Abstract B13: Perineural invasion in Ewing sarcoma—a novel mechanism and new therapeutic opportunities

Tumor dissemination and relapse are the major problems in Ewing sarcoma (ES) treatment, yet the mechanisms driving these processes are unknown. To elucidate the routes of ES metastatic spread, we used an orthotopic xenograft model. ES cells were injected into the gastrocnemius muscles of SCID/beige mice. Once the primary tumors reached the desired volume, they were excised by limb amputation. Subsequently, tumor dissemination was monitored by MRI and confirmed by histopathologic analysis. Interestingly, aside from typical hematogenous metastases, such as bone and lung lesions, we have also observed frequent perineural tumor dissemination manifested by the presence of migratory ES cells along the nerves adjacent to the primary tumors. This phenomenon was associated with formation of recurrent tumors at the amputation sites, as well as pelvic tumors with spine involvement. Interestingly, the level of perineural invasion (PNI) was dependent on the expression of neuropeptide Y (NPY) in ES cells. NPY is a neuronal protein released from peripheral sympathetic neurons, but also highly expressed in ES cells along with its receptors. The xenografts derived from ES cell lines not releasing endogenous NPY (TC71, TC32) exhibited frequent PNI in tumor-bearing limbs, as well as a high number of recurrent tumors at the surgery site and spine metastases (70% and 100% of mice with evidence of PNI for TC71 and TC32 xenografts, respectively). This phenomenon was less common in ES xenografts derived from NPY-rich SK-ES1 cells (17% of mice with signs of PNI). In line with these observations, NPY knockdown in SK-ES1 xenografts drastically accelerated formation of spinal tumors (60% of mice). Notably, in 40% of mice bearing SK-ES1/NPY shRNA xenografts the spinal tumors developed before the primary tumor growth was detectable at the site of ES cell injection. Thus, our in vivo experiments suggested that a lack of endogenous NPY in ES cells expressing high levels of its receptors triggers chemotactic effects of this peptide released from neighboring peripheral nerves, facilitating PNI. Indeed, in a transwell migration assay, NPY exerted significant chemotactic activity in SK-ES1/NPY shRNA cells, but not in the original SK-ES1 cell line. An even more profound chemotactic effect specific to the SK-ES1/NPY shRNA cells was observed with NPY-rich conditioned media obtained from neuroblastoma cells, which can serve as a model of peripheral sympathetic neurons. Further studies are required to determine which NPY receptors are responsible for its chemotactic properties. If the presence of perineural tumor growth is confirmed in human tumors, factors responsible for PNI in ES, e.g., NPY receptors, may become targets for novel therapies preventing disease dissemination and recurrence. Citation Format: Susana Galli, Sung-Hyeok Hong, Jason U. Tilan, Mina Adnani, Shiya Zhu, Yassi Fallah, Yi-Chien Lee, Olga Rodriguez, Chris Albanese, Ewa Izycka-Swieszewska, Joanna Kitlinska. Perineural invasion in Ewing sarcoma—a novel mechanism and new therapeutic opportunities [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr B13.