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.

α-Tocopheryl Succinate Affects Malignant Cell Viability, Proliferation, and Differentiation

The widespread occurrence of malignant tumors motivates great attention to finding and investigating effective new antitumor preparations. Such preparations include compounds of the vitamin E family. Among them, α-tocopheryl succinate (vitamin E succinate (VES)) has the most pronounced antitumor properties. In this review, various targets and mechanisms of the antitumor effect of vitamin E succinate are characterized. It has been shown that VES has multiple intracellular targets and effects, and as a result VES is able to induce apoptosis in tumor cells, inhibit their proliferation, induce differentiation, prevent metastasizing, and inhibit angiogenesis. However, VES has minimal effects on normal cells and tissues. Due to the variety of targets and selectivity of action, VES is a promising agent against malignant neoplasms. More detailed studies in this area can contribute to development of effective and safe chemotherapeutic preparations.

Vitamin E analogues as mitochondria-targeting compounds: from the bench to the bedside?

Despite considerable effort focusing on designing and finding efficient anti-cancer drugs over the last decade, little progress has been achieved, in particular in case of highly recalcitrant malignancies. Also, since there is a trend suggesting that deaths from cancers may be more frequent than from cardiovascular diseases, it is important to look for novel efficient and selective therapeutic approaches to gradually start winning the battle with cancer. Redox-silent vitamin E analogues, epitomised by alpha-tocopheryl succinate, give some hope in the quest for drugs with such properties. Thus far, these agents have been successfully tested in experimental animals with different types of cancer, showing high efficacy against malignancies including HER2-positive breast carcinomas or malignant mesotheliomas. Further research will provide additional, necessary data to launch clinical trials, possibly in near future, translating into development of innovative anti-cancer drugs acting by targeting mitochondria selectively in cancer cells.

Involvement of JNK/p73/NOXA in vitamin E analog-induced apoptosis of human breast cancer cells

Microarray analyses of human MDA-MB-435 breast cancer cells treated with vitamin E analog 2,5,7,8-tetramethyl-2R-(4R,8R,12-trimethyltridecyl) chroman-6-yloxy acetic acid (alpha-TEA) showed over 400 genes to be modulated. Thirty-four genes deemed of interest based on potential involvement in anticancer activities of alpha-TEA fell into six categories: apoptosis related, signal transduction, cell cycle related, cell adhesion and motility, transcriptional regulators, and membrane traffic related. The gene (PMAIP1) for NOXA was studied further. NOXA mRNA and protein levels were elevated in a time and dose-dependent fashion following alpha-TEA treatment. Functional knockdowns using small interfering RNA (siRNA) showed NOXA to contribute to alpha-TEA-induced apoptosis. A correlation between alpha-TEA's ability to upregulate NOXA and induce apoptosis was seen among several human breast cancer cell lines. Efforts to identify upstream regulators of NOXA in alpha-TEA-induced apoptosis identified the necessity of both c-Jun N-terminal kinase (JNK) activation and p73 expression. Additionally, protein levels of full length p73 were decreased by JNK siRNA treatment, suggesting that the signal transduction module of JNK-p73-NOXA is involved in alpha-TEA induced apoptosis of human breast cancer cells. Taken together, these findings suggest a role for JNK activation in mediating full length p73 expression and add to our understanding of the mechanisms of anticancer actions of alpha-TEA, a potential chemotherapeutic agent.

Vitamin E analogs, a novel group of "mitocans," as anticancer agents: the importance of being redox-silent

The search for a selective and efficient anticancer agent for treating all neoplastic disease has yet to deliver a universally suitable compound(s). The majority of established anticancer drugs either are nonselective or lose their efficacy because of the constant mutational changes of malignant cells. Until recently, a largely neglected target for potential anticancer agents was the mitochondrion, showing a considerable promise for future clinical applications. Vitamin E (VE) analogs, epitomized by alpha-tocopheryl succinate, belong to the group of "mitocans" (mitochondrially targeted anticancer drugs). They are selective for malignant cells, cause destabilization of their mitochondria, and suppress cancer in preclinical models. This review focuses on our current understanding of VE analogs in the context of their proapoptotic/anticancer efficacy and suggests that their effect on mitochondria may be amplified by modulation of alternative pathways operating in parallel. We show here that the analogs of VE that cause apoptosis (which translates into their anticancer efficacy) generally do not possess antioxidant (redox) activity and are prototypical of the mitocan group of anticancer compounds. Therefore, by analogy to Oscar Wilde's play The Importance of Being Earnest, we use the motto in the title "the importance of being redox-silent" to emphasize an essentially novel paradigm for cancer therapy, in which redox-silence is a prerequisite property for most of the anticancer activities described in this communication.

