Selective cancer cell killing by alpha-tocopheryl succinate

α-Tocopheryl succinate induces cytostasis and apoptosis in osteosarcoma cells: the role of E2F1

Alpha-tocopheryl succinate (alpha-TOS), a redox-inactive analog of vitamin E, induces cell cycle arrest, differentiation, and triggers apoptosis. We examined the ability of alpha-TOS to induce cytostasis and/or apoptosis in two human osteosarcoma cell lines, which carry wild-type pRb but differ in the p53 status. In the wt-p53 cells, alpha-TOS induced apoptosis, which was associated with p53 activation and enhanced E2F1 expression. Mutant p53 cells failed to undergo apoptosis when challenged with alpha-TOS. The cell growth arrest after alpha-TOS treatment was associated with a reduced expression of E2F1. Knocking down E2F1 rendered the alpha-TOS-sensitive cells rather resistant to the apoptotic stimulus inducing a marked and prolonged cell growth arrest. We conclude that alpha-TOS induces cell growth arrest or apoptosis involving E2F1.

Chemopreventive effect of dietary d-alpha-tocopheryl succinate supplementation on precancer colon aberrant crypt formation and vitamin E analogue levels in young and old rats

This study examined the effects of dietary d-alpha-tocopheryl succinate (TS) in female rats, 20 mo (OLD) or 2 mo (YNG) of age, on azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) and tissue distribution of d-alpha-tocopherol (alphaT), d-gamma-tocopherol (gammaT), and alphaTS. Rats were fed a commercial rodent chow supplemented with or without 1 (YNG) or 2 (OLD) g alphaTS/kg diet for 1 week prior to ip administration of AOM to induce colon ACF. The animals were sacrificed after 49 days of exposure. The results showed that OLD rats had significantly fewer ACF than YNG animals, and the percent body fat and serum triglycerides were significantly higher in the OLD group compared with the YNG. However, only OLD animals receiving alphaTS had significantly reduced numbers of larger ACF and significantly higher levels of colonic alphaT, gammaT, and alphaTS. These data support previous studies demonstrating that dietary alphaTS administration is protective against intestinal cancer. Also, this is the first study to show that alphaTS accumulates in most tissues following dietary exposure. We hypothesize that increased colon accumulation of fat-soluble vitamin E compounds and subsequent chemoprevention may be related to greater percent body fat and serum triglycerides in OLD animals receiving dietary TS.

Multiple dietary antioxidants enhance the efficacy of standard and experimental cancer therapies and decrease their toxicity

Cancer patients can be divided into 3 groups: those receiving standard or experimental therapy, those who have become unresponsive to these therapies, and those in remission at risk for recurrence or a second new cancer. While impressive progress in standard cancer therapy has been made, the value of this therapy in the management of solid tumors may have reached a plateau. At present, there is no strategy to reduce the risk of recurrence of the primary tumors or of a second cancer among survivors. Patients unresponsive to standard or experimental therapies have little option except for poor quality of life for the remainder of life. Therefore, additional approaches should be developed to improve the efficacy of current management of cancer. In this review, the author proposes that an active nutritional protocol that includes high doses of multiple dietary antioxidants and their derivatives (vitamin C, alpha-tocopheryl succinate, and natural beta-carotene), but not endogenously made antioxidants (glutathione- and antioxidant enzyme-elevating agents), when administered as an adjunct to radiation therapy, chemotherapy, or experimental therapy, may improve its efficacy by increasing tumor response and decreasing toxicity. This nutritional protocol can also be used when patients become unresponsive to standard therapy or experimental therapy to improve quality of life and possibly increase the survival time. The authors also propose that after completion of standard therapy and/or experimental therapy, a maintenance nutritional protocol that contains lower doses of antioxidants and their derivatives, together with modification in diet and lifestyle, may reduce the risk of recurrence of the original tumor and development of a second cancer among survivors. Experimental data and limited human studies suggest that use of these nutritional approaches may improve oncologic outcomes and decrease toxicity. This review also discusses the reasons for the current debates regarding the use of antioxidants during radiation or chemotherapy.

Hepatic processing determines dual activity of α-tocopheryl succinate: a novel paradigm for a shift in biological activity due to pro-vitamin-to-vitamin conversion

Redox-silent vitamin E analogues, represented by alpha-tocopheryl succinate, are potent anti-cancer drugs with potential secondary bioactivity due to their processing in vivo. Here we verified the hypothesis that hepatic processing of these agents determines the secondary effect. Mice were repeatedly injected with alpha-tocopheryl succinate, and their systemic and hepatic vein blood was assessed for alpha-tocopheryl succinate and its hydrolysis product, vitamin E (alpha-tocopherol). While levels of alpha-tocopherol doubled compared to control mice and alpha-tocopheryl succinate accumulated in the systemic blood, no alpha-tocopheryl succinate was detected in blood draining the liver. We conclude that hepatic processing endows compounds like alpha-tocopheryl succinate with a secondary, anti-oxidant/anti-inflammatory activity due to converting it to the redox-active alpha-tocopherol. Our finding epitomises a novel, general paradigm, according to which a drug can be converted in the liver into a product that has a different beneficial bioactivity.

