Natural killer cells and their therapeutic role in pancreatic cancer: A systematic review. Pharmacol Ther. 2018;189:31-44. [PMID: 29660367 DOI: 10.1016/j.pharmthera.2018.04.003]

The power and the promise of CAR-mediated cell immunotherapy for clinical application in pancreatic cancer

BACKGROUND

Pancreatic cancer, referred to as the "monarch of malignancies," is a neoplastic growth mostly arising from the epithelial cells of the pancreatic duct and acinar cells. This particular neoplasm has a highly unfavorable prognosis due to its marked malignancy, inconspicuous initial manifestation, challenging early detection, rapid advancement, and limited survival duration. Cellular immunotherapy is the ex vivo culture and expansion of immune effector cells, granting them the capacity to selectively target malignant cells using specialized techniques. Subsequently, these modified cells are reintroduced into the patient's organism with the purpose of eradicating tumor cells and providing therapeutic intervention for cancer.

PRESENT SITUATION

Presently, the primary cellular therapeutic modalities employed in the treatment of pancreatic cancer encompass CAR T-cell therapy, TCR T-cell therapy, NK-cell therapy, and CAR NK-cell therapy.

AIM OF REVIEW

This review provides a concise overview of the mechanisms and primary targets associated with various cell therapies. Additionally, we will explore the prospective outlook of cell therapy in the context of treating pancreatic cancer.

Pancreatic ductal adenocarcinoma microenvironment: Soluble factors and cancer associated fibroblasts as modulators of NK cell functions

Pancreatic Ductal Adenocarcinoma (PDAC) is the most frequent pancreatic cancer and represents one of the most aggressive human neoplasms. Typically identified at advance stage disease, most PDAC tumors are unresectable and resistant to standard therapies. The immunosuppressive microenvironment in PDAC impedes tumor control but a greater understanding of the complex stromal interactions within the tumor microenvironment (TME) and the development of strategies capable of restoring antitumor effector immune responses could be crucial to fight this aggressive tumor and its spread. Natural Killer (NK) cells play a crucial role in cancer immunosurveillance and represent an attractive target for immunotherapies, both as cell therapy and as a pharmaceutical target. This review describes some crucial components of the PDAC TME (collagens, soluble factors and fibroblasts) that can influence the presence, phenotype and function of NK cells in PDAC patients tumor tissue. This focused overview highlights the therapeutic relevance of dissecting the complex stromal composition to define new strategies for NK cell-based immunotherapies to improve the treatment of PDAC.

Natural killer cells associate with epithelial cells in the pancreatic ductal adenocarcinoma tumor microenvironment

Background

Pancreatic ductal adenocarcinoma (PDAC) is the most common form of pancreatic cancer. PDAC's poor prognosis and resistance to immunotherapy are attributed in part to its dense, fibrotic tumor microenvironment (TME), which is known to inhibit immune cell infiltration. We recently demonstrated that PDAC patients with higher natural killer (NK) cell content and activation have better survival rates. However, NK cell interactions in the PDAC TME have yet to be deeply studied. We show here that NK cells are present and active in the human PDAC TME.

Methods

We used imaging mass cytometry (IMC) to assess NK cell content, function, and spatial localization in human PDAC samples. Then, we used CellChat, a tool to infer ligand-receptor interactions, on a human PDAC scRNAseq dataset to further define NK cell interactions in PDAC.

Results

Spatial analyses showed for the first time that active NK cells are present in the PDAC TME, and both associate and interact with malignant epithelial cell ducts. We also found that fibroblast-rich, desmoplastic regions limit NK cell infiltration in the PDAC TME. CellChat analysis identified that the CD44 receptor on NK cells interacts with PDAC extracellular matrix (ECM) components such as collagen, fibronectin and laminin expressed by fibroblasts and malignant epithelial cells. This led us to hypothesize that these interactions play roles in regulating NK cell motility in desmoplastic PDAC TMEs. Using 2D and 3D in vitro assays, we found that CD44 neutralization significantly increased NK cell invasion through matrix.

Conclusions

Targeting ECM-immune cell interactions may increase NK cell invasion into the PDAC TME.

Vitamin B6 Competition in the Tumor Microenvironment Hampers Antitumor Functions of NK Cells

Nutritional factors play crucial roles in immune responses. The tumor-caused nutritional deficiencies are known to affect antitumor immunity. Here, we demonstrate that pancreatic ductal adenocarcinoma (PDAC) cells can suppress NK-cell cytotoxicity by restricting the accessibility of vitamin B6 (VB6). PDAC cells actively consume VB6 to support one-carbon metabolism, and thus tumor cell growth, causing VB6 deprivation in the tumor microenvironment. In comparison, NK cells require VB6 for intracellular glycogen breakdown, which serves as a critical energy source for NK-cell activation. VB6 supplementation in combination with one-carbon metabolism blockage effectively diminishes tumor burden in vivo. Our results expand the understanding of the critical role of micronutrients in regulating cancer progression and antitumor immunity, and open new avenues for developing novel therapeutic strategies against PDAC.

SIGNIFICANCE

The nutrient competition among the different tumor microenvironment components drives tumor growth, immune tolerance, and therapeutic resistance. PDAC cells demand a high amount of VB6, thus competitively causing NK-cell dysfunction. Supplying VB6 with blocking VB6-dependent one-carbon metabolism amplifies the NK-cell antitumor immunity and inhibits tumor growth in PDAC models. This article is featured in Selected Articles from This Issue, p. 5.

