Macrophage C/EBPδ Drives Gemcitabine, but Not 5-FU or Paclitaxel, Resistance of Pancreatic Cancer Cells in a Deoxycytidine-Dependent Manner

A novel DNA repair protein, N-Myc downstream regulated gene 1 (NDRG1), links stromal tumour microenvironment to chemoresistance

In pancreatic ductal adenocarcinoma cancer (PDAC) drug resistance is a severe clinical problem and patients relapse within a few months after receiving the standard-of-care chemotherapy. One contributing factor to treatment resistance is the desmoplastic nature of PDAC; the tumours are surrounded by thick layers of stroma composing up to 90% of the tumour mass. This stroma, which is mostly comprised of extracellular matrix (ECM) proteins, is secreted by cancer-associated fibroblasts (CAFs) residing in the tumour microenvironment. However, the mechanistic basis by which the tumour stroma directly contributes to chemoresistance remains unclear. Here, we show that CAF-secreted ECM proteins induce chemoresistance by blunting chemotherapy-induced DNA damage. Mechanistically, we identify N-myc downstream regulated gene 1 (NDRG1) as a key protein required for stroma-induced chemoresistance that responds to signals from the ECM and adhesion receptors. We further show that NDRG1 is a novel DNA repair protein that physically interacts with replication forks, maintains DNA replication and functions to resolve stalled forks caused by chemotherapy. More specifically, NDRG1 reduces R-loops, RNA-DNA hybrids that are known to cause genomic instability. R-loops occur during replication-transcription conflicts in S-phase and after chemotherapy treatments, thus posing a major threat to normal replication fork homeostasis. We identify NDRG1 as highly expressed in PDAC tumours, and its high expression correlates with chemoresistance and poor disease-specific survival. Importantly, knock-out of NDRG1 or inhibition of its phosphorylation restores chemotherapy-induced DNA damage and resensitizes tumour cells to treatment. In conclusion, our data reveal an unexpected role for CAF-secreted ECM proteins in enhancing DNA repair via NDRG1, a novel DNA repair protein, directly linking tumour stroma to replication fork homeostasis and R-loop biology, with important therapeutic implications for restoring DNA damage response pathways in pancreatic cancer.

Summary paragraph

Drug resistance is a severe clinical problem in stroma-rich tumours, such as pancreatic ductal adenocarcinoma (PDAC), and patients often relapse within a few months on chemotherapy 1-9 . The stroma, comprised of extracellular matrix (ECM) proteins, is secreted by cancer-associated fibroblasts (CAFs) residing in the tumour microenvironment 10-13 . Prior work show that ECM proteins provide survival benefits to cancer cells 14,15 . However, the precise role of CAF-secreted ECM in resistance to DNA damaging chemotherapies remains poorly understood. Here, we link ECM proteins to chemoresistance by enhanced DNA damage repair (DDR). Mechanistically, we identify N-myc downstream-regulated gene 1 (NDRG1) as a key effector downstream of ECM and the integrin-Src-SGK1-signalling axis that mediates enhanced DDR. We show that NDRG1 loss, mutation of conserved His194, or inhibition of NDRG1 phosphorylation by SGK1 lead to replication fork stalling, increased R-loops, and higher transcription-replication conflicts, resulting in genomic instability and sensitivity to chemotherapies. Our analysis of PDAC patient cohorts 16 found that high NDRG1 expression correlates with chemoresistance and poor patient survival. In conclusion, we uncover an unexpected role for CAF-secreted ECM proteins in promoting therapeutic resistance by enhancing DDR and establish NDRG1 as a novel DNA repair protein directly linking tumour stroma to DDR.

A stumbling block in pancreatic cancer treatment: drug resistance signaling networks

The primary node molecules in the cell signaling network in cancer tissues are maladjusted and mutated in comparison to normal tissues, which promotes the occurrence and progression of cancer. Pancreatic cancer (PC) is a highly fatal cancer with increasing incidence and low five-year survival rates. Currently, there are several therapies that target cell signaling networks in PC. However, PC is a "cold tumor" with a unique immunosuppressive tumor microenvironment (poor effector T cell infiltration, low antigen specificity), and targeting a single gene or pathway is basically ineffective in clinical practice. Targeted matrix therapy, targeted metabolic therapy, targeted mutant gene therapy, immunosuppressive therapy, cancer vaccines, and other emerging therapies have shown great therapeutic potential, but results have been disappointing. Therefore, we summarize the identified and potential drug-resistant cell signaling networks aimed at overcoming barriers to existing PC therapies.

