Abstract 4861: The role of PRAME in promoting uveal melanoma metastasis

Uveal melanoma (UM) is the most common primary eye cancer and has a predisposition for fatal metastasis. Our group has shown that UMs can be categorized by gene expression profiling (GEP) into two molecular classes associated with metastatic risk: Class 1 (low metastatic risk) and Class 2 (high metastatic risk). While the majority of Class 2 UMs (71%) metastasize, only 38% of Class 1 UMs metastasize. Our group was the first to identify the cancer-testis antigen PRAME as a biomarker for increased metastatic risk in Class 1 UMs, and sub-categorized these tumors into Class1 PRAME+ (intermediate metastatic risk) and Class1 PRAME- (low metastatic risk) subgroups. Further we identified PRAME+ was associated with shorter time to metastasis and worse prognosis in class 2 patients. We have now shown that this PRAME expression is correlated with hypomethylation in the promoter region of the gene, suggesting a mechanism for its expression. Since we have previously shown that PRAME is associated with early metastasis in Class 1 and Class 2 UMs, we hypothesized that PRAME plays a direct role in UM metastasis. To better understand the role of PRAME in UM, we used Class1PRAME+ (F41) and Class1PRAME– (Mel290) UM cell lines to develop in vitro models to study the role of PRAME. Since F41 cells are PRAME+ and highly metastatic, we constitutively silenced PRAME with a V5 tag (F41 shPRAME-V5). For Mel290 cells, we overexpressed PRAME to see whether this cell line, which does not induce metastatic death, became more malignant. We confirmed the silencing and overexpression of PRAME in our transformed cells with western blot. For cell proliferation, we found a slight increase in the Mel290 PRAME+ cells compared to non-transformed Mel290. Strikingly, in F41 cells, knockdown of PRAME led to complete cell death. In a xenograft animal model, NSG male mice were injected with either Mel290 PRAME-V5, Mel290, F41 shPRAME-V5 or F41 TET-empty vector cells. We found that PRAME overexpressing cell lines (Mel290 PRAME-V5 and F41 TET-empty vector) induced rapid, multiple and aggressive liver metastases that led to death, whereas the non-expressing PRAME cells (Mel290 and F41 shPRAME-V5) did not present macro or micrometastasis in any cases. This data highly suggests that PRAME overexpression is involved in UM metastasis. Thus, PRAME mRNA expression is not only a prognostic biomarker but also could be an important target for treatment. Citation Format: Margaret I. Sanchez, Matthew G. Field, Je