Decreased expressions of c-myc and H-ras oncogenes in vitamin E succinate induced morphologically differentiated murine B-16 melanoma cells in culture

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 Analogs as Radiation Response Modifiers

The potentially life-threatening effects of total body ionizing radiation exposure have been known for more than a century. Despite considerable advances in our understanding of the effects of radiation over the past six decades, efforts to identify effective radiation countermeasures for use in case of a radiological/nuclear emergency have been largely unsuccessful. Vitamin E is known to have antioxidant properties capable of scavenging free radicals, which have critical roles in radiation injuries. Tocopherols and tocotrienols, vitamin E analogs together known as tocols, have shown promise as radioprotectors. Although the pivotal mechanisms of action of tocols have long been thought to be their antioxidant properties and free radical scavenging activities, other alternative mechanisms have been proposed to drive their activity as radioprotectors. Here we provide a brief overview of the effects of ionizing radiation, the mechanistic mediators of radiation-induced damage, and the need for radiation countermeasures. We further outline the role for, efficacy of, and mechanisms of action of tocols as radioprotectors, and we compare and contrast their efficacy and mode of action with that of another well-studied chemical radioprotector, amifostine.

Vitamins and Melanoma

A tremendous amount of information was published over the past decades in relation to the role of vitamins in various neoplastic diseases. In particular, several studies showed an inverse relationship between selected vitamins intake and cancer risk. In this review we will focus on the role played by vitamins in melanoma with particular regard to vitamin A, D, K, E and C. Given that vitamin supplementation is easy, convenient, and readily accepted by patients, in the future the use of vitamins in chemoprevention and therapy of melanoma could be encouraged if supported by pre-clinical and clinical evidence.

Nanoparticle-mediated delivery of a rapidly activatable prodrug of SN-38 for neuroblastoma therapy

Nanomedicine-based strategies have the potential to improve therapeutic performance of a wide range of anticancer agents. However, the successful implementation of nanoparticulate delivery systems requires the development of adequately sized nanocarriers delivering their therapeutic cargo to the target in a protected, pharmacologically active form. The present studies focused on a novel nanocarrier-based formulation strategy for SN-38, a topoisomerase I inhibitor with proven anticancer potential, whose clinical application is compromised by toxicity, poor stability and incompatibility with conventional delivery vehicles. SN-38 encapsulated in biodegradable sub-100 nm sized nanoparticles (NP) in the form of its rapidly activatable prodrug derivative with tocopherol succinate potently inhibited the growth of neuroblastoma cells in a dose- and exposure time-dependent manner, exhibiting a delayed response pattern distinct from that of free SN-38. In a xenograft model of neuroblastoma, prodrug-loaded NP caused rapid regression of established large tumors, significantly delayed tumor regrowth after treatment cessation and markedly extended animal survival. The NP formulation strategy enabled by a reversible chemical modification of the drug molecule offers a viable means for SN-38 delivery achieving sustained intratumoral drug levels and contributing to the potency and extended duration of antitumor activity, both prerequisites for effective treatment of neuroblastoma and other cancers.

Multifunctional dendrimers modified with alpha-tocopheryl succinate for targeted cancer therapy

Multifunctional generation 5-poly(amidoamine) dendrimers can be used as a platform to conjugate covalently alpha-tocopheryl succinate for targeted cancer therapy.

Tocopherol succinate: modulation of antioxidant enzymes and oncogene expression, and hematopoietic recovery

PURPOSE

A class of naturally occurring isoforms of tocopherol (tocols) was shown to have varying degrees of protection when administered before radiation exposure. We recently demonstrated that α-tocopherol succinate (TS) is a potential radiation prophylactic agent. Our objective in this study was to further investigate the mechanism of action of TS in mice exposed to (60)Co γ-radiation.

METHODS AND MATERIALS

We evaluated the effects of TS on expression of antioxidant enzymes and oncogenes by quantitative RT-PCR in bone marrow cells of (60)Co γ-irradiated mice. Further, we tested the ability of TS to rescue and repopulate hematopoietic stem cells by analyzing bone marrow cellularity and spleen colony forming unit in spleen of TS-injected and irradiated mice.