Vitamin E analogs trigger apoptosis in HER2/erbB2-overexpressing breast cancer cells by signaling via the mitochondrial pathway

Alpha-tocopheryl succinate (alpha-TOS) is a redox-silent vitamin E (VE) analog with high pro-apoptotic and anti-neoplastic activity. Here we investigated whether alpha-TOS and several novel VE analogs kill breast cancer cells over-expressing the anti-apoptotic receptor protein HER2/erbB2. The agents induced apoptosis at comparable levels in both erbB2-low and -high cells. Generation of reactive oxygen species (ROS) preceded mitochondrial destabilization and execution of apoptosis, as evidenced by the anti-apoptotic effects of exogenous superoxide dismutase and mitochondrially targeted coenzyme Q. Dissipation of DeltaPsi(m) was followed by cytochrome c and Smac/Diablo re-localization and caspase-dependent cleavage of death substrate. A resistance to apoptosis for the corresponding rho(0) counterparts confirmed a critical dependency for mitochondria during the induction of apoptosis in breast cancer cells mediated by VE analogs and linked apoptosis to generation of radicals as judged by the delayed accumulation of ROS in the cybrid cell types. We conclude that alpha-TOS causes efficient apoptosis in breast cancer cells independent of their erbB2 status. Since erbB2 is frequently over-expressed in breast cancers and renders the neoplastic disease resistant to established treatment, our findings are of clinical interest.

Vitamin E amides, a new class of vitamin E analogues with enhanced proapoptotic activity

Vitamin E (VE) analogues, epitomized by alpha-tocopheryl succinate (alpha-TOS), are proapoptotic agents with selective antineoplastic activity. The molecule of alpha-TOS comprises several structurally and functionally distinct moieties that can be modified in order to yield analogues with higher activity. In order to find analogues with higher apoptogenic efficacy, we prepared novel compounds where the ester bond was replaced by an amide bond. All of these analogues were significantly more proapoptotic than their ester counterparts, with alpha-tocopheryl maleyl amide being the most effective. Importantly, methylation of the free carboxylic group completely obliterated apoptogenic activity of the compounds. Similarly as shown for the ester analogues, the amides induced apoptosis by mitochondrial destabilization. Superiority of amides over the ester analogues may be due to their higher partitioning into the lipid phase, as suggested by the log p-values that were lower for the amides than the corresponding esters. In conclusion, we present evidence that modification of the ester bond of agents such as alpha-TOS can be used as a basis for generating novel analogues with higher efficacy of killing malignant cells, an activity that suggests anticancer effect of the agents.

Potentiation by alpha-tocopheryl succinate of the etoposide response in multidrug resistance protein 1-expressing glioblastoma cells

Multidrug resistance protein 1 (MRP1) is one of the representative members of the ATP-binding cassette superfamily of transporters that is involved in resistance to chemotherapeutic agents in cancer patients. MRP1 functions as an efflux pump of drugs, primarily those conjugated to glutathione (GSH). Decreases in the intracellular concentration of GSH have been shown to enhance the response of MRP1-overexpressing cells to MRP1-substrate drugs by limiting the available drug-GSH conjugates. We report here that alpha-tocopheryl succinate (TOS), a vitamin E analogue, decreased intracellular GSH concentration and blocked MRP1 function in glioblastoma cells. Functional blockade by TOS of MRP1 was confirmed by the enhanced accumulation of etoposide (VP-16), an MRP1-substrate drug. As a result, co-treatment of TOS with VP-16 or treatment with liposomes containing both TOS and VP-16 greatly enhanced the response of MRP1-expressing glioblastoma cells to VP-16. TOS may be a promising adjuvant for enhancing the therapeutic efficacy of VP-16 in patients with MRP1-expressing glioblastomas.

Pro-apoptotic mechanisms of action of a novel vitamin E analog (alpha-TEA) and a naturally occurring form of vitamin E (delta-tocotrienol) in MDA-MB-435 human breast cancer cells

Vitamin E derivative, RRR-alpha-tocopheryl succinate (vitamin E succinate, VES), is a potent pro-apoptotic agent, inducing apoptosis by restoring both transforming growth factor-beta (TGF-beta) and Fas (CD95) apoptotic signaling pathways that contribute to the activation of c-Jun N-terminal kinase (JNK)-mediated apoptosis. Objectives of these studies were to characterize signaling events involved in the pro-apoptotic actions of a naturally occurring form of vitamin E, delta-tocotrienol, and a novel vitamin E analog, alpha-tocopherol ether acetic acid analog [alpha-TEA; 2,5,7,8-tetramethyl-2R-(4R,8R,12-trimethyltridecyl)chroman-6-yloxyacetic acid]. Like VES, alpha-TEA and delta-tocotrienol induced estrogen-nonresponsive MDA-MB-435 and estrogen-responsive MCF-7 human breast cancer cells to undergo high levels of apoptosis in a concentration- and time-dependent fashion. Like VES, the two compounds induced either no or lower levels of apoptosis in normal human mammary epithelial cells and immortalized but nontumorigenic human MCF-10A cells. The pro-apoptotic mechanisms triggered by the structurally distinct alpha-TEA and delta-tocotrienol were identical to those previously reported for VES, that is, alpha-TEA- and delta-tocotrienol-induced apoptosis involved up-regulation of TGF-beta receptor II expression and TGF-beta-, Fas- and JNK-signaling pathways. These data provide a better understanding of the anticancer actions of a dietary form of vitamin E (delta-tocotrienol) and a novel nonhydrolyzable vitamin E analog (alpha-TEA).

Comparison of vitamin E derivatives alpha-TEA and VES in reduction of mouse mammary tumor burden and metastasis

A novel nonhydrolyzable ether derivative of RRR-alpha-tocopherol, RRR-alpha-tocopherol ether acetic acid analog [2,5,7,8-tetramethyl-2R-(4R,8R,12-trimethyltridecyl)chroman-6-yloxyacetic acid (alpha-TEA)], and a hydrolyzable ester derivative RRR-alpha-tocopheryl succinate (vitamin E succinate; VES) inhibited BALB/c mouse 66cl-4-GFP mammary tumor cell growth in vitro and in vivo. Treatment of 66cl-4-GFP cells in culture with alpha-TEA or VES induced dose-dependent DNA synthesis arrest and apoptosis and inhibited colony formation. Liposomal formulations of alpha-TEA delivered orally or by aerosol significantly reduced subcutaneous 66cl-4-GFP tumor burden and metastasis to lung and lymph nodes. Liposomal formulations of VES delivered by aerosol significantly reduced tumor burden and lung metastasis, but not lymph node metastasis. Unlike alpha-TEA, VES was ineffective in reducing tumor burden and metastasis to lungs and lymph nodes when administered orally. Analyses of tumor sections showed that alpha-TEA delivered by either method significantly reduced tumor cell proliferation as measured by Ki67, and increased apoptosis as measured by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL), whereas VES delivered by aerosol reduced tumor cell proliferation and increased apoptosis, but not significantly. In summary, the nonhydrolyzable ether vitamin E derivative alpha-TEA was effective in reducing tumor burden and metastasis when delivered either by aerosol or orally, whereas the hydrolyzable ester vitamin E derivative VES was effective only when delivered by aerosol.