Optimizing the cryopreservation and post-thaw recovery of natural killer cells is critical for the success of off-the-shelf platforms

Natural killer (NK) cells are a promising allogeneic, off-the-shelf, cellular immunotherapy product. These cells can be manipulated ex vivo, genetically edited to enhance tumor targeting and expanded to produce large cell banks for multiple patient infusions. Therapeutic efficacy of these products depends on the recovery of viable and functional cells post-thaw. Post-thaw loss of viability and cytolytic activity results in large, and often variable, discrepancies between the intended cell dose (based on counts at cryopreservation) and the actual dose administered. Compared to their highly activated state in fresh culture, post-thaw NK cells demonstrate critical changes in cytokine production, cytotoxic activity, in vivo proliferation and migration. When these NK cells are introduced into the highly immunosuppressive tumor microenvironment, the functional changes induced by cryopreservation further limits the clinical potential of these products. This report will review the impact of cryopreservation on ex vivo expanded NK cells and outlines strategies described in published studies to recover post-thaw function.

Novel strategies optimize immunotherapy by improving the cytotoxic function of T cells for pancreatic cancer treatment

Pancreatic cancer (PC) is considered highly malignant due to its unsatisfying prognosis and limited response to therapies. Immunotherapy has therefore been developed to harness the antigen-specific properties and cytotoxicity of the immune system, aiming to induce a robust anti-tumor immune response that specifically demolishes PC cells while minimizing lethality in healthy tissue. The activation and augmentation of cytotoxic T cells play a critical role in the initiation and final success of immunotherapy. PC, however, is often immunotherapy resistant due to its intrinsic immunosuppressive tumor microenvironment that consequently hampers effective T cell priming. Emerging therapeutic approaches are orientated to modulate the tumor microenvironment in PC to enhance immune system involvement and heighten T cell efficacy. These novel strategies have shown promising therapeutic effects in the treatment of PC either as standalone approaches or combinatorial with other therapeutic schemes. The objective of this article is to explore innovative approaches to optimize immunotherapy for PC patients through T cell cytotoxic function augmentation.

Acute toxicities of intravenous, intraperitoneal, or intratumoral injection of natural killer cells in human pancreatic adenocarcinoma-bearing mice: Randomized study

AIMS

To investigate the possible acute toxicities and pathological changes associated with intravenous, intraperitoneal, or intratumoral injection of natural killer (NK) cells in mice subcutaneously bearing human pancreatic adenocarcinoma (PaC).

METHODS

100 NPG tumor-bearing mice (50/sex) were engrafted subcutaneously with human PaC BXPC-3 cells 9 days before administration. They were randomly divided into 10 groups with 5 males and 5 females in each group. Mice in Group 1 were given sodium chloride intravenously as vehicle control, and mice in Groups 2-4 human peripheral blood-derived NK cells intravenously at doses of 2 × 107, 1 × 108, and 5 × 108 cells/kg, respectively; mice in Groups 5-7 were injected with NK cells intraperitoneally at doses of 2 × 107, 1 × 108, and 5 × 108 cells/kg, respectively, and mice in Groups 8-10 with NK cells intratumorally at doses of 4 × 103, 2 × 104, and 1 × 105 cells/mm3, respectively. Each group was given a single dose; the mice were observed clinically, and body weight, food intake, blood biochemistry, and tumor volume were measured. On Day 15, the mice were euthanized for gross anatomy and histopathology.

RESULTS

On planned euthanasia, in Groups 2-4 no gross or microscopic pathological changes related to cells injection were found; in Groups 5-7 mice of both sexes showed a decrease in extramedullary hematopoiesis of spleen, and at the dose of 5 × 108 cells/kg, mice of both sexes showed an increase in the composition of spleen white pulp cells. In Groups 8-10, mice of both sexes at doses of 4 × 103 and 1 × 105 cells/mm3 and female mice at the dose of 2 × 104 cells/mm3 showed a decrease in extramedullary hematopoiesis of spleen, and female mice at a dose of 4 × 103 cells/mm3 and mice of both sexes at doses of ≥ 2 × 104 cells/mm3 showed an increase in the composition of spleen white pulp cells; perivascular/peribronchiolar inflammatory cell infiltration in lung and bronchus was observed in mice of both sexes at doses of ≥ 2 × 104 cells/mm3, and inflammatory cell infiltration in liver was observed in mice of both sexes at a dose of 1 × 105 cells/mm3. No other abnormal changes with toxicological significance in clinical observation, body weight, food intake, or blood biochemistry were observed in each group.

CONCLUSIONS

In our study intravenous injection appears the safest way to give NK cells to human PaC-bearing mice. Using intraperitoneal or intratumoral administration, spleen, liver, and lung were the most often affected organs, albeit with mostly mild pathological changes.

The SIX1/LDHA Axis Promotes Lactate Accumulation and Leads to NK Cell Dysfunction in Pancreatic Cancer

Background

Pancreatic cancer (PC) is a malignant cancer with poor prognosis and high mortality rate. Sine oculis homeobox homolog 1 (SIX1) participates in the development of many cancers. However, the function of SIX1 in PC is not fully understood.

