Senescence Defines a Distinct Subset of Myofibroblasts That Orchestrates Immunosuppression in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) therapeutic resistance is largely attributed to a unique tumor microenvironment embedded with an abundance of cancer-associated fibroblasts (CAF). Distinct CAF populations were recently identified, but the phenotypic drivers and specific impact of CAF heterogeneity remain unclear. In this study, we identify a subpopulation of senescent myofibroblastic CAFs (SenCAF) in mouse and human PDAC. These SenCAFs are a phenotypically distinct subset of myofibroblastic CAFs that localize near tumor ducts and accumulate with PDAC progression. To assess the impact of endogenous SenCAFs in PDAC, we used an LSL-KRASG12D;p53flox;p48-CRE;INK-ATTAC (KPPC-IA) mouse model of spontaneous PDAC with inducible senescent cell depletion. Depletion of senescent stromal cells in genetic and pharmacologic PDAC models relieved immune suppression by macrophages, delayed tumor progression, and increased responsiveness to chemotherapy. Collectively, our findings demonstrate that SenCAFs promote PDAC progression and immune cell dysfunction.

SIGNIFICANCE

CAF heterogeneity in PDAC remains poorly understood. In this study, we identify a novel subpopulation of senescent CAFs that promotes PDAC progression and immunosuppression. Targeting CAF senescence in combination therapies could increase tumor vulnerability to chemo- or immunotherapy. See related article by Ye et al.

Senescent CAFs Mediate Immunosuppression and Drive Breast Cancer Progression

The tumor microenvironment (TME) profoundly influences tumorigenesis, with gene expression in the breast TME capable of predicting clinical outcomes. The TME is complex and includes distinct cancer-associated fibroblast (CAF) subtypes whose contribution to tumorigenesis remains unclear. Here, we identify a subset of myofibroblast CAFs (myCAF) that are senescent (senCAF) in mouse and human breast tumors. Utilizing the MMTV-PyMT;INK-ATTAC (INK) mouse model, we found that senCAF-secreted extracellular matrix specifically limits natural killer (NK) cell cytotoxicity to promote tumor growth. Genetic or pharmacologic senCAF elimination unleashes NK cell killing, restricting tumor growth. Finally, we show that senCAFs are present in HER2+, ER+, and triple-negative breast cancer and in ductal carcinoma in situ (DCIS) where they predict tumor recurrence. Together, these findings demonstrate that senCAFs are potently tumor promoting and raise the possibility that targeting them by senolytic therapy could restrain breast cancer development.

SIGNIFICANCE

senCAFs limit NK cell-mediated killing, thereby contributing to breast cancer progression. Thus, targeting senCAFs could be a clinically viable approach to limit tumor progression.

Combined KRAS-MAPK pathway inhibitors and HER2-directed drug conjugate is efficacious in pancreatic cancer

Targeting the mitogen-activated protein kinase (MAPK) cascade in pancreatic ductal adenocarcinoma (PDAC) remains clinically unsuccessful. We aim to develop a MAPK inhibitor-based therapeutic combination with strong preclinical efficacy. Utilizing a reverse-phase protein array, we observe rapid phospho-activation of human epidermal growth factor receptor 2 (HER2) in PDAC cells upon pharmacological MAPK inhibition. Mechanistically, MAPK inhibitors lead to swift proteasomal degradation of dual-specificity phosphatase 6 (DUSP6). The carboxy terminus of HER2, containing a TEY motif also present in extracellular signal-regulated kinase 1/2 (ERK1/2), facilitates binding with DUSP6, enhancing its phosphatase activity to dephosphorylate HER2. In the presence of MAPK inhibitors, DUSP6 dissociates from the protective effect of the RING E3 ligase tripartite motif containing 21, resulting in its degradation. In PDAC patient-derived xenograft (PDX) models, combining ERK and HER inhibitors slows tumour growth and requires cytotoxic chemotherapy to achieve tumour regression. Alternatively, MAPK inhibitors with trastuzumab deruxtecan, an anti-HER2 antibody conjugated with cytotoxic chemotherapy, lead to sustained tumour regression in most tested PDXs without causing noticeable toxicity. Additionally, KRAS inhibitors also activate HER2, supporting testing the combination of KRAS inhibitors and trastuzumab deruxtecan in PDAC. This study identifies a rational and promising therapeutic combination for clinical testing in PDAC patients.