RESULTS

Our results demonstrate that TS modulated the expression of antioxidant enzymes and inhibited expression of oncogenes in irradiated mice at different time points. TS also increased colony forming unit-spleen numbers and bone marrow cellularity in irradiated mice.

CONCLUSIONS

Results provide additional support for the observed radioprotective efficacy of TS and insight into mechanisms.

Global analysis of gene expression changes during retinoic acid-induced growth arrest and differentiation of melanoma: comparison to differentially expressed genes in melanocytes vs melanoma

Background

The incidence of malignant melanoma has significantly increased over the last decade. Some of these malignancies are susceptible to the growth inhibitory and pro-differentiating effects of all-trans-retinoic acid (RA). The molecular changes responsible for the biological activity of RA in melanoma are not well understood.

Results

In an analysis of sequential global gene expression changes during a 4–48 h RA treatment of B16 mouse melanoma cells, we found that RA increased the expression of 757 genes and decreased the expression of 737 genes. We also compared the gene expression profile (no RA treatment) between non-malignant melan-a mouse melanocytes and B16 melanoma cells. Using the same statistical test, we found 1495 genes whose expression was significantly higher in melan-a than in B16 cells and 2054 genes whose expression was significantly lower in melan-a than in B16 cells. By intersecting these two gene sets, we discovered a common set of 233 genes whose RNA levels were significantly different between B16 and melan-a cells and whose expression was altered by RA treatment. Within this set, RA treatment altered the expression of 203 (87%) genes toward the melan-a expression level. In addition, hierarchical clustering showed that after 48 h of RA treatment expression of the 203 genes was more closely related to the melan-a gene set than any other RA treatment time point. Functional analysis of the 203 gene set indicated that RA decreased expression of mRNAs that encode proteins involved in cell division/cell cycle, DNA replication, recombination and repair, and transcription regulation. Conversely, it stimulated genes involved in cell-cell signaling, cell adhesion and cell differentiation/embryonic development. Pathway analysis of the 203 gene set revealed four major hubs of connectivity: CDC2, CHEK1, CDC45L and MCM6.

Conclusion

Our analysis of common genes in the 48 h RA-treatment of B16 melanoma cells and untreated B16 vs. melan-a data set show that RA "normalized" the expression of genes involved in energy metabolism, DNA replication, DNA repair and differentiation. These results are compatible with the known growth inhibitory and pro-differentiating effects of RA. Pathway analysis suggests that CDC2, CHEK1, CDC45L and MCM6 are key players in mediating the biological activity of RA in B16 melanoma cells.

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.

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.

Cysteine peptidase and its inhibitor activity levels and vitamin E concentration in normal human serum and colorectal carcinomas

AIM: Cysteine peptidase (CP) and its inhibitor (CPI) are a matrix protease that may be associated with colorectal carcinoma invasion and progression, and vitamin E is also a stimulator of the immunological system. Our purpose was to determine the correlation between the expression of cysteine peptidases and their endogenous inhibitors, and the level of vitamin E in sera of patients with colorectal cancer in comparison with healthy individuals.

METHODS: The levels of cysteine peptidases and their inhibitors were determined in the sera of patients with primary and metastatic colorectal carcinoma and healthy individuals using fluorogenic substrate, and the level of vitamin E was determined by HPLC.

RESULTS: The levels of cysteine peptidases and their inhibitors were significantly higher in the metastatic colorectal cancer patients than that in the healthy controls (P<0.05). The activity of CP increased 2.2-fold, CPI 2.8-fold and vitamin E decreased 3.4-fold in sera of patients with metastasis in comparison with controls. The level of vitamin E in healthy individuals was higher, whereas the activity of cysteine peptidases and their inhibitors associated with complexes was lower than that in patients with cancer of the digestive tract.

CONCLUSION: These results suggest that the serum levels of CP and their inhibitors could be an indicator of the prognosis for patients with metastatic colorectal cancer. Vitamin E can be administered prophylactically to prevent digestive tract neoplasmas.

Effect of vitamin E and human placenta cysteine peptidase inhibitor on expression of cathepsins B and L in implanted hepatoma Morris 5123 tumor model in Wistar rats

AIM: To examine the effectiveness of human placental inhibitors, by injecting vitamin E to rats with transplanted Morris-5123 hepatoma, on the expression of cathepsins B and L in tumor, liver, lung and blood sera after transplantation of Morris 5123 hepatoma.

