Long-Term Gemcitabine Treatment Reshapes the Pancreatic Tumor Microenvironment and Sensitizes Murine Carcinoma to Combination Immunotherapy

Exosomal lncRNA UCA1 Derived From Pancreatic Stellate Cells Promotes Gemcitabine Resistance in Pancreatic Cancer via the SOCS3/EZH2 Axis

Objective

Pancreatic cancer is associated with poor prognosis and dismal survival rates. This study aims to investigate roles of lncRNA UCA1-loaded exosomes secreted by pancreatic stellate cells (PSCs) in Gemcitabine (Gem) resistance of pancreatic cancer under hypoxia, which involves the methylation of SOCS3 and EZH2 recruitment.

Methods

The exosomes were isolated from PSCs and hypoxic PSCs (HPSCs), and co-cultured with pancreatic cancer cells transduced with manipulated lncRNA UCA1, EZH2, and SOCS3. The interaction among lncRNA UCA1, EZH2, and SOCS3 was characterized by RIP and ChIP assays. Next, MTT assay, flow cytometry and TUNEL staining and Transwell assay were used to detect cell viability, apoptosis, invasion, and migration. Gem-resistant pancreatic cancer cell line (GemMIA-R3) was established, which was applied in a mouse xenograft model of pancreatic cancer, with MTT assay to determine Gem sensitivity.

Results

LncRNA UCA1 was highly expressed, while SOCS3 was poorly expressed in pancreatic cancer tissues. Hypoxia induced activation of PSCs and promoted release of exosomes. LncRNA UCA1 delivered by hypoxic PSC-derived exosomes (HPSC-EXO) regulated histone methylation level in SOCS3 gene region through recruitment of EZH2. In vitro and in vivo experimental results confirmed that lncRNA UCA1-loaded HPSC-EXO promoted malignant phenotypes, inhibited apoptosis, and promoted Gem resistance of pancreatic cancer cells as well as tumorigenesis in mice.

Conclusion

Under hypoxic conditions, exosomes secreted by hypoxia-induced PSCs deliver lncRNA UCA1 into pancreatic cancer cells, where lncRNA UCA1 recruits EZH2 and regulates histone methylation level in SOCS3 gene region, thereby augmenting pancreatic cancer resistance to Gem.

Peptide-Based Drug Delivery Systems

Peptide-based drug delivery systems have many advantages when compared to synthetic systems in that they have better biocompatibility, biochemical and biophysical properties, lack of toxicity, controlled molecular weight via solid phase synthesis and purification. Lysosomes, solid lipid nanoparticles, dendrimers, polymeric micelles can be applied by intravenous administration, however they are of artificial nature and thus may induce side effects and possess lack of ability to penetrate the blood-brain barrier. An analysis of nontoxic drug delivery systems and an establishment of prospective trends in the development of drug delivery systems was needed. This review paper summarizes data, mainly from the past 5 years, devoted to the use of peptide-based carriers for delivery of various toxic drugs, mostly anticancer or drugs with limiting bioavailability. Peptide-based drug delivery platforms are utilized as peptide–drug conjugates, injectable biodegradable particles and depots for delivering small molecule pharmaceutical substances (500 Da) and therapeutic proteins. Controlled drug delivery systems that can effectively deliver anticancer and peptide-based drugs leading to accelerated recovery without significant side effects are discussed. Moreover, cell penetrating peptides and their molecular mechanisms as targeting peptides, as well as stimuli responsive (enzyme-responsive and pH-responsive) peptides and peptide-based self-assembly scaffolds are also reviewed.

TGFβ Signaling in the Pancreatic Tumor Microenvironment

Pancreatic ductal adenocarcinoma (PDAC) is associated with poor clinical outcomes, largely attributed to incomplete responses to standard therapeutic approaches. Recently, selective inhibitors of the Transforming Growth Factor β (TGFβ) signaling pathway have shown early promise in the treatment of PDAC, particularly as a means of augmenting responses to chemo- and immunotherapies. However, TGFβ is a potent and pleiotropic cytokine with several seemingly paradoxical roles within the pancreatic tumor microenvironment (TME). Although TGFβ signaling can have potent tumor-suppressive effects in epithelial cells, TGFβ signaling also accelerates pancreatic tumorigenesis by enhancing epithelial-to-mesenchymal transition (EMT), fibrosis, and the evasion of the cytotoxic immune surveillance program. Here, we discuss the known roles of TGFβ signaling in pancreatic carcinogenesis, the biologic consequences of the genetic inactivation of select components of the TGFβ pathway, as well as past and present attempts to advance TGFβ inhibitors in the treatment of PDAC patients.

Heterogeneity in Pancreatic Cancer Fibroblasts-TGFβ as a Master Regulator?

Pancreatic ductal adenocarcinoma is an aggressive disease for which there are very few available therapies. It is notable for its high degree of tumour complexity, with the tumour microenvironment often accounting for the majority of the tumour volume. Until recently, the biology of the stroma was poorly understood, particularly in terms of heterogeneity. Recent research, however, has shed light on the intricacy of signalling within the stroma and particularly the molecular and functional heterogeneity of the cancer associated fibroblasts. In this review, we summarise the recent improvements in our understanding of the different fibroblast populations within PDAC, with a focus on the role TGFβ plays to dictate their formation and function. These studies have highlighted some of the reasons for the failure of trials targeting the tumour stroma, however, there are still considerable gaps in our knowledge, and more work is needed to make effective fibroblast targeting a reality in the clinic.