Intratumoral T-cell receptor repertoire composition predicts overall survival in patients with pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy that is refractory to immune checkpoint inhibitor therapy. However, intratumoral T-cell infiltration correlates with improved overall survival (OS). Herein, we characterized the diversity and antigen specificity of the PDAC T-cell receptor (TCR) repertoire to identify novel immune-relevant biomarkers. Demographic, clinical, and TCR-beta sequencing data were collated from 353 patients across three cohorts that underwent surgical resection for PDAC. TCR diversity was calculated using Shannon Wiener index, Inverse Simpson index, and "True entropy." Patients were clustered by shared repertoire specificity. TCRs predictive of OS were identified and their associated transcriptional states were characterized by single-cell RNAseq. In multivariate Cox regression models controlling for relevant covariates, high intratumoral TCR diversity predicted OS across multiple cohorts. Conversely, in peripheral blood, high abundance of T-cells, but not high diversity, predicted OS. Clustering patients based on TCR specificity revealed a subset of TCRs that predicts OS. Interestingly, these TCR sequences were more likely to encode CD8+ effector memory and CD4+ T-regulatory (Tregs) T-cells, all with the capacity to recognize beta islet-derived autoantigens. As opposed to T-cell abundance, intratumoral TCR diversity was predictive of OS in multiple PDAC cohorts, and a subset of TCRs enriched in high-diversity patients independently correlated with OS. These findings emphasize the importance of evaluating peripheral and intratumoral TCR repertoires as distinct and relevant biomarkers in PDAC.

"RIPping" off Pancreas Cancer's Blockage of Immune Surveillance

SUMMARY

MHC-I downregulation is correlated with immunotherapy resistance in PDAC, but efficient strategies to increase cell-surface MHC-I are still lacking. This study by Sang, Zhou, Chen, Yu, and colleagues identified inhibition of tumor-intrinsic RIPK2 as a pharmacologic target to block the degradation of MHC-I on tumor cells and improved PDAC responses to anti-PD-1 immunotherapy. See related article by Sang et al., p. 326 (1) .

Pancreatic Cancer's PD1-Roadblock: When T-Cell Reinvigoration Is Not Enough

PD1-blockade combinations in pancreatic ductal adenocarcinoma have been poorly effective, and the underlying reasons for this are unknown. A recent study revealed that chemoradiation plus PD1-blockade reinvigorates tumor-specific T cells; however, this T-cell activation is accompanied with exaggerated NFκB signaling, which may limit productive tumor-controlling immunity. See related article by Ali et al., p. 542.

Chemokine Receptor 2 Targeted PET/CT Imaging Distant Metastases in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive and treatment-refractory malignancies. The lack of an effective screening tool results in the majority of patients being diagnosed at late stages, which underscores the urgent need to develop more sensitive and specific imaging modalities, particularly in detecting occult metastases, to aid clinical decision-making. The tumor microenvironment of PDAC is heavily infiltrated with myeloid-derived suppressor cells (MDSCs) that express C-C chemokine receptor type 2 (CCR2). These CCR2-expressing MDSCs accumulate at a very early stage of metastasis and greatly outnumber PDAC cells, making CCR2 a promising target for detecting early, small metastatic lesions that have scant PDAC cells. Herein, we evaluated a CCR2 targeting PET tracer (68Ga-DOTA-ECL1i) for PET imaging on PDAC metastasis in two mouse models. Positron emission tomography/computed tomography (PET/CT) imaging of 68Ga-DOTA-ECL1i was performed in a hemisplenic injection metastasis model (KI) and a genetically engineered orthotopic PDAC model (KPC), which were compared with 18F-FDG PET concurrently. Autoradiography, hematoxylin and eosin (H&E), and CCR2 immunohistochemical staining were performed to characterize the metastatic lesions. PET/CT images visualized the PDAC metastases in the liver/lung of KI mice and in the liver of KPC mice. Quantitative uptake analysis revealed increased metastasis uptake during disease progression in both models. In comparison, 18F-FDG PET failed to detect any metastases during the time course studies. H&E staining showed metastases in the liver and lung of KI mice, within which immunostaining clearly demonstrated the overexpression of CCR2 as well as CCR2+ cell infiltration into the normal liver. H&E staining, CCR2 staining, and autoradiography also confirmed the expression of CCR2 and the uptake of 68Ga-DOTA-ECL1i in the metastatic foci in KPC mice. Using our novel CCR2 targeted radiotracer 68Ga-DOTA-ECL1i and PET/CT, we demonstrated the sensitive and specific detection of CCR2 in the early PDAC metastases in two mouse models, indicating its potential in future clinical translation.

