Elsevier

Life Sciences

Volume 84, Issues 19–20, 8 May 2009, Pages 650-656
Life Sciences

A redox-silent analogue of tocotrienol acts as a potential cytotoxic agent against human mesothelioma cells

https://doi.org/10.1016/j.lfs.2009.02.007Get rights and content

Abstract

Aims

Malignant mesothelioma is an aggressive cancer with no effective treatment options. A redox-silent analogue of α-tocotrienol, 6-O-carboxypropyl-α-tocotrienol (T3E) is a new potential anti-carcinogenic agent with less toxic effect on non-tumorigenic cells. Here, we evaluated the effect of T3E on killing of chemoresistant mesothelioma cell (H28).

Main methods

The cytotoxic effect of T3E was evaluated by a WST-1 assay, and cell cycle and apoptosis analysis were done by FACS. Each signal molecule's activity was determined by protein array and immunoblot analysis.

Key findings

T3E effectively inhibited H28 cell growth at practical pharmacological concentrations (10–20 μM) without any effect on non-tumorigenic mesothelial cell (Met-5A). Inhibition of H28 cell growth by T3E mediated through G2/M arrest in cell cycle and induction of apoptosis. Protein array and immunoblot analyses revealed that T3E inhibited the activation of epidermal growth factor receptor (EGFR) via the inactivation of the Src family of protein tyrosine kinases (Src). However, the blockade of the EGFR signaling was not associated with the T3E-dependent H28 cell growth control. In addition to Src inactivation, T3E inhibited signal transduction and activation of transcription Stat3. A combination of an Src inhibitor, PP2, and a Stat3 inhibitor, AG490, induced G2/M arrest and enhanced apoptosis compared with PP2 alone. These results suggest that T3E suppresses H28 cell growth via the inhibition of Src activation and Src-independent Stat3 activation.

Significance

T3E can be a new effective therapeutic agent against chemoresistant mesothelioma cells.

Introduction

Malignant mesothelioma (MM) from the serosal membranes of the body cavities, is a particular aggressive cancer which is characterised by rapid progression, late metastases, and poor prognosis (Carbone et al. 2002). Although surgery, radiotherapy, chemotherapy, and/or their combinations have been used as therapeutic modalities, median patient survival is 8–18 months (Nowak et al. 2002). MM cells exhibit resistance to many chemotherapeutic agents, including doxorubicin and cisplatin, which are nevertheless widely used to treat MM (Tomek et al. 2003). A recent report of a phase III study showed that the combination of pemetrexed and cisplatin is more effective than cisplatin alone with differences in response rate of 41.3 versus 16.3% (Vogelzang et al. 2003). However, most of the patients relapsed within a year after starting the treatment. Therefore, new therapeutic approaches are urgently needed for MM patients.

Vitamin E, a fat soluble vitamin, is well known for its cellular antioxidant and lipid lowering properties (Packer and Landvik 1989). It is now been increasingly accepted as a generic term for tocotrienols and tocopherols. Although both classes of compounds share the same aromatic chromanol ‘head’, the two isoforms of vitamin E differ in their side chains. Tocopherols posses saturated phytyl side chain while tocotrienols have an unsaturated isoprenoid chain along their ‘tails’. Due to the structural difference of the two compounds, tocotrienols have more potential physiological functions than tocopherols (Pearce et al. 1992). In previous studies including those of our group, α-tocopherol (T), a representative tocopherol, is inactive for the negative growth control of cancer cells. In contrast an ether derivative of T, 6-O-carboxypropyl-α-tocopherol (TE), a redox-silent analogue of T, is a potent growth inhibitor against cancer cells, both in vitro and in vivo (Yano et al., 2001, Nishikawa et al., 2003). Similarly, an ether derivative of α-tocotrienol (T3), 6-O-carboxypropyl-α-tocotorienol (T3E), has cytotoxicity against a lung adenocarcinoma cell line (A549) in vitro much stronger than that of T3 or TE (Yano et al. 2005). In previous studies, a redox-silent analogue of T, α-tocopheryl succinate (TS) effectively suppressed MM cell growth in vitro as well as in vivo (Kogure et al., 2002, Kogure et al., 2003). From our previous report, it is clear that the redox-silent analogue of T3 is much stronger that that of T as an anti-cancer agent (Yano et al. 2005), thus we hypothesized that T3E may be a potential anti-mesothelioma agent.