Differential response of human ovarian cancer cells to induction of apoptosis by vitamin E Succinate and vitamin E analogue, alpha-TEA

A vitamin E derivative, vitamin E succinate (VES; RRR-alpha-tocopheryl succinate), and a vitamin E analogue, 2,5,7,8-tetramethyl-2R-(4R,8R,12-trimethyltridecyl)chroman-6-yloxy acetic acid (alpha-TEA), induce human breast, prostate, colon, lung, cervical, and endometrial tumor cells in culture to undergo apoptosis but not normal human mammary epithelial cells, immortalized, nontumorigenic breast cells, or normal human prostate epithelial cells. Human ovarian and cervical cancer cell lines are exceptions, with alpha-TEA exhibiting greater proapoptotic effects. Although both VES and alpha-TEA can induce A2780 and subline A2780/cp70 ovarian cancer cells to undergo DNA synthesis arrest within 24 h of treatment, only alpha-TEA is an effective inducer of apoptosis. VES or alpha-TEA treatment of cp70 cells with 5, 10, or 20 microg/ml for 3 days induced 5, 6, and 19% versus 9, 36, and 71% apoptosis, respectively. Colony formation data provide additional evidence that cp70 cells are more sensitive to growth inhibition by alpha-TEA than VES. Differences in stability of the ester-linked succinate moiety of VES versus the ether-linked acetic acid moiety of alpha-TEA were demonstrated by high-performance liquid chromatography analyses that showed alpha-TEA to remain intact, whereas VES was hydrolyzed to the free phenol, RRR-alpha-tocopherol. Pretreatment of cp70 cells with bis-(p-nitrophenyl) phosphate, an esterase inhibitor, before VES treatment, resulted in increased levels of intact VES and apoptosis. Taken together, these data show alpha-TEA to be a potent and stable proapoptotic agent for human ovarian tumor cells and suggest that endogenous ovarian esterases can hydrolyze the succinate moiety of VES, yielding RRR-alpha-tocopherol, an ineffective apoptotic-inducing agent.

alpha-Tocopheryl succinate sensitizes established tumors to vaccination with nonmatured dendritic cells

PURPOSE

Dendritic cells (DCs) are considered potential candidates for cancer immunotherapy due to their ability to process and present antigens to T cells and stimulate immune responses. However, DC-based vaccines have exhibited minimal effectiveness against established tumors in mice and human cancer patients. The use of appropriate adjuvants can enhance the efficacy of DC-based cancer vaccines in treating established tumors.

METHODS

In this study we have employed alpha-tocopheryl succinate (alpha-TOS), a nontoxic esterified analogue of vitamin E, as an adjuvant to enhance the effectiveness of DC vaccines in treating established murine Lewis lung (3LL) carcinomas.

RESULTS

We demonstrate that locally or systemically administered alpha-TOS in combination with nonmatured DCs injected intratumorally (i.t.) or subcutaneously (s.c.) significantly inhibits the growth of preestablished 10-day tumors (mean tumor volume of 77.5 +/- 17.8 mm3 on day 30 post-tumor injection) as compared to alpha-TOS alone (mean tumor volume of 471 +/- 68 mm3 on day 30 post-tumor injection). Additionally, the adjuvant effect of alpha-TOS was superior to that of cyclophosphamide (CTX). The mean tumor volume on day 28 post-tumor injection in mice treated with CTX+DCs was 611 +/- 94 mm3 as compared to 105 +/- 36 mm3 in mice treated with alpha-TOS+DCs. Analysis of purified T lymphocytes from mice treated with alpha-TOS+DC revealed significantly increased secretion of IFN-gamma as compared to T cells from the various control groups.

CONCLUSION

This study demonstrates the potential usefulness of alpha-tocopheryl succinate, an agent nontoxic to normal cell types, as an adjuvant to augment the effectiveness of DC-based vaccines in treating established tumors.

Structural characteristic of terminal dicarboxylic moiety required for apoptogenic activity of alpha-tocopheryl esters

alpha-Tocopheryl succinate (TS) is known to induce apoptosis in various cells and has attracted attention as a chemotherapeutic agent. Recently, we reported the structural significance of the terminal dicarboxylic moiety for the action of TS [J. Nutr. Sci. Vitaminol. 49 (2003) 310-314]. In this study, to determine details of the relationship between the structure and the function of the terminal ester moiety of alpha-tocopherol (alpha-T), we synthesized four novel esters, alpha-tocopheryl oxalate (TO), alpha-tocopheryl malonate (TM), alpha-tocopheryl pimelate (TP) and alpha-tocopheryl succinate ethyl ester (TSE), and compared their apoptogenic activities with those of TS, alpha-T, gamma-tocopherol (gamma-T) and two commercially available alpha-T derivatives, alpha-tocopheryl nicotinate (TN) and alpha-tocopheryl acetate (TA), in vascular smooth muscle cells and a mouse breast cancer cell line C127I. TO and TM in addition to TS, but not the others, induced apoptosis in both cells. Particularly, TO was the most potent of all alpha-T derivatives used. The addition of exogenous superoxide dismutase (SOD) significantly prevented the apoptosis induced by TM as well as that by TS as reported previously, but did not affect TO-induced apoptosis. These results suggest that O(2)(-) generated exogenously participates in TM-induced apoptosis but not in TO-induced apoptosis. The difference in their apoptotic effects is attributed to structural properties of the terminal dicarboxylic moiety, which has an inflexible plane conformation in TO, while it is highly flexible in TM and TS.