Epigenetic regulation during cancer transitions across 11 tumour types

Chromatin accessibility is essential in regulating gene expression and cellular identity, and alterations in accessibility have been implicated in driving cancer initiation, progression and metastasis1-4. Although the genetic contributions to oncogenic transitions have been investigated, epigenetic drivers remain less understood. Here we constructed a pan-cancer epigenetic and transcriptomic atlas using single-nucleus chromatin accessibility data (using single-nucleus assay for transposase-accessible chromatin) from 225 samples and matched single-cell or single-nucleus RNA-sequencing expression data from 206 samples. With over 1 million cells from each platform analysed through the enrichment of accessible chromatin regions, transcription factor motifs and regulons, we identified epigenetic drivers associated with cancer transitions. Some epigenetic drivers appeared in multiple cancers (for example, regulatory regions of ABCC1 and VEGFA; GATA6 and FOX-family motifs), whereas others were cancer specific (for example, regulatory regions of FGF19, ASAP2 and EN1, and the PBX3 motif). Among epigenetically altered pathways, TP53, hypoxia and TNF signalling were linked to cancer initiation, whereas oestrogen response, epithelial-mesenchymal transition and apical junction were tied to metastatic transition. Furthermore, we revealed a marked correlation between enhancer accessibility and gene expression and uncovered cooperation between epigenetic and genetic drivers. This atlas provides a foundation for further investigation of epigenetic dynamics in cancer transitions.

Fibrosis induced by resident macrophages has divergent roles in pancreas inflammatory injury and PDAC

Tissue-resident macrophages (TRMs) are long-lived cells that maintain locally and can be phenotypically distinct from monocyte-derived macrophages. Whether TRMs and monocyte-derived macrophages have district roles under differing pathologies is not understood. Here, we showed that a substantial portion of the macrophages that accumulated during pancreatitis and pancreatic cancer in mice had expanded from TRMs. Pancreas TRMs had an extracellular matrix remodeling phenotype that was important for maintaining tissue homeostasis during inflammation. Loss of TRMs led to exacerbation of severe pancreatitis and death, due to impaired acinar cell survival and recovery. During pancreatitis, TRMs elicited protective effects by triggering the accumulation and activation of fibroblasts, which was necessary for initiating fibrosis as a wound healing response. The same TRM-driven fibrosis, however, drove pancreas cancer pathogenesis and progression. Together, these findings indicate that TRMs play divergent roles in the pathogenesis of pancreatitis and cancer through regulation of stromagenesis.

Systemic Alterations in Type-2 Conventional Dendritic Cells Lead to Impaired Tumor Immunity in Pancreatic Cancer

Intratumoral T-cell dysfunction is a hallmark of pancreatic tumors, and efforts to improve dendritic cell (DC)-mediated T-cell activation may be critical in treating these immune therapy unresponsive tumors. Recent evidence indicates that mechanisms that induce dysfunction of type 1 conventional DCs (cDC1) in pancreatic adenocarcinomas (PDAC) are drivers of the lack of responsiveness to checkpoint immunotherapy. However, the impact of PDAC on systemic type 2 cDC2 development and function has not been well studied. Herein, we report the analysis of 3 cohorts, totaling 106 samples, of human blood and bone marrow (BM) from patients with PDAC for changes in cDCs. We found that circulating cDC2s and their progenitors were significantly decreased in the blood of patients with PDAC, and repressed numbers of cDC2s were associated with poor prognosis. Serum cytokine analyses identified IL6 as significantly elevated in patients with PDAC and negatively correlated with cDC numbers. In vitro, IL6 impaired the differentiation of cDC1s and cDC2s from BM progenitors. Single-cell RNA sequencing analysis of human cDC progenitors in the BM and blood of patients with PDAC showed an upregulation of the IL6/STAT3 pathway and a corresponding impairment of antigen processing and presentation. These results suggested that cDC2s were systemically suppressed by inflammatory cytokines, which was linked to impaired antitumor immunity.