TLR2 activation promotes tumour growth and associates with patient survival and chemotherapy response in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has an extremely poor prognosis, and is plagued by a paucity of targeted treatment options and tumour resistance to chemotherapeutics. The causal link between chronic inflammation and PDAC suggests that molecular regulators of the immune system promote disease pathogenesis and/or therapeutic resistance, yet their identity is unclear. Here, we couple endoscopic ultrasound-guided fine-needle aspiration, which captures tumour biopsies from all stages, with whole transcriptome profiling of PDAC patient primary tumours to reveal enrichment of the innate immune Toll-like receptor 2 (TLR2) molecular pathway. Augmented TLR2 expression associated with a 4-gene "TLR2 activation" signature, and was prognostic for survival and predictive for gemcitabine-based chemoresistance. Furthermore, antibody-mediated anti-TLR2 therapy suppressed the growth of human PDAC tumour xenografts, independent of a functional immune system. Our results support TLR2-based therapeutic targeting for precision medicine in PDAC, with further clinical utility that TLR2 activation is prognostic and predictive for chemoresponsiveness.

Mirage or long-awaited oasis: reinvigorating T-cell responses in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is plagued by a dismal 5-year survival rate, early onset of metastasis and limited efficacy of systemic therapies. This scenario highlights the need to fervently pursue novel therapeutic strategies to treat this disease. Recent research has uncovered complicated dynamics within the tumor microenvironment (TME) of PDAC. An abundant stroma provides a framework for interactions between cancer-associated fibroblasts, suppressive myeloid cells and regulatory lymphocytes, which together create an inhospitable environment for adaptive immune responses. This accounts for the poor infiltration and exhausted phenotypes of effector T cells within pancreatic tumors. Innovative studies in genetically engineered mouse models have established that with appropriate pharmacological modulation of suppressive elements in the TME, T cells can be prompted to regress pancreatic tumors. In light of this knowledge, innovative combinatorial strategies involving immunotherapy and targeted therapies working in concert are rapidly emerging. This review will highlight recent advances in the field related to immune suppression in PDAC, emerging preclinical data and rationale for ongoing immunotherapy clinical trials. In particular, we draw attention to foundational findings involving T-cell activity in PDAC and encourage development of novel therapeutics to improve T-cell responses in this challenging disease.

Towards precision medicine for clinically non-functioning pituitary tumours

OBJECTIVE

Clinically non-functioning pituitary tumours (NFPT) are a heterogenous group of neoplasms with diverse outcomes. The purpose of this narrative review was to summarize available data on predictive factors, both in routine practice and research settings.

DESIGN

A literature review was conducted for papers published in peer-reviewed journals, investigating clinical, radiological, pathological and genetic predictive factors in NFPT.

RESULTS

Several clinical and radiological factors have been associated with NFPT recurrence and/or aggressiveness, including larger size and pre-/post-operative growth rates. Application of transcription factor immunohistochemistry has given rise to improved subtype identification, including 'higher-risk' subtypes, in routine clinical practice. Numerous other pathological and genetic biomarkers have demonstrated promise for prognostication in the research setting.

CONCLUSION

NFPT are a heterogenous group of tumours, characterized by diverse presentation, pathogenesis and outcomes. Ongoing refinements in understanding of tumour biology are likely to pave the way to improved integrative prognostication and precision medicine for NFPT.

Ref-1 redox activity alters cancer cell metabolism in pancreatic cancer: exploiting this novel finding as a potential target

BACKGROUND

Pancreatic cancer is a complex disease with a desmoplastic stroma, extreme hypoxia, and inherent resistance to therapy. Understanding the signaling and adaptive response of such an aggressive cancer is key to making advances in therapeutic efficacy. Redox factor-1 (Ref-1), a redox signaling protein, regulates the conversion of several transcription factors (TFs), including HIF-1α, STAT3 and NFκB from an oxidized to reduced state leading to enhancement of their DNA binding. In our previously published work, knockdown of Ref-1 under normoxia resulted in altered gene expression patterns on pathways including EIF2, protein kinase A, and mTOR. In this study, single cell RNA sequencing (scRNA-seq) and proteomics were used to explore the effects of Ref-1 on metabolic pathways under hypoxia.

METHODS

scRNA-seq comparing pancreatic cancer cells expressing less than 20% of the Ref-1 protein was analyzed using left truncated mixture Gaussian model and validated using proteomics and qRT-PCR. The identified Ref-1's role in mitochondrial function was confirmed using mitochondrial function assays, qRT-PCR, western blotting and NADP assay. Further, the effect of Ref-1 redox function inhibition against pancreatic cancer metabolism was assayed using 3D co-culture in vitro and xenograft studies in vivo.

RESULTS

Distinct transcriptional variation in central metabolism, cell cycle, apoptosis, immune response, and genes downstream of a series of signaling pathways and transcriptional regulatory factors were identified in Ref-1 knockdown vs Scrambled control from the scRNA-seq data. Mitochondrial DEG subsets downregulated with Ref-1 knockdown were significantly reduced following Ref-1 redox inhibition and more dramatically in combination with Devimistat in vitro. Mitochondrial function assays demonstrated that Ref-1 knockdown and Ref-1 redox signaling inhibition decreased utilization of TCA cycle substrates and slowed the growth of pancreatic cancer co-culture spheroids. In Ref-1 knockdown cells, a higher flux rate of NADP + consuming reactions was observed suggesting the less availability of NADP + and a higher level of oxidative stress in these cells. In vivo xenograft studies demonstrated that tumor reduction was potent with Ref-1 redox inhibitor similar to Devimistat.

CONCLUSION

Ref-1 redox signaling inhibition conclusively alters cancer cell metabolism by causing TCA cycle dysfunction while also reducing the pancreatic tumor growth in vitro as well as in vivo.

