EXTH-19. The oncolytic adenovirus Delta-24-RGD achieves antitumor polarization of the chordoma tumor microenvironment in human and murine models of chordoma

Abstract Chordomas are locally aggressive neoplasms accounting for approximately 20% of primary spinal tumors. Patients experience high rates of disease progression and limited treatment options, highlighting an unmet clinical need and the importance of identifying novel therapeutic strategies for chordomas. Oncolytic viral (OV) therapy uses genetically modified viruses which selectively replicate in tumor cells, mediate tumor cell lysis, and initiate a pro-inflammatory response within the infected tumor microenvironment (TME). This study evaluates the anti-chordoma effect of the oncolytic adenovirus Delta-24-RGD. The efficacy of Delta-24-RGD was assessed using in vitro approaches, ex vivo bone scaffolds, and in vivomurine models. Additionally, we explored the underlying mechanism of OV cytotoxicity, immunogenic cell death (ICD), brachyury modulation, and reshaping of the TME towards a pro-inflammatory state. Delta-24-RGD achieved viral infectivity, oncolysis and ICD across multiple human chordoma cell lines and ex vivo bone scaffold models. Viral infection was associated with concomitant brachyury downregulation within both infected and uninfected chordoma cells in vitro. In vivo murine xenograft models of human CH22 and U-CH1 chordoma treated with Delta-24-RGD resulted in tumor volume reduction and enhanced overall survival. RNA-Seq analysis followed by Ingenuity Pathway Analysis predicted activation of tumor-associated extracellular matrix remodeling and host immune response pathways. Analyzing a human chordoma tissue microarray, the immunosuppressive macrophage marker CD163 was associated with shortened recurrence-free survival. Using macrophage/chordoma co-culture, OV infection reduced CD163 expression, induced a concomitant pro-inflammatory macrophage polarization, and enhanced cytotoxicity against chordoma cells. This synergistic cytotoxic effect was further validated in co-cultures of chordoma cell lines with healthy donor and chordoma patient-derived peripheral blood mononuclear cells (PBMCs). Lastly, histological evaluation of patient-derived chordoma tumor slice cultures confirmed infectivity of Delta-24-RGD, underscoring the clinical potential of this oncolytic virus. These studies provide a framework for future clinical translation amongst patients with recurrent or metastatic chordoma.