Abstract 2727: Elucidating genes that mediate brain colonization by metastatic melanoma cells
Authors: Holovanchuk Denys , Lee Rebecca , Cannistraci Alessio , Dhomen Nathalie , Pavet Valeria , Marais Richard 
Published: September 2020

Abstract
Metastatic melanoma shows remarkable tropism for the brain, affecting up to 75% of stage 4 patients, causing devastating symptoms and dramatically reducing survival. Patients with brain metastases have limited treatment options and short-lived unpredictable responses to therapy, probably due to our poor understanding of the biology driving this particular metastatic process. In this work we hypothesize that the brain microenvironment induces particular gene expression changes in melanoma cells as compared to melanoma cells colonizing extra-cranial sites, allowing cells to rewire, survive and proliferate in the brain.
To elucidate the molecular basis supporting brain metastasis in melanoma, we enriched for cancer cells from patient blood and established a metastatic circulating tumor cells derived explant (CDX) model of cutaneous melanoma. CDX-derived cell lines were injected intra-dermally in the flank of immunocompromised mice and tumor growth as well as metastatic incidence was quantified. Our data shows that both the CDX and its corresponding derived cell line showed tropism for the brain, liver and kidneys, similar to what was observed in the patient. Notably, the intradermal flank-tumors were predominantly highly pigmented, whereas the liver metastases were either pigmented or non-pigmented. In contrast, the brain metastases located in the parenchyma were exclusively non-pigmented. Cell lines derived from either pigmented or non-pigmented liver lesions as well as non-pigmented lesions from the brain maintained their pigmentation and morphological features in vitro.
When injected intradermally into immunocompromised mice, the pigmented cells metastasized to the visceral organs and, even though leptomeningeal metastasis may be observed, these cells did not invade brain parenchyma. In contrast, the non-pigmented cells (derived either from the liver or brain) metastasized to the visceral organs and additionally metastasized to the brain parenchyma; feature that was enhanced following successive in vivo passages. Gene expression analysis revealed an enrichment of genes encoding proteins that regulate extracellular matrix reorganization, angiogenesis and epithelial-to-mesenchymal transition in the non-pigmented cells. Moreover, TGF-beta signalling was found to be one of the most enriched pathways in the cells derived from parenchymal brain metastases, suggesting that increased TGF-beta signalling regulates brain tropism in metastatic melanoma.
In conclusion, our experimental model recapitulates the propensity of melanoma to metastasize to the brain parenchyma and our preliminary data suggests that TGF-beta signalling play a key role in supporting this process. Further experiments are currently ongoing for testing our hypothesis that, if corroborated, may open new avenues of treatment options for melanoma patients displaying metastases in the brain.
Citation Format: Denys Holovanchuk, Rebecca Lee, Alessio Cannistraci, Nathalie Dhomen, Valeria Pavet, Richard Marais. Elucidating genes that mediate brain colonization by metastatic melanoma cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2727.