The Roles of α‐Vitamin E and Its Analogues in Prostate Cancer

Prostate cancer is the second most commonly diagnosed cancer and the third leading fatal cancer in American men. Comprehensive studies from human epidemiological studies, animal tumor models, and cellular molecular levels suggested that alpha-vitamin E and its derivatives possess remarkable chemopreventive and chemotherapeutic against prostate cancer. This chapter details the facts of alpha-vitamin E and its nonantioxidant functions in prostate cancer, focuses on the biological mechanisms for the alpha-vitamin E and its ester analogue, alpha-vitamin E succinate (VES), in prevention and therapy of prostate cancer, and raises specific questions that remain for intensive investigation in the future.

Vitamin E and cancer

Perhaps not surprisingly, vitamin E which has been touted to be potentially beneficial for a variety of disorders, including cancer, heart disease, and even Alzheimer's disorder, based on its function as an antioxidant has failed to withstand the scrutiny of recent, double-blinded, placebo-controlled clinical trials, including failure to provide science-based support for vitamin E as a potent anticancer agent. Although less studied, vitamin E forms other than RRR-alpha-tocopherol or synthetic all-rac-alpha-tocopherol show promise as anticancer agents in preclinical studies. This chapter will (1) review basic information about natural and synthetic vitamin E compounds as well as vitamin E analogues, (2) summarize the current status of human intervention trials, (3) review data from preclinical cell culture and animal model studies of vitamin E compounds and novel vitamin E-based analogues in regards to future potential for cancer treatment, and (4) summarize some of the insights that have been gained into the anticancer mechanisms of action of vitamin E-based compounds which are providing interesting insights into their potent proapoptotic effects, which include restoration of apoptotic signaling pathways and blockage of prosurvival signaling events.

Effect of vitamin E on tamoxifen-treated breast cancer cells

BACKGROUND

Induction of apoptosis by tamoxifen has been postulated to involve oxidative stress. Tamoxifen (TAM) may act on estrogen receptors (ER) located in the plasma membrane. Our hypothesis that supplemental antioxidant vitamin E (alpha-tocopherol) acts at the plasma membrane to alter the effectiveness of tamoxifen was tested in ER-positive breast cancer cell lines, MCF-7 and T47D.

METHODS

Cells were treated in vitro with 20-muM TAM alone and in combination with 10-muM alpha-tocopherol (AT). Estrogen growth signals were quantified by immunohistochemical staining for the mitogen-activated protein kinase p-ERK. Rapid changes in intracellular calcium were detected in TAM-treated MCF-7 and T-47D cells by fluorescence microscopy of cells loaded with the calcium-sensitive dye Fluo 4AM. Apoptosis was assayed by flow cytometry.

RESULTS

Proliferating cells in normal medium exhibited strong p-ERK staining. Addition of TAM abolished p-ERK staining and caused cell rounding and death. The addition of AT led to the restoration of cell proliferation and p-ERK expression even in the presence of high-dose TAM. Intracellular calcium rapidly increased in MCF-7 and T47D cells upon exposure to TAM, followed by an increase in caspase activation and eventual apoptosis. The increase in intracellular calcium was abolished by the addition of 10muM AT to TAM, and pan-caspase staining decreased at 5 hours from 72% to 41%.

CONCLUSIONS

These studies suggest that supplemental vitamin E decreases the inhibitory effect of TAM on the proliferation of ER+ breast cancer cells and eliminates the rapid rise in intracellular calcium that leads to apoptosis stimulated by TAM. The use of vitamin E acetate supplements may be inadvisable for women taking tamoxifen.