Biomimetic stiffening of cell-laden hydrogels via sequential thiol-ene and hydrazone click reactions

Hydrogels with dynamically tunable crosslinking are invaluable for directing stem cell fate and mimicking a stiffening matrix during fibrosis or tumor development. The increases in matrix stiffness during tissue development are often accompanied by the accumulation of extracellular matrices (e.g., collagen, hyaluronic acid (HA)), a phenomenon that has received little attention in the development of dynamic hydrogels. In this contribution, we present a gelatin-based cell-laden hydrogel system capable of being dynamically stiffened while accumulating HA, a key glycosaminoglycans (GAG) increasingly deposited by stromal cells during tumor progression. Central to this strategy is the synthesis of a dually-modified gelatin macromer - gelatin-norbornene-carbohydrazide (GelNB-CH), which is susceptible to both thiol-norbornene photopolymerization and hydrazone click chemistry. We demonstrate that the crosslinking density of cell-laden thiol-norbornene hydrogels can be dynamically tuned via simple incubation with aldehyde-bearing macromers (e.g., oxidized dextran (oDex) or oHA). The GelNB-CH hydrogel system is highly cytocompatible, as demonstrated by in situ encapsulation of pancreatic cancer cells (PCC) and cancer-associated fibroblasts (CAF). This unique dynamic stiffening scheme provides a platform to study tandem accumulation of HA and elevation in matrix stiffness in the pancreatic tumor microenvironment. STATEMENT OF SIGNIFICANCE: Hydrogels permitting on-demand and secondary crosslinking are ideal for mimicking a stiffening tumor microenvironment (TME). However, none of the current dynamic hydrogels account for both stiffening and accumulation of hyaluronic acid (HA), a major extracellular matrix component increasingly deposited in tumor stromal tissues, including pancreatic ductal adenocarcinoma (PDAC). The current work addresses this gap by developing a dynamic hydrogel system capable of simultaneously increasing stiffness and HA accumulation. This is achieved by a new gelatin macromer permitting sequential thiol-norbornene (for primary network crosslinking) and hydrazone click chemistry (for bioinert or biomimetic stiffening with oxidized dextran (oDex) or oHA, respectively). The results of this study provide new insights into how dynamically changing physicochemical matrix properties guide cancer cell fate processes.

A therapeutic DNA vaccine and gemcitabine act synergistically to eradicate HPV-associated tumors in a preclinical model

Although active immunotherapies are effective strategies to induce activation of CD8⁺ T cells, advanced stage tumors require further improvements for efficient control. Concerning the burden of cancer-related to Human papillomavirus (HPV), particularly the high incidence and mortality of cervical cancer, our group developed an approach based on a DNA vaccine targeting the HPV-16 E7 oncoprotein (pgDE7h). This immunotherapy is capable of inducing an antitumour CD8⁺ T cell response but show only partial control of tumors in more advanced growth stages. Here, we combined a chemotherapeutic agent (gemcitabine- Gem) with pgDE7h to overcome immunosuppression and improve antitumour responses in a preclinical mouse tumor model. Our results demonstrated that administration of Gem had synergistic antitumor effects when combined with pgDE7h leading to eradication of both early-stages and established tumors. Overall, the antiproliferative effects of Gem observed in vitro and in vivo provided an optimal window for immunotherapy. In addition, the enhanced antitumour responses induced by the combined therapeutic regimen included enhanced frequencies of antigen-presenting cells (APCs), E7-specific IFN-γ-producing CD8⁺ T cells, and cytotoxic CD8⁺ T cells and, concomitantly, less pronounced accumulation of immunosuppressive myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs). These findings demonstrated that the combination of Gem and an active immunotherapy strategy show increased effectiveness, leading to a reduced need for multiple drug doses and, therefore, decreased deleterious side effects avoiding resistance and tumor relapses. Altogether, our results provide evidence for a new and feasible chemoimmunotherapeutic strategy that supports future clinical translation.

The Current Treatment Paradigm for Pancreatic Ductal Adenocarcinoma and Barriers to Therapeutic Efficacy

Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis, with a median survival time of 10-12 months. Clinically, these poor outcomes are attributed to several factors, including late stage at the time of diagnosis impeding resectability, as well as multi-drug resistance. Despite the high prevalence of drug-resistant phenotypes, nearly all patients are offered chemotherapy leading to modest improvements in postoperative survival. However, chemotherapy is all too often associated with toxicity, and many patients elect for palliative care. In cases of inoperable disease, cytotoxic therapies are less efficacious but still carry the same risk of serious adverse effects, and clinical outcomes remain particularly poor. Here we discuss the current state of pancreatic cancer therapy, both surgical and medical, and emerging factors limiting the efficacy of both. Combined, this review highlights an unmet clinical need to improve our understanding of the mechanisms underlying the poor therapeutic responses seen in patients with PDAC, in hopes of increasing drug efficacy, extending patient survival, and improving quality of life.

HAI-1 is an independent predictor of lung cancer mortality and is required for M1 macrophage polarization

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death worldwide. Though immune checkpoint inhibitors (ICIs) have revolutionized lung cancer therapy in recent years, there are several factors limiting the therapeutic efficacy of ICI-based immunotherapy in lung cancer. Recent evidence suggests that one such mechanism is the phenotypic shift of tumor-infiltrating macrophages away from an anti-tumor M1 phenotype and towards an anti-inflammatory and tumor-permissive M2 phenotype. Though this phenomenon is well documented, the means through which the lung tumor microenvironment (TME) usurps macrophage function are poorly described. Hepatocyte growth factor (HGF) is a known driver of both lung cancer pathobiology as well as M2 polarization, and its signaling is antagonized by the tumor suppressor gene HAI-1 (SPINT1). Using a combination of genomic databases, primary NSCLC specimens, and in vitro models, we determined that patients with loss of HAI-1 have a particularly poor prognosis, hallmarked by increased HGF expression and an M2-dominant immune infiltrate. Similarly, conditioned media from HAI-1-deficient tumor cells led to a loss of M1 and increased M2 polarization in vitro, and patient NSCLC tissues with loss of HAI-1 showed a similar loss of M1 macrophages. Combined, these results suggest that loss of HAI-1 is a potential means through which tumors acquire an immunosuppressive, M2-dominated TME, potentially through impaired M1 macrophage polarization. Hence, HAI-1 status may be informative when stratifying patients that may benefit from therapies targeting the HGF pathway, particularly as an adjuvant to ICI-based immunotherapy.

