Live imaging of neolymphangiogenesis identifies acute antimetastatic roles of dsRNA mimics

Long‐range communication between tumor cells and the lymphatic vasculature defines competency for metastasis in different cancer types, particularly in melanoma. Nevertheless, the discovery of selective blockers of lymphovascular niches has been compromised by the paucity of experimental systems for whole‐body analyses of tumor progression. Here, we exploit immunocompetent and immunodeficient mouse models for live imaging of Vegfr3‐driven neolymphangiogenesis, as a versatile platform for drug screening in vivo . Spatiotemporal analyses of autochthonous melanomas and patient‐derived xenografts identified double‐stranded RNA mimics (dsRNA nanoplexes) as potent inhibitors of neolymphangiogenesis, metastasis, and post‐surgical disease relapse. Mechanistically, dsRNA nanoplexes were found to exert a rapid dual action in tumor cells and in their associated lymphatic vasculature, involving the transcriptional repression of the lymphatic drivers Midkine and Vegfr3, respectively. This suppressive function was mediated by a cell‐autonomous type I interferon signaling and was not shared by FDA‐approved antimelanoma treatments. These results reveal an alternative strategy for targeting the tumor cell‐lymphatic crosstalk and underscore the power of Vegfr3‐lymphoreporters for pharmacological testing in otherwise aggressive cancers. SYNOPSIS This study reports the “Lymphoreporter‐MetAlert” mice as a platform for non‐invasive imaging and screening for antimetastatic agents. The focus is on melanoma, but these animals can be used for other tumor types and other pathologies that involve an aberrant activation of the lymphatic vasculature. MetAlert mice allow for in vivo analyses of drug response in patient‐derived xenografts (PDX) and genetically modified melanoma models (GEMM). Inhibitors of BRAF or immune checkpoints result in a limited anti‐lymphangiogenic and antitumoral activity in MetAlert (as in the clinic). dsRNA nanoplexes (BO‐110) were identified to blunt neo‐lymphangiogenesis after just one systemic administration. BO‐110 blocked neolymphangiogenesis at two levels: in melanoma cells via repression of Midkine (MDK) and in lymphatic cells via VEGFR3. Imaging metastatic relapse after surgical excision set the proof of principle for BO‐110 in adjuvant treatment. Graphical Abstract This study reports the “Lymphoreporter‐MetAlert” mice as a platform for non‐invasive imaging and screening for antimetastatic agents. The focus is on melanoma, but these animals can be used