α-TEA inhibits survival and enhances death pathways in cisplatin sensitive and resistant human ovarian cancer cells

RRR-alpha-tocopherol ether linked acetic acid analog (alpha-TEA), is a potential chemotherapeutic agent for ovarian cancer. Pro-death and pro-life signaling pathways were studied to understand the anti-cancer actions of alpha-TEA on cisplatin-sensitive (A2780S) and -resistant (A2780/cp70R) human ovarian cancer cells. Both cell lines were refractory to Fas; whereas, alpha-TEA sensitized them to Fas signaling. alpha-TEA increased levels of Fas message, protein and membrane-associated Fas. Neutralizing antibodies to Fas or Fas L partially blocked alpha-TEA-induced apoptosis. alpha-TEA induced prolonged activation of c-Jun N-terminal kinase (JNK) and its substrate c-Jun; Bax conformational change; and cleavage of Bid and caspases-8, -9 and -3. Chemical inhibitors of JNK, and caspases blocked alpha-TEA-induced apoptosis. alpha-TEA decreased phosphorylation of protein kinase B (Akt/PKB) and extracellular signal-regulated kinase (ERK1/2), as well as cellular FLICE-like inhibitory protein (c-FLIP) and Survivin protein levels. Knockdown of Akt and ERK activity using phosphoinositide- 3-kinase (PI3K) and mitogen-activated protein kinase kinase (MKK1) inhibitors enhanced alpha-TEA-induced apoptosis. Over-expression of constitutively active Akt2 and MKK1 blocked alpha-TEA-induced apoptosis. Collectively, data show alpha-TEA to be a potent apoptotic inducer of both cisplatin-sensitive and -resistant human ovarian cancer cells via activating death receptor Fas signaling and suppressing anti-apoptotic AKT and ERK targets.

α-Tocopheryl succinate induces DR4 and DR5 expression by a p53-dependent route: Implication for sensitisation of resistant cancer cells to TRAIL apoptosis

We evaluated the ability of alpha-tocopheryl succinate (alpha-TOS) to sensitise TRAIL-resistant malignant mesothelioma (MM) cells to TRAIL-induced apoptosis. We show that alpha-TOS activates expression of DR4/DR5 in a p53-dependent manner and re-establishes sensitivity of resistant MM cells to TRAIL-mediated apoptosis, as documented in p53wt MM cells but not in their p53null counterparts. MM cells selected for TRAIL resistance expressed low cell surface levels of DR4 and DR5. Treatment with sub-lethal doses of alpha-TOS restored expression of DR4 and DR5. The ability of alpha-TOS to modulate expression of pro-apoptotic genes may play a role in sensitisation of tumour cells to immunological stimuli.

RRR-α-Tocopherol succinate down-regulates oncogenic Ras signaling

alpha-Tocopherol succinate (TS), an analogue of vitamin E, has growth-inhibitory activity in a wide spectrum of in vitro and in vivo cancer models. Here, we report that modulation of oncogenic Ras is associated with TS activity. TS inhibits the proliferation and induces apoptosis of NIH3T3 cells stably transfected with oncogenic K-Ras and H-Ras, but not NIH3T3 cells expressing empty vector. TS treatment resulted in decreased Ras protein levels in oncogenic Ras expressing NIH3T3 cells but not in parental NIH3T3 cells. Treatment with TS suppressed the levels of phospho-Akt and phospho-Erk1/2 in oncogenic Ras expressing NIH3T3 cells. Overexpression of constitutively active phosphoinositide-3-kinase, Akt, and Mek1/2 significantly attenuated TS growth inhibition of oncogenic Ras-transformed NIH3T3 mouse fibroblast cell lines. In addition, transcriptional targets of oncogenic Ras such as c-Myc, cyclin D1, and E2F1 were down-regulated by TS in oncogenic Ras-expressing cells. The above TS effects on oncogenic Ras signaling were also observed in endogenous oncogenic K-Ras expressing HCT 116 (human colon cancer) and MDA-MB-231 (human breast cancer) cells. Taken together, these data show that TS down-regulation of the Ras signaling pathways that are mediated by Mek/Erk and phosphoinositide-3-kinase/Akt plays, at least in part, a critical role in TS inhibition of proliferation and survival of transformed cells. This data supports further investigation of the chemopreventive and therapeutic potential of TS in tumors that are dependent on activated Ras signaling and identifies phosphor-Erk and phosphor-Akt as potential biomarkers of TS activity.