In this context, we evaluated the effect of T3E on MM cell growth and its possible mechanism. Human MM cell line, H28 was chosen to evaluate the inhibitory effect of T3E on MM cell growth, due to its resistance to cisplatin (CDDP), a representative agent to treat MM clinically.

Section snippets

Reagents

All culture and chemicals were purchased from Gibco BRL (Tokyo, Japan) and Sigma (St. Louis, MO, USA), unless otherwise indicated. PP2 (a Src inhibitor), PP3 (a negative control of PP2), AG490 (a signal transducer and activator of transcription (Stat)3 inhibitor) and AG1478 (a epidermal growth factor receptor (EGFR) inhibitor) were purchased from Calbiochem–Novabiochem (La Jolla, CA, USA). T3 was purchased from Tama Biochemicals (Tokyo, Japan). All antibodies were obtained from Cell Signaling

Effect of T3E on growth of H28 and Met-5A cells

To compare effect of T3E on H28 cell growth with that of CDDP and T3, we first examined time-dependent change in cell viability after each agent exposure for 48 h. As shown in Fig. 1A, only T3E decreased cell viability in a dose-dependent manner (0–20 μM). However, T3 and CDDP did not influence the cell viability within the doses (Fig. 1A). Furthermore, we evaluated the toxic effect of T3E on non-tumorigenic mesothelial cells (Met-5A cell) to estimate selective toxicity of T3E against MM cells.

Discussion

MM is an aggressive malignancy, the incidence of which is expected to increase due to its association with asbestos exposure. A number of chemotherapeutic agents have been used, either alone or in combination, to treat MM with the latter multi-agent regimes generally having the highest response rates (Pistolesi and Rusthoven 2004). Nonetheless, despite the current therapies, the prognosis for many MM patients is very poor. Several signal molecules related to growth and survival are

Conclusion

In conclusion, we demonstrated that T3E could effectively suppress growth of human MM cells (H28 cells) having chemoresistance to CDDP in pharmacological doses, based on simultaneous inactivation of Src and Stat3, and that T3E had no influence on non-tumorigenic mesothelial cells (Met5-A cells). These findings suggest that T3E is a promising and potential anti-MM agent compared with conventional chemotherapeutic agents.

Acknowledgment

This study was supported by a research grant for Health Sciences Focusing on Drug Innovation from the Japan Health Sciences Foundation (KHC1023).

References (37)

  • WhitsonB.A. et al.

    Molecular pathways in malignant pleural mesothelioma

    Cancer Letters

    (2006)
  • YanoT. et al.

    The suppression of ornithine decarboxylase expression and cell proliferation at the promotion stage of lung tumorigenesis in mice by α-tocopheryloxybutyric acid

    Biochemical Pharmacology

    (2001)
  • ZinggJ.M.

    Modulation of signal transduction by vitamin E

    Molecular Aspects of Medicine

    (2007)
  • BenatiD. et al.

    SRC family kinases as potential therapeutic targets for malignancies and immunological disorders

    Current Medical Chemistry

    (2008)
  • BirringerM. et al.

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

    British Journal of Cancer

    (2003)
  • BiscardiJ.S. et al.

    Tyrosine kinase signalling in breast cancer: epidermal growth factor receptor and c-Src interactions in breast cancer

    Breast Cancer Research

    (2000)
  • FarissM.W. et al.

    The selective antiproliferative effects of α-tocopheryl hemisuccinate and cholesteryl hemisuccinate on murine leukemia cells result from the action of the intact compounds

    Cancer Research

    (1994)
  • JagadeeswaranR. et al.

    Functional analysis of C-Met/hepatocyte growth factor pathway in malignant pleural mesothelioma

    Cancer Research

    (2006)
  • Cited by (0)

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