Tumor-Derived CCL2 Mediates Resistance to Radiotherapy in Pancreatic Ductal Adenocarcinoma

Abstract

Purpose Local tumor growth is a major cause of morbidity and mortality in nearly 30% of patients with pancreatic ductal adenocarcinoma (PDAC). Radiotherapy (RT) is commonly used for local disease control in PDAC, but efficacy is limited. We studied the impact of selectively intervening on RT-induced inflammation as an approach to overcome resistance to RT in PDAC. Experimental Design PDAC cell lines derived from primary pancreatic tumors arising spontaneously in KrasLSL-G12D/+;Trp53LSL-R172H/+;Pdx-1 Cre (KPC) mice were implanted into syngeneic mice and tumors were focally irradiated using the Small Animal Radiation Research Platform (SARRP). We determined the impact of depleting T cells and Ly6C+ monocytes as well as inhibiting the chemokine CCL2 on RT efficacy. Tumors were analyzed by flow cytometry and immunohistochemistry to detect changes in leukocyte infiltration, tumor viability and vascularity. Assays were performed on tumor tissues to detect cytokines and gene expression. Results Ablative RT alone had minimal impact on PDAC growth but led to a significant increase in CCL2 production by tumor cells and recruitment of Ly6C+CCR2+ monocytes. A neutralizing anti-CCL2 antibody selectively inhibited RT-dependent recruitment of monocytes/macrophages and delayed tumor growth but only in combination with RT (p<0.001). This anti-tumor effect was associated with decreased tumor proliferation and vascularity. Genetic deletion of CCL2 in PDAC cells also improved RT efficacy. Conclusions PDAC responds to RT by producing CCL2, which recruits Ly6C+CCR2+ monocytes to support tumor proliferation and neovascularization after RT. Disrupting the CCL2-CCR2 axis in combination with RT holds promise for improving RT efficacy in PDAC.

Inflammatory Monocytes Promote Perineural Invasion via CCL2-Mediated Recruitment and Cathepsin B Expression

“…Notably, in vivo studies of human tumors have demonstrated that cancer cells can also release CCL2 (4, 13). The stimuli that trigger cancer CCL2 secretion are not fully understood, although in pancreatic cancer this may occur in response to treatment (45). While our data support other evidence from nerve repair studies showing that Schwann cells are an important source of CCL2, nerve invasion develops within the context of a complex tumor microenvironment in which there may be additional cellular sources of CCL2 that vary as a function of disease progression and treatment.…”

IL6 Receptor Blockade Enhances Chemotherapy Efficacy in Pancreatic Ductal Adenocarcinoma

“…Previously described murine PDAC cell lines derived from KPC mice backcrossed onto the B6 background were used including 152.PDA (derived August 2012) (10), 7940B.PDA (derived June 2013) (12), and 69.PDA (derived August 2012) (24). Cell lines were authenticated based on histologic analysis of the implanted cell line with comparison to the primary tumor from which the cell line was derived.…”

“…Inhibiting the recruitment of myeloid cells to tumors using inhibitors of chemokine receptor signaling pathways (e.g. CCL2/CCR2) can enhance the efficacy of chemotherapy and radiotherapy (8–10). Myeloid cell depletion using a colony stimulating factor 1 receptor (CSF1R) inhibitor has also been shown to enhance the efficacy of chemotherapy in PDAC mouse models (11).…”

Role of the immunosuppressive microenvironment in immunotherapy

“…In preclinical studies, macrophages are the most abundant infiltrating cell in the tumor stroma after tumor irradiation and exhibit M2 properties that suppress subsequent immune responses 53, 61, 62. Depleting macrophages with anti–colony stimulating factor 1 antibodies or chemokine ligand 2 blockade slowed growth and improved responses to immune therapy and ionizing radiation in a number of tumor models 63, 64. Apart from depletion, several strategies have been demonstrated to repolarize macrophages to an M1 phenotype, which restores adaptive immune control of tumors 65 .…”