Vitamin E succinate suppresses prostate tumor growth by inducing apoptosis

Prostate cancer is a major cause of cancer death and morbidity in western countries. However, because of its intrinsic nature of chemoresistance, there is only limited systemic therapy available for the patients. Vitamin E (VE) has been under intensive study as a chemopreventive agent for various types of cancers. Preclinical studies suggest that vitamin E succinate (VES) is the most effective antitumor analogue of VE, yet there are scarce studies of VES in prostate cancer. In this study, we investigated the effects of VES on a panel of prostate cancer cells, and a xenograft model of prostate cancer. Our results indicate that VES significantly inhibited proliferation and induced apoptosis of prostate cancer cell lines in a dose and time dependent manner. The results of microarray analysis followed by real-time RT-PCR and inhibitor analyses indicated that the VES-induced apoptosis is mediated by caspase-4 in prostate tumor cells. In our animal model of prostate cancer in SCID mouse, daily injection of VES significantly suppressed tumor growth as well as lung metastases. These results suggest a potential therapeutic utility of VES for patients with prostate cancer.

1,25-dihydroxycholecalciferol inhibits apoptosis in C3H10T1/2 murine fibroblast cells through activation of nuclear factor kappaB

1,25-dihydroxycholecalciferol [1,25(OH)(2)D(3)] is important in the regulation of cell growth, differentiation, and apoptosis. Previous results from our laboratory demonstrate that 1,25(OH)(2)D(3) inhibits vitamin E succinate (VES) mediated apoptosis in untransformed C3H10T1/2 mouse fibroblast cells. The current work investigated cell survival signaling pathways that may be activated by 1,25(OH)(2)D(3), leading to protection from apoptosis. Results showed that nuclear factor kappaB (NFkappaB) transcriptional activity was significantly increased 1.8-fold over vehicle controls by 1,25(OH)(2)D(3) after 4 h of treatment. Protein kinase B/AKT, a downstream effector of phosphoinositide 3-kinase (PI3K), was activated 4-fold and 8-fold at 2 and 4 h, respectively, after treatment with 1,25(OH)(2)D(3). Pretreatment with two PI3K inhibitors, LY294002 and wortmannin, abolished the activation of NFkappaB by 1,25(OH)(2)D(3), suggesting that this pathway is essential for NFkappaB transcriptional activation. Additionally, the use of a p-21 activated kinase (PAK1) inhibitory construct (PAK(R299)) demonstrated that PAK1 was also required for NFkappaB transcriptional activation by 1,25(OH)(2)D(3). Inhibition of NFkappaB activity with transfection of the NFkappaB inhibitory construct (IkappaB(Ala32)) abolished the protective effect of 1,25(OH)(2)D(3) on VES-mediated apoptosis. In summary, NFkappaB transcriptional activation was essential to 1,25(OH)(2)D(3) protection from VES-mediated apoptosis and 1,25(OH)(2)D(3) regulated NFkappaB activity through PI3K and PAK pathways.

Cholesteryl-hemisuccinate-induced apoptosis of promyelocytic leukemia HL-60 cells through a cyclosporin A-insensitive mechanism

We reported previously that alpha-tocopheryl-succinate (VES) induced apoptosis of cultured human promyelocytic leukemia cells (HL-60) (Free Radic Res 2000;33:407-18). We have now studied the effect of cholesteryl-hemisuccinate (CS) on the fate of HL-60 cells to clarify whether CS has an effect similar to that of VES. CS inhibited the growth of HL-60 cells without differentiation to granulocytes and induced DNA fragmentation and ladder formation. CS inhibited the phosphorylation of pleckstrin homology domain-containing protein kinase B (Akt) and initiated the activation of a caspase cascade. CS triggered the reaction leading to the cleavage of Bid and also released cytochrome c (Cyt. c) from mitochondria. In addition, CS induced mitochondrial membrane depolarization and translocation of Bax to mitochondria in HL-60 cells. However, CS did not induce an increase in the concentration of intracellular calcium ions in HL-60 cells. The membrane depolarization, Cyt. c release, and DNA fragmentation were inhibited by z-VAD-fluoromethylketone (z-VAD-fmk), a pan-caspase inhibitor, but not by cyclosporin A, an inhibitor of membrane permeability transition. These results suggested that CS-induced apoptosis of HL-60 cells might be caused by inhibiting Akt phosphorylation following cleavage of Bid through caspase-8 activation and subsequently via an Apaf complex-caspase cascade pathway.