Mechanisms of Berberine in anti-pancreatic ductal adenocarcinoma revealed by integrated multi-omics profiling

This study integrates pharmacology databases with bulk RNA-seq and scRNA-seq to reveal the latent anti-PDAC capacities of BBR. Target genes of BBR were sifted through TargetNet, CTD, SwissTargetPrediction, and Binding Database. Based on the GSE183795 dataset, DEG analysis, GSEA, and WGCNA were sequentially run to build a disease network. Through sub-network filtration acquired PDAC-related hub genes. A PPI network was established using the shared genes. Degree algorithm from cytoHubba screened the key cluster in the network. Analysis of differential mRNA expression and ROC curves gauged the diagnostic performance of clustered genes. CYBERSORT uncovered the potential role of the key cluster on PDAC immunomodulation. ScRNA-seq analysis evaluated the distribution and expression profile of the key cluster at the single-cell level, assessing enrichment within annotated cell subpopulations to delineate the target distribution of BBR in PDAC. We identified 425 drug target genes and 771 disease target genes, using 57 intersecting genes to construct the PPI network. CytoHubba anchored the top 10 highest contributing genes to be the key cluster. mRNA expression levels and ROC curves confirmed that these genes showed good robustness for PDAC. CYBERSORT revealed that the key cluster influenced immune pathways predominantly associated with Macrophages M0, CD8 T cells, and naïve B cells. ScRNA-seq analysis clarified that BBR mainly acted on epithelial cells and macrophages in PDAC tissues. BBR potentially targets CDK1, CCNB1, CTNNB1, CDK2, TOP2A, MCM2, RUNX2, MYC, PLK1, and AURKA to exert therapeutic effects on PDAC. The mechanisms of action appear to significantly involve macrophage polarization-related immunological responses.

Targeting tumor-associated macrophages to reverse antitumor drug resistance

Currently, antitumor drugs show limited clinical outcomes, mainly due to adaptive resistance. Clinical evidence has highlighted the importance of the tumor microenvironment (TME) and tumor-associated macrophages (TAMs) in tumor response to conventional antitumor drugs. Preclinical studies show that TAMs following antitumor agent can be reprogrammed to an immunosuppressive phenotype and proangiogenic activities through different mechanisms, mediating drug resistance and poor prognosis. Potential extrinsic inhibitors targeting TAMs repolarize to an M1-like phenotype or downregulate proangiogenic function, enhancing therapeutic efficacy of anti-tumor therapy. Moreover, pharmacological modulation of macrophages that restore the immune stimulatory characteristics is useful to reshaping the tumor microenvironment, thus further limiting tumor growth. This review aims to introduce macrophage response in tumor therapy and provide a potential therapeutic combination strategy of TAM-targeting immunomodulation with conventional antitumor drugs.

Crude polysaccharide from Danggui Buxue decoction enhanced the anti-tumor effect of gemcitabine by remodeling tumor-associated macrophages

Tumor-associated macrophages (TAMs) with an M2-phenotype mediate gemcitabine resistance to cancer by influencing the metabolic enzymes of gemcitabine and releasing competitive deoxycytidine (dC). Our previous studies showed that Danggui Buxue Decoction (DBD), a traditional Chinese medicinal recipe, enhances the anti-tumor activity of gemcitabine in vivo and alleviates gemcitabine-induced myelosuppression. However, the material basis and exact mechanism underlying its enhanced effects remain unclear. In this study, a bioactive polysaccharide consisting of arabinose, mannose, ribose, and glucose was isolated from DBD. In vivo results demonstrated that DBD crude polysaccharide (DBDP) ameliorated gemcitabine-induced immune system disorders. Moreover, DBDP improved the sensitivity of Lewis lung carcinoma-bearing mice to gemcitabine by reshaping the tumor-promoting M2-like macrophages into tumor-inhibiting M1-phenotypes. Furthermore, in vitro results further revealed that DBDP blocked the protective effects of TAMs and M2-macrophages against gemcitabine by inhibiting the excessive secretion of dC and decreasing the high expression of cytidine deaminase. In conclusion, our results demonstrated that DBDP, as the pharmacodynamic material basis of DBD, enhanced the anti-tumor activity of gemcitabine against lung cancer in vitro and in vivo, which was associated with remodeling of the M2-phenotype.