Overexpression of Interferon-Inducible Protein 16 Promotes Progression of Human Pancreatic Adenocarcinoma Through Interleukin-1β-Induced Tumor-Associated Macrophage Infiltration in the Tumor Microenvironment

Activation of inflammasomes has been reported in human pancreatic adenocarcinoma (PAAD); however, the expression pattern and functional role of inflammasome-related proteins in PAAD have yet to be identified. In this study, we systemically examined the expression and role of different inflammasome proteins by retrieving human expression data. Several genes were found to be differentially expressed; however, only interferon-inducible protein 16 (IFI16) expression was found to be adversely correlated with the overall survival of PAAD patients. Overexpression of IFI16 significantly promoted tumor growth, increased tumor size and weight in the experimental PAAD model of mice, and specifically increased the population of tumor-associated macrophages (TAMs) in the tumor microenvironment. Depletion of TAMs by injection of liposome clodronate attenuated the IFI16 overexpression-induced tumor growth in PAAD. In vitro treatment of conditioned medium from IFI16-overexpressing PAAD cells induced maturation, proliferation, and migration of bone marrow-derived monocytes, suggesting that IFI16 overexpression resulted in cytokine secretion that favored the TAM population. Further analysis suggested that IFI16 overexpression activated inflammasomes, thereby increasing the release of IL-1β. Neutralization of IL-1β attenuated TAM maturation, proliferation, and migration induced by the conditioned medium from IFI16-overexpressing PAAD cells. Additionally, knockdown of IFI16 could significantly potentiate gemcitabine treatment in PAAD, which may be associated with the reduced infiltration of TAMs in the tumor microenvironment. The findings of our study shed light on the role of IFI16 as a potential therapeutic target for PAAD.

Regulatory T-Cells as an Emerging Barrier to Immune Checkpoint Inhibition in Lung Cancer

Immune checkpoint inhibitors (ICIs) have revolutionized the treatment paradigm for lung cancer in recent years. These strategies consist of neutralizing antibodies against negative regulators of immune function, most notably cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), and PD-1 ligand 1 (PD-L1), thereby impeding the ability of tumor cells to escape immune surveillance. Though ICIs have proven a significant advance in lung cancer therapy, overall survival rates remain low, and lung cancer continues to be the leading cause of cancer-related death in the United States. It is therefore imperative to better understand the barriers to the efficacy of ICIs, particularly additional mechanisms of immunosuppression within the lung cancer microenvironment. Recent evidence suggests that regulatory T-lymphocytes (Tregs) serve as a central mediator of immune function in lung cancer, suppressing sterilizing immunity and contributing to the clinical failure of ICIs. Here, we provide a comprehensive summary of the roles of Tregs in lung cancer pathobiology and therapy, as well as the potential means through which these immunosuppressive mechanisms can be overcome.

Overcoming the Tumor Microenvironmental Barriers of Pancreatic Ductal Adenocarcinomas for Achieving Better Treatment Outcomes

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive disease with the lowest survival rate among all solid tumors. The lethality of PDAC arises from late detection and propensity of the tumor to metastasize and develop resistance against chemo and radiation therapy. A highly complex tumor microenvironment composed of dense stroma, immune cells, fibroblast, and disorganized blood vessels, is the main obstacle to current PDAC therapy. Despite the tremendous success of immune checkpoint inhibitors (ICIs) in cancers, PDAC remains one of the poorest responders of ICIs therapy. The immunologically "cold" phenotype of PDAC is attributed to the low mutational burden, high infiltration of myeloid-derived suppressor cells and T-regs, contributing to a significant immunotherapy resistance mechanism. Thus, the development of innovative strategies for turning immunologically "cold" tumor into "hot" ones is an unmet need to improve the outcome of PDAC ICIs therapies. Other smart strategies, such as nanomedicines, sonic Hedgehog inhibitor, or smoothened inhibitor, are discussed to enhance chemotherapeutic agents' efficiency by disrupting the PDAC stroma. This review highlights the current challenges and various preclinical and clinical strategies to overcome current PDAC therapy difficulties, thus significantly advancing PDAC research knowledge.