Induction of cancer neoantigens facilitates development of clinically relevant models for the study of pancreatic cancer immunobiology

Neoantigen burden and CD8 T cell infiltrate are associated with clinical outcome in pancreatic ductal adenocarcinoma (PDAC). A shortcoming of many genetic models of PDAC is the lack of neoantigen burden and limited T cell infiltrate. The goal of the present study was to develop clinically relevant models of PDAC by inducing cancer neoantigens in KP2, a cell line derived from the KPC model of PDAC. KP2 was treated with oxaliplatin and olaparib (OXPARPi), and a resistant cell line was subsequently cloned to generate multiple genetically distinct cell lines (KP2-OXPARPi clones). Clones A and E are sensitive to immune checkpoint inhibition (ICI), exhibit relatively high T cell infiltration, and have significant upregulation of genes involved in antigen presentation, T cell differentiation, and chemokine signaling pathways. Clone B is resistant to ICI and is similar to the parental KP2 cell line in terms of relatively low T cell infiltration and no upregulation of genes involved in the pathways noted above. Tumor/normal exome sequencing and in silico neoantigen prediction confirms successful generation of cancer neoantigens in the KP2-OXPARPi clones and the relative lack of cancer neoantigens in the parental KP2 cell line. Neoantigen vaccine experiments demonstrate that a subset of candidate neoantigens are immunogenic and neoantigen synthetic long peptide vaccines can restrain Clone E tumor growth. Compared to existing models, the KP2-OXPARPi clones better capture the diverse immunobiology of human PDAC and may serve as models for future investigations in cancer immunotherapies and strategies targeting cancer neoantigens in PDAC.

Context-dependent activation of STING-interferon signaling by CD11b agonists enhances anti-tumor immunity

Chronic activation of inflammatory pathways and suppressed interferon are hallmarks of immunosuppressive tumors. Previous studies have shown that CD11b integrin agonists could enhance anti-tumor immunity through myeloid reprograming, but the underlying mechanisms remain unclear. Herein we find that CD11b agonists alter tumor-associated macrophage (TAM) phenotypes by repressing NF-κB signaling and activating interferon gene expression simultaneously. Repression of NF-κB signaling involves degradation of p65 protein and is context independent. In contrast, CD11b agonism induces STING/STAT1 pathway-mediated interferon gene expression through FAK-mediated mitochondrial dysfunction, with the magnitude of induction dependent on the tumor microenvironment and amplified by cytotoxic therapies. Using tissues from phase I clinical studies, we demonstrate that GB1275 treatment activates STING and STAT1 signaling in TAMs in human tumors. These findings suggest potential mechanism-based therapeutic strategies for CD11b agonists and identify patient populations more likely to benefit.

Tumor-associated fibrosis impairs immune surveillance and response to immune checkpoint blockade in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a leading cause of cancer-related deaths. Immune checkpoint blockade has improved survival for many patients with NSCLC, but most fail to obtain long-term benefit. Understanding the factors leading to reduced immune surveillance in NSCLC is critical in improving patient outcomes. Here, we show that human NSCLC harbors large amounts of fibrosis that correlates with reduced T cell infiltration. In murine NSCLC models, the induction of fibrosis led to increased lung cancer progression, impaired T cell immune surveillance, and failure of immune checkpoint blockade efficacy. Associated with these changes, we observed that fibrosis leads to numerically and functionally impaired dendritic cells and altered macrophage phenotypes that likely contribute to immunosuppression. Within cancer-associated fibroblasts, distinct changes within the Col13a1-expressing population suggest that these cells produce chemokines to recruit macrophages and regulatory T cells while limiting recruitment of dendritic cells and T cells. Targeting fibrosis through transforming growth factor-β receptor signaling overcame the effects of fibrosis to enhance T cell responses and improved the efficacy of immune checkpoint blockade but only in the context of chemotherapy. Together, these data suggest that fibrosis in NSCLC leads to reduced immune surveillance and poor responsiveness to checkpoint blockade and highlight antifibrotic therapies as a candidate strategy to overcome immunotherapeutic resistance.

Stromal and therapy-induced macrophage proliferation promotes PDAC progression and susceptibility to innate immunotherapy

Tumor-associated macrophages (TAMs) are abundant in pancreatic ductal adenocarcinomas (PDACs). While TAMs are known to proliferate in cancer tissues, the impact of this on macrophage phenotype and disease progression is poorly understood. We showed that in PDAC, proliferation of TAMs could be driven by colony stimulating factor-1 (CSF1) produced by cancer-associated fibroblasts. CSF1 induced high levels of p21 in macrophages, which regulated both TAM proliferation and phenotype. TAMs in human and mouse PDACs with high levels of p21 had more inflammatory and immunosuppressive phenotypes. p21 expression in TAMs was induced by both stromal interaction and/or chemotherapy treatment. Finally, by modeling p21 expression levels in TAMs, we found that p21-driven macrophage immunosuppression in vivo drove tumor progression. Serendipitously, the same p21-driven pathways that drive tumor progression also drove response to CD40 agonist. These data suggest that stromal or therapy-induced regulation of cell cycle machinery can regulate both macrophage-mediated immune suppression and susceptibility to innate immunotherapy.