Induction of apoptosis in a human breast cancer cell overexpressing ErbB-2 receptor by alpha-tocopheryloxybutyric acid

The overexpression of ErbB-2 receptor relates to malignant transformation of breast cancer. The present study was carried out to establish the usefulness of alpha-tocopheryloxybutyric acid (TE) as a chemotherapeutic agent for human breast cancer. TE caused induction of apoptosis in MDA-MB-453 cells overexpressing the ErbB-2 receptor. TE reduced levels of activated ErbB-2 receptor and Akt. In contrast, TE induced the activation of p38, and SB203580, a specific inhibitor for p38, attenuated the TE-induced apoptosis. These data indicate that simultaneous occurrences of Akt inhibition and p38 activation by TE result in the cell death.

Role of extracellular signal-regulated kinase pathway in RRR-alpha-tocopheryl succinate-induced differentiation of human MDA-MB-435 breast cancer cells

RRR-alpha-tocopheryl succinate (vitamin E succinate, VES) induces differentiation of human breast cancer cells. Previous studies ruled out transforming growth factor-beta and c-jun N-terminal kinase involvement in VES-induced differentiation but implicated extracellular signal-regulated kinases (ERKs). Here we show that dominant-negative mutants of either mitogen-activated protein kinase kinase (MEK) 1 or ERK1 blocked VES-induced differentiation of MDA-MB-435 cells, as measured by induction of cytokeratin 18 and p21 (Waf1/Cip1) proteins. Blockage of c-jun protein expression using c-jun antisense oligonucleotides or expression of an inducible dominant-negative c-jun mutant protein inhibited VES-induced differentiation. Elevated expression of wild-type c-jun alone was sufficient to induce cellular differentiation. A role for p21 (Waf1/Cip1) is implicated, in that p21 antisense oligomers blocked VES-induced differentiation. In summary, MEK1, ERK1, the transcription factor c-jun, and the cyclin-dependent kinase inhibitor p21 (Waf1/Cip1) play a part in VES-induced differentiation of human MDA-MB-435 breast cancer cells.

Vitamin E analogues as inducers of apoptosis: implications for their potential antineoplastic role

Recent evidence suggests that vitamin E and its analogues, which have been used for many years as antioxidants, may not only protect cells from free radical damage but also induce apoptotic cell death in various cell types. While alpha-tocopherol (alpha-TOH) is mainly known as an anti-apoptotic agent, its redox-silent analogues either have no influence on cell survival (alpha-tocopheryl acetate, alpha-TOA), or induce apoptosis (alpha-tocopheryl succinate, alpha-TOS). Although precise mechanisms of apoptosis induction by alpha-TOS remain to be elucidated, there is evidence that this process involves both the antiproliferative and membrane destabilising activities of the agent. Alpha-TOS has been shown to induce apoptosis in malignant cell lines but not, in general, in normal cells, and to inhibit tumorigenesis in vivo. These features suggest that this semi-synthetic analogue of vitamin E could be a promising antineoplastic agent.

Does lack of tocopherols and tocotrienols put women at increased risk of breast cancer?