Alpha-tocopheryl succinate and TRAIL selectively synergise in induction of apoptosis in human malignant mesothelioma cells

Malignant mesothelioma (MM) is a fatal type of neoplasia with poor therapeutic prognosis, largely due to resistance to apoptosis. We investigated the apoptotic effect of α-tocopheryl succinate (α-TOS), a strong proapoptotic agent, in combination with the immunological apoptogen TNF-related apoptosis-inducing ligand (TRAIL) on both MM and nonmalignant mesothelial cells, since MM cells show low susceptibility to the clinically intriguing TRAIL. All MM cell lines tested were sensitive to α-TOS-induced apoptosis, and exerted high sensitivity to TRAIL in the presence of subapoptotic doses of the vitamin E analogue. Neither TRAIL or α-TOS alone or in combination caused apoptosis in nonmalignant mesothelial cells. Isobologram analysis of the cytotoxicity assays revealed a synergistic interaction between the two agents in MM cells and their antagonistic effect in nonmalignant mesothelial cells. TRAIL-induced apoptosis and its augmentation by α-TOS were inhibited by the caspase-8 inhibitor Z-IETD-FMK and the pan-caspase inhibitor Z-VAD-FMK. Activation of caspase-8 was required to induce apoptosis, which was amplified by α-TOS via cytochrome c release following Bid cleavage, with ensuing activation of caspase-9. Enhancement of TRAIL-induced apoptosis in MM cells by α-TOS was also associated with upregulation of the TRAIL cognate death receptors DR4 and DR5. Our results show that α-TOS and TRAIL act in synergism to kill MM cells via mitochondrial pathway, and are nontoxic to nonmalignant mesothelial cells. These findings are indicative of a novel strategy for treatment of thus far fatal MM.

A vitamin E analogue suppresses malignant mesothelioma in a preclinical model: a future drug against a fatal neoplastic disease?

Malignant mesothelioma is a fatal type of neoplasia of the pleura and the peritoneum with currently no known cure. Therefore, discovery of an efficient antimesothelioma drug with low deleterious side effects is desirable. Here, we studied in vivo the effect of alpha-tocopheryl succinate, a semisynthetic vitamin E analogue with proapoptotic and anticancer activity and selectivity for malignant cells, on experimental peritoneal mesothelioma using immunocompromised mice. Compared to untreated animals, the agent increased their survival >3-fold. Our finding warrants further testing of vitamin E analogues as potential antimesothelioma drugs.

c-Jun N-terminal kinase is required for vitamin E succinate-induced apoptosis in human gastric cancer cells

AIM: To investigate the roles of c-Jun N-terminal kinase (JNK) signaling pathway in vitamin E succinate-induced apoptosis in human gastric cancer SGC-7901 cells.

METHODS: Human gastric cancer cell lines (SGC-7901) were treated with vitamin E succinate (VES) at 5, 10, 20 mg/L. Succinic acid and vitamin E were used as vehicle controls and condition medium only as an untreated (UT) control. Apoptosis was observed by 4’, 6-diamidine-2’-phenylindole dihydrochloride (DAPI) staining for morphological changes and by DNA fragmentation for biochemical alterations. Western blot analysis was applied to measure the expression of JNK and phosphorylated JNK. After the cells were transiently transfected with dominant negative mutant of JNK (DN-JNK) followed by treatment of VES, the expression of JNK and c-Jun protein was determined.

RESULTS: The apoptotic changes were observed after VES treatment by DNA fragmentation. DNA ladder in the 20 mg/L VES group was more clearly seen than that in 10 mg/L VES group and was not detected following treatment of UT control, succinate and vitamin E. VES at 5, 10 and 20 mg/L increased the expression of p-JNK by 2.5-, 2.8- and 4.2-fold, respectively. VES induced the phosphorylation of JNK beginning at 1.5 h and produced a sustained increase for 24 h with the peak level at 12 h. Transient transfection of DN-JNK blocked VES-triggered apoptosis by 52%. DN-JNK significantly increased the level of JNK, while decreasing the expression of VES-induced c-Jun protein.

CONCLUSION: VES-induced apoptosis in human gastric cancer SGC-7901 cells involves JNK signaling pathway via c-Jun and its downstream transcription factor.

Effects of vitamin E succinate on the expression of Fas and PCNA proteins in human gastric carcinoma cells and its clinical significance

AIM

To investigate the effects of vitamin E succinate (VES) on the expression of Fas and PCNA proteins as well as its clinical significance in human gastric carcinoma, and to explore the mechanism of VES-induced inhibition of gastric carcinoma cell growth.

METHODS

Immunohistochemical methods were used to detect Fas and PCNA expression both in human gastric cancer SGC-7901 cells treated with VES at different doses and in human gastric carcinoma tissues.

RESULTS

After the SGC-7901 cells were treated with VES at 5, 10, 20 mg/L for 48 h, the positive rates of Fas expression were 16%, 27% and 48%, respectively, significantly increased compared to that of control group (P< 0.05); while the positive rates of PCNA expression in groups treated with different doses of VES were 20%, 18% and 7%, respectively, which were significantly decreased compared to that of the control group (P<0.05). In human gastric carcinoma tissues, the Fas positive expression rate was 42.4%(25/59), which declined with the decrease in the degree of tumor differentiation (P<0.05) and with the existence of lymph node metastasis (P<0.001). While the PCNA positive expression rate was 91.5%(54/59), no relationship was observed between PCNA expression and clinicopathologic parameters.