Methods

SIX1 expression was determined using immunohistochemistry in PC tissues and cell lines. Glucose consumption, lactate production, and ATP assays were used to detect the function of SIX1. PC cells and NK cells were cocultured to study the effect of SIX1 overexpression in PC cells on NK cell function. Chromatin immunoprecipitation (ChIP) assays were used to study the relationship between SIX1 and lactate dehydrogenase A (LDHA). A series of in vitro and in vivo assays were further applied to elucidate the important role of the SIX1/LDHA axis in metabolism and NK cell dysfunction in PC.

Results

SIX1 was significantly upregulated in PC tissue; SIX1 overexpression promoted the glycolysis capacity of PANC-1 and CFPAC-1 cells and resulted in NK cell dysfunction after the NK cells had been cultured with PC cells. LDHA inhibitor partially restored the promotion of PC caused by SIX1 overexpression. According to ChIP assays, SIX1 directly binds to the LDHA promoter region. Moreover, LDHA inhibitor and lactate transporter blocker treatment promoted the function of NK cells cocultured with PC cells. In vivo experiments yielded the same results.

Conclusion

The SIX1/LDHA axis promotes lactate accumulation and leads to NK cell dysfunction in PC.

Clinical Strategies Targeting the Tumor Microenvironment of Pancreatic Ductal Adenocarcinoma

Pancreatic cancer has a complex tumor microenvironment which engages in extensive crosstalk between cancer cells, cancer-associated fibroblasts, and immune cells. Many of these interactions contribute to tumor resistance to anti-cancer therapies. Here, new therapeutic strategies designed to modulate the cancer-associated fibroblast and immune compartments of pancreatic ductal adenocarcinomas are described and clinical trials of novel therapeutics are discussed. Continued advances in our understanding of the pancreatic cancer tumor microenvironment are generating stromal and immune-modulating therapeutics that may improve patient responses to anti-tumor treatment.

Intestinal microbiota modulates pancreatic carcinogenesis through intratumoral natural killer cells

Preclinical data demonstrate that the gut microbiota can promote pancreatic ductal adenocarcinoma (PDAC), but mechanisms remain unclear. We hypothesized that intestinal microbiota alters anti-tumor innate immunity response to facilitate PDAC progression. Human PDAC L3.6pl cells were heterotopically implanted into Rag1^-/- mice after microbiota depletion with antibiotics, while syngeneic murine PDAC Pan02 cells were implanted intrapancreatic into germ-free (GF) C57BL/6 J mice. Natural killer (NK) cells and their IFNγ expression were quantitated by flow cytometry. NK cells were depleted in vivo using anti-Asialo GM1 antibody to confirm the role of NK cells. Bacteria-free supernatant from SPF and GF mice feces was used to test its effect on NK-92MI cell anti-tumor response in vitro. SPF and ex-GF mice (reconstituted with SPF microbiota) developed larger PDAC tumors with decreased NK cell tumor infiltration and IFNγ expression versus GF-Rag1^-/-. Microbiota-induced PDAC tumorigenesis was attenuated by antibiotic exposure, a process reversed following NK cell depletion in both Rag1^-/- and C57BL/6 J mice. Compared to GF, SPF-Rag1^-/- abiotic stool culture supernatant inhibited NK-92MI cytotoxicity, migration, and anti-cancer related gene expression. Gut microbiota promotes PDAC tumor progression through modulation of the intratumoral infiltration and activity of NK cells.

Role of CD155/TIGIT in Digestive Cancers: Promising Cancer Target for Immunotherapy

The tumor microenvironment restricts the function and survival of various immune cells by up-regulating inhibitory immune checkpoints, and participates in the immune escape of tumors. The development of immunotherapies targeting immune checkpoints, such as programmed cell death receptor 1 antibody and anti-cytotoxic T lymphocyte-associated antigen 4 antibody, has provided many options for cancer treatment. The efficacy of other immune checkpoint inhibitors is also under development and research. Among them, T cell immunoreceptor with Ig and ITIM domains (TIGIT) has shown excellent clinical application prospects. Correspondingly, poliovirus receptor (PVR, CD155), one of the main ligands of TIGIT, is mainly expressed in various human malignant tumors and myeloid cells. CD155 interacts with TIGIT on natural killer cells and T cells, mediating inhibitory immunomodulatory regulation. This study summarized the mechanism of CD155/TIGIT in regulating immune cells and its role in the occurrence and development of digestive system tumors, aiming to provide a new perspective for immunotherapy of digestive cancers.

The Trinity: Interplay among Cancer Cells, Fibroblasts, and Immune Cells in Pancreatic Cancer and Implication of CD8+ T Cell-Orientated Therapy

The microenvironment in tumors is complicated and is constituted by different cell types and stromal proteins. Among the cell types, the abundance of cancer cells, fibroblasts, and immune cells is high and these cells work as the “Trinity” in promoting tumorigenesis. Although unidirectional or bidirectional crosstalk between two independent cell types has been well characterized, the multi-directional interplays between cancer cells, fibroblasts, and immune cells in vitro and in vivo are still unclear. We summarize recent studies in addressing the interaction of the “Trinity” members in the tumor microenvironment and propose a functional network for how these members communicate with each other. In addition, we discuss the underlying mechanisms mediating the interplay. Moreover, correlations of the alterations in the distribution and functionality of cancer cells, fibroblasts, and immune cells under different circumstances are reviewed. Finally, we point out the future application of CD8⁺ T cell-oriented therapy in the treatment of pancreatic cancer.

