Brain metastases occur frequently in melanoma patients with advanced stage disease whereby the prognosis is dismal. The underlying mechanisms of development of melanoma brain metastasis are not well understood. We generated a reproducible melanoma brain metastasis model, consisting of brain-metastasizing variants and local, sub-dermal variants that originate from the same melanomas thus sharing a common genetic background. The brain metastasizing variants were obtained by intra-cardiac inoculation. We developed brain metastasis variants when inoculated sub-dermally yielded spontaneous brain dormant micrometastasis. Cells from the spontaneous brain micrometastasis when removed from the brain microenvironment grew very well in vitro and generated tumors when orthotopic injection in the skin was performed. CGH array demonstrated that brain micro-metastatic melanoma cells have a different gene expression profile than fully fledged brain metastases. Further
analysis of brain metastasis compared to cutaneous variants was assessed by expression arrays. The brain metastasis and micrometastasis cells expressed higher levels of ANGPTL4, COX-2, MMP1, MMP2 and PRAME and lower levels of CLDN1, CYR61 and IL-6R than the cutaneous variants.
To examine whether the low expression levels of CLDN1 in brain metastasizing melanoma cells contribute to melanoma brain metastasis, we created, using CLDN1-cDNA infection, metastatic melanoma variants over-expressing CLDN1. Using these genetically manipulated melanoma cells, we have shown that increasing CLDN1 expression in brain metastatic melanoma cells attenuated the malignancy phenotype and metastatic potential of melanoma cells.
The reproducible models of human melanoma metastasizing experimentally and spontaneously to the brain can therefore serve as an unlimited source of transcriptomic and proteomic material. Such models can facilitate future studies on melanoma metastasis and the identification of novel biomarkers and targets for therapy.
This study was supported by the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation(Needham,MA,USA).
