α-TEA cooperates with MEK or mTOR inhibitors to induce apoptosis via targeting IRS/PI3K pathways

An Update on Tamoxifen and the Chemo-Preventive Potential of Vitamin E in Breast Cancer Management

Breast cancer (BC) is the most common female cancer in terms of incidence and mortality worldwide. Tamoxifen (Nolvadex) is a widely prescribed, oral anti-estrogen drug for the hormonal treatment of estrogen-receptor-positive BC, which represents 70% of all BC subtypes. This review assesses the current knowledge on the molecular pharmacology of tamoxifen in terms of its anticancer and chemo-preventive actions. Due to the importance of vitamin E compounds, which are widely taken as a supplementary dietary component, the review focuses only on the potential importance of vitamin E in BC chemo-prevention. The chemo-preventive and onco-protective effects of tamoxifen combined with the potential effects of vitamin E can alter the anticancer actions of tamoxifen. Therefore, methods involving an individually designed, nutritional intervention for patients with BC warrant further consideration. These data are of great importance for tamoxifen chemo-prevention strategies in future epidemiological studies.

How vitamin E and its derivatives regulate tumour cells via the MAPK signalling pathway?'

In tumour cells, vitamin E and its derivatives play a critical role in the regulation of multiple signalling pathways through their oxidative and nonoxidative functions. To date, there are 8 known natural vitamin E forms and many kinds of derivatives, among which VES and α-TEA have excellent anticancer activities. The MAPK pathway consists of a complex cascade of proteins that control the proliferation, differentiation and apoptosis of tumour cells. The MAPK pathway includes four subfamilies, ERK1/2, JNK1/2, p38 MAPK, and ERK5. Most of the proteins in these subfamilies interact with each other in a complex manner. The anticancer function of vitamin E and its derivatives is closely related to the MAPK cascade. Studies have shown that in tumour cells, α-T/γ-T/γ-T3/δ-T3/VES/α-TEA regulated ERK1/2, prevent tumorigenesis, inhibit tumour cell growth and metastasis and induce cell differentiation, apoptosis, and cell cycle arrest; γ-T3/δ-T3/VES/α-TEA regulates JNK1/2, induce apoptosis, reduce ceramide synthesis and inhibit proliferation; and γ-T3/δ-T3/VES regulate p38 MAPK and induce apoptosis. This paper reviews the role of vitamin E and its derivatives in the MAPK cascade, and tumour cells are used as a model in an attempt to explore the mechanism of their interactions.

Effect of α-tocopheryloxy acetic acid, a vitamin E derivative mitocan, on the experimental infection of mice with Plasmodium yoelii

Background

Malaria parasites are known to be vulnerable to oxidative stress. In this study, the effects of the administration of α-tocopheryloxy acetic acid (α-TEA), which is a vitamin E analogue mitocan, on Plasmodium yoelii infection in mice were examined.

Methods

Alpha-TEA was mixed with diet and fed to C57BL/6J mice before and/or after infection. For parasite infection, 4 × 10⁴ red blood cells infected with P. yoelii (strain 17XL) were inoculated by intraperitoneal injection. In another series of experiment, the effect of the oral administration of α-TEA on P. yoelii 17XL infection in mice was examined. Finally, the combined effect of α-TEA and dihydroartemisinin or chloroquine on P. yoelii 17XL infection was examined.

Results

When 0.25% α-TEA was mixed with the diet for 7 days before infection and 14 days after infection (in total for 21 days), for 14 days after infection, and for 11 days from the third day after infection, all P. yoelii 17XL-infected mice survived during the observation period. However, all control mice died within 12 days after infection. These results indicated that α-TEA functions effectively even when administered post-infection. The oral administration of α-TEA for P. yoelii 17XL infection was also significant. Although the infected mice in the solvent control died within 10 days after infection, 90% of the mice infected with P. yoelii 17XL survived during the observation period when treated with 10 mg/head/day of α-TEA for 3 days from day 3 after infection. Although the combined effect of α-TEA and dihydroartemisinin (DHA) or chloroquine on P. yoelii 17XL infection was significant, no synergistic or additive effects were observed from the survival curve.

