Efficient engineering of human and mouse primary cells using peptide-assisted genome editing

Simple, efficient and well-tolerated delivery of CRISPR genome editing systems into primary cells remains a major challenge. Here we describe an engineered Peptide-Assisted Genome Editing (PAGE) CRISPR-Cas system for rapid and robust editing of primary cells with minimal toxicity. The PAGE system requires only a 30-min incubation with a cell-penetrating Cas9 or Cas12a and a cell-penetrating endosomal escape peptide to achieve robust single and multiplex genome editing. Unlike electroporation-based methods, PAGE gene editing has low cellular toxicity and shows no significant transcriptional perturbation. We demonstrate rapid and efficient editing of primary cells, including human and mouse T cells, as well as human hematopoietic progenitor cells, with editing efficiencies upwards of 98%. PAGE provides a broadly generalizable platform for next-generation genome engineering in primary cells.

Hepatocytes direct the formation of a pro-metastatic niche in the liver

The liver is the most common site of metastatic disease1. Although this metastatic tropism may reflect the mechanical trapping of circulating tumour cells, liver metastasis is also dependent, at least in part, on the formation of a 'pro-metastatic' niche that supports the spread of tumour cells to the liver2,3. The mechanisms that direct the formation of this niche are poorly understood. Here we show that hepatocytes coordinate myeloid cell accumulation and fibrosis within the liver and, in doing so, increase the susceptibility of the liver to metastatic seeding and outgrowth. During early pancreatic tumorigenesis in mice, hepatocytes show activation of signal transducer and activator of transcription 3 (STAT3) signalling and increased production of serum amyloid A1 and A2 (referred to collectively as SAA). Overexpression of SAA by hepatocytes also occurs in patients with pancreatic and colorectal cancers that have metastasized to the liver, and many patients with locally advanced and metastatic disease show increases in circulating SAA. Activation of STAT3 in hepatocytes and the subsequent production of SAA depend on the release of interleukin 6 (IL-6) into the circulation by non-malignant cells. Genetic ablation or blockade of components of IL-6-STAT3-SAA signalling prevents the establishment of a pro-metastatic niche and inhibits liver metastasis. Our data identify an intercellular network underpinned by hepatocytes that forms the basis of a pro-metastatic niche in the liver, and identify new therapeutic targets.

Abstract 1102: IL-6/STAT3 activation in hepatocytes drives pro-metastatic niche formation in the liver

The liver is the most common site of metastasis in pancreatic ductal adenocarcinoma (PDAC). This metastatic tropism is dependent, at least in part, on the formation of a “pro-metastatic” niche that supports tumor cell seeding and colonization in the liver. However, mechanisms that direct the formation of this niche remain poorly understood. We show using the LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre (KPC) model of PDAC that pancreatic tumor development enhances the susceptibility of the liver to metastatic seeding by inducing recruitment of F4/80+ and Ly6G+ myeloid cells and fibrosis within the liver. 3' mRNA sequencing (QuantSeq) on RNA isolated from the liver of KPC mice versus control PC mice revealed that the liver produces a specific set of myeloid chemoattractants, particularly serum amyloid A1 and A2 (SAA1/2), early during PDAC development. In addition, gene set enrichment analysis (GSEA) on genes upregulated in the liver of KPC mice demonstrated a significant enrichment of the interleukin 6 (IL-6)/Signal Transducer and Activator of Transcription 3 (STAT3) signaling pathway. Consistent with this finding, phosphorylation of STAT3 was detected in 20-30% of F4/80+ myeloid cells and 80-90% of hepatocytes. A requirement for IL-6/STAT3 signaling in the formation of a pro-metastatic niche was determined by comparing the metastatic potential of wild type mice, Il-6 knockout (Il-6-/-) mice, and mice treated with anti-IL-6 receptor (IL-6R) antibody after orthotopic implantation of KPC-derived PDAC cells. Compared to wild type mice, the liver of Il-6-/- mice and mice treated with anti-IL-6R antibody was less susceptible to metastatic seeding and showed significantly less accumulation of myeloid cells, fibrosis, and production of SAA1/2 in the liver. We obtained similar results with mice that lack Stat3 specifically in hepatocytes (Stat3flox/flox Alb-Cre), demonstrating that IL-6/STAT3 signaling in hepatocytes is necessary for the formation of a pro-metastatic niche in the liver. Further, using Saa1/2 double knockout (Saa-/-) mice, we found that SAA1/2 production by hepatocytes was required for formation of the pro-metastatic niche in the liver and increased susceptibility to metastatic seeding. Patients with a history of liver metastasis also showed higher levels of SAA1/2 in the plasma compared to normal donors, and SAA overexpression was detected in hepatocytes in liver biopsy samples collected from PDAC patients. Collectively, our study reveals a novel role for hepatocytes in directing the formation of a pro-metastatic niche in the liver during PDAC development and identifies IL-6/STAT3/SAA1/2 signaling as a promising therapeutic target for prevention of metastasis in PDAC.