Breast cancer is the leading site of new cancers in women and the second leading cause (after lung cancer) of cancer mortality in women. Observational studies that have collected data for dietary exposure to alpha-tocopherol with or without the other related tocopherols and tocotrienols have suggested that vitamin E from dietary sources may provide women with modest protection from breast cancer. However, there is no evidence that vitamin E supplements confer any protection whatever against breast cancer. Observational studies that have assessed exposure to vitamin E by plasma or adipose tissue concentrations of alpha-tocopherol have failed to provide consistent support for the idea that alpha-tocopherol provides any protection against breast cancer. In addition, evidence from studies in experimental animals suggest that alpha-tocopherol supplementation alone has little effect on mammary tumors. In contrast, studies in breast cancer cells indicate that alpha- gamma-, and delta-tocotrienol, and to a lesser extent delta-tocopherol, have potent antiproliferative and proapoptotic effects that would be expected to reduce risk of breast cancer. Many vegetable sources of alpha-tocopherol also contain other tocopherols or tocotrienols. Thus, it seems plausible that the modest protection from breast cancer associated with dietary vitamin E may be due to the effects of the other tocopherols and the tocotrienols in the diet. Additional studies will be required to determine whether this may be the case, and to identify the most active tocopherol/tocotrienol.

Activation of PKC but not of ERK is required for vitamin E-succinate-induced apoptosis of HL-60 cells

Vitamin E-succinate (VES) induced HL-60 human leukemia cells to undergo apoptosis. Treatment with VES induced membrane translocation of Fas; cleavages of caspase-3, PARP, and lamin B; hypophosphorylation of retinoblastoma protein; and increase of p21(WAF1) protein level. During the induction of apoptosis, activity of PKC was gradually increased with downregulation of VES-induced ERK activity and accompanied by activation of caspase-3. Inhibition of PKC by GF109203X blocked VES-mediated membrane translocation of PKC-alpha and cleavage of caspase-3 cascade, resulting in prevention of VES-induced apoptosis. On the contrary, PKC activation by cotreatment with LPC or thapsigargin and VES synergistically increased VES-mediated apoptosis. However, inhibition of ERK activity by PD98059 showed no significant effect on VES-induced PKC activity and apoptosis. Taken together, our data suggest that VES induces activation of PKC and PKC-dependent hypophosphorylation of retinoblastoma protein, which results in induction of apoptosis, and that VES-induced early activation of ERK and ERK-dependent induction of p21(WAF1) are not required for apoptosis.

Vitamin E succinate promotes breast cancer tumor dormancy

BACKGROUND

Vitamin E succinate (VES) is the most potent antitumor analogue of vitamin E. Despite many reports of VES's antitumor activity in vitro, there is little information about its antitumor effects in vivo.

MATERIALS AND METHODS

We investigated the effect of VES on the growth of human breast cancer cells in vitro and in vivo.

RESULTS

VES decreased cell viability in MDA-MB-231 and MCF-7 human breast cancer cells. Although VES increased apoptosis in MDA-MB-231 cells, it had no effect on apoptosis in MCF-7 cells. The inhibitory effect of VES on cell growth was specific for the intact molecule because a markedly reduced effect was noted when either vitamin E or succinic acid was administered alone. VES inhibited the growth of MDA-MB-231 cells in nude mice. Also, VES was found to inhibit vascular endothelial growth factor (VEGF) gene expression in MDA-MB-231 cells.

CONCLUSIONS

VES inhibits the growth of breast cancer cells in vitro and in vivo. This is the first report of VES inhibition of established tumor growth in vivo. The mechanism of VES's in vivo effects may involve inhibition of tumor angiogenesis since VES inhibits VEGF gene expression.

Chemoprevention of breast cancer

Despite a recent trend toward improvement in the U.S. breast cancer mortality rate, breast cancer incidence (182,800 new cases anticipated in 2000) and mortality figures (over 40,800 anticipated deaths) remain the highest and second highest, respectively, of all cancers in U.S. women. In 1998, the selective-estrogen-receptor-modulator (SERM) tamoxifen achieved positive results in the Breast Cancer Prevention Trial (BCPT), leading to the Food and Drug Administration (FDA) approval of tamoxifen for risk reduction in women at high risk of breast cancer (the historic first FDA approval of a cancer preventive agent). This brought about a paradigm shift in new approaches for controlling breast cancer toward pharmacologic preventive regimens, called chemoprevention. This paper presents a comprehensive clinical review of breast cancer prevention study, highlighting issues of the extensive study of tamoxifen. These issues include the record of primary tamoxifen results in several breast-cancer risk-reduction settings (primary, adjuvant, and ductal carcinoma in situ [DCIS]); critical secondary BCPT risk-benefit findings (including quality of life issues) and their effects on counseling patients on use of tamoxifen for prevention; ethic minorities; optimal tamoxifen dose/duration; and potential impact on mortality and other issues involved with potential net benefit to society. Other breast-cancer chemoprevention issues reviewed here include women at high genetic risk (especially BRCA1 mutation carriers); raloxifene in breast cancer prevention; other SERMs; SERM resistance; and new agents and combinations currently in development. Very recent developments involving PPAR-gamma ligands, COX-2 inhibitors, and RXR-ligands are discussed in the section on new drug development.