CONCLUSION

VES inhibited the growth of gastric cancer cells by inducing Fas expression and inhibiting PCNA expression. It is, therefore, considered that the expression of Fas and PCNA genes, through tumor cell apoptosis and proliferation, respectively, may be useful as a clinical predictive index in the application of VES to gastric carcinoma therapy, where as Fas may be of more value than PCNA.

Role of reactive oxygen species in the induction of apoptosis by ?-tocopheryl succinate

Alpha-tocopheryl succinate (TOS), a vitamin E analog, is a promising anticancer agent due to its abilities to inhibit proliferation and to induce apoptosis in a variety of human malignant cell lines, while being relatively less active toward normal cells. However, the molecular mechanisms underlying the apoptotic effects of TOS are not precisely understood. Reports that TOS can generate reactive oxygen species (ROS) prompted us to investigate the role of ROS in TOS-induced apoptosis in cancer cells. We found that the human lung cancer A549 and H460 cell lines were much more sensitive to TOS-induced apoptosis than the human glioblastoma T98G and U87MG cell lines. Our data suggested that the differential TOS sensitivity was not caused by differences in the uptake and retention of TOS between TOS-sensitive and -resistant cancer cells. The differential ability of cancer cells to generate ROS in response to TOS appears to be an important factor in determining the susceptibility of cells to TOS-induced apoptosis. Our results further suggest that TOS-induced generation of ROS is involved in caspase-independent apoptosis. Taken together, our findings suggest an important role of ROS generation in TOS-induced, caspase-independent apoptosis of cancer cells.

Vitamin E succinate and cancer treatment: a vitamin E prototype for selective antitumour activity

Great hope has been given to micronutrients as anticancer agents, since they present natural compounds with beneficial effects for normal cells and tissues. One of these is vitamin E (VE), an antioxidant and an essential component of biological membranes and circulating lipoproteins. In spite of a number of epidemiological and intervention studies, little or no correlation between VE intake and incidence of cancer has been found. Recent reports have identified a redox-silent analogue of VE, alpha-tocopheryl succinate (alpha-TOS), as a potent anticancer agent with a unique structure and pharmacokinetics in vivo. alpha-TOS is highly selective for malignant cells, inducing them into apoptotic death largely via the mitochondrial route. The molecule of alpha-TOS may be modified so that analogues with higher activity are generated. Finally, alpha-TOS and similar agents are metabolised to VE, thereby yielding a compound with a secondary beneficial activity. Thus, alpha-TOS epitomises a group of novel compounds that hold substantial promise as future anticancer drugs. The reasons for this optimistic notion are discussed in the following paragraphs.

α-Tocopheryloxybutyric acid enhances necrotic cell death in breast cancer cells treated with chemotherapy agent

The overexpression of HER-2 receptor contributes to malignant transformation of breast cancer cells. We have reported that alpha-tocopheryloxybutyric acid (TE), non-antioxidative vitamin E ether derivative inhibits the activation of HER-2 receptor. The present study was undertaken to estimate if TE could act as a useful anti-cancer agent against a breast cancer cell overexpressing HER-2 receptor (MDA-MB-453 cell line) in combination with a conventional chemotherapy agent, adriamycin (ADR). TE enhanced cytotoxic effect of ADR against the human breast cancer cell at low doses less than IC(50). The enhancing effect was mainly dependent on the elevation of necrotic-like cell death but not apoptotic cell death. In conjugation with this event, the inactivation of HER-2 receptor in the breast cancer cell was caused by the combination of TE with ADR. These results suggest that TE enhances necrotic-like cell death in the breast cancer cells and that the cell death relates to the inactivation of HER-2 receptor in the breast cancer cells.

Vitamin E analogues as inducers of apoptosis: structure-function relation

Recent results show that alpha-tocopheryl succinate (alpha-TOS) is a proapoptotic agent with antineoplastic activity. As modifications of the vitamin E (VE) molecule may affect its apoptogenic activity, we tested a number of newly synthesised VE analogues using malignant cell lines. Analogues of alpha-TOS with lower number of methyl substitutions on the aromatic ring were less active than alpha-TOS. Replacement of the succinyl group with a maleyl group greatly enhanced the activity, while it was lower for the glutaryl esters. Methylation of the free succinyl carboxyl group on alpha-TOS and delta-TOS completely prevented the apoptogenic activity of the parent compounds. Both Trolox and its succinylated derivative were inactive. alpha-tocotrienol (alpha-T3 H) failed to induce apoptosis, while gamma-T3 H was apoptogenic, and more so when succinylated. Shortening the aliphatic side chain of gamma-T3 by one isoprenyl unit increased its activity. Neither phytyl nor oleyl succinate caused apoptosis. These findings show that modifications of different functional moieties of the VE molecule can enhance apoptogenic activity. It is hoped that these observations will lead to the synthesis of analogues with even higher apoptogenic and, consequently, antineoplastic efficacy.

RRR-alpha-tocopheryl succinate induction of DNA synthesis arrest of human MDA-MB-435 cells involves TGF-beta-independent activation of p21Waf1/Cip1

RRR-alpha-tocopheryl succinate (vitamin E succinate, VES), a derivative of vitamin E, is a potent antitumor agent. Cellular events involved in VES-induced DNA synthesis arrest of human MDA-MB-435 breast cancer cells were studied. VES induces a dose- and time-dependent inhibition of DNA synthesis and a G0/G1 cell cycle arrest. VES induces expression of p21Waf1/Cip1 mRNA and protein, and antisense oligomers to p21 block VES-induced growth arrest. Evidence suggesting that VES modulates p21 expression in a transforming growth factor-beta (TGF-beta)-independent fashion includes failure of TGF-beta-neutralizing antibodies to block VES-induced DNA synthesis arrest or VES activation of a p21 promoter-regulated reporter gene; VES is not capable of inducing the translocation of green fluorescent protein-Smad2 into the nucleus and is not capable of stimulating a TGF-beta-dependent reporter gene, and VES induces growth inhibition and upregulates p21 mRNA levels in TGF-beta receptor-defective cells.

