Faculty Bibliography

PURPOSE/OBJECTIVE:Brain metastases are a common preterminal event in patients with metastatic melanoma and require radiation therapy. Our group has previously shown that human GRM1 (hGRM1) expressing melanoma cells release excess extracellular glutamate and are growth inhibited by riluzole, an inhibitor of glutamate release. Riluzole-treated cells accumulate in G(2)/M phase of the cell cycle at 24 hours, and then undergo apoptotic cell death. We evaluated whether riluzole enhanced radiosensitivity in melanoma cells. EXPERIMENTAL DESIGN/METHODS:Clonogenic assays were performed to evaluate clonogenic survival after treatment in hGRM1 expressing and nonexpressing melanoma cells. Western immunoblots were performed to confirm apoptotic cell death. A xenograft mouse model was used to validate the in vitro experiments. Tumors harvested from the xenografts were fixed and stained for apoptosis and DNA damage markers. RESULTS:In the hGRM1-positive cell lines C8161 and UACC903, riluzole enhanced the lethal effects of ionizing radiation; no difference was seen in the hGRM1-negative UACC930 cell line. C8161 cells treated with riluzole plus irradiation also showed the highest levels of the cleaved forms of PARP and caspase-3; excised C8161 xenografts showed the greatest number of apoptotic cells by immunohistochemistry (P < 0.001). On cell cycle analysis, a sequence-dependent enrichment in the G(2)/M phase was shown with the combination of riluzole and irradiation. Xenografts treated with riluzole and weekly radiation fractions showed significant growth inhibition and revealed markedly increased DNA damage. CONCLUSIONS:We have shown, in vitro and in vivo, that the combination of riluzole and ionizing radiation leads to greater cytotoxicity. These results have clinical implications for patients with brain metastases receiving whole brain radiation therapy.

Angiogenesis is required for progression and metastasis of melanoma. Analysis of angiogenic molecules in benign and malignant tissues may allow identification of markers useful for prediction of sensitivity to antiangiogenic agents. We hypothesized that differential expression of vascular endothelial growth factor (VEGF) and its receptors VEGF-R1, VEGF-R2, and VEGF-R3 would be higher in melanomas than nevi and higher in advanced melanoma. Using automated quantitative analysis, we quantified VEGF, -R1, -R2 and -R3 expression in melanoma tissue microarrays composed of 540 nevi and 468 melanoma specimens (198 primaries, 270 metastases). VEGF, VEGF-R1, VEGF-R2, and VEGF-R3 expression was significantly higher in melanomas than nevi by unpaired t tests (P < .0001). VEGF-R2 expression was higher in metastatic specimens (P < .0001), but VEGF-R3 expression was higher in primaries (P < .0001). VEGF was coexpressed with all 3 receptors when assessed by Spearman's rank correlation. VEGF, VEGF-R1, VEGF-R2, and VEGF-R3 expression is higher in melanomas than nevi. Higher expression of VEGF-R2 was found in metastases versus primaries, supporting the idea that selection for an angiogenic phenotype in metastatic melanoma is conferred via up-regulation of VEGF-R2. However, higher expression of VEGF-R3 was seen on primary lesions, potentially implicating this receptor in initiation of lymphatic tumor spread. Clinical trials using antiangiogenic agents in melanoma should include correlative assays of VEGF, VEGF-R1, VEGF-R2, and VEGF-R3 as biomarkers of response to therapy, preferably using quantitative methods such as automated quantitative analysis. Such assessments could assist with evaluation of these molecules as therapeutic targets in melanoma, ultimately facilitating improved selection of patients for treatment.

Histone deacetylases (HDACs) and histone acetyltransferases are enzymes that regulate chromatin structure and function through the removal and addition, respectively, of the acetyl group from the lysine residues of core nucleosomal histones. This posttranslational modification of histones is an important process in the regulation of gene expression. Aberrant expression and recruitment and disrupted activities of HDACs and histone acetyltransferases have been found in malignant tissues, implicating their involvement in cancer. HDAC inhibitors (HDACIs) function through diverse mechanisms, including the promotion of cell cycle arrest and apoptosis and the inhibition of angiogenesis. Malignant cells appear more sensitive to the proapoptotic effects of HDACIs, underscoring the therapeutic potential of these agents. Multiple HDACIs are currently under investigation in clinical trials, including vorinostat (suberoylanilide hydroxamic acid), which was recently approved by the U.S. Food and Drug Administration for the treatment of cutaneous manifestations of cutaneous T-cell lymphoma in patients with progressive, persistent, or recurrent disease on or after 2 systemic therapies.

Vasoactive intestinal peptide (VIP), a regulator of embryonic growth, increased the concentration of nerve growth factor (NGF)-like immunoreactivity in the conditioned medium of cultured explanted embryonic day (E) 9.5 neural tube preparations compared to control preparations. VIP treatment also induced an increase of NGF-like immunoreactivity (NGF-IR) within the neural tube preparation tissue. A 60 kDa isoform was the primary form of NGF detected. VIP is shown to be a regulator of NGF in the E9.5 embryonic mouse and stimulates the release of a high molecular weight isoform of NGF.