Tumor-associated macrophages promote PD-L1 expression in tumor cells by regulating PKM2 nuclear translocation in pancreatic ductal adenocarcinoma

In many types of cancer, tumor cells prefer to use glycolysis as a major energy acquisition method. Here, we found that the 18fluoro-deoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT)-based markers were positively associated with the expression of programmed cell death ligand 1 (PD-L1), pyruvate kinase M2 (PKM2), both of which indicate poor prognosis in patients with pancreatic ductal adenocarcinoma (PDAC). However, the regulatory mechanism of PD-L1 remains elusive. In this study, we confirmed that transforming growth factor-beta1 (TGF-β1) secreted by tumor-associated macrophages (TAMs) was a key factor contributing to the expression of PD-L1 in PDAC cells by inducing the nuclear translocation of PKM2. Using co-immunoprecipitation and chromatin immunoprecipitation assays, we demonstrated that the interaction between PKM2 and signal transducer and activator of transcription 1 (STAT1) was enhanced by TGF-β1 stimulation, which facilitated the transactivation of PD-L1 by the binding of PKM2 and STAT1 to its promoter. In vivo, PKM2 knockdown decreased PD-L1 expression in PDAC cells and inhibited tumor growth partly by promoting natural killer cell activation and function, and the combination of PD-1/PD-L1 blockade with PKM2 knockdown limited tumor growth. In conclusion, PKM2 significantly contributes to TAM-induced PD-L1 overexpression and immunosuppression, providing a novel target for immunotherapies for PDAC.

Immune normalization strategy against suboptimal health status: safe and efficacious therapy using mixed-natural killer cells

"Immune normalization" has emerged as a new paradigm in immunotherapy, which is proposed in cancer patients instead of conventional "immune-enhancement" therapy. Immune normalization may also be implemented in cancer prevention of "sub-healthy" individuals. We established in vitro cultured mixed-natural killer (NKM) cells to achieve immune normalization. The in vitro cytotoxicity of NKM cells was tenfold higher than that of peripheral blood mononuclear cells (PBMCs). The cytotoxicity of NKM cells was negatively correlated with the proportion of T-helper cells (cluster of differentiation: CD3+CD4+ T), and positively correlated with the proportion of NK cells (especially CD56^brightCD16^bright NK cells). Then, we defined "sub-healthy individuals" after measuring Programmed cell death protein-1 (PD-1) expression in PBMCs from 95 donors aged > 50 years. Furthermore, we evaluated the potential clinical application of NKM-cell therapy in 11 patients with malignant lymphoma, one patient with pancreatic cancer, and four sub-healthy individuals. NKM-cell therapy elicited good tolerance and side-effects were not found. In sub-healthy individuals, the proportion of CD3⁺PD-1⁺ T cells and CD3⁺CD8⁺PD-1⁺ T cells was reduced significantly after NKM-cell treatment. We demonstrated that a new method using NKM cells was safe and efficacious as adjuvant treatment for cancer patients as well as therapy for sub-healthy individuals. Normalization of the peripheral immune system through NKM-cell therapy could expand its scope of application in different disorders.

PKCι regulates the expression of PDL1 through multiple pathways to modulate immune suppression of pancreatic cancer cells

To investigate the impact of oncogenic protein kinase C isoform ι (PKCι) on the microenvironment and the immunogenic properties of pancreatic tumors, we prohibit PKCι activity in various pancreatic ductal adenocarcinoma (PDAC) cell lines and co-culture them with human natural killer NK92 cells. The results demonstrate that PKCι suppression enhances the susceptibility of PDAC to NK cytotoxicity and promotes the degranulation and cytolytic activity of co-cultured NK92 cells. Mechanistic studies pinpoint that downstream of KRAS, both YAP1 and STAT3 are recruited by oncogenic PKCι to elevate the expression of PDL1, contributing to constitute an immune suppressive microenvironment in PDAC. Co-culture with NK92 further induces PDL1 upregulation via STAT3 to stimulate immune escape of PDAC cells. Subsequently, inhibition of PKCι in PDAC alleviates the immune suppression and enhances the cytotoxicity of NK92 towards PDAC through restraining PDL1 overexpression. Combined with PD1/PDL1 blocker, PKCι inhibitor remarkably elevates the cytotoxicity of NK92 against PDAC cells in vitro, establishing PKCι inhibitor as a promising candidate for boosting the immunotherapy of PDAC.

Natural killer cells in pancreatic cancer stroma

Pancreatic cancer remains one of medicine's largest areas of unmet need. With five-year survival rates of < 8%, little improvement has been made in the last 50 years. Typically presenting with advance stage disease, treatment options are limited. To date, surgery remains the only potentially curative option, however, with such late disease presentation, the majority of patients are unresectable. Thus, new therapeutic options and a greater understanding of the complex stromal interactions within the tumour microenvironment are sorely needed to revise the dismal outlook for pancreatic cancer patients. Natural killer (NK) cells are crucial effector units in cancer immunosurveillance. Often used as a prognostic biomarker in a range of malignancies, NK cells have received much attention as an attractive target for immunotherapies, both as cell therapy and as a pharmaceutical target. Despite this interest, the role of NK cells in pancreatic cancer remains poorly defined. Nevertheless, increasing evidence of the importance of NK cells in this dismal prognosis disease is beginning to come to light. Here, we review the role of NK cells in pancreatic cancer, examine the complex interactions of these crucial effector units within pancreatic cancer stroma and shed light on the increasingly attractive use of NK cells as therapy.