Citation Format: Jae W. Lee, Stacy K. Thomas, Chad A. Komar, Whitney L. Gladney, Xia Hua, Dong Xin, Abraham Shaked, Mitesh J. Borad, Ramesh K. Ramanathan, Ailing Ji, Nancy R. Webb, Maria C. de Beer, Frederick C. de Beer, Paige M. Porrett, Gregory L. Beatty. IL-6/STAT3 activation in hepatocytes drives pro-metastatic niche formation in the liver [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1102.

Abstract 2682: IL-6/STAT3 activation in hepatocytes drives the formation of a pro-metastatic niche in the liver during pancreatic tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC) is the fourth-leading cause of cancer-related deaths in the United States with metastasis to the liver as the major cause of mortality. While the propensity of PDAC to spread to the liver may reflect mechanical trapping of tumor cells that enter the portal circulation, primary tumor cells have also been suggested to secrete factors that may promote recruitment of myeloid cells to establish a pro-metastatic niche. In this study, we used the LSL-KrasG12D/+;LSL-Trp53R127H/+;Pdx-1-Cre (KPC) mouse model of PDAC to investigate the impact of PDAC development on the formation of a pro-metastatic niche in the liver. We found that KPC mice (compared to age- and gender-matched control mice) demonstrated an increased susceptibility to tumor seeding in the liver even prior to development of invasive PDAC. Examination of the liver of KPC mice revealed diffuse activation of Signal Transducer and Activator of Transcription 3 (STAT3) signaling, particularly in hepatocytes. Although hepatocytes are recognized as important regulators of inflammation, their role in establishing a pro-metastatic niche is unknown. To define changes in the liver associated with development of a pro-metastatic niche, we performed QuantSeq analysis on RNA isolated from the liver of KPC versus control PC mice. Our results showed increased transcriptional levels of myeloid chemoattractants, particularly serum amyloid A proteins that are predominantly produced by hepatocytes. Consistent with this finding, we observed an accumulation of F4/80+ and Ly6G+ myeloid cells in the liver of KPC mice by immunofluorescence microscopy. We next determined the role of tumor cells in driving cellular activation seen in the liver by establishing intraperitoneal and orthotopic models of PDAC. Using these models, we found that implantation of pancreatic tumor cells induced STAT3 activation in hepatocytes and stimulated F4/80+ and Ly6G+ myeloid cell recruitment to the liver. To determine whether cellular activation in the liver was associated with systemic release of soluble factors, we performed parabiotic joining of tumor-implanted mice and control wild type mice, and we found evidence of STAT3 activation and myeloid recruitment to the liver in parabiotic pairs. As interleukin-6 (IL-6) is a key inflammatory cytokine that can activate STAT3 signaling, we hypothesized a role for IL-6 directed STAT3 activation in hepatocytes for development of a pro-metastatic niche in the liver. Consistent with this hypothesis, we found that IL-6 receptor blocking antibodies administered after tumor implantation reduced STAT3 activation in hepatocytes and decreased transcriptional levels of hepatocyte-derived chemoattractants. Together, our findings support a role for IL-6/STAT3 signaling in hepatocytes in driving a pro-metastatic niche in the liver during PDAC development.

Citation Format: Jae W. Lee, Paige M. Porrett, Chad A. Komar, Whitney L. Gladney, Gregory L. Beatty. IL-6/STAT3 activation in hepatocytes drives the formation of a pro-metastatic niche in the liver during pancreatic tumorigenesis [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 2682. doi:10.1158/1538-7445.AM2017-2682

Genetically Engineered Mouse Models of Pancreatic Cancer: The KPC Model (LSL-Kras(G12D/+) ;LSL-Trp53(R172H/+) ;Pdx-1-Cre), Its Variants, and Their Application in Immuno-oncology Drug Discovery

Pancreatic ductal adenocarcinoma (PDAC) ranks fourth among cancer-related deaths in the United States. For patients with unresectable disease, treatment options are limited and lack curative potential. Preclinical mouse models of PDAC that recapitulate the biology of human pancreatic cancer offer an opportunity for the rational development of novel treatment approaches that may improve patient outcomes. With the recent success of immunotherapy for subsets of patients with solid malignancies, interest is mounting in the possible use of immunotherapy for the treatment of PDAC. Considered in this unit is the value of genetic mouse models for characterizing the immunobiology of PDAC and for investigating novel immunotherapeutics. Several variants of these models are described, all of which may be used in drug development and for providing information on unique aspects of disease biology and therapeutic responsiveness. © 2016 by John Wiley & Sons, Inc.