analyze studies published to date about novel small-molecule kinase inhibitors and evaluate if they would be useful to develop new treatment strategies for breast cancer patients.