METHODS: Animals were divided into 10 groups receiving three different concentrations of vitamin E and inhibitors along or in combination and compared with negative control (healthy rats) and positive control (tumor rats). Effectiveness of treatment was evaluated with regard to survival time, tumor response and determination of the activities of proteolytic enzymes and their inhibitors using flurogenic substrates.

RESULTS: Cathepsins B and L activities were elevated by 16-fold in comparison with negative control tissues, and their endogenous inhibitor activity decreased by 1.2-fold before treatment. In several cases, tumors completely disappeared following vitamin E plus human placental cyteine protease inhibitor (CPI) compared with controls. The number of complete tumor responses was higher when 20 m/kg vitamin E plus 400 μg of CPI was used, i.e., 7/10 rats survived more than two mo. Cathepsins B and L were expressed significantly in tumor, liver, lung tissues and sera in parallel to the increasing of the endogenous inhibitor activity compared with the controls after treatment (P<0.0001).

CONCLUSION: The data indicate formation of metastasis significantly reduced in treated rats, which might provide a therapeutic basis for anti-cancer therapy.

α-Tocopheryl succinate inhibits proliferation of mesothelioma cells by selective down-regulation of fibroblast growth factor receptors

alpha-Tocopheryl succinate (alpha-TOS), a redox-silent analogue of vitamin E, inhibits malignant mesotheliomas (MM) in a pre-clinical model. Here we investigated the underlying mechanism. Exposure of MM cells to alpha-TOS triggered apoptosis at higher and inhibited proliferation at lower concentrations, while this effect was not observed in non-malignant mesothelial cells. Sub-apoptotic doses of alpha-TOS caused down-regulation of fibroblast growth factor receptor-1 (FGFR1) selectively in MM cells, while the effect on FGFR2 was only marginal. FGF1 and FGF2 enhanced MM cell proliferation that was suppressed by alpha-TOS. Over-expression of E2F1, a transcriptional factor of FGFR1, but not its dominant-negative counterpart, partially blocked the inhibitory activity of alpha-TOS on MM cell proliferation. Our data suggest a novel mechanism by which a clinically intriguing agent selectively suppresses proliferation of cancer cells, as shown here for the untreatable mesotheliomas.

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.

D-alpha-tocopheryl succinate (vitamin E) enhances radiation-induced chromosomal damage levels in human cancer cells, but reduces it in normal cells

OBJECTIVE

The purpose of this study was to measure and compare the effect of d-alpha-tocopheryl succinate (alpha-TS) in modifying radiation-induced chromosomal damage in human normal cells and cancer cells in culture.

METHODS

Three human normal fibroblast cell lines (GM2149, AG1522 and HF19) and three human cancer cell lines, cervical cancer (HeLa) and ovarian carcinoma cells (OVGI and SKOV3) were treated with alpha-TS (37.6 microM) 20 hours before 100 cGy gamma-irradiation. After 30 minutes of irradiation, colcemid was added and cells were fixed. One hundred randomly selected metaphase cells were scored for the presence of chromatid gaps and breaks. To study the cellular accumulation of alpha-TS. cells were incubated in the presence of alpha-TS (18.8 and 37.6 microM) for 24 hours, and alpha-TS was extracted with hexane using a-tocopheryl acetate as an internal standard. The levels of alpha-TS were determined by HPLC.

RESULTS

Results showed that alpha-TS induced chromosomal damage in both human cervical cancer cells and ovarian cancer cells, but not in human normal fibroblasts in culture. In addition, alpha-TS enhanced the level of radiation-induced chromosomal damage in cancer cells, but it protected normal cells against such damage. Both cancer cells and normal cells accumulated similar levels of alpha-TS, suggesting that increased sensitivity of cancer cells to alpha-TS is acquired during transformation.

CONCLUSION

The use of alpha-TS during radiation therapy may improve the efficacy of radiation therapy by enhancing tumor response and decreasing some of the toxicities on normal cells.

c-Myc oncoprotein: a dual pathogenic role in neoplasia and cardiovascular diseases?