p38MAPKα Stromal Reprogramming Sensitizes Metastatic Breast Cancer to Immunotherapy

Metastatic breast cancer is an intractable disease that responds poorly to immunotherapy. We show that p38MAPKα inhibition (p38i) limits tumor growth by reprogramming the metastatic tumor microenvironment in a CD4+ T cell-, IFNγ-, and macrophage-dependent manner. To identify targets that further increased p38i efficacy, we utilized a stromal labeling approach and single-cell RNA sequencing. Thus, we combined p38i and an OX40 agonist that synergistically reduced metastatic growth and increased overall survival. Intriguingly, patients with a p38i metastatic stromal signature had better overall survival that was further improved by the presence of an increased mutational load, leading us to ask if our approach would be effective in antigenic breast cancer. The combination of p38i, anti-OX40, and cytotoxic T-cell engagement cured mice of metastatic disease and produced long-term immunologic memory. Our findings demonstrate that a detailed understanding of the stromal compartment can be used to design effective antimetastatic therapies.

SIGNIFICANCE

Immunotherapy is rarely effective in breast cancer. We dissected the metastatic tumor stroma, which revealed a novel therapeutic approach that targets the stromal p38MAPK pathway and creates an opportunity to unleash an immunologic response. Our work underscores the importance of understanding the tumor stromal compartment in therapeutic design. This article is highlighted in the In This Issue feature, p. 1275.

A Cre-deleter specific for embryo-derived brain macrophages reveals distinct features of microglia and border macrophages

Genetic tools to target microglia specifically and efficiently from the early stages of embryonic development are lacking. We generated a constitutive Cre line controlled by the microglia signature gene Crybb1 that produced nearly complete recombination in embryonic brain macrophages (microglia and border-associated macrophages [BAMs]) by the perinatal period, with limited recombination in peripheral myeloid cells. Using this tool in combination with Flt3-Cre lineage tracer, single-cell RNA-sequencing analysis, and confocal imaging, we resolved embryonic-derived versus monocyte-derived BAMs in the mouse cortex. Deletion of the transcription factor SMAD4 in microglia and embryonic-derived BAMs using Crybb1-Cre caused a developmental arrest of microglia, which instead acquired a BAM specification signature. By contrast, the development of genuine BAMs remained unaffected. Our results reveal that SMAD4 drives a transcriptional and epigenetic program that is indispensable for the commitment of brain macrophages to the microglia fate and highlight Crybb1-Cre as a tool for targeting embryonic brain macrophages.

Defactinib, Pembrolizumab, and Gemcitabine in Patients with Advanced Treatment Refractory Pancreatic Cancer: A Phase I Dose Escalation and Expansion Study

PURPOSE

Targeting focal adhesion kinase (FAK) renders checkpoint immunotherapy effective in pancreatic ductal adenocarcinoma (PDAC) mouse model. Defactinib is a highly potent oral FAK inhibitor that has a tolerable safety profile.

PATIENTS AND METHODS

We conducted a multicenter, open-label, phase I study with dose escalation and expansion phases. In dose escalation, patients with refractory solid tumors were treated at five escalating dose levels of defactinib and gemcitabine to identify a recommended phase II dose (RP2D). In expansion phase, patients with metastatic PDAC who progressed on frontline treatment (refractory cohort) or had stable disease (SD) after at least 4 months of standard gemcitabine/nab-paclitaxel (maintenance cohort) were treated at RP2D. Pre- and posttreatment tumor biopsies were performed to evaluate tumor immunity.

RESULTS

The triple drug combination was well-tolerated, with no dose-limiting toxicities. Among 20 treated patients with refractory PDAC, the disease control rate (DCR) was 80%, with one partial response (PR) and 15 SDs, and the median progression-free survival (PFS) and overall survival (OS) were 3.6 and 7.8 months, respectively. Among 10 evaluable patients in the maintenance cohort, DCR was 70% with one PR and six SDs. Three patients with SD came off study due to treatment- or disease-related complications. The median PFS and OS on study treatment were 5.0 and 8.3 months, respectively.

CONCLUSIONS

The combination of defactinib, pembrolizumab, and gemcitabine was well-tolerated and safe, had promising preliminary efficacy, and showed biomarker activity in infiltrative T lymphocytes. Efficacy of this strategy may require incorporation of more potent chemotherapy in future studies.

