Abstract Ewing sarcoma (ES) is the second most prevalent malignant bone tumor after osteosarcoma in children and adolescents. While survival of patients with localized ES has improved, patients with metastatic ES still lack adequate therapies, which results in poor survival rates. Thus, there is an important need for new therapies targeting ES metastases and preventing its dissemnation. Previously, we have shown that ES cells constitutively express high levels of NPY and its receptors - Y1R and Y5R. However, tumor hypoxia changes expression pattern and functions of NPY system, leading to the activation of its Y2R and Y5R, which stimulate ES cell motility and invasiveness under these conditions. Hence, the goal of this study was to determine the role of NPY in hypoxia-induced ES metastases. Here, we focused on Y5R, since our data from other malignancies implicated this receptor as the major mediator of NPY's pro-metastatic effects. To this end, we used doxycycline (DOX)-inducible CRIPSR/Cas9 system to create an SK-ES1/Y5R knockout (KO) cell line. The Y5R KO significantly decreased motility of SK-ES1 cells. To determine the impact of this phenomenon on ES metastases, SK-ES1/Cas9/Y5RsgRNA cells were injected into gastrocnemius muscles of SCID/bg mice and the animals were fed with DOX+ or control diet. The Y5R KO did not affect primary tumor growth. Once the xenografts reached a volume of 0.25cm3, a femoral artery ligation (FAL) was performed in the tumor-bearing limbs to induce hypoxic conditions. Both primary tumors and their corresponding metastases were sequenced to confirm the efficiency of gene editing. Notably, majority of metastases arising in mice bearing SKES-1/Y5RsgRNA+DOX xenografts were initiated by the clones without Y5R gene modification, confirming the role of Y5R in ES dissemination. The frequency of metastases with efficient Y5R KO originating from hypoxic tumors was markedly decreased, as compared to the control group (-DOX). Moreover, Y5R KO prevented hypoxia-induced increase in osseous metastases previously reported by our group. Collectively, these data validate NPY/Y5R axis as a crucial mediator of the hypoxia-induced ES metastasis and implicate Y5R receptor as a novel target for therapies preventing ES dissemination. Importantly, the Y5R antagonist is already available and used in clinical trials. Citation Format: Mina T. Adnani, Susana Galli, Sung Hyeok Hong, Jason U. Tilan, Joanna Kitlinska. Blocking neuropeptide Y Y5 receptor prevents hypoxia-induced Ewing sarcoma metastasis [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 6159.