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Rapid Monocyte Recruitment Dictates the Therapeutic Efficacy of Focal Radiotherapy

ABSTRACT: The recruitment of monocytes and their differentiation into immunosuppressive cells is associated with the negative outcome of non-conformal radiotherapy (RT). However, non-conformal RT is irrelevant in the clinic, and little is known about the role of monocytes following radiotherapy modes used in patients, such as conformal radiotherapy (CRT). Here, we investigated the acute immune infiltration post-CRT. Contrary to non-conformal RT approaches, we found that CRT induces a rapid and robust recruitment of monocytes to the tumor that minimally differentiate into tumor-associated macrophages (TAM) or dendritic cells (DC), but instead upregulate major histocompatibility complex II (MHCII) and costimulatory molecules. We establish that these large numbers of infiltrating monocytes are responsible for increasing type I interferon in the tumor microenvironment (TME), activation of CD8+ T cells and the reduction in tumor burden. Importantly, we demonstrate that rapid monocyte infiltration to the TME is hindered when RT inadvertently affects healthy tissues. Our results unravel a positive role of monocytes during clinically relevant modes of RT and demonstrate that limiting exposure of healthy tissues to radiation has a positive therapeutic effect on the overall immune response within the tumor.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Mus Musculus (ncbitaxon:10090)

SUBMITTER: Juliana Idoyaga

PROVIDER: MSV000089775 | MassIVE | Thu Jun 30 07:37:00 BST 2022

SECONDARY ACCESSION(S): PXD035046

REPOSITORIES: MassIVE

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Project description:Immunotherapeutics represent highly promising agents with the potential to improve patient outcomes in a variety of cancer types. Unfortunately, single-agent immunotherapy has achieved limited clinical benefit to date in patients suffering from pancreatic ductal adenocarcinoma (PDAC). This may be due to the presence of a uniquely immunosuppressive tumor microenvironment (TME) present in PDACs, which creates a barrier to effective immune surveillance. Critical obstacles to immunotherapy in PDAC tumors include the dense desmoplastic stroma that acts as a barrier to T-cell infiltration and the high numbers of tumor-associated immunosuppressive cells. We have identified hyperactivated focal adhesion kinase (FAK) activity in neoplastic PDAC cells as a significant regulator of the fibrotic and immunosuppressive TME. We found that FAK activity was elevated in human PDAC tissues and correlates with high levels of fibrosis and poor CD8+ cytotoxic T-cell infiltration. Single-agent FAK inhibition (VS-4718) dramatically limited tumor progression, resulting in a doubling of survival in the p48-Cre/LSL-KrasG12D/p53Flox/+ (KPC) mouse model of human PDAC. This alteration in tumor progression was associated with dramatically reduced tumor fibrosis, decreased numbers of tumor-infiltrating immature myeloid cells and immunosuppressive macrophages. We postulated that these desirable effects of FAK inhibition on the TME might render PDAC tumors more sensitive to immunotherapy. Accordingly, we found that VS-4718 rendered the previously unresponsive KPC mouse model responsive to anti-PD1 and anti-CTLA4 antagonists leading to a nearly tripling of survival times. These data suggest that FAK inhibition increases immune surveillance by overcoming the fibrotic and immunosuppressive PDAC TME thus rendering tumors more responsive to immunotherapy. We treated KP orthotopic tumor-bearing mice with vehicle and FAK inhibitor (FAKi) for 14 days, then extracted total RNA from tumor tissues.

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Rapid Monocyte Recruitment Dictates the Therapeutic Efficacy of Focal Radiotherapy

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