Combination TIGIT/PD-1 blockade enhances the efficacy of neoantigen vaccines in a model of pancreatic cancer

Background

Cancer neoantigens are important targets of cancer immunotherapy and neoantigen vaccines are currently in development in pancreatic ductal adenocarcinoma (PDAC) and other cancer types. Immune regulatory mechanisms in pancreatic cancer may limit the efficacy of neoantigen vaccines. Targeting immune checkpoint signaling pathways in PDAC may improve the efficacy of neoantigen vaccines.

Methods

We used KPC4580P, an established model of PDAC, to test whether neoantigen vaccines can generate therapeutic efficacy against PDAC. We focused on two immunogenic neoantigens associated with genetic alterations in the CAR12 and CDK12 genes. We tested a neoantigen vaccine comprised of two 20-mer synthetic long peptides and poly IC, a Toll-like receptor (TLR) agonist. We investigated the ability of neoantigen vaccine alone, or in combination with PD-1 and TIGIT signaling blockade to impact tumor growth. We also assessed the impact of TIGIT signaling on T cell responses in human PDAC.

Results

Neoantigen vaccines induce neoantigen-specific T cell responses in tumor-bearing mice and slow KPC4580P tumor growth. However, KPC4580P tumors express high levels of PD-L1 and the TIGIT ligand, CD155. A subset of neoantigen-specific T cells in KPC4580P tumors are dysfunctional, and express high levels of TIGIT. PD-1 and TIGIT signaling blockade in vivo reverses T cell dysfunction and enhances neoantigen vaccine-induced T cell responses and tumor regression. In human translational studies, TIGIT signaling blockade in vitro enhances neoantigen-specific T cell function following vaccination.

Conclusions

Taken together, preclinical and human translational studies support testing neoantigen vaccines in combination with therapies targeting the PD-1 and TIGIT signaling pathways in patients with PDAC.

Stromal Reprogramming by FAK Inhibition Overcomes Radiation Resistance to Allow for Immune Priming and Response to Checkpoint Blockade

The effects of radiotherapy (RT) on tumor immunity in pancreatic ductal adenocarcinoma (PDAC) are not well understood. To better understand if RT can prime antigen-specific T-cell responses, we analyzed human PDAC tissues and mouse models. In both settings, there was little evidence of RT-induced T-cell priming. Using in vitro systems, we found that tumor-stromal components, including fibroblasts and collagen, cooperate to blunt RT efficacy and impair RT-induced interferon signaling. Focal adhesion kinase (FAK) inhibition rescued RT efficacy in vitro and in vivo, leading to tumor regression, T-cell priming, and enhanced long-term survival in PDAC mouse models. Based on these data, we initiated a clinical trial of defactinib in combination with stereotactic body RT in patients with PDAC (NCT04331041). Analysis of PDAC tissues from these patients showed stromal reprogramming mirroring our findings in genetically engineered mouse models. Finally, the addition of checkpoint immunotherapy to RT and FAK inhibition in animal models led to complete tumor regression and long-term survival.

SIGNIFICANCE

Checkpoint immunotherapeutics have not been effective in PDAC, even when combined with RT. One possible explanation is that RT fails to prime T-cell responses in PDAC. Here, we show that FAK inhibition allows RT to prime tumor immunity and unlock responsiveness to checkpoint immunotherapy. This article is highlighted in the In This Issue feature, p. 2711.

Spatially restricted drivers and transitional cell populations cooperate with the microenvironment in untreated and chemo-resistant pancreatic cancer

Pancreatic ductal adenocarcinoma is a lethal disease with limited treatment options and poor survival. We studied 83 spatial samples from 31 patients (11 treatment-naïve and 20 treated) using single-cell/nucleus RNA sequencing, bulk-proteogenomics, spatial transcriptomics and cellular imaging. Subpopulations of tumor cells exhibited signatures of proliferation, KRAS signaling, cell stress and epithelial-to-mesenchymal transition. Mapping mutations and copy number events distinguished tumor populations from normal and transitional cells, including acinar-to-ductal metaplasia and pancreatic intraepithelial neoplasia. Pathology-assisted deconvolution of spatial transcriptomic data identified tumor and transitional subpopulations with distinct histological features. We showed coordinated expression of TIGIT in exhausted and regulatory T cells and Nectin in tumor cells. Chemo-resistant samples contain a threefold enrichment of inflammatory cancer-associated fibroblasts that upregulate metallothioneins. Our study reveals a deeper understanding of the intricate substructure of pancreatic ductal adenocarcinoma tumors that could help improve therapy for patients with this disease.