Mitochondria play a central role in apoptosis induced by alpha-tocopheryl succinate, an agent with antineoplastic activity: comparison with receptor-mediated pro-apoptotic signaling

alpha-Tocopheryl succinate (alpha-TOS) is a semisynthetic vitamin E analogue with high pro-apoptotic and anti-neoplastic activity [Weber, T et al. (2002) Clin. Cancer Res. 8, 863-869]. Previous studies suggested that it acts through destabilization of subcellular organelles, including mitochondria, but compelling evidence is missing. Cells treated with alpha-TOS showed altered mitochondrial structure, generation of free radicals, activation of the sphingomyelin cycle, relocalization of cytochrome c and Smac/Diablo, and activation of multiple caspases. A pan-caspase inhibitor suppressed caspase-3 and -6 activation and phosphatidyl serine externalization, but not decrease of mitochondrial membrane potential or generation of radicals. For alpha-TOS, but not Fas or TRAIL, apoptosis was suppressed by caspase-9 inhibition, while TRAIL- and Fas-resistant cells overexpressing cFLIP or CrmA were susceptible to alpha-TOS. The central role of mitochondria was confirmed by resistance of mtDNA-deficient cells to alpha-TOS, by regulation of alpha-TOS apoptosis by Bcl-2 family members, and by anti-apoptotic activity of mitochondrially targeted radical scavengers. Co-treatment with alpha-TOS and anti-Fas IgM showed their cooperative effect, probably by signaling via different, convergent pathways. These data provide an insight into the molecular mechanism, by which alpha-TOS kills malignant cells, and advocate its testing as a potential anticancer agent or adjuvant.

Alpha-tocopheryl succinate, the most effective form of vitamin E for adjuvant cancer treatment: a review

In 1982, it was established that alpha-tocopheryl succinate (alpha-TS) was the most effective form of vitamin E in comparison to alpha-tocopherol, alpha-tocopheryl acetate and alpha-tocopheryl nicotinate in inducing differentiation, inhibition of proliferation and apoptosis in cancer cells, depending upon its concentration. During the last two decades, several studies have confirmed this observation in rodent and human cancer cells in culture and in vivo (animal model). The most exciting aspect of this alpha-TS effect is that it does not affect the proliferation of most normal cells. In spite of several studies published on the anti-cancer properties of alpha-TS, the value of this form of vitamin E has not drawn significant attention from researchers and clinicians. Therefore, a critical review on the potential role of alpha-TS in the management of cancer is needed. In addition, such a review can also provide in-depth analysis of existing literature on this subject. alpha-TS treatment causes extensive alterations in gene expression; however, only some can be attributed to differentiation, inhibition of proliferation and apoptosis. alpha-TS also enhances the growth-inhibitory effect of ionizing radiation, hyperthermia, some chemotherapeutic agents and biological response modifiers on tumor cells, while protecting normal cells against some of their adverse effects. Thus, alpha-TS alone or in combination with dietary micronutrients can be useful as an adjunct to standard cancer therapy by increasing tumor response and possibly decreasing some of the toxicities to normal cells.

Potentiation of anti-cancer effect by intravenous administration of vesiculated alpha-tocopheryl hemisuccinate on mouse melanoma in vivo

We examined the effect of alpha-tocopheryl hemisuccinate (TS) on the growth of mouse melanoma cells B16-F1 inoculated on the back of hairless mice by two administration procedures of TS, i.p. administration of TS dissolved with dimethyl sulfoxide (TS i.p.) and i.v. administration of TS vesicles (TS-vesicle i.v.). TS i.p. significantly prevented the tumor growth of only half the mice in the group. However, TS-vesicle i.v. almost completely inhibited the tumor growth of all mice. Furthermore, the mean survival of the TS-vesicle i.v. group was 1.4-fold those of the control and TS i.p. groups.

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.

Alpha-tocopheryl succinate sensitises a T lymphoma cell line to TRAIL-induced apoptosis by suppressing NF-kappaB activation

Activation of nuclear factor-kappaB (NF-kappaB) can interfere with induction of apoptosis triggered by the tumour necrosis factor-related apoptosis-inducing ligand (TRAIL; Apo2L). Therefore, agents that suppress NF-kappaB activation may sensitise cells to TRAIL-dependent apoptosis. Exposure of Jurkat cells to TRAIL resulted in massive and saturable apoptosis induction, following an initial lag time. This lag was abolished by pretreatment of the cells with subapoptotic doses of alpha-tocopheryl succinate (alpha-TOS) or the proteasome inhibitor MG132. Exposure of the cells to TRAIL led to a rapid, transient activation of NF-kappaB, a process that was suppressed by cell pretreatment with alpha-TOS or MG132. Activation of NF-kappaB by TNF-alpha prior to TRAIL exposure increased resistance of the cells to TRAIL-mediated apoptosis. We conclude that alpha-TOS sensitises cells to TRAIL killing, at least in some cases, through inhibition of NF-kappaB activation. This further supports the possibility that this semisynthetic analogue of vitamin E is a potential adjuvant in cancer treatment, such as in the case of TRAIL-mediated inhibition of cancer.