The Dual Role of C/EBPδ in Cancer

CCAAT/Enhancer-Binding Protein delta (C/EBPδ) is a transcription factor involved in differentiation and inflammation. While sparsely expressed in adult tissues, aberrant expression of C/EBPδ has been associated with different cancers. Initially, re-expression of C/EBPδ in cell cultures limited tumor cell proliferation, assigning it a tumor suppressor role. However, opposing observations were made in pre-clinical models and patients, suggesting that C/EBPδ not only mediates cell proliferation but dictates a broader spectrum of tumorigenesis-related effects. It is now widely accepted that C/EBPδ contributes to an inflammatory, tumor-promoting microenvironment, aids hypoxia adaption and contributes to the recruitment of blood vessels for improved nutrient supply to tumor cells and facilitated extravasation. This review summarizes the work published on this transcription factor in the field of cancer over the past decade. It points out areas in which a consensus on C/EBPδ's role appears to emerge and seek to explain seemingly contradictory results.

C/EBP-Family Redundancy Determines Patient Survival and Lymph Node Involvement in PDAC

Pancreatic ductal adenocarcinoma (PDAC) is a dismal disease with a poor clinical prognosis and unsatisfactory treatment options. We previously found that the transcription factor CCAAT/Enhancer-Binding Protein Delta (C/EBPδ) is lowly expressed in PDAC compared to healthy pancreas duct cells, and that patient survival and lymph node involvement in PDAC is correlated with the expression of C/EBPδ in primary tumor cells. C/EBPδ shares a homologous DNA-binding sequence with other C/EBP-proteins, leading to the presumption that other C/EBP-family members might act redundantly and compensate for the loss of C/EBPδ. This implies that patient stratification could be improved when expression levels of multiple C/EBP-family members are considered simultaneously. In this study, we assessed whether the quantification of C/EBPβ or C/EBPγ in addition to that of C/EBPδ might improve the prediction of patient survival and lymph node involvement using a cohort of 68 resectable PDAC patients. Using Kaplan-Meier analyses of patient groups with different C/EBP-expression levels, we found that both C/EBPβ and C/EBPγ can partially compensate for low C/EBPδ and improve patient survival. Further, we uncovered C/EBPβ as a novel predictor of a decreased likelihood of lymph node involvement in PDAC, and found that C/EBPβ and C/EBPδ can compensate for the lack of each other in order to reduce the risk of lymph node involvement. C/EBPγ, on the other hand, appears to promote lymph node involvement in the absence of C/EBPδ. Altogether, our results show that the redundancy of C/EBP-family members might have a profound influence on clinical prognoses and that the expression of both C/EPBβ and C/EBPγ should be taken into account when dichotomizing patients according to C/EBPδ expression.

Role of the Tumor Microenvironment in Regulating Pancreatic Cancer Therapy Resistance

Pancreatic cancer has a notoriously poor prognosis, exhibits persistent drug resistance, and lacks a cure. Unique features of the pancreatic tumor microenvironment exacerbate tumorigenesis, metastasis, and therapy resistance. Recent studies emphasize the importance of exploiting cells in the tumor microenvironment to thwart cancers. In this review, we summarize the hallmarks of the multifaceted pancreatic tumor microenvironment, notably pancreatic stellate cells, tumor-associated fibroblasts, macrophages, and neutrophils, in the regulation of chemo-, radio-, immuno-, and targeted therapy resistance in pancreatic cancer. The molecular insight will facilitate the development of novel therapeutics against pancreatic cancer.