A growing body of evidence indicates that c-Myc can play a pivotal role both in neoplasia and cardiovascular diseases. Indeed, alterations of the basal machinery of the cell and perturbations of c-Myc-dependent signaling network are involved in the pathogenesis of certain cardiovascular disorders. Down-regulation of c-Myc induced by intervention with antioxidants or by antisense technology may protect the integrity of the arterial wall as well as neoplastic tissues. Further intervention studies are necessary to investigate the effects of tissue-specific block of c-Myc overexpression in the development of cardiovascular diseases.

Pros and cons of antioxidant use during radiation therapy

Radiation therapy is one of the major treatment modalities in the management of human cancer. While impressive progress like more accurate dosimetry and more precise methods of radiation targeting to tumor tissue has been made, the value of radiation therapy in tumor control may have reached a plateau. At present, two opposing hypotheses regarding the use of antioxidants during radiation therapy have been proposed. One hypothesis states that supplementation with high doses of multiple micronutrients including high dose dietary antioxidants (vitamins C and E, and carotenoids) may improve the efficacy of radiation therapy by increasing tumor response and decreasing some of its toxicity on normal cells. The other hypothesis suggests that antioxidants (dietary or endogenously made) should not be used during radiation therapy, because they would protect cancer cells against radiation damage. Each of these hypotheses is based on different conceptual frameworks that are derived from results obtained from specific experimental designs, and thus, each may be correct within its parameters. The question arises whether any of these concepts and experimental designs can be used during radiation therapy to improve the management of human cancer by this modality. This review has analyzed published data that are used in support of each hypothesis, and has revealed that the current controversies can be resolved, if the results obtained from one experimental design are not extrapolated to the other. This review has also discussed the scientific rationale for a micronutrient protocol that includes high doses of dietary antioxidants (vitamin C, vitamin E succinate and natural beta-carotene) which can be used adjunctively with radiation therapy.

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 inhibits melanoma growth in mice

BACKGROUND

Previous work has demonstrated that vitamin E succinate (VES), an ester analogue of vitamin E, inhibits the growth of melanoma in vitro. However, there is no information about the effect of VES on melanoma in vivo. We investigated the effect of VES on melanoma in vitro and in vivo.

METHODS

The effect of VES on the proliferation and apoptosis of the B16F10 murine melanoma cell line was determined by a modified Cell Titer 96 AQ assay and a cell death detection enzyme-linked immunosorbent assay, respectively. The in vivo effect of VES on B16F10 melanoma cells allografted in athymic nude mice was investigated. The mechanism of the in vivo antitumor effect of VES was determined by immunohistochemical detection of proliferation and apoptosis.

RESULTS

VES decreased cell proliferation (P =.0001) and increased cell apoptosis (P =.0001) in a dose-dependent manner in vitro. Also, VES significantly inhibited melanoma growth in mice (P =.0013). The VES antitumor effect in vivo was associated with a significant increase in the melanoma apoptosis rate (P =.0256).

CONCLUSIONS

This is the first report of the antimelanoma effect of VES in vivo. The mechanism of the antimelanoma effect of VES in vivo involves the promotion of tumor cell apoptosis. These findings support future investigations of VES as a therapeutic micronutrient against melanoma.

Evidence for oxidative activation of c-Myc-dependent nuclear signaling in human coronary smooth muscle cells and in early lesions of Watanabe heritable hyperlipidemic rabbits: protective effects of vitamin E

BACKGROUND

Oxidized LDL (oxLDL) promotes atherogenesis, and antioxidants reduce lesions in experimental models. OxLDL-mediated effects on c-Myc are poorly characterized, and those on c-Myc nuclear pathways are completely unknown. c-Myc stimulates smooth muscle cell (SMC) proliferation and could be involved in atherosclerosis. We investigated the early effects of oxLDL and alpha-tocopherol on c-Myc, its binding partner Max, and the carboxy-terminal domain-binding factors activator protein-2 and elongation 2 factor in human coronary SMCs. We also investigated whether 9-week treatment of Watanabe heritable hyperlipidemic (WHHL) rabbits with diet-enriched alpha-tocopherol reduces c-Myc expression and oxLDL in the left coronary artery.

