α-Tocopheryl succinate inhibits malignant mesothelioma by disrupting the Fibroblast Growth Factor Autocrine Loop: Mechanism and the role of oxidative stress

Abstract

We have studied the potential effect against human malignant mesotheliomas (MM) of α-tocopheryl succinate (α-TOS), a redox-silent vitamin E analog with strong pro-apoptotic and anti-cancer activity. α-TOS at sub-apoptotic levels inhibited proliferation of MM cell lines, while being nontoxic to nonmalignant mesothelial cells. Because MM cells are typified by a highly metastatic phenotype, we investigated the effect of α-TOS on genes playing a major role in MM progression. Of these, α-TOS down regulated fibroblast growth factor (FGF)-1 and, in particular, FGF-2 on the transcriptional level in MM cells, and this was not observed in their nonmalignant counterparts. FGF-2 short interfering RNA suppressed proliferation of MM cells. Down-regulation of FGF-2 was likely because of inhibition of the egr-1 transcription activity that was decreased in MM cells via oxidative stress induced by α-TOS, as evidenced by EPR spectroscopy, whereas nonmalignant cells did not show this response. Treatment of MM cells with egr-1 short interfering RNA suppressed proliferation, which was overridden by exogenously added recombinant FGF-1 and, in particular, FGF-2. An analog of coenzyme Q targeted to mitochondria and superoxide dismutase overrode inhibition ofMMcell proliferation by α-TOS as well as α-TOS-induced inhibition of egr-1-dependent transactivation. Finally, α-TOS significantly suppressed experimental MM in immunocompromised mice. Our data suggest that α-TOS suppresses MM cell proliferation by disrupting the FGF-FGF receptor autocrine signaling loop by generating oxidative stress and point to the agent as a selective drug against thus far fatal mesotheliomas.