421P - Triggering anti-GBM immune response with EGFR-mediated photoimmunotherapy

Abstract

BackgroundGlioblastoma (GBM) employs a variety of mechanisms to suppress the tumour immune microenvironment. A therapeutic approach aiming to abolish immunosuppressive cells and activate anti-GBM immunity would provide a powerful treatment strategy against GBM. We investigated whether photoimmunotherapy (PIT) targeting epidermal growth factor receptor (EGFR) can promoteT cell activation, whilst overcoming the immunologically cold status of GBM. MethodsThe phthalocyanine dye (IR700) was conjugated to affibody molecule (ZEGFR:03115). Cell viability, reactive oxygen species (ROS) production and major damage associated molecular patterns (calreticulin (CRT), heat shock protein 70 (Hsp70), high mobility group box 1 (HMGB1), and ATP) were studied in human and murine glioma cell lines post-ZEGFR:03115–IR700 PIT using flow cytometry (FC), Western blot and ELISA. Maturation of dendritic cells (DCs) stimulated by ZEGFR:03115-IR700 PIT was verified by FC. Xenografts and syngeneic murine tumour models (subcutaneous and orthotopic) were used to determine therapeutic and tumour-specific immune response following PIT. Post-treatment tumours were evaluated ex vivo. ResultsCells treated with ZEGFR:03115–IR700 PIT showed a significant decrease in cell viability. Generation of ROS post-PIT resulted in translocation of CRT to the cell membrane and the release of HMGB1, Hsp70 and ATP. FC analysis showed significant increase in the surface expression of CD86 and HLA-DR molecules on DCs stimulated by ZEGFR:03115–IR700 PIT compared to the negative controls. In vivo, PIT led to a significant delay in subcutaneous tumour growth. A therapeutic efficacy of the conjugate was observed in brain tumours as early as 24h post-irradiation. Ki-67, CD31, H&E staining of tumour sections showed a reduced cell proliferation index, distinct differences in vessel density, extensive tumour necrosis and microhaemorrhage on the margins of the treated tumours. In addition, tumour-infiltrating lymphocytes were elevated in the treated mice compared with the controls. ConclusionsEGFR-targeted PIT is an attractive therapeutic strategy that boosts the anti-tumour T cell response which might influence the suppressed immune microenvironment in GBM patients. Legal entity responsible for the studyThe authors. FundingThe Institute of Cancer Research; The National Science Centre (NCNOPUS13#2017/25/B/NZ5/00039); and CRUK Convergence Science Centre Fund. DisclosureAll authors have declared no conflicts of interest.