The RPL/RPS Gene Signature of Melanoma CTCs Associates with Brain Metastasis

Melanoma brain metastasis (MBM) is linked to poor prognosis and low overall survival. We hypothesized that melanoma circulating tumor cells (CTC) possess a gene signature significantly expressed and associated with MBM. Employing a multipronged approach, we provide first-time evi-dence identifying a common CTC gene signature for ribosomal protein large/small subunits (RPL/RPS) which associate with MBM onset and progression. Experimental strategies involved capturing, transcriptional profiling, and interrogating CTCs, either directly isolated from blood of patients with melanoma at distinct stages of MBM progression or from CTC-driven MBM in experimental animals. Second, we developed the first MRI CTC-derived MBM xenograft model (MRI-MBM CDX) to dis-criminate MBM spatial and temporal growth, recreating MBM clinical presentation and progression. Third, we performed the comprehensive transcriptional profiling of MRI-MBM CDXs, along with longitudinal monitoring of CTCs from CDXs possessing and/or not possessing MBM. Our findings suggest that enhanced ribosomal protein content/ribogenesis may contribute to MBM onset. Because ribosome modifications drive tumor progression and metastatic development by remodeling CTC trans-lational events, overexpression of the CTC RPL/RPS gene signature could be implicated in MBM development. Collectively, this study provides im-portant insights for relevance of the CTC RPL/RPS gene signature in MBM, and identify potential targets for therapeutic intervention to improve pa -tient care for patients with melanoma diagnosed with or at high risk of developing MBM.Significance: This study reports first evidence of RPL/RPS gene signature driving melanoma brain metastasis. Complex multilevel approach was per-formed to identify MBM signature and confirm its relevance to clinical settings. Novel MRI CTC-derived MBM mouse xenograft was established to monitor MBM spatial and temporal development and progression.