METHODS AND RESULTS

OxLDL enhanced c-Myc/Max expression and transcription by cotransfection assay and the nuclear activities of E2F and activator protein-2 by binding shift and supershift in coronary SMCs. alpha-Tocopherol significantly reduced these molecular events. Furthermore, alpha-tocopherol reduced early lesions, SMC density, and the immunohistochemical presence of c-Myc, which colocalized with oxLDL/foam cells in the coronaries of WHHL rabbits.

CONCLUSIONS

We provide the first evidence that oxLDL and alpha-tocopherol may influence c-Myc activation and several c-Myc-dependent signaling pathways in human coronary SMCs. The observation that in vivo, an antioxidant reduces both c-Myc and oxLDL in early coronary lesions of rabbits is consistent with, but does not prove, the hypothesis that c-Myc-dependent factors activated by oxidative processes contribute to atherogenesis and coronary heart disease.

Butyric acid and pivaloyloxymethyl butyrate, AN-9, a novel butyric acid derivative, induce apoptosis in HL-60 cells

A novel butyric acid derivative, pivaloyloxymethyl butyrate, AN-9, was previously shown to be a potent differentiating agent. AN-9 exerts a significant anticancer activity in vitro and in vivo. In all the activities examined, AN-9 was more potent than butyric acid. Here we show that AN-9 and butyric acid induce cell death by apoptosis. Exposure of HL-60 cells to butyric acid and AN-9 decreased cell numbers and induced cell differentiation and the appearance of typical apoptotic features. Induction of apoptosis and/or differentiation by AN-9 and butyric acid was dependent on the concentration and the time of exposure to the drugs. The advantage of AN-9 over butyric acid was further confirmed. Apoptosis induced by AN-9 occurred after a shorter exposure and at lower drug concentrations than that induced by butyric acid. Apoptosis by AN-9 was accompanied by reduction in Bcl-2 expression. Preincubation with antioxidants did not protect HL-60 cells from apoptosis induced by AN-9. HL-60 cells that were induced to differentiate by preincubation with retinoic acid or low AN-9 concentrations were more resistant to apoptosis, induced later by high concentrations of AN-9, than were undifferentiated cells.

Vitamin E succinate inhibits proliferation and migration of retinal pigment epithelial cells in vitro: therapeutic implication for proliferative vitreoretinopathy

BACKGROUND

Retinal pigment epithelial (RPE) cells play an important role in proliferative vitreoretinopathy (PVR). Vitamin E succinate is an ester form of a potent biological antioxidant, vitamin E, and has unique effects on various cells. We examined the effect of vitamin E succinate on proliferation and migration of cultured bovine RPE cells, since these are critical steps in the development of PVR.

METHODS

Bovine RPE cells were cultured in minimal essential medium (MEM) containing 10% fetal calf serum (MEM-10). Cells were incubated with MEM-10 containing 25 microM vitamin E, vitamin E succinate, butylated hydroxytoluene (BHT) or d-mannitol. Cell proliferation was assessed by counting cell numbers on days 2, 4 and 6. 3H-Thymidine uptake was also examined in RPE cells incubated with various forms of vitamin E-- vitamin E, vitamin E succinate, Trolox, gamma-tocopherol, vitamin E acetate, vitamin E phosphate, vitamin E nicotinate--or antioxidants-- BHT or d-mannitol (25 microM each). RPE cell migration was studied as follows: A small area (5 x 15 mm) of confluent cultured RPE cells was denuded using a straight razor blade and incubation was continued for 20 h with MEM-10 containing vitamin E, vitamin E succinate, gamma-tocopherol or BHT. The number of cells that migrated into the denuded area from the wound edge in each microscopic field (x20) was counted and expressed as a percentage of control (MEM-10 alone).

RESULTS

The antioxidants, vitamin E and BHT, stimulated RPE cell proliferation and 3H-thymidine incorporation compared with the control, while vitamin E succinate significantly inhibited both proliferation and 3H-thymidine uptake (IC50, 23 microM). Other forms of vitamin E or d-mannitol had no effect. Neither vitamin E nor BHT had a significant effect on RPE cell migration (108.2% and 112.6% of control, respectively), but vitamin E succinate inhibited migration (58.3%). Cell viability, assessed by the trypan blue dye exclusion test, was not impaired by a 3-day incubation with 50 microM of vitamin E succinate.