Conclusions

This study showed the beneficial effects of α-TEA on the experimental infection of mice with P. yoelii 17XL. The stimulatory action of α-TEA on mitochondria and the accompanying reactions, such as reactive oxygen species production, and induction of apoptosis might have some effect on malarial infection.

Blockade of insulin receptor substrate-1 inhibits biological behavior of choroidal endothelial cells

AIM

To investigate the effects of blockade of insulin receptor substrate-1 (IRS-1) on the bio-function of tube formation of human choroidal endothelial cells (HCECs).

METHODS

Quantitative reverse transcription-polymerase chain reaction (RT-PCR) and Western blot were performed to determine the expression level of IRS-1 and phospho-IRS-1 in HCECs. Tube formation of HCECs was analyzed using three dimensional in vitro Matrigel assay with or without IRS-1 blockage via IRS-1 inhibitor (GS-101) and vascular endothelial growth factor receptor 2 (VEGFR2) inhibitor. In addition, cell counting kit (CCK)-8 and Transwell migration assay were exerted to analyze the effects of blockade of IRS-1 on the bio-function of proliferation and migration of HCECs, respectively. The apoptosis of HCECs was examined using flow cytometry (FCM).

RESULTS

RT-PCR and Western blot revealed that IRS-1 phospho-IRS-1 were expressed in HCECs and the expression level was enhanced by stimulation of VEGF-A. The number of tube formation was decreased significantly in GS-101 treated groups compared to phosphate buffered saline (PBS) treated control groups. Furthermore, both cell proliferation and migration of HCECs were decreased in the presence of GS-101. FCM analysis showed that the apoptosis of HCECs was enhanced when the cells were treated with GS-101. Western blot also showed that the expression level of cleaved-caspase 3 in GS-101 treated group was higher than that in control group.

CONCLUSION

Blockade of IRS-1 can inhibit tube formation of HCECs through reducing cell proliferation and migration and promoting cell apoptosis.

Tocopherols in cancer: An update

Tocopherols exist in four forms designated as α, β, δ, and γ. Due to their strong antioxidant properties, tocopherols have been suggested to reduce the risk of cancer. Cancer prevention studies with tocopherols have mostly utilized α-tocopherol. Large-scale clinical trials with α-tocopherol provided inconsistent results regarding the cancer-preventive activities of tocopherols. This review summarizes our current understanding of the anticancer activities of different forms of tocopherols based on follow-up of the clinical trials, recent epidemiological evidences, and experimental studies using in vitro and in vivo models. The experimental data provide strong evidence in support of the anticancer activities of δ-tocopherol, γ-tocopherol, and the natural tocopherol mixture rich in γ-tocopherol, γ-TmT, over α-tocopherol. Such outcomes emphasize the need for detailed investigation into the cancer-preventive activities of different forms of tocopherols to provide a strong rationale for intervention studies in the future.

Drug Delivery Innovations for Enhancing the Anticancer Potential of Vitamin E Isoforms and Their Derivatives

Vitamin E isoforms have been extensively studied for their anticancer properties. Novel drug delivery systems (DDS) that include liposomes, nanoparticles, and micelles are actively being developed to improve Vitamin E delivery. Furthermore, several drug delivery systems that incorporate Vitamin E isoforms have been synthesized in order to increase the bioavailability of chemotherapeutic agents or to provide a synergistic effect. D-alpha-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) is a synthetic derivative of natural alpha-tocopherol which is gaining increasing interest in the development of drug delivery systems and has also shown promising anticancer effect as a single agent. This review provides a summary of the properties and anticancer effects of the most potent Vitamin E isoforms and an overview of the various formulations developed to improve their efficacy, with an emphasis on the use of TPGS in drug delivery approaches.