Combined Gemcitabine and Immune-Checkpoint Inhibition Conquers Anti-PD-L1 Resistance in Low-Immunogenic Mismatch Repair-Deficient Tumors

Tumors arising in the context of Lynch Syndrome or constitutional mismatch repair deficiency are hypermutated and have a good response towards immune-checkpoint inhibitors (ICIs), including α-PD-L1 antibodies. However, in most cases, resistance mechanisms evolve. To improve outcomes and prevent resistance development, combination approaches are warranted. Herein, we applied a combined regimen with an α-PD-L1 antibody and gemcitabine in a preclinical tumor model to activate endogenous antitumor immune responses. Mlh1^−/− mice with established gastrointestinal tumors received the α-PD-L1 antibody (clone 6E11; 2.5 mg/kg bw, i.v., q2wx3) and gemcitabine (100 mg/kg bw, i.p., q4wx3) in mono- or combination therapy. Survival and tumor growth were recorded. Immunological changes in the blood were routinely examined via multi-color flow cytometry and complemented by ex vivo frameshift mutation analysis to identify alterations in Mlh1^−/−-tumor-associated target genes. The combined therapy of α-PD-L1 and gemcitabine prolonged median overall survival of Mlh1^−/− mice from four weeks in the untreated control group to 12 weeks, accompanied by therapy-induced tumor growth inhibition, as measured by ^[18F]-FDG PET/CT. Plasma cytokine levels of IL13, TNFα, and MIP1β were increased and also higher than in mice receiving either monotherapy. Circulating splenic and intratumoral myeloid-derived suppressor cells (MDSCs), as well as M2 macrophages, were markedly reduced. Besides, residual tumor specimens from combi-treated mice had increased numbers of infiltrating cytotoxic T-cells. Frameshift mutations in APC, Tmem60, and Casc3 were no longer detectable upon treatment, likely because of the successful eradication of single mutated cell clones. By contrast, novel mutations appeared. Collectively, we herein confirm the safe application of combined chemo-immunotherapy by long-term tumor growth control to prevent the development of resistance mechanisms.

Progress for Immunotherapy in Inflammatory Breast Cancer and Emerging Barriers to Therapeutic Efficacy

Simple Summary

Despite recent advances in the treatment of other breast cancer subtypes, inflammatory breast cancer (IBC) remains a significant clinical challenge, with an overall 5-year survival rate of 39%. Though immunotherapy has shown remarkable efficacy in other difficult-to-treat cancers, such approaches have yet to show substantial therapeutic efficacy in IBC. Here, we summarize the known immune composition of IBC tumors, as well as past and present efforts to advance immunotherapy in the treatment of IBC.

Abstract

Inflammatory breast cancer (IBC) is a rare and aggressive subtype of breast cancer that carries a particularly poor prognosis. Despite the efficacy of immunotherapy in other difficult to treat forms of breast cancer, progress for immunotherapy in IBC has been difficult. Though immunotherapy has been under clinical investigation in IBC since the 1970s, few approaches have shown significant therapeutic efficacy, and no immunotherapy regimens are currently used in the treatment of IBC. Here, we provide a comprehensive summary of what is known about the immune composition of IBC tumors, clinical and basic science evidence describing the role for immune checkpoints such as PD-L1 in IBC pathobiology, as well as past and present attempts to advance ICIs in the treatment of IBC.

Advances in research of extracellular mechanisms underlying gemcitabine resistance in pancreatic cancer

Pancreatic cancer is a solid malignant tumor with the worst prognosis worldwide, and about 90% of cases are pancreatic ductal adenocarcinoma (PDAC). Although surgical resection is the only potential way to cure PDAC, the overall survival rate after surgery is still not optimistic. Consequently, gemcitabine (GEM)-based chemotherapy is still one of the most important treatment options for PDAC. However, the survival improvement by GEM monotherapy for advanced PDAC is very limited, and GEM resistance is the key reason. The mechanism underlying gemcitabine resistance is complex and still unclear in PDAC. The extensive and dense fibrous mesenchyme in the tumor microenvironment (TME) is an important feature of PDAC. More and more evidence has shown that TME is not only an active participant in tumor growth and spread, but also a contributor to the induction of GEM resistance. This article will review the recent advances in the understanding of the cellular and molecular mechanisms underlying GEM resistance in PDAC, and discuss potential GEM chemosensitization strategies, in order to improve the effective rate of chemotherapy and the outcome.

The matrix in cancer

The extracellular matrix is a fundamental, core component of all tissues and organs, and is essential for the existence of multicellular organisms. From the earliest stages of organism development until death, it regulates and fine-tunes every cellular process in the body. In cancer, the extracellular matrix is altered at the biochemical, biomechanical, architectural and topographical levels, and recent years have seen an exponential increase in the study and recognition of the importance of the matrix in solid tumours. Coupled with the advancement of new technologies to study various elements of the matrix and cell-matrix interactions, we are also beginning to see the deployment of matrix-centric, stromal targeting cancer therapies. This Review touches on many of the facets of matrix biology in solid cancers, including breast, pancreatic and lung cancer, with the aim of highlighting some of the emerging interactions of the matrix and influences that the matrix has on tumour onset, progression and metastatic dissemination, before summarizing the ongoing work in the field aimed at developing therapies to co-target the matrix in cancer and cancer metastasis.

Tumor-infiltrating CD8+ T cell antitumor efficacy and exhaustion: molecular insights

Host immunity has an essential role in the clinical management of cancers. Therefore, it is advantageous to choose therapies that can promote tumor cell death and concurrently boost host immunity. The dynamic tumor microenvironment (TME) determines whether an antineoplastic drug will elicit favorable or disparaging immune responses from tumor-infiltrating lymphocytes (TILs). CD8+ T cells are one of the primary tumor-infiltrating immune cells that deliver antitumor responses. Here, we review the influence of various factors in the TME on CD8+ T cell exhaustion and survival, and possible strategies for restoring CD8+ T cell effector function through immunotherapy.