UXT antisense RNA 1 sever as a novel prognostic long non-coding RNA in early stage pancreatic ductal adenocarcinoma patients after receiving pancreaticoduodenectomy

Objective: The principal objective of this project was to investigate the prognostic value of UXT antisense RNA 1 (UXT-AS1) in pancreatic ductal adenocarcinoma (PDAC), as well as its biological function mechanisms and the screening of targeted drugs using The Cancer Genome Atlas (TCGA) PDAC genome-wide RNA sequencing (RNA-seq) dataset.

Methods: We used TCGA 112 early stage PDAC patients to screen the prognostic value of UXT-AS1. Biological functions and mechanisms of UXT-AS1 were investigated by co-expression analysis, differentially expressed genes (DEGs) and gene set enrichment analysis, while targeted drug screening was investigated by connectivity Map (CMap).

Results: By analyzing the dataset from TCGA cohort, we found that UXT-AS1 was significantly up-regulated in pancreatic cancer tissues. Multivariate survival analysis demonstrated that PDAC patients with high UXT-AS1 expression had an unfavourable prognosis (adjusted P=0.033, HR=1.830, 95%CI=1.051-3.188). Genome-wide co-expression analysis and gene set enrichment analysis suggested that UXT-AS1 may act as a pivotal part in PDAC by participating in nuclear factor kappa beta, regulation of tumor necrosis factor, cell adhesion, T cell receptor signaling pathway, and numerous immune-related biological processes and signaling pathways. Functional enrichment analysis of DEGs between high- and low-UXT-AS1 expression groups suggested that these DEGs were significant enriched in B cell receptor complex, response to drug chemical carcinogenesis and drug metabolism-cytochrome P450. CMap analysis revealed that quipazine and terazosin may be targeted drugs for UXT-AS1 in PDAC.

Conclusion: Our current study has identified UXT-AS1 as a novel biomarker for the prognosis of early stage PDAC. We also clarified its biological functional mechanisms and identified two targeted drugs of UXT-AS1 in PDAC.

Autophagy-Mediated Exosomes as Immunomodulators of Natural Killer Cells in Pancreatic Cancer Microenvironment

Pancreas ductal adenocarcinoma is a highly aggressive cancer with an incredible poor lifespan. Different chemotherapeutic agents' schemes have been tested along the years without significant success. Furthermore, immunotherapy also fails to cope with the disease, even in combination with other standard approaches. Autophagy stands out as a chemoresistance mechanism and is also becoming relevant as responsible for the inefficacy of immunotherapy. In this complex scenario, exosomes have emerged as a new key player in tumor environment. Exosomes act as messengers among tumor cells, including tumor microenvironment immune cells. For instance, tumor-derived exosomes are capable of generating a tolerogenic microenvironment, which in turns conditions the immune system behavior. But also, immune cells-derived exosomes, under non-tolerogenic conditions, induce tumor suppression, although they are able to promote chemoresistance. In that way, NK cells are well known key regulators of carcinogenesis and the inhibition of their function is detrimental for tumor suppression. Additionally, increasing evidence suggests a crosstalk between exosome biogenesis and the autophagy pathway. This mini review has the intention to summarize the available data in the complex relationships between the autophagy pathway and the broad spectrum of exosomes subpopulations in pancreatic cancer, with focus on the NK cells response.

Therapeutic Status and Available Strategies in Pancreatic Ductal Adenocarcinoma

One of the most severe and devastating cancer is pancreatic cancer. Pancreatic ductal adenocarcinoma (PDAC) is one of the major pancreatic exocrine cancer with a poor prognosis and growing prevalence. It is the most deadly disease, with an overall five-year survival rate of 6% to 10%. According to various reports, it has been demonstrated that pancreatic cancer stem cells (PCSCs) are the main factor responsible for the tumor development, proliferation, resistance to anti-cancer drugs, and recurrence of tumors after surgery. PCSCs have encouraged new therapeutic methods to be explored that can specifically target cancer cells. Furthermore, stem cells, especially mesenchymal stem cells (MSCs), are known as influential anti-cancer agents as they function through anti-inflammatory, paracrine, cytokines, and chemokine's action. The properties of MSCs, such as migration to the site of infection and host immune cell activation by its secretome, seem to control the microenvironment of the pancreatic tumor. MSCs secretome exhibits similar therapeutic advantages as a conventional cell-based therapy. Moreover, the potential for drug delivery could be enhanced by engineered MSCs to increase drug bioactivity and absorption at the tumor site. In this review, we have discussed available therapeutic strategies, treatment hurdles, and the role of different factors such as PCSCs, cysteine, GPCR, PKM2, signaling pathways, immunotherapy, and NK-based therapy in pancreatic cancer.