FOXP1 regulation via the PI3K/Akt/p70S6K signaling pathway in breast cancer cells

Loss of Forkhead box P1 (FOXP1) protein expression confers a poor prognosis in sporadic and familial breast cancer patients, and the FOXP1 gene maps to a tumor suppressor locus at chromosome 3p14. Although correlation studies have indicated that FOXP1 has a role in tumor suppression, determination of the regulatory mechanism of FOXP1 is required to establish its function in breast cancer. It has previously been identified that FOXP1 is regulated by estrogen in breast cancer and that treatment with bisphenol A is effective for regulating the transformation of the normal human breast epithelial cell line, MCF-10F. In addition, FOXO-regulated activation of FOXP1 inhibits the apoptosis of MCF-10F cells following tamoxifen and Akt inhibitor VIII administration. The present study indicates that FOXP1 regulation occurs via a PI3K/Akt/p70S6 kinase (p70S6K) signaling pathway. Following treatment with wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K)/Akt, MCF7 and MDA-MB-231 breast cancer cells demonstrated decreased FOXP1 protein expression levels; this result was also observed in the small interfering (si)RNA silencing of Akt. By contrast, overexpression of Akt resulted in increased FOXP1 protein expression levels in the MDA-MB-231 cells compared with the control cell lysates. Furthermore, treatment with rapamycin, a specific inhibitor of the mammalian target of rapamycin/p70S6K cascade, resulted in decreased FOXP1 expression in the MCF7 cells, but not in the MDA-MB-231 cells, which were resistant to rapamycin-induced inhibition. In addition, silencing of p70S6K using siRNA produced a marked decrease in FOXP1 expression. These data indicate that FOXP1 protein expression is regulated by a PI3K/Akt/p70S6K signaling cascade in breast cancer.

The vitamin E analogue α-TEA stimulates tumor autophagy and enhances antigen cross-presentation

The semisynthetic vitamin E derivative alpha-tocopheryloxyacetic acid (α-TEA) induces tumor cell apoptosis and may offer a simple adjuvant supplement for cancer therapy if its mechanisms can be better understood. Here we report that α-TEA also triggers tumor cell autophagy and that it improves cross-presentation of tumor antigens to the immune system. α-TEA stimulated both apoptosis and autophagy in murine mammary and lung cancer cells and inhibition of caspase-dependent apoptosis enhanced α-TEA-induced autophagy. Cell exposure to α-TEA generated double-membrane-bound vesicles indicative of autophagosomes, which efficiently cross-primed antigen-specific CD8(+) T cells. Notably, vaccination with dendritic cells pulsed with α-TEA-generated autophagosomes reduced lung metastases and increased the survival of tumor-bearing mice. Taken together, our findings suggest that both autophagy and apoptosis signaling programs are activated during α-TEA-induced tumor cell killing. We suggest that the ability of α-TEA to stimulate autophagy and enhance cross-priming of CD8(+) T cells might be exploited as an adjuvant strategy to improve stimulation of antitumor immune responses.

Mammalian target of rapamycin regulates isoliquiritigenin-induced autophagic and apoptotic cell death in adenoid cystic carcinoma cells

Previous studies, including those from our laboratory, have demonstrated that isoliquiritigenin (ISL), a flavonoid isolated from licorice, is a promising cancer chemotherapeutic agent. However the mechanisms underlying its anticancer effects are still far from clear. We now show, for the first time, that ISL triggers the mammalian target of rapamycin (mTOR)-dependent autophagic and apoptotic cell death in adenoid cystic carcinoma (ACC). Exposure of both ACC-2 and ACC-M cells to ISL resulted in several specific features for autophagy, including the appearance of membranous vacuoles, formation of acidic vesicular organelles, punctate pattern of LC3 immunostaining, and an increase in autophagic flux. Moreover, ISL treatment also resulted in significantly increased apoptosis in ACC cells. The ISL-mediated autophagic and apoptotic cell death were obviously attenuated by transfection with dominant negative Atg5 (DN-Atg5(K130R)) plasmids or treatment with 3-methyladenine(3-MA). In additon, the data also revealed that the autophagic and apoptotic cell death induced by ISL occurred through a mTOR-dependent pathway. More importantly, the xenograft model using ACC-M cells provided further evidence of the occurrence of ISL-induced autophagy and apoptosis in vivo, correlating with the suppresson of mTOR activation as well as up-regulation of Atg5 expression. Taken together, these findings in our study suggest that induction of mTOR-dependent autophagic and apoptotic cell death may be an important mechanism in cancer chemotherapy by ISL.

Up-regulation of endogenous PML induced by a combination of interferon-beta and temozolomide enhances p73/YAP-mediated apoptosis in glioblastoma

Interferon-beta (IFN-β) is reported to augment anti-tumor effects by temozolomide in glioblastoma via down-regulation of MGMT. Promyelocytic leukemia (PML), a gene induced by IFN-β, is a tumor suppressor. Here, we report for the first time that in combination therapy, an IFN-β-induced increase in endogenous PML contributes to anti-tumor effects in p53 wild- and mutant glioma cells in a xenograft mice model. The increased PML promoted the accumulation of p73, a structural and functional homolog of p53, to fuse the coactivator Yes-associated-protein in the PML nuclear bodies. The adjuvant therapy targeted at PML may be a promising therapeutic strategy for glioblastoma.

Targeting cholesterol-rich microdomains to circumvent tamoxifen-resistant breast cancer

INTRODUCTION

Adjuvant treatment with tamoxifen substantially improves survival of women with estrogen-receptor positive (ER+) tumors. Tamoxifen resistance (TAMR) limits clinical benefit. RRR-α-tocopherol ether-linked acetic acid analogue (α-TEA) is a small bioactive lipid with potent anticancer activity. We evaluated the ability of α-TEA in the presence of tamoxifen to circumvent TAMR in human breast cancer cell lines.

METHODS

Two genotypically matched sets of TAM-sensitive (TAMS) and TAM-resistant (TAMR) human breast cancer cell lines were assessed for signal-transduction events with Western blotting, apoptosis induction with Annexin V-FITC/PI assays, and characterization of cholesterol-rich microdomains with fluorescence staining. Critical involvement of selected mediators was determined by using RNA interference and chemical inhibitors.

RESULTS

Growth-factor receptors (total and phosphorylated forms of HER-1 and HER-2), their downstream prosurvival mediators pAkt, pmTOR, and pERK1/2, phosphorylated form of estrogen receptor-α (pER-α at Ser-167 and Ser-118, and cholesterol-rich lipid microdomains were highly amplified in TAMR cell lines and enhanced by treatment with TAM. α-TEA disrupted cholesterol-rich microdomains, acted cooperatively with TAM to reduce prosurvival mediators, and induced DR5-mediated mitochondria-dependent apoptosis via an endoplasmic reticulum stress-triggered pro-death pJNK/CHOP/DR5 amplification loop. Furthermore, methyl-β-cyclodextrin (MβCD), a chemical disruptor of cholesterol rich microdomains, acted cooperatively with TAM to reduce prosurvival mediators and to induce apoptosis.

CONCLUSIONS

Data for the first time document that targeting cholesterol-rich lipid microdomains is a potential strategy to circumvent TAMR, and the combination of α-TEA + TAM can circumvent TAMR by suppression of prosurvival signaling via disruption of cholesterol-rich lipid microdomains and activation of apoptotic pathways via induction of endoplasmic reticulum stress.

p73 as a pharmaceutical target for cancer therapy

About half of all human tumors contain an inactivating mutation of p53, while in the remaining tumors, the p53 pathway is frequently abrogated by alterations of other components of its signaling pathway. In humans, the p53 tumor suppressor is part of a small gene family that includes two other members, p73 and p63, structurally and functionally related to p53. Accumulating evidences indicate that all p53-family proteins function as molecular hubs of a highly interconnected signaling network that coordinates cell proliferation, differentiation and death in response to physiological inputs and oncogenic stress. Therefore, not only the p53-pathway but the entire “p53-family pathway” is a primary target for cancer drug development. In particular, the p53-related protein p73 has a crucial role in determining cellular responses to chemotherapy, and can vicariate p53 functions in triggering cell death after DNA damage in multiple experimental models. The biology and regulation of p73 is complex, since the TP73 gene incorporates both tumor-suppressive and proto-oncogenic functions. However, the p73 gene is rarely mutated in tumors, so appropriate pharmacological manipulation of the p73 pathway is a very promising approach for cancer therapy. Here we provide an overview of the principal mechanism of p73 regulation, and describe several examples of pharmacological tools that can induce p73 accumulation and function by acting on upstream p73 modulators or displacing inhibitory p73 interactors. A better understanding of how the p73 pathway works is mandatory to discover additional players intervening in this pathway and has important implications for the improvement of cancer treatment with the development of new molecules or with the reposition of currently available drugs.