Trials and tribulations of pancreatic cancer immunotherapy

Immunotherapy has revolutionized cancer treatment in the last decade, and strategies to re-activate cytotoxic immunity are now standard of care in several malignancies. Despite rapid advances in immunotherapy for most solid cancers, progress in immunotherapy against pancreatic ductal adenocarcinoma (PDAC) has been exceptionally difficult. This is true for several approaches, most notably immune checkpoint inhibitors (ICIs) and GM-CSF cell-based vaccines (GVAX). Though many immunotherapies have been explored in clinical trials, few have shown significant therapeutic efficacy. Further, many have shown high rates of serious adverse effects and dose-limiting toxicities, and to date, immunotherapy regimens have not been successfully implemented in PDAC. Here, we provide a comprehensive summary of the key clinical trials exploring immunotherapy in PDAC, followed by a brief discussion of emerging molecular mechanisms that may explain the relative failure of immunotherapy in pancreas cancer thus far.

Chemotherapeutic and targeted agents can modulate the tumor microenvironment and increase the efficacy of immune checkpoint blockades

The development of immune checkpoint blockade (ICB)-based immunotherapy has dramatically changed methods of cancer treatment. This approach triggers a durable treatment response and prolongs patients' survival; however, not all patients can benefit. Accumulating evidence demonstrated that the efficacy of ICB is dependent on a robust antitumor immune response that is usually damaged in most tumors. Conventional chemotherapy and targeted therapy promote the antitumor immune response by increasing the immunogenicity of tumor cells, improving CD8+ T cell infiltration, or inhibiting immunosuppressive cells in the tumor microenvironment. Such immunomodulation provides a convincing rationale for the combination therapy of chemotherapeutics and ICBs, and both preclinical and clinical investigations have shown encouraging results. However, the optimal drug combinations, doses, timing, and sequence of administration, all of which affect the immunomodulatory effect of chemotherapeutics, as well as the benefit of combination therapy, are not yet determined. Future studies should focus on these issues and help to develop the optimal combination regimen for each cancer.

Implications of the microbiome in the development and treatment of pancreatic cancer: Thinking outside of the box by looking inside the gut

Pancreatic ductal adenocarcinoma is the third leading cause of cancer-related death in the United States. As one of the most lethal cancer types, the prognosis for patients diagnosed with pancreatic cancer remains dismal and novel investigations are urgently needed. Evidence for an association of microbes with pancreatic cancer risk, development, treatment response, and post-treatment survivorship is rapidly developing. Herein, we provide an overview on the role of the microbiome as it relates to the natural history of pancreatic cancer, including host immune interactions, alterations in metabolism, direct carcinogenic effect, and its role in treatment response.

Preclinical Models of Pancreatic Ductal Adenocarcinoma and Their Utility in Immunotherapy Studies

Simple Summary

Immune checkpoint blockade has provided durable clinical responses in a number of human malignancies, but not in patients with pancreatic cancer. Efforts to understand mechanisms of resistance and increase efficacy of immune checkpoint blockade in pancreatic cancer require the use of appropriate preclinical models in the laboratory. Here, we discuss the benefits, caveats, and potentials for improvement of the most commonly used models, including murine-based and patient-derived models.

Abstract

The advent of immunotherapy has transformed the treatment landscape for several human malignancies. Antibodies against immune checkpoints, such as anti-PD-1/PD-L1 and anti-CTLA-4, demonstrate durable clinical benefits in several cancer types. However, checkpoint blockade has failed to elicit effective anti-tumor responses in pancreatic ductal adenocarcinoma (PDAC), which remains one of the most lethal malignancies with a dismal prognosis. As a result, there are significant efforts to identify novel immune-based combination regimens for PDAC, which are typically first tested in preclinical models. Here, we discuss the utility and limitations of syngeneic and genetically-engineered mouse models that are currently available for testing immunotherapy regimens. We also discuss patient-derived xenograft mouse models, human PDAC organoids, and ex vivo slice cultures of human PDAC tumors that can complement murine models for a more comprehensive approach to predict response and resistance to immunotherapy regimens.

Pharmacologic Normalization of Pancreatic Cancer-Associated Fibroblast Secretome Impairs Prometastatic Cross-Talk With Macrophages

BACKGROUND & AIMS

Cancer-associated fibroblasts (CAFs) from pancreatic adenocarcinoma (PDA) present high protein synthesis rates. CAFs express the G-protein-coupled somatostatin receptor sst1. The sst1 agonist SOM230 blocks CAF protumoral features in vitro and in immunocompromised mice. We have explored here the therapeutic potential of SOM230, and underlying mechanisms, in immunocompetent models of murine PDA mimicking the heavy fibrotic and immunosuppressive stroma observed in patient tumors.

METHODS

Large-scale mass spectrometry analyses were performed on media conditioned from 9 patient PDA-derived CAF primary cultures. Spontaneous transgenic and experimental (orthotopic co-graft of tumor cells plus CAFs) PDA-bearing mice were longitudinally ultrasound-monitored for tumor and metastatic progression. Histopathology and flow cytometry analyses were performed on primary tumors and metastases. Stromal signatures were functionally validated through bioinformatics using several published, and 1 original, PDA database.

RESULTS

Proteomics on the CAF secretome showed that SOM230 controls stromal activities including inflammatory responses. Among the identified secreted proteins, we validated that colony-stimulating factor 1 (CSF-1) (a macrophage growth factor) was reduced by SOM230 in the tumor and plasma of PDA-harboring mice, alongside intratumor stromal normalization (reduced CAF and macrophage activities), and dramatic metastasis reduction. In transgenic mice, these SOM230 benefits alleviate the chemotherapy-induced (gemcitabine) immunosuppressive stroma reshaping. Mechanistically, SOM230 acts in vivo on CAFs through sst1 to disrupt prometastatic CAF production of CSF-1 and cross-talk with macrophages. We found that in patients, stromal CSF-1 was associated with aggressive PDA forms.

CONCLUSIONS

We propose SOM230 as an antimetastatic therapy in PDA for its capacity to remodel the fibrotic and immunosuppressive myeloid stroma. This pharmacotherapy should benefit PDA patients treated with chemotherapies.

