Abstract PR001: The CTC RPL/RPS gene signature: Targeting translation and the cell cycle inversely affects CTC metabolism but not metastasis

Abstract Melanoma brain metastasis (MBM) is the most devastating consequence of melanoma, is increasing in frequency, and is linked to poor prognosis and dismal survival. By employing an unbiased, multipronged approach, we discovered a CTC gene signature for ribosomal protein large/small subunits (RPL/RPS) which associated with MBM onset and progression. Experimental strategies involved capturing, transcriptional profiling, and interrogating CTCs, either directly isolated from blood of melanoma patients at distinct stages of progression, from CTC-driven MBM in experimental animals, or by developing/applying the first MRI CTC- derived MBM xenograft model (MRI-MBM CDX) to discriminate MBM spatial and temporal growth, thus faithfully recreating its clinical presentation. Accordingly, we hypothesized that targeting CTC ribogenesis can prevent melanoma metastasis in general, MBM in particular. We treated CDX cohorts with FDA-approved protein translation inhibitor omacetaxine in the presence or absence of CDK4/CDK6 inhibitor palbociclib, and monitored metastatic development and cell proliferation. Necropsies and IVIS imaging showed decreased MBM/extracranial metastasis in drug-treated mice, and RNA-Seq on mouse-blood-derived CTCs revealed downregulation of four RPL/RPS genes of the CTC signature. Notably, by performing the first-ever functional metabolic characterization of circulating neoplastic cells/CTCs in real- time, coupled with confirmatory RT-qPCR, we found that omacetaxine and palbociclib inversely affected glycolytic metabolism, and demonstrated that dual targeting of cell translation and proliferation is critical to suppress plasticity in metastasis-competent CTCs. This study identifies the relevance of targeting the CTC RPL/RPS signature to suppress melanoma metastasis, and set forward notions for novel therapies to affect metastasis by the deregulation of translation controlling CTC states. Studies involving structural and mechanistic analyses of CTC dormant vs active ribosomes by cryogenic electron microscopy are in progress. Citation Format: Dario Marchetti. The CTC RPL/RPS gene signature: Targeting translation and the cell cycle inversely affects CTC metabolism but not metastasis [abstract]. In: Proceedings of the AACR Special Conference: Liquid Biopsy: From Discovery to Clinical Implementation; 2024 Nov 13-16; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(21_Suppl):Abstract nr PR001.