Poster Presentation 36th Lorne Cancer Conference 2024

Transcriptional reprogramming of tumour associated macrophages in glioblastoma (#215)

Samuel S. Widodo 1 , Marija Dinevska 1 , Laraib A. Ali 2 3 , Miguel Á. Berrocal-Rubio 4 , Christine A. Wells 5 , Alexander D. Barrow 2 , Stanley S. Stylli 1 6 , Laura Cook 2 3 7 , Theo Mantamadiotis 1 2 5
  1. Department of Surgery (RMH), The University of Melbourne, Melbourne, VIC, Australia
  2. Department of Microbiology and Immunology, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
  3. Department of Critical Care, Melbourne Medical School, The University of Melbourne, Melbourne, VIC, Australia
  4. Department of Anatomy and Physiology, The University of Melbourne, Melbourne, VIC, Australia
  5. The Centre for Stem Cell Systems, The University of Melbourne, Melbourne, VIC, Australia
  6. Department of Neurosurgery, Royal Melbourne Hospital, Parkville, VIC, Australia
  7. Division of Infectious Diseases, Department of Medicine, University of British Columbia, Vancouver, BC, Canada

Glioblastoma (GBM) is the most common and aggressive adult primary brain cancer, characterised by an immunosuppressive tumour microenvironment (TME). Immunosuppression is largely driven by infiltrating tumour associated macrophages (TAMs), which constitute up to 30% of cells in the GBM TME. The expression of key immunosuppressive factors in macrophages is regulated by the kinase inducible transcription factor, cyclic AMP response element binding protein (CREB). We have previously shown that CREB regulates GBM oncogenesis, however little is known about the role of CREB in TAM-mediated immunosuppression.

 

To investigate this, we exposed primary human monocyte-derived and THP-1 macrophages to patient-derived GBM cell line conditioned media and analysed CREB activation and downstream signalling pathways in vitro. Western blots were used to measure the activated form of CREB, phospho-CREB (pCREB), and secreted cytokines were quantified using cytometric bead array. Multiplex immunohistochemistry (mIHC) was used to detect expression of pCREB and M2-like markers CD163 and CD206 in TAMs on primary human GBM tissue samples.

 

Following exposure to GBM conditioned media, macrophages increased CREB activation and secretion of IL-10 and CCL-2. Together, this indicates that GBM secreted factors stimulate CREB activation and promote polarisation of macrophages towards an immunosuppressive TAM phenotype. We used small molecule inhibitors to confirm these activation and polarisation effects were dependent on CREB activation and were regulated by the cyclic-AMP pathway. This was supported by our mIHC data, where pCREB and CD163 expression was detected in the majority of TAMs.

 

These data point to a key role for CREB as a transcriptional regulator of immunosuppressive TAMs in GBM. Therefore, CREB may be an effective therapeutic target, to both inhibit GBM cell intrinsic functions and reprogram the TME. Ongoing experiments are investigating the transcriptome and proteome of GBM-stimulated macrophages, treated with or without a CREB inhibitor and their subsequent effects on the function of tumour infiltrating T cells.