Targeting the Microenvironment to Overcome Gemcitabine Resistance in Pancreatic Cancer

Pancreatic cancer is characterized by an extensive and complex microenvironment, and is resistant to both chemotherapy and immune checkpoint blockade. The study by Principe and colleagues in this issue of Cancer Research proposes a combinatorial approach based on targeting the very mechanisms of resistance to gemcitabine, a commonly used chemotherapeutic agent. The authors show that gemcitabine treatment causes profound changes in the pancreatic cancer microenvironment, including elevated TGFβ signaling and immune checkpoint expression, as well as increased antigen presentation in tumor cells. Accordingly, they show that the combination of chemotherapy, TGFβ signaling inhibition, and immune checkpoint blockade effectively restores antitumor immunity and results in a significant survival benefit.See related article by Principe et al., p. 3101.

Novel Liver X Receptor Ligand GAC0001E5 Disrupts Glutamine Metabolism and Induces Oxidative Stress in Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDAC) is the predominant form of pancreatic cancer with a high mortality rate due to the lack of early detection and effective treatment options for advanced diseases. Metabolic reprogramming, a common hallmark of malignant transformation in pancreatic cancer, is critical for the growth and survival of cancer cells and a potential target mechanism for the treatment of pancreatic cancer. PDAC cells have upregulated glutamine metabolism to meet their biosynthetic and oxidative demands. Liver X receptors (LXRs) are ligand-dependent transcription factors involved in maintaining metabolic homeostasis. LXRs regulate critical cancer-related processes and pathways, including cholesterol, glucose and lipid metabolism, and inflammatory and immune responses. Analysis of transcriptomic data from PDAC clinical samples reveals overexpression of LXRs and their target genes in tumors as compared to normal tissue controls. Targeting LXRs with the novel LXR inverse agonist and degrader GAC0001E5 inhibited PDAC cell proliferation. Using a metabolomics approach, we discovered that 1E5 inhibits glutamine anaplerosis and induces oxidative stress, which are detrimental to PDAC cells. These findings highlight a novel role for LXR in regulating cancer metabolism and the potential application of LXR modulators in targeting cancer metabolism in pancreatic cancer and other malignancies.

Differential Gemcitabine Sensitivity in Primary Human Pancreatic Cancer Cells and Paired Stellate Cells Is Driven by Heterogenous Drug Uptake and Processing

Simple Summary

Pancreatic ductal adenocarcinoma (PDAC, also known as pancreatic cancer) is one of the deadliest tumor types, characterized by poor prognosis, profound chemoresistance and overall low survival. Gemcitabine remains the standard of care for all stages of PDAC, however, with poor clinical benefits which is considered to be due to reduced drug availability in tumor cells. Gemcitabine-induced cytotoxicity depends upon sufficient drug uptake followed by intracellular activation. Pancreatic stellate cells (PSCs), a major stromal component of PDAC, were recently reported to scavenge active metabolites of gemcitabine, thereby making it unavailable for cancer cells. Gemcitabine uptake and processing in both tumor cells and PSCs, as well as expression analysis of its molecular metabolic regulators, was investigated in this study. We observed heterogeneous gemcitabine-induced cytotoxicity in different pancreatic cancer cells whereas it was absent in PSCs. The gemcitabine-induced cytotoxicity in pancreatic cancer cells was driven by differential expression of its molecular regulators.

Abstract

Gemcitabine resistance in pancreatic ductal adenocarcinoma (PDAC) is attributed to cancer cell-intrinsic drug processing and the impact of the tumor microenvironment, especially pancreatic stellate cells (PSCs). This study uses human PDAC-derived paired primary cancer cells (PCCs) and PSCs from four different tumors, and the PDAC cell lines BxPC-3, Mia PaCa-2, and Panc-1, to assess the fate of gemcitabine by measuring its cellular uptake, cytotoxicity, and LC-MS/MS-based metabolite analysis. Expression analysis and siRNA-mediated knockdown of key regulators of gemcitabine (hENT1, CDA, DCK, NT5C1A) was performed. Compared to PSCs, both the paired primary PCCs and cancer cell lines showed gemcitabine-induced dose-dependent cytotoxicity, high uptake, as well as high and variable intracellular levels of gemcitabine metabolites. PSCs were gemcitabine-resistant and demonstrated significantly lower drug uptake, which was not influenced by co-culturing with their paired PCCs. Expression of key gemcitabine regulators was variable, but overall strong in the cancer cells and significantly lower or undetectable in PSCs. In cancer cells, hENT1 inhibition significantly downregulated gemcitabine uptake and cytotoxicity, whereas DCK knockdown reduced cytotoxicity. In conclusion, heterogeneity in gemcitabine processing among different pancreatic cancer cells and stellate cells results from the differential expression of molecular regulators which determines the effect of gemcitabine.

Frequency and prognostic value of mutations associated with the homologous recombination DNA repair pathway in a large pan cancer cohort

PARP inhibitors have shown remarkable efficacy in the clinical management of several BRCA-mutated tumors. This approach is based on the long-standing hypothesis that PARP inhibition will impair the repair of single stranded breaks, causing synthetic lethality in tumors with loss of high-fidelity double-strand break homologous recombination. While this is now well accepted and has been the basis of several successful clinical trials, emerging evidence strongly suggests that mutation to several additional genes involved in homologous recombination may also have predictive value for PARP inhibitors. While this notion is supported by early clinical evidence, the mutation frequencies of these and other functionally related genes are largely unknown, particularly in cancers not classically associated with homologous recombination deficiency. We therefore evaluated the mutation status of 22 genes associated with the homologous recombination DNA repair pathway or PARP inhibitor sensitivity, first in a pan-cancer cohort of 55,586 patients, followed by a more focused analysis in The Cancer Genome Atlas cohort of 12,153 patients. In both groups we observed high rates of mutations in a variety of HR-associated genes largely unexplored in the setting of PARP inhibition, many of which were associated also with poor clinical outcomes. We then extended our study to determine which mutations have a known oncogenic role, as well as similar to known oncogenic mutations that may have a similar phenotype. Finally, we explored the individual cancer histologies in which these genomic alterations are most frequent. We concluded that the rates of deleterious mutations affecting genes associated with the homologous recombination pathway may be underrepresented in a wide range of human cancers, and several of these genes warrant further and more focused investigation, particularly in the setting of PARP inhibition and HR deficiency.

