Abstract C60: FRIZZLED7 and ERBB3 regulate distinct metastatic properties in melanoma

Abstract

Abstract Metastasis accounts for a majority of deaths from cancer. Metastatic melanoma is a type of highly aggressive cancer and accounts for ~75% of deaths in patients with skin cancer. The low 5-year survival rate of late-stage melanoma patients (~15%) treated with current methods calls for novel interventions. A constitutively active form of BRAF ( BRAFCA) is present in 60% to 70% of melanoma cases; the remaining 30% express wild type BRAF. Recently, a BRAFCA inhibitor, vemurafenib, has provided some initial benefits in melanoma patients, but resistance quickly developed in these patients. Also, the drug was ineffective in melanomas expressing wild type BRAF, begging for alternative therapeutic strategies. Metastasis is a multistep process, which involves detachment of cancer cells from primary tumor, intravasation into circulation, survival and extravasation into tissue parenchyma, and metastatic growth initiation and expansion. The last two steps are considered rate-limiting steps during metastasis and were examined using the experimental metastasis assay. Our prior studies showed that highly metastatic melanoma cells differentially express a set of 150 genes compared to low metastatic melanoma cells. Among the 150 genes, 44 were positively correlated with poor patient survival and were particularly enriched for genes encoding secreted proteins. We analyzed two of them, FZD7 and ERBB3, in the context of metastatic growth. FRIZZLED7 is a WNT receptor and ERBB3 is a receptor tyrosine kinase. Both were found to be highly expressed in melanomas from patients with poor survival. We showed that shRNA mediated knockdown of FZD7 or ERBB3 reduced the lung colonization ability of melanoma cell lines expressing the constitutively active mutant of BRAF (BRAFCA) in the experimental metastasis assay. In addition, FZD7 or ERBB3 knockdown reduced the metastatic potential of melanoma cells that have developed resistance to BRAF inhibitor. These results provided preclinical evidence for using FZD7 and ERBB3 as intervention entry points to treat both vemurafenib-sensitive and resistant melanomas. We are currently testing whether perturbing these two genes also abolishes metastasis from melanoma cells that carry wild type BRAF in the SKMEL2 cell line, which expresses a wild type BRAF. We are also examining at which step FZD7 and ERBB3 affect metastasis. Our data indicated that, though either FZD7 or ERBB3 knockdown can reduce the number of lung metastases in experimental metastasis assay, only FZD7 knockdown affected the tumor initiating cell frequency and subcutaneous tumor growth. This suggested that ERBB3 and FZD7 may regulate distinct aspects of metastasis. Taken together, we investigated the roles of two cell surface receptors, FZD7 and ERBB3, on melanoma metastasis. Our results revealed signaling pathways that potentially influence distinct steps of metastasis process. Combinatorial therapies that perturb these pathways thus may prove more effective in treating metastatic melanoma than single regimens. Citation Format: Shweta Tiwary, Morgan Preziosi, Sonali Mohanti, Brad Martin, Nathalie Zeitouni, Lei Xu. FRIZZLED7 and ERBB3 regulate distinct metastatic properties in melanoma. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr C60.