Mingen Liu

Tumor-derived CCL2 mediates resistance to radiotherapy in pancreatic ductal adenocarcinoma

Purpose: Local tumor growth is a major cause of morbidity and mortality in nearly 30% of patients with pancreatic ductal adenocarcinoma (PDAC). Radiotherapy is commonly used for local disease control in PDAC, but its efficacy is limited. We studied the impact of selectively intervening on radiotherapy-induced inflammation as an approach to overcome resistance to radiotherapy in PDAC. Experimental Design: PDAC cell lines derived from primary pancreatic tumors arising spontaneously in KrasLSL-G12D/+;Trp53LSL-R172H/+;Pdx-1 Cre 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 radiotherapy efficacy. Tumors were analyzed by flow cytometry and IHC to detect changes in leukocyte infiltration, tumor viability, and vascularity. Assays were performed on tumor tissues to detect cytokines and gene expression. Results: Ablative radiotherapy 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 radiotherapy-dependent recruitment of monocytes/macrophages and delayed tumor growth but only in combination with radiotherapy (P < 0.001). This antitumor effect was associated with decreased tumor proliferation and vascularity. Genetic deletion of CCL2 in PDAC cells also improved radiotherapy efficacy. Conclusions: PDAC responds to radiotherapy by producing CCL2, which recruits Ly6C+CCR2+ monocytes to support tumor proliferation and neovascularization after radiotherapy. Disrupting the CCL2–CCR2 axis in combination with radiotherapy holds promise for improving radiotherapy efficacy in PDAC. Clin Cancer Res; 23(1); 137–48. ©2016 AACR.

Functio Laesa: Cancer Inflammation and Therapeutic Resistance

Tumor, calor, rubor, and dolor describe four cardinal signs of inflammation. The fifth-functio laesa, or loss of function-was promulgated by Rudolf Virchow, who, in the 19th century, also noted an intricate link between inflammation and cancer. However, the role of cancer inflammation in driving loss of therapeutic efficacy has only recently been fully appreciated, as a result of molecular and immunohistochemical approaches applied in clinical medicine and the availability of novel agents for modulating inflammation. This review focuses on clinical evidence from solid malignancies that have shaped our view of how the immune system regulates cancer development, progression, and response to treatment. Understanding the multifaceted relationship between inflammation and patient outcomes has the potential to advance prognostic tools and uncover therapeutic opportunities for improving clinical outcomes.

Lysosomes support the degradation, signaling, and mitochondrial metabolism necessary for human epidermal differentiation

Keratinocytes undergo significant structural remodeling during epidermal differentiation, including a broad transformation of the proteome coupled with a reduction in total cellular biomass. This suggests that intracellular digestion of proteins and organelles is necessary for keratinocyte differentiation. Here, we use both genetic and pharmacologic approaches to demonstrate that autophagy and lysosomal functions are required for keratinocyte differentiation in organotypic human skin. Lysosomal activity was required for mechanistic target of rapamycin signaling and mitochondrial oxidative metabolism. In turn, mitochondrial reactive oxygen species, produced as a natural byproduct of oxidative phosphorylation, were necessary for keratinocyte differentiation. Finally, treatment with exogenous reactive oxygen species rescued the differentiation defect in lysosome-inhibited keratinocytes. These findings highlight a reciprocal relationship between lysosomes and mitochondria, in which lysosomes support mitochondrial metabolism and the associated production of mitochondrial reactive oxygen species. The mitochondrial reactive oxygen species released to the cytoplasm in suprabasal keratinocytes triggers autophagy and lysosome-mediated degradation necessary for epidermal differentiation. As defective lysosome-dependent autophagy is associated with common skin diseases including psoriasis and atopic dermatitis, a better understanding of the role of lysosomes in epidermal homeostasis may guide future therapeutic strategies.

Abstract 4621: Metabolic activation of macrophages by CpG stimulates anti-tumor activity and overcomes CD47-independent inhibition by tumor cells in pancreatic ductal adenocarcinoma

Macrophages dominate the immune infiltrate present in pancreatic ductal adenocarcinoma (PDAC). Although tumor-infiltrating macrophages have the potential to mediate anti-tumor activity, they most commonly acquire an immunosuppressive role in cancer. We have found that CpG oligonucleotides - containing unmethylated cytosine-guanine motifs - potently induce macrophages to phagocytose PDAC cells and mediate anti-tumor effects. When delivered in vivo, in a fully immunocompetent murine model of PDAC, CpG increased the presence of macrophages within PDAC tumors and suppressed tumor outgrowth in a macrophage-dependent manner. Though CpG did not polarize macrophages toward classical anti-tumor (M1) or pro-tumor (M2) phenotypes, CpG treatment increased the basal rate of oxygen consumption in macrophages. Reversing this metabolic shift by inhibiting fatty acid oxidation abolished pro-phagocytic and anti-tumor effects by macrophages in vitro and in vivo. We investigated the impact of CpG in overcoming anti-phagocytic signals from CD47, a membrane protein overexpressed in multiple malignancies, including PDAC. While targeted knockout of CD47 in PDAC cells was not sufficient to activate in vitro phagocytosis by macrophages or anti-tumor effects in vivo, delivery of CpG potentiated anti-tumor and phagocytic activity that was independent of CD47 expression by tumor cells. However, the combination of CD47 loss in tumor cells and systemic CpG treatment enhanced the survival of tumor-bearing mice, indicating that disruption of CD47 can sensitize tumors to macrophage-directed immunotherapy. Together, our findings demonstrate a key role for cellular metabolism in directing the anti-tumor functions of macrophages and overcoming negative regulatory signals imposed by malignant cells. Citation Format: Mingen Liu, Gregory Beatty. Metabolic activation of macrophages by CpG stimulates anti-tumor activity and overcomes CD47-independent inhibition by tumor cells in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4621. doi:10.1158/1538-7445.AM2017-4621