In pancreatic cancer, chemotherapy increases antitumor responses to tumor-associated antigens and potentiates DNA vaccination

BACKGROUND

Pancreatic ductal adenocarcinoma (PDA) is an almost incurable tumor that is mostly resistant to chemotherapy (CT). Adaptive immune responses to tumor-associated antigens (TAA) have been reported, but immunotherapy (IT) clinical trials have not yet achieved any significant increase in survival, confirming the suppressive environment of PDA. As CT has immune-modulating properties, we investigated the effect of gemcitabine (GEM) in antitumor effector responses to TAA in patients with PDA.

METHODS

The IgG antibody repertoire in patients with PDA before and after CT was profiled by serological proteome analysis and ELISA and their ability to activate complement-dependent cytotoxicity (CDC) was measured. Peripheral T cells were stimulated in vitro with recombinant TAA, and specific proliferation, IFN-γ/IL-10 and CD8⁺/Treg ratios were measured. Mice that spontaneously developed PDA were treated with GEM and inoculated with an ENO1 (α-Enolase) DNA vaccine. In some experimental groups, the effect of depleting CD4, CD8 and B cells by specific antibodies was also evaluated.

RESULTS

CT increased the number of TAA recognized by IgG and their ability to activate CDC. Evaluation of the IFN-γ/IL-10 ratio and CD8+/Treg ratios revealed that CT treatment shifted T cell responses to ENO1, G3P (glyceraldheyde-3-phosphate dehydrogenase), K2C8 (keratin, type II cytoskeletal 8) and FUBP1 (far upstream binding protein 1), four of the most recognized TAA, from regulatory to effector. In PDA mice models, treatment with GEM prior to ENO1 DNA vaccination unleashed CD4 antitumor activity and strongly impaired tumor progression compared with mice that were vaccinated or GEM-treated alone.

CONCLUSIONS

Overall, these data indicate that, in PDA, CT enhances immune responses to TAA and renders them suitable targets for IT.

PD-1 Expression by Lymph Node and Intratumoral Regulatory T Cells Is Associated with Lymph Node Metastasis in Pancreatic Cancer

Simple Summary

Pancreatic cancer is a devastating disease and among the most immune-resistant tumor types. Single-agent immunotherapy has not demonstrated clinical benefits in pancreatic cancer patients, and combinational therapies targeting multiple mechanisms of immunosuppression are likely needed. T cell activation in lymph nodes is required for the efficacy of immunotherapy. Here, we phenotypically and functionally analyze T cells from tumor-draining lymph nodes, blood and tumors from patients with pancreatic cancer to decipher unknown immunosuppressive mechanisms and to identify potential immunotherapeutic targets.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a mostly immunosuppressive microenvironment. Tumor-draining lymph nodes (TDLN) are a major site for priming of tumor-reactive T cells and also tumor metastasis. However, the phenotype and function of T cells in TDLNs from PDAC patients is unknown. In this study, lymph nodes from the pancreatic head (PH), the hepatoduodenal ligament (HDL) and the interaortocaval (IAC) region were obtained from 25 patients with adenocarcinoma of the pancreatic head. Additionally, tumors and matched blood were analyzed from 16 PDAC patients. Using multicolor flow cytometry, we performed a comprehensive analysis of T cells. CD4⁺ T cells were the predominant T cell subset in PDAC-draining lymph nodes. Overall, lymph node CD4⁺ and CD8⁺ T cells had a similar degree of activation, as measured by CD69, inducible T cell co-stimulator (ICOS) and CD137 (4-1BB) expression and interferon-γ (IFNγ) secretion. Expression of the inhibitory receptor programmed death 1 (PD-1) by lymph node and tumor-infiltrating regulatory T cells (Tregs) correlated with lymph node metastasis. Collectively, Treg cells and PD-1 are two relevant components of the immunosuppressive network in PDAC-draining lymph nodes and may be particularly attractive targets for combinatorial immunotherapeutic strategies in selected patients with node-positive PDAC.

Updated risk factors to inform early pancreatic cancer screening and identify high risk patients

Pancreatic adenocarcinoma (PDAC) is associated with poor clinical outcomes and incomplete responses to conventional therapy. Therefore, there is an unmet clinical need to better understand the predisposing factors for pancreatic cancer in hopes of providing early screening to high-risk patients. While select risk factors such as age, race, and family history, or predisposing syndromes are unavoidable, there are several new and established risk factors that allow for intervention, namely by counseling patients to make the appropriate lifestyle modifications. Here, we discuss the best-studied risk factors for PDAC such as tobacco use and chronic pancreatitis, as well as newly emerging risk factors including select nutritional deficits, bacterial infections, and psychosocial factors. As several of these risk factors appear to be additive or synergistic, by understanding their relationships and offering coordinated, multidisciplinary care to high-risk patients, it may be possible to reduce pancreatic cancer incidence and improve clinical outcomes through early detection.