Lipoprotein-associated alpha-tocopheryl-succinate inhibits cell growth and induces apoptosis in human MCF-7 and HBL-100 breast cancer cells

alpha-Tocopheryl succinate (alpha-TS) is a potent inhibitor of tumor cell proliferation. The goal of the present study was to investigate whether and to what extent alpha-TS associates with plasma lipoproteins and if alpha-TS-enriched lipoproteins inhibit breast cancer cell growth in a manner comparable to the free drug. In vitro enrichment of human plasma revealed that alpha-TS readily associated with the main lipoprotein classes, findings confirmed in vivo in mice. At the highest alpha-TS concentrations, lipoproteins carrying 50000 (VLDL), 5000 (LDL) and 700 (HDL) alpha-TS molecules per lipoprotein particle were generated. alpha-TS enrichment generated lipoprotein particles with slightly decreased density and increased particle radius. To study whether the level of LDL-receptor (LDL-R) expression affects alpha-TS uptake from apoB/E containing lipoprotein particles human breast cancer cells with low (MCF-7) and normal (HBL-100) LDL-R expression were used. The uptake of free, VLDL- and (apoE-free) HDL(3)-associated alpha-TS was nearly identical for both cell lines. In contrast, uptake of LDL-associated alpha-TS by HBL-100 cells (normal LDL-R expression) was about twice as high as compared to MCF-7 cells (low LDL-R expression). VLDL and LDL-associated alpha-TS inhibited proliferation most effectively at the highest concentration of alpha-TS used (100% inhibition of MCF-7 growth with 20 microg/ml of lipoprotein-associated alpha-TS). However, also alpha-TS-free VLDL and LDL inhibited HBL-100 cell proliferation up to 55%. In both cell lines, alpha-TS-enriched HDL(3) inhibited cell growth by 40-60%. Incubation of both cell lines in the presence of free or lipoprotein-associated alpha-TS resulted in DNA fragmentation indicative of apoptosis. Collectively, the present findings demonstrate that: (1) alpha-TS readily associates with lipoproteins in vitro and in vivo; (2) the lipoprotein-enrichment efficacy was dependent on the particle size and/or the triglyceride content of the lipoprotein; (3) uptake of LDL-associated alpha-TS was apparently dependent on the level of LDL-R expression; and (4) lipoproteins were efficient alpha-TS carriers inducing reduced cell proliferation rates and apoptosis in human breast cancer cells as observed for the free drug.

Biological and clinical associations of c-jun activation in human breast cancer

Sub-units and regulators of the activating protein-1(AP-1) complex have been implicated in breast-cancer biology, therapeutic response and prognosis. This study has immunocytochemically examined the impact of c-jun-protein activation on biological and clinical parameters in human primary breast cancers, employing an antibody specific for the serine 63-phosphorylated c-jun protein. Substantial nuclear immunostaining was commonly apparent, indicative of an activated c-jun pool, with associations with MAP-kinase-signalling elements, e.g., transforming growth factor-alpha (p = 0.04), epidermal growth factor receptor (p = 0.08), phosphorylated erk 1/2 MAP kinase (p = 0.001) and phosphorylated jun kinase (p = 0.05) Little association was noted with c-fos protein, perhaps indicating alternative AP-1 partners for c-jun with a diversity of cellular end-points. This may explain the lack of relationship with proliferation and grade, the imperfect association between increased c-jun activation and poorer survival (p = 0.061), and the apparent relationship with distant metastasis (p = 0.05). While increased c-jun activation related to poorer quality (p = 0.09) and shortened duration of endocrine response in oestrogen-receptor-positive patients (p = 0.018), no generalized effects on oestrogen-regulated gene products were noted, indicating that AP-1 influences on oestrogen-receptor/oestrogen-response element transactivation are unlikely to explain endocrine insensitivity. These data reinforce our belief that elevated AP-1 signalling influences aspects of the breast-cancer phenotype.