Netrin G1 Promotes Pancreatic Tumorigenesis through Cancer-Associated Fibroblast-Driven Nutritional Support and Immunosuppression

Pancreatic ductal adenocarcinoma (PDAC) has a poor 5-year survival rate and lacks effective therapeutics. Therefore, it is of paramount importance to identify new targets. Using multiplex data from patient tissue, three-dimensional coculturing in vitro assays, and orthotopic murine models, we identified Netrin G1 (NetG1) as a promoter of PDAC tumorigenesis. We found that NetG1+ cancer-associated fibroblasts (CAF) support PDAC survival, through a NetG1-mediated effect on glutamate/glutamine metabolism. Also, NetG1+ CAFs are intrinsically immunosuppressive and inhibit natural killer cell-mediated killing of tumor cells. These protumor functions are controlled by a signaling circuit downstream of NetG1, which is comprised of AKT/4E-BP1, p38/FRA1, vesicular glutamate transporter 1, and glutamine synthetase. Finally, blocking NetG1 with a neutralizing antibody stunts in vivo tumorigenesis, suggesting NetG1 as potential target in PDAC. SIGNIFICANCE: This study demonstrates the feasibility of targeting a fibroblastic protein, NetG1, which can limit PDAC tumorigenesis in vivo by reverting the protumorigenic properties of CAFs. Moreover, inhibition of metabolic proteins in CAFs altered their immunosuppressive capacity, linking metabolism with immunomodulatory function.See related commentary by Sherman, p. 230.This article is highlighted in the In This Issue feature, p. 211.

Integrated genomic and transcriptomic analysis reveals unique characteristics of hepatic metastases and pro-metastatic role of complement C1q in pancreatic ductal adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers due to its high metastasis rate in the liver. However, little is known about the molecular features of hepatic metastases due to difficulty in obtaining fresh tissues and low tumor cellularity.

RESULTS

We conduct exome sequencing and RNA sequencing for synchronous surgically resected primary tumors and the paired hepatic metastases from 17 hepatic oligometastatic pancreatic ductal adenocarcinoma and validate our findings in specimens from 35 of such cases. The comprehensive analysis of somatic mutations, copy number alterations, and gene expressions show high similarity between primary tumors and hepatic metastases. However, hepatic metastases also show unique characteristics, such as a higher degree of 3p21.1 loss, stronger abilities of proliferation, downregulation of epithelial to mesenchymal transition activity, and metabolic rewiring. More interesting, altered tumor microenvironments are observed in hepatic metastases, especially a higher proportion of tumor infiltrating M2 macrophage and upregulation of complement cascade. Further experiments demonstrate that expression of C1q increases in primary tumors and hepatic metastases, C1q is mainly produced by M2 macrophage, and C1q promotes migration and invasion of PDAC cells.

CONCLUSION

Taken together, we find potential factors that contribute to different stages of PDAC metastasis. Our study broadens the understanding of molecular mechanisms driving PDAC metastasis.

Assessment of NK Cell Activity Based on NK Cell-Specific Receptor Synergy in Peripheral Blood Mononuclear Cells and Whole Blood

Natural killer (NK) cells are cytotoxic innate lymphocytes endowed with a unique ability to kill a broad spectrum of cancer and virus-infected cells. Given their key contribution to diverse diseases, the measurement of NK cell activity (NKA) has been used to estimate disease prognosis or the effect of therapeutic treatment. Currently, NKA assays are primarily based on cumbersome procedures related to careful labeling and handling of target cells and/or NK cells, and they require a rapid isolation of peripheral blood mononuclear cells (PBMCs) which often necessitates a large amount of blood. Here, we developed an ELISA-based whole blood (WB) NKA assay involving engineered target cells (P815-ULBP1+CD48) providing defined and synergistic stimulation for NK cells via NKG2D and 2B4. WB collected from healthy donors (HDs) and patients with multiple myeloma (MM) was stimulated with P815-ULBP1+CD48 cells combined with IL-2. Thereafter, it utilized the serum concentrations of granzyme B and IFN-γ originating in NK cells as independent and complementary indicators of NKA. This WB NKA assay demonstrated that MM patients exhibit a significantly lower NKA than HDs following stimulation with P815-ULBP1+CD48 cells and had a good correlation with the commonly used flow cytometry-based PBMC NKA assay. Moreover, the use of P815-ULBP1+CD48 cells in relation to assessing the levels of NKG2D and 2B4 receptors on NK cells facilitated the mechanistic study and led to the identification of TGF-β1 as a potential mediator of compromised NKA in MM. Thus, our proposed WB NKA assay facilitates the reliable measurement of NKA and holds promise for further development as both a clinical and research tool.

Mechanistic target of rapamycin in the tumor microenvironment and its potential as a therapeutic target for pancreatic cancer

Pancreatic cancer(PC) is a devastating disease with a poor prognosis; however, few treatment options are available and the search continues for feasible molecular therapeutic targets, both in the tumor itself and in the tumor microenvironment. The mechanistic target of rapamycin (mTOR) signaling pathway has emerged as an attractive target due to its regulatory role in multiple cellular processes, including metabolism, proliferation, survival, and differentiation, under physiological and pathological conditions. Although mTOR-regulated events in tumor cells and the tumor microenvironment are known to restrict the development and growth of tumor cells, monotherapy with mTOR inhibitors has shown limited efficacy against PC to date, suggesting the need for alternative approaches. In this review, we describe the mechanisms by which mTOR modulates the PC microenvironment and suggest ways its function in immune cells might be exploited for the treatment of PC. We also discuss preclinical and clinical studies with mTOR inhibitors in combination with other therapeutic strategies, most notably immunotherapy. Finally, we highlight the promise that mTOR combinatorial therapy may hold for the treatment of PC in the near future.