Vitamin E succinate inhibits human prostate cancer cell growth via modulating cell cycle regulatory machinery

Several epidemiological studies have demonstrated that vitamin E is a chemopreventative agent for prostate cancer. alpha-Tocopheryl succinate (VES), a derivative of vitamin E, effectively modulates prostate cancer cell growth. However, little is known about the mechanisms regarding this action. Here we show that VES causes human prostate cancer cell LNCaP arrest at G1 phase. This effect is accomplished through VES significantly decreasing expression of the cell cycle regulatory proteins cyclin D1, D3, and E, cdk2 and 4, but not cdk6. Furthermore, VES reduces cdk4 kinase activity, Rb phosphorylation, and cyclin E mRNA expression. Recently there is increasing interest in the protective effect of the VES and selenium combination on prostate cancer. Here we show that VES and selenium work through different mechanisms to exert their inhibitory effects on prostate cancer cells. Taken together, our studies suggest that VES-mediated prostate cancer cell G1/S arrest is a consequence of the regulation of multiple molecules of the cell cycle regulatory machinery.

High cytotoxicity of alpha-tocopheryl hemisuccinate to cancer cells is due to failure of their antioxidative defense systems

Alpha-tocopheryl hemisuccinate (TS) has been reported to induce apoptosis in various cells, and to show higher toxicity to cancer cells than to normal cells. In this study, although TS induced apoptosis in both a mouse breast normal cell line NMuMG and a mouse breast cancer cell line C127I, the latter were more susceptible to TS. TS-induced apoptosis in C127I was inhibited by superoxide dismutase, alpha-tocopherol and butylated hydroxyanisol. From these results, superoxide (O(2)(-)) itself and reactive oxygen species derived from O(2)(-) and/or free radicals are assumed to be associated with TS toxicity, and the high toxicity of TS to cancer cells is suggested to be due to failure of their antioxidative defense systems.

Roles of Fas signaling pathway in vitamin E succinate-induced apoptosis in human gastric cancer SGC-7901 cells

AIM

To investigate the roles of Fas signaling pathway in vitamin E succinate-induced apoptosis in human gastric cancer SGC-7901 cells.

METHODS

Human gastric cancer SGC-7901 cells were treated with VES at 5, 10, 20 mg x L(-1), succinic acid and vitamin E as vehicle control and condition media only as untreated (UT) control. Apoptotic morphology was observed by DAPI staining. Western blot analysis was applied to measure the expression of Fas, FADD and caspase-8 proteins. After the cells were transiently transfected with Fas and FADD antisense oligonucleotides, respectively, caspase-8 activity was determined by flurometric method.

RESULTS

The morphologically apoptotic changes were observed after VES treatment by DAPI staining. 23.7 % and 89.6 % apoptosis occurred after 24 h and 48 h of 20 mg x L(-1) VES treatment, respectively. The protein levels of Fas, FADD and caspase-8 were evidently increased in a dose-dependent manner after 24 h of VES treatment. The blockage of Fas by transfection with Fas antisense oligonucleotides obviously inhibited the expression of FADD protein. After SGC-7901 cells were transfected with Fas and FADD antisense oligonucleotides, caspase-8 activity was obviously decreased (P<0.01), whereas Fas blocked more than FADD.

CONCLUSION

VES-induced apoptosis in human gastric cancer SGC-7901 cells involves Fas signaling pathway including the interaction of Fas, FADD and caspase-8.

The effects of vitamin E succinate on the expression of c-jun gene and protein in human gastric cancer SGC-7901 cells

AIM

To investigate the effects of vitamin E succinate (VES) on the expression of c-jun gene and protein in human gastric cancer SGC-7901 cells.

METHODS

After SGC-7901 cells were treated with VES at different doses (5,10,20 mg x L(-1)) at different time, reverse transcription-PCR technique was used to detect the level of c-jun mRNA; Western Blot was applied to measure the expression of c-jun protein.

RESULTS

After the cells were treated with VES at 20 mg x L(-1) for 3 h, the expression rapidly reached its maximum that was 3.5 times of UT control (P<0.01). The level of c-jun mRNA was also increased following treatment of VES for 6 h. However,the expression after treatment of VES at 5 mg x L(-1) for 24 h was 1.6 times compared with UT control (P<0.01). Western blot analysis showed that the level of c-jun protein was obviously elevated in VES-treated SGC-7901 cells at 20 mg x L(-1) for 3 h. The expression of c-jun protein was gradually increased after treatment of VES at 20 mg x L(-1) for 3, 6, 12 and 24 h, respectively, with an evident time-effect relationship.

CONCLUSION

The levels of c-jun mRNA and protein in VES-treated SGC-7901 cells were increased in a dose- and time-dependent manner; the expression of c-jun was prolonged by VES, indicating that c-jun is involved in VES-induced apoptosis in SGC-7901 cells.

Alpha-tocopheryl succinate epitomizes a compound with a shift in biological activity due to pro-vitamin-to-vitamin conversion

With the advent of the third millennium, a number of pathologies have been eradicated or taken under control. However, the incidences, of cancer and atherosclerosis, the two most common causes of death in developed countries, have increased or, in some instances, only stagnated. Therefore there has been an intensive search for agents effective against such life-threatening conditions. Accordingly, the potential anti-atherogenic activity of vitamin E analogs has been studied extensively. Interestingly, recent reports strongly suggest that certain vitamin E analogs, represented in particular by alpha-tocopheryl succinate (alpha-TOS), also possess anti-neoplastic activity. In this communication, we review our current understanding of the molecular basis for these double effects of alpha-TOS and propose a testable hypothesis, according to which this semi-synthetic analog exerts both anti-atherogenic and anti-neoplastic activities. We propose that the prevalence of each activity depends on the actual form of the vitamin E analog. That is, the conversion of the pro-vitamin E form, alpha-TOS, to the corresponding vitamin form, alpha-tocopherol, makes this anti-neoplastic agent active against inflammatory diseases like atherosclerosis.

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.