Abstract 251: Inhibition of stromal p38MAPKalpha triggers innate-adaptive anti-tumor immunity in metastatic breast cancer

Metastases are the main cause of death in breast cancer patients. Among breast metastatic sites, bone is the most prevalent site that can also seed secondary metastases. Moreover, once tumor cells reach the bone, the disease is considered incurable and treatments are only palliative. For this reason, new therapies that limit metastatic growth are desperately needed. We previously showed that pharmacological inhibition of p38MAPKα (p38i) limited visceral and bone metastases in several clinically relevant models of breast cancer metastasis. Indeed, we found that this approach had no impact on tumor cells but instead limited the supporting nature of the stromal compartment. These findings led us to ask how p38i impacted the stromal compartment. Using a novel strategy to segregate tumor-infiltrating from non-tumor-infiltrating stromal cells in the bone metastatic site, we carried out single cell RNA sequencing (scRNA-Seq) to investigate how p38i altered immune and non-immune tumor stroma. Our analyses revealed that p38i treatment shifts tumor-associated macrophages in the bone towards a tumor-suppressive phenotype with increased signatures for IFNγ signaling and adaptive immunity. Importantly, the gene signature we identified in bone macrophages under p38i treatment correlated with better survival among patients with luminal B breast tumors. Given the importance of the p38i gene signature in patient samples, we next depleted macrophages and also blocked IFNγ and found both approaches reversed the p38i anti-tumor effect. Because T cells are an important source of IFNγ in vivo, we next assessed whether T cells were required by p38i to limit tumor growth. Depletion of CD4+ T cells, but not CD8+ T cells, blunted the p38i anti-tumor effect. Although p38i did not increase CD4+ T cell infiltration, p38i increased the percentage of activated CD4+ T cells infiltrating bone metastases. The requirement for CD4+ T cells in our model and the lack of evident OX40 ligand in our scRNA-Seq data led us to ask if p38i could be used in combination with immunotherapy to further limit metastases. Indeed, combination of p38i and agonist anti-OX40 (agOX-40) immunotherapy synergistically reduced metastatic growth and increased overall survival in our mouse models. Finally, because our work revealed no obvious role for CD8+ T cells in this model, we next asked if introduction of a CD8+ T cell antigen could further increase the anti-tumor effects of p38i. We thus modified PyMT-BO1 cells to express ovalbumin, which contains a strong CD8 antigen and combined it with p38i and agOX40. This combination led to a greater than 90% cure rate of mice with metastatic lesions. Although the mechanisms by which inhibition of p38MAPKα shapes the metastatic tumor microenvironment are still under investigation, our findings indicate that metastatic breast cancer patients may benefit from immunotherapy when carried out in combination with p38i.

Citation Format: Douglas Vendas Faget, Xianmin Luo, Qihao Ren, Jiayu Ye, Thomas Cole, Zhangting Yao, Bhavna Murali, Xinming Su, Yalin Xu, Joseph B. Monahan, Katherine N. Weilbaecher, David G. DeNardo, Sheila A. Stewart. Inhibition of stromal p38MAPKalpha triggers innate-adaptive anti-tumor immunity in metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 251.

Phase I dose escalation and expansion study of defactinib, pembrolizumab, and gemcitabine in patients with advanced treatment-refractory pancreatic cancer

4146

Background: Targeting focal adhesion kinase (FAK) renders checkpoint immunotherapy effective in pancreatic ductal adenocarcinoma (PDAC) mouse models. Defactinib is a highly potent oral FAK inhibitor shown to have a tolerable safety profile. We evaluated the safety and recommended phase 2 dose (RP2D) of defactinib in combination with pembrolizumab and gemcitabine for PDAC patients. Methods: We conducted a multicenter, open-label, phase I study with dose escalation and expansion phases. In 3x3 dose escalation, patients with refractory solid tumors were treated at five escalating dose levels of defactinib and gemcitabine to identify a RP2D. In expansion phase, patients with metastatic PDAC who progressed on frontline treatment (refractory cohort) or had treatment response or stable disease (SD) on standard gemcitabine/nab-paclitaxel (maintenance cohort) were treated at RP2D. Pre- and post-treatment tumor biopsies were performed to evaluate changes in tumor immunity. Results: The triple drug combination was well-tolerated with no dose-limiting toxicities. Among 17 treated patients with refractory PDAC, the disease control rate (DCR) was 58.8% with one partial response (PR) and nine SDs and the median progression-free survival (PFS) and overall survival (OS) were 4.2 months and 9.1 months, respectively. Among the evaluable patients in the maintenance cohort, DCR was 63.6% with one PR and six SD. Three patients with SD came off study due to treatment- or disease-related complications. The median PFS and OS were 5.0 months and 8.3 months, respectively. Conclusions: The combination of defactinib, pembrolizumab, and gemcitabine was well-tolerated, had promising preliminary efficacy, and showed increased infiltrative T lymphocytes in post-treatment tumor biopsies. Incorporation of a more potent chemotherapy backbone should be considered to achieve better clinical response in future trial design. Clinical trial information: NCT02546531.