Regulation of pancreatic cancer TRAIL resistance by protein O-GlcNAcylation

TRAIL-activating therapy is promising in treating various cancers, including pancreatic cancer, a highly malignant neoplasm with poor prognosis. However, many pancreatic cancer cells are resistant to TRAIL-induced apoptosis despite their expression of intact death receptors (DRs). Protein O-GlcNAcylation is a versatile posttranslational modification that regulates various biological processes. Elevated protein O-GlcNAcylation has been recently linked to cancer cell growth and survival. In this study, we evaluated the role of protein O-GlcNAcylation in pancreatic cancer TRAIL resistance, and identified higher levels of O-GlcNAcylation in TRAIL-resistant pancreatic cancer cells. With gain- and loss-of-function of the O-GlcNAc-adding enzyme, O-GlcNActransferase (OGT), we determined that increasing O-GlcNAcylation rendered TRAIL-sensitive cells more resistant to TRA-8-induced apoptosis, while inhibiting O-GlcNAcylation promoted TRA-8-induced apoptosis in TRAIL-resistance cells. Furthermore, we demonstrated that OGT knockdown sensitized TRAIL-resistant cells to TRA-8 therapy in a mouse model in vivo. Mechanistic studies revealed direct O-GlcNAc modifications of DR5, which regulated TRA-8-induced DR5 oligomerization. We further defined that DR5 O-GlcNAcylation was independent of FADD, the adapter protein for the downstream death-inducing signaling. These studies have demonstrated an important role of protein O-GlcNAcylation in regulating TRAIL resistance of pancreatic cancer cells; and uncovered the contribution of O-GlcNAcylation to DR5 oligomerization and thus mediating DR-inducing signaling.

From tumor microenvironment communicants to biomarker discovery: Selectively packaged extracellular vesicular cargoes in pancreatic cancer

Virtually all cells release various types of vesicles into the extracellular environment. These extracellular vesicles (EVs) transport molecular cargoes, performing as communicants for information exchange both within the tumor microenvironment (TME) and to distant organs. Thus, understanding the selective packaging of EV cargoes and the mechanistic impact of those cargoes - including metabolites, lipids, proteins, and/or nucleic acids - offers an opportunity to increase our knowledge of cancer biology and identify EV cargoes that might serve as cancer biomarkers in blood, saliva, or urine samples. In this review, we collect and organize recent advances in this field with an emphasis on pancreatic cancer (pancreatic adenocarcinoma, PDAC) and the concept that cells selectively package cargo into EVs. These studies demonstrate PDAC EV cargoes signal to reprogram and remodel the TME and impact distant organs. EV cargoes identified as potential PDAC diagnostic and prognostic biomarkers are summarized.

Natural Killer Cell-Derived Exosomal miR-3607-3p Inhibits Pancreatic Cancer Progression by Targeting IL-26

Increasing evidences have suggested that natural killer (NK) cells in the tumor microenvironment are involved in the regulation of cancer development. However, the potential biological roles and regulatory mechanisms of NK cells in pancreatic cancer (PC) remain unclear. Co-culture system of NK cells with PC cells is used to test the ability of cancer cell proliferation, migration and invasion both in vitro and in vivo. And tail vein intravenous transfer was used to test metastasis in vivo. Meanwhile, extracellular vesicles (EVs) were separated and examined. Furthermore, reporter assay and Biotin-RNA pull down assay were performed to verify the interaction between molecules. NK cells can inhibit the malignant transformation of co-cultured PC cells both in vivo and in vitro, which requires miR-3607-3p. miR-3607-3p is found enriched in the EVs of NK cells and transmitted to PC cells, and low level of miR-3607-3p predicts poor prognosis in PC patients. It can also inhibit proliferation, migration and invasion of PC cells in vitro. Importantly, IL-26 is found to be a direct target of miR-3607-3p in PC cells. miR-3607-3p enriched in EVs derived from NK cells can inhibit the malignant transformation of PC probably through directly targeting of IL-26.

CXCL14 suppresses human papillomavirus-associated head and neck cancer through antigen-specific CD8+ T-cell responses by upregulating MHC-I expression

Evasion of the host immune responses is critical for both persistent human papillomavirus (HPV) infection and associated cancer progression. We have previously shown that expression of the homeostatic chemokine CXCL14 is significantly downregulated by the HPV oncoprotein E7 during cancer progression. Restoration of CXCL14 expression in HPV-positive head and neck cancer (HNC) cells dramatically suppresses tumor growth and increases survival through an immune-dependent mechanism in mice. While CXCL14 recruits natural killer (NK) and T cells to the tumor microenvironment, the mechanism by which CXCL14 mediates tumor suppression through NK and/or T cells remained undefined. Here, we report that CD8⁺ T cells are required for CXCL14-mediated tumor suppression. Using a CD8⁺ T cell receptor transgenic model, we show that the CXCL14-mediated antitumor CD8⁺ T cell responses require antigen specificity. Interestingly, CXCL14 expression restores major histocompatibility complex class I (MHC-I) expression on HPV-positive HNC cells downregulated by HPV, and knockdown of MHC-I expression in HNC cells results in loss of tumor suppression even with CXCL14 expression. These results suggest that CXCL14 enacts antitumor immunity through restoration of MHC-I expression on tumor cells and promoting antigen-specific CD8⁺ T cell responses to suppress HPV-positive HNC.