CONCLUSIONS

An ester form of a physiological antioxidant, vitamin E succinate, inhibits RPE cell proliferation and migration without causing cellular toxicity. These findings suggest its therapeutic potential for the pharmacological treatment of PVR.

A novel styryl diphenylamine derivative reverts the transformed phenotype of human fibrosarcoma HT1080 cells

Revertant cells, which can be isolated from transformed cells, are flat, non-transformed variants that have contributed to the elucidation of mechanisms involved in cell transformation. We have discovered that a novel styryl diphenylamine derivative converts human fibrosarcoma HT1080 cells into revertant cells. This compound induces flat cell morphology and causes a decrease in proliferative rate. The flat revertant cells not only exhibit a reduction in saturation density at confluence, but also lose the ability to proliferate in soft agar. Furthermore, their tumorigenicity is reduced when injected s.c. into athymic nude mice. The compound alters morphology in three out of seven cancer cell lines and has a potent growth inhibitory effect in six of these lines. In contrast, it has only low levels of cytotoxicity for three normal diploid cell lines. These findings indicate that this styryl diphenylamine derivative has the potential to suppress the malignant phenotype of cancer cells without profound cytotoxicity in non-transformed cells.

Rapid alteration of c-myc and c-jun expression in leukemic cells induced to differentiate by a butyric acid prodrug

The novel prodrug of butyric acid (BA), pivaloyloxymethyl butyrate, has been shown, in vitro, to induce differentiation and inhibit leukemic cell proliferation. The prodrug affects the cells in vitro at lower concentration and at least 100 times faster than does (BA). We have compared the ability of BA with that of its prodrug AN-9 to modulate the expression of the early regulating genes, c-myc and c-jun, in HL-60 cells. Exposure of HL-60 cells to the prodrug resulted in a decrease of c-myc and an increase of c-jun expression. The prodrug elicited this effect at lower concentrations and at least 100 times faster than BA. Since changes in the expression of c-myc and c-jun occur minutes after exposure of the cells to the prodrug, these genes are likely to play a major role in the early stages of the differentiation pathway.

Spontaneous and induced differentiation of human melanoma cells

Malignant melanoma cells can differentiate spontaneously in vivo and in vitro into cells with a finite lifespan. Analysis of differentiating cells from primary melanomas in culture revealed a flat, fibroblast-like morphology and expression of the fibroblast-associated marker leucine aminopeptidase (LAP). Differentiation was also observed in a minor sub-population of permanent cell lines derived from metastatic lesions. An experimental model of melanoma cell differentiation was then developed, using the pyrimidine analog bromodeoxyuridine (BUdR). BUdR-treated cells had a flat morphology, were contact-inhibited, had up to 20-fold increased surface area, expressed LAP, no longer proliferated anchorage-independently in soft agar, and 3 out of 4 cell lines were non-tumorigenic in athymic nude mice. Our results show that models of differentiation of melanoma cells can be established that help to define pathways of differentiation.

Vitamin E and cancer prevention: recent advances and future potentials

Many animal and in vitro experiments have shown that the supplementation of diet with vitamin E within a certain dose range reduced the risk of chemical- and radiation-induced cancers. In vitro studies revealed that alpha-tocopheryl succinate (TS) induced differentiation and growth-inhibition in certain animal and human tumor cells in culture, whereas alpha-tocopherol (alpha-T), alpha-tocopheryl acetate (alpha-TA) and alpha-tocopheryl nicotinate (alpha-TN) were ineffective, alpha-TS also reduced basal and ligand-stimulated adenylate cyclase activity, and expression of c-myc and H-ras oncogenes in certain tumor cells in culture. The relative efficacy of various forms of vitamin E in cancer prevention in animal or human models has not been evaluated. Human epidemiologic studies utilizing retrospective and prospective case-control experimental designs are not suitable for evaluating the role of vitamin E in cancer prevention due to several inherent problems associated with these methodologies. Intervention trials utilizing vitamin E with appropriate biological and statistical rationales are most suitable for testing the role of vitamin E in cancer prevention in humans. Some human trials utilizing vitamin E alone or in combination with other nutrients are in progress.