Phase I trial of CA-4948, an IRAK4 inhibitor, in combination with FOLFOX/PD-1 inhibitor +/- trastuzumab for untreated unresectable gastric and esophageal cancer

TPS4168

Background: Activated NFκB has been linked to aggressive phenotype, poor survival outcomes and resistance to chemotherapy in multiple gastrointestinal cancers including gastroesophageal cancer (GEC). Preclinical studies established that: 1) Genotoxic stress incurred by chemotherapy induces TLR9, which signals through IRAK4 to drive pro-survival NFκB signaling; 2) The survival mechanism through IRAK4 is independent of cancer types and mutational profiles based on colorectal and pancreatic cancer models; and 3) IRAK4 inhibition reduces tumor desmoplasia and revitalizes intratumoral T cells, setting the stage for successful combination with immune checkpoint inhibitors in a highly aggressive autochthonous pancreatic cancer mouse model. These data combined provide a strong rationale to add CA-4948 to systemic therapy for multiple advanced gastrointestinal malignancies, where resistance to chemotherapy is inevitable and benefit of PD-1 inhibitors is limited to small population. CA-4948 is a novel, first-in-class reversible inhibitor of IRAK4. In a phase I trial, patients with relapsed/refractory hematologic malignancies tolerated CA-4948 monotherapy well with mild fatigue, neutropenia, and nausea as most common adverse events. Recommended phase 2 dose (RP2D) was determined as 300 mg orally twice daily. CA-4948 has not been tested in combination with cytotoxic chemotherapy or immune checkpoint inhibitors for solid tumors in clinic. We hypothesize that inhibition of IRAK4 with CA-4948 will potentiate the effect of immune checkpoint inhibitor while deepening the efficacy of cytotoxic chemotherapy in GEC. Methods: This is a phase I trial of CA-4948 in combination with FOLFOX/PD-1 inhibitor with or without trastuzumab for unresectable GEC. During Dose Escalation, we will investigate CA-4948 in combination with FOLFOX/nivolumab by BOIN algorithm evaluating 4 different dose levels. Starting dose of CA-4948 for Part A will be 200 mg twice daily. Once RP2D is determined, the study will proceed to Dose Expansion, including Cohorts A and B. Cohort A will enroll up to 12 patients with HER2 negative disease at the RP2D of CA-4948 determined at the Dose Escalation phase. Cohort B will investigate CA-4948 in combination with FOLFOX/pembrolizumab and trastuzumab. The initial 6 patients in Cohort B will be considered safety lead-in to confirm the safety and tolerability at the RP2D, followed by additional patients, up to 12 patients treated at the RP2D. The primary objective is to determine the safety and RP2D of CA-4948 in combination with FOLFOX/PD-1 inhibitor with or without trastuzumab. Secondary objectives are to determine the preliminary efficacy of the combination. Correlative studies to evaluate pharmacodynamic effects and to identify biomarkers associated with disease response are planned. Clinical trial information: NCT05187182.

IRAK4 Signaling Drives Resistance to Checkpoint Immunotherapy in Pancreatic Ductal Adenocarcinoma

BACKGROUND & AIMS

Checkpoint immunotherapy is largely ineffective in pancreatic ductal adenocarcinoma (PDAC). The innate immune nuclear factor (NF)-κB pathway promotes PDAC cell survival and stromal fibrosis, and is driven by Interleukin-1 Receptor Associated Kinase-4 (IRAK4), but its impact on tumor immunity has not been directly investigated.

METHODS

We interrogated The Cancer Genome Atlas data to identify the correlation between NF-κB and T cell signature, and a PDAC tissue microarray (TMA) to correlate IRAK4 activity with CD8⁺ T cell abundance. We performed RNA sequencