The effects of 1-(biphenyl-4-ylmethyl)-1,2,3,4-tetrahydroisoquinoline-6,7-diol (EDL-155) on the growth of glioma was tested in vitro and in vivo. Normal cultured rat astrocytes and C6 rat glioma were used as a differential screen to test the effects of EDL-155. The compound was preferentially cytotoxic for C6 glioma (EC50=1.5 micromol/l) relative to cultured neonatal astrocytes (EC50=27.4 micromol/l). When compared with a standard chemotherapeutic agent, carmustine (1,3-bis[2-chloroethyl]-1-nitrosourea), or temozolomide, EDL-155 was more selective and more potent in our differential tissue culture assay. The effect of EDL-155 was also tested in an animal model in which C6 glioma was transplanted into the brains of Sprague-Dawley rats. EDL-155 was delivered directly onto the tumor by an osmotic minipump directly into the brain or by intraperitoneal injection. Animals treated with EDL-155 had significantly smaller tumors than did control animals treated with carrier solution. We observed anatomical changes in cultured glioma cells treated with EDL-155 that were consistent with selective destruction of mitochondria and the induction of autophagy. These changes were not observed in normal astrocytes cultured from rat pups. The selective killing of glioma in tissue culture and in the rat brain models indicates that EDL-155 has potential therapeutic value in treating this type of brain cancer.
Cite this articleGoldsmith ZK, McEwen MW, Kibe MW, et al. Sirtuin inhibitor as a novel cell cycle checkpoint and regulator of the TP53-MDM2 pathway in uveal melanoma. ABSTRACT PurposeThe liver is the most common site of uveal melanoma (UM) metastasis with approximately 50% of UM patients being affected. With no proven therapies that mitigate metastases the mortality rate is 85% within the first year after detection of the liver disease. In this study, we provide a mechanistic understanding of the de-regulation of the TP53-MDM2 pathway in UM, which plays a central role in tumor biology. MethodsWe investigated the TP53-MDM2 signaling pathway in the microenvironment of liver metastases taken from both a murine orthotopic xenograft and post-mortem metastatic UM human liver. These findings were studied in-depth using both primary and metastatic UM cell lines treated with the MDM2 antagonist Nutlin-3a and the sirtuin inhibitor and transcriptional activator of TP53, Tenovin-6. ResultsDe-regulation of the TP53-MDM2 signaling pathway is specific to the liver microenvironment, providing a survival mechanism for UM metastases. Tenovin-6, not Nutlin-3a, reduced UM cell survival by increasing the percentage of cell death and reducing the percentage of proliferating cells. Tenovin-6 increased acetylation of p53, reduced ubiquitination of the protein, and acted as a cell cycle regulator. ConclusionOur findings suggest that in patients with metastatic UM de-regulation of TP53-MDM2 signaling pathway promotes growth of the liver metastases and provides pre-clinical information on the potential of targeting of the TP53-MDM2 signaling pathway via Tenovin-6.
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