Progressive Impairment of NK Cell Cytotoxic Degranulation Is Associated With TGF-β1 Deregulation and Disease Progression in Pancreatic Cancer

Natural killer (NK) cells are key effectors in cancer immunosurveillance and can be used as a prognostic biomarker in diverse cancers. Nonetheless, the role of NK cells in pancreatic cancer (PC) remains elusive, given conflicting data on their association with disease prognosis. In this study, using conventional K562 target cells and complementary engineered target cells providing defined and synergistic stimulation for NK cell activation, a correlation between impaired NK cell cytotoxic degranulation and PC progression was determined. Peripheral blood mononuclear cells (PBMCs) from 31 patients with newly diagnosed PC, 24 patients with non-malignant tumors, and 37 healthy controls were analyzed by flow cytometry. The frequency, phenotype, and effector functions of the NK cells were evaluated, and correlations between NK cell functions and disease stage and prognosis were analyzed. The results demonstrated that effector functions, but not frequency, of NK cells was progressively decreased on a per-cell basis during PC progression. Impaired cytotoxic degranulation, but not IFN-γ production, was associated with clinical features indicating disease progression, such as high serum CA19-9 and high-grade tumors. Significantly, this impairment correlated with cancer recurrence and mortality in a prospective analysis. Furthermore, the impaired cytotoxic degranulation was unrelated to NKG2D downregulation but was associated with increased circulating and tumor-associated TGF-β1 expression. Thus, NK cell cytotoxic activity was associated with PC progression and may be a favorable biomarker with predictive and prognostic value in PC.

Ping-Pong-Tumor and Host in Pancreatic Cancer Progression

Metastasis is the main cause of high pancreatic cancer (PaCa) mortality and trials dampening PaCa mortality rates are not satisfying. Tumor progression is driven by the crosstalk between tumor cells, predominantly cancer-initiating cells (CIC), and surrounding cells and tissues as well as distant organs, where tumor-derived extracellular vesicles (TEX) are of major importance. A strong stroma reaction, recruitment of immunosuppressive leukocytes, perineural invasion, and early spread toward the peritoneal cavity, liver, and lung are shared with several epithelial cell-derived cancer, but are most prominent in PaCa. Here, we report on the state of knowledge on the PaCIC markers Tspan8, alpha6beta4, CD44v6, CXCR4, LRP5/6, LRG5, claudin7, EpCAM, and CD133, which all, but at different steps, are engaged in the metastatic cascade, frequently via PaCIC-TEX. This includes the contribution of PaCIC markers to TEX biogenesis, targeting, and uptake. We then discuss PaCa-selective features, where feedback loops between stromal elements and tumor cells, including distorted transcription, signal transduction, and metabolic shifts, establish vicious circles. For the latter particularly pancreatic stellate cells (PSC) are responsible, furnishing PaCa to cope with poor angiogenesis-promoted hypoxia by metabolic shifts and direct nutrient transfer via vesicles. Furthermore, nerves including Schwann cells deliver a large range of tumor cell attracting factors and Schwann cells additionally support PaCa cell survival by signaling receptor binding. PSC, tumor-associated macrophages, and components of the dysplastic stroma contribute to perineural invasion with signaling pathway activation including the cholinergic system. Last, PaCa aggressiveness is strongly assisted by the immune system. Although rich in immune cells, only immunosuppressive cells and factors are recovered in proximity to tumor cells and hamper effector immune cells entering the tumor stroma. Besides a paucity of immunostimulatory factors and receptors, immunosuppressive cytokines, myeloid-derived suppressor cells, regulatory T-cells, and M2 macrophages as well as PSC actively inhibit effector cell activation. This accounts for NK cells of the non-adaptive and cytotoxic T-cells of the adaptive immune system. We anticipate further deciphering the molecular background of these recently unraveled intermingled phenomena may turn most lethal PaCa into a curatively treatable disease.

TRAIL/NF-κB/CX3CL1 Mediated Onco-Immuno Crosstalk Leading to TRAIL Resistance of Pancreatic Cancer Cell Lines

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignant neoplasms and registers rising death rates in western countries. Due to its late detection in advanced stages, its extremely aggressive nature and the minimal effectiveness of currently available therapies, PDAC is a challenging problem in the clinical field. One characteristic of PDAC is a distinct desmoplasia consisting of fibroblasts, endothelial and immune cells as well as non-cellular components, contributing to therapy resistance. It is well established that the NF-κB signaling pathway controls inflammation, cancer progression and apoptosis resistance in PDAC. This study attempts to identify NF-κB target genes mediating therapy resistance of humane PDAC cell lines towards death ligand induced apoptosis. By using a genome wide unbiased approach the chemokine CX3CL1 was established as a central NF-κB target gene mediating therapy resistance. While no direct impact of CX3CL1 expression on cancer cell apoptosis was identified in co-culture assays it became apparent that CX3CL1 is acting in a paracrine fashion, leading to an increased recruitment of inflammatory cells. These inflammatory cells in turn mediate apoptosis resistance of PDAC cells. Therefore, our data dissect a bifunctional cross-signaling pathway in PDAC between tumor and immune cells giving rise to therapy resistance.