Alpha-tocopheryl succinate, an agent with in vivo anti-tumour activity, induces apoptosis by causing lysosomal instability

Certain vitamin E analogues, such as alpha-tocopheryl succinate (alpha-TOS), exhibit in vivo anti-tumour activity and, in vitro, induce apoptosis of cultured tumour cells. In the present study we report that these effects may be explained, at least in part, by destabilization of lysosomal membranes. alpha-TOS, but not alpha-tocopheryl acetate or alpha-tocopherol (alpha-TOH), induced early lysosomal destabilization followed by apoptosis. Similar effects were observed with beta-TOS, whereas beta-TOH was inactive. Cathepsin D-deficient cells were more resistant to alpha-TOS than their normal counterparts, and featured delayed caspase activation. Possible detergent and lysosomotropic effects of alpha- and beta-TOS were suggested by their haemolytic activity in an in vitro test and their release of beta-galactosidase from isolated lysosomes, whereas the non-succinylated analogues were inactive. The pro-apoptotic activity of alpha-TOS was pH-dependent, being greater at lower pH, typical of the interstitium of solid tumours. These findings indicate that lysosomal destabilization may partially or fully explain the induction of apoptosis in cultured cells by alpha-TOS and the mechanism whereby this agent exerts in vivo anti-tumour effects.

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.

RRR-alpha-tocopheryl succinate inhibits human gastric cancer SGC-7901 cell growth by inducing apoptosis and DNA synthesis arrest

AIM

To investigate the effects of growth inhibition of human gastric cancer SGC-7901 cell with RRR-alpha-tocopheryl succinate (VES), a derivative of natural Vitamin E, via inducing apoptosis and DNA synthesis arrest.

METHODS

Human gastric cancer SGC-7901 cells were regularly incubated in the presence of VES at 5, 10 and 20mg x L(-1) (VES was dissolved in absolute ethanol and diluted in RPMI 1640 complete condition media correspondingly to a final concentration of VES and 1 mL x L(-1) ethanol), succinic acid and ethanol equivalents as vehicle (VEH) control and condition media only as untreated (UT) control. Trypan blue dye exclusion analysis and MTT assay were applied to detect the cell proliferation. Cells were pulsed with 37kBq of tritiated thymidine and (3H) TdR uptake was measured to observe DNA synthesis. Apoptotic morphology was observed by electron microscopy and DAPI staining. Flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay were performed to detect VES-triggered apoptosis.

RESULTS

VES inhibited SGC-7901 cell growth in a dose-dependent manner. The growth curve showed suppression by 24.7%, 49.2% and 68.7% following 24h of VES treatment at 5, 10 and 20 mg x L(-1), respectively, similar to the findings from MTT assay. DNA synthesis was evidently reduced by 35%, 45% and 98% after 24h VES treatment at 20mg x L(-1) and 48 h at 10 and 20mg x L(-1), respectively. VES induced SGC-7901 cells to undergo apoptosis with typically apoptotic characteristics, including morphological changes of chromatin condensation, chromatin crescent formation/margination, nucleus fragmentation and apoptotic body formation, typical apoptotic sub-G1 peak by flow cytometry and increase of apoptotic cells by TUNEL assay in which 90% of cells underwent apoptosis after 48 h of VES treatment at 20 mg x L(-1).

CONCLUSION

VES can inhibit human gastric cancer SGC-7901 cell growth by inducing apoptosis and DNA synthesis arrest. Inhibition of SGC-7901 cell growth by VES is dose- and time-dependent. Therefore VES can function as a potent chemotherapeutic agent against human gastric carcinogenesis.

The role of vitamin E in atherogenesis: linking the chemical, biological and clinical aspects of the disease

Atherosclerosis is a disease involving both oxidative modifications and disbalance of the immune system. Vitamin E, an endogenous redox-active component of circulating lipoproteins and (sub)cellular membranes whose levels can be manipulated by supplementation, has been shown to play a role in the initiation and progression of the disease. Recent data reveal that the activities of vitamin E go beyond its redox function. Moreover, it has been shown that vitamin E can exacerbate certain processes associated with atherogenesis. In this essay we review the role of biology of atherosclerosis, and suggest that these two facets decide the clinical manifestation and outcome of the disease.

Inhibition of inflammatory endothelial responses by a pathway involving caspase activation and p65 cleavage

Suppression of NF kappa B activation has been involved in the elimination of survival programs during endothelial cell (EC) apoptosis. We used alpha-tocopheryl succinate (alpha-TOS) to trigger apoptosome formation and the subsequent activation of executioner caspases. The level of bcl-2 was reduced by alpha-TOS, and its downregulation potentiated and its overexpression suppressed pro-apoptotic effects of alpha-TOS, indicating a mitochondrial role in alpha-TOS-induced apoptosis in EC. alpha-TOS treatment was associated with induction of TUNEL-positive apoptosis in EC with a high but not with a low proliferation index. The use of the pan-caspase inhibitor z-VAD.fmk suggested the involvement of caspases in cleavage of p65, and in inhibition of nuclear translocation of p65 and NF kappa B-dependent transactivation of a gene construct encoding the green fluorescence protein elicited by TNF alpha in contact-arrested EC. The suppression by alpha-TOS of inflammatory EC responses induced by TNF alpha such as VCAM-1 mRNA and surface protein expression and shear-resistant arrest of monocytic cells were also reversed by z-VAD.fmk. NF kappa B-dependent transactivation was preserved in alpha-TOS-treated EC stably transfected with a caspase-noncleavable p65 mutant but not with its truncated form, thus establishing a direct link between alpha-TOS-induced effects and p65 cleavage. Our data infer a pathway by which caspase activation in EC inhibits NF kappa B-dependent inflammatory activation and monocyte recruitment, and provide evidence for a relationship between pro-apoptotic and anti-inflammatory pathways.