Peptide YY augments gross inhibition by vitamin E succinate of human pancreatic cancer cell growth

BACKGROUND

Vitamin E succinate (VES) significantly inhibits cell growth in vitro in breast, prostate, and skin cancer cell lines. Our study demonstrated similar inhibitory effects on Mia PaCa-2 pancreatic cancer cells at the same concentration of VES (10 pg/ml). Peptide YY (PYY) also inhibits pancreatic cancer cell growth in vitro. We observed a significant additive effect on growth inhibition in Mia PaCa cells treated with both VES and PYY.

METHODS

Human pancreatic ductal adenocarcinoma Mia PaCa-2 cells were cultured and treated once with either 10 pg/ml of VES or 500 pmols of PYY or with both agents together. The control group received an equivalent volume of solvents. MTT assay was performed at 24, 48, and 72 h to evaluate cell viability.

RESULTS

Pancreatic cancer cell growth was reduced in all groups treated with PYY and VES. Student's t test was used to analyze the data for each treatment group. At 72 h, both PYY and vitamin E significantly inhibited cell growth compared to control. Combining the agents resulted in a dramatic additive inhibition of growth.

CONCLUSION

PYY and vitamin E both inhibit growth of pancreatic cancer cells in vitro with a significant increase in effect when used in combination.

Nutritional determinants of survival among patients with breast cancer

Recent data leave little doubt that nutritional factors modulate the growth of breast cancer cells. Nonetheless, the question of what type of diet is best for patients with a history of early-stage breast cancer or for patients with metastatic breast cancer continues to loom despite a growing number of studies on nutrition and cancer. Recommendations for the general population from the American Cancer Society and the Dietary Guidelines for Americans outline 25% of calories from fat, multiple servings of fruits and vegetables, and an emphasis on eating a variety of different foods. Although these recommendations likely constitute prudent advice for patients with breast cancer who have completed treatment for early-stage disease, they remain unproved. Specific, beneficial recommendations for patients currently receiving adjuvant chemotherapy or for patients with metastatic disease may well differ from those for the general population. Future clinical trials will play an important role in clarifying such issues.

Trichothecene mycotoxins trigger a ribotoxic stress response that activates c-Jun N-terminal kinase and p38 mitogen-activated protein kinase and induces apoptosis

The trichothecene family of mycotoxins inhibit protein synthesis by binding to the ribosomal peptidyltransferase site. Inhibitors of the peptidyltransferase reaction (e.g. anisomycin) can trigger a ribotoxic stress response that activates c-Jun N-terminal kinase (JNK)/p38 mitogen-activated protein kinases, components of a signaling cascade that regulates cell survival in response to stress. We have found that selected trichothecenes strongly activate JNK/p38 kinases and induce rapid apoptosis in Jurkat T cells. Although the ability of individual trichothecenes to inhibit protein synthesis and activate JNK/p38 kinases are dissociable, both effects contribute to the induction of apoptosis. Among trichothecenes that strongly activate JNK/p38 kinases, induction of apoptosis increases linearly with inhibition of protein synthesis. Among trichothecenes that strongly inhibit protein synthesis, induction of apoptosis increases linearly with activation of JNK/p38 kinases. Trichothecenes that inhibit protein synthesis without activating JNK/p38 kinases inhibit the function (i.e. activation of JNK/p38 kinases and induction of apoptosis) of apoptotic trichothecenes and anisomycin. Harringtonine, a structurally unrelated protein synthesis inhibitor that competes with trichothecenes (and anisomycin) for ribosome binding, also inhibits the activation of JNK/p38 kinases and induction of apoptosis by trichothecenes and anisomycin. Taken together, these results implicate the peptidyltransferase site as a regulator of both JNK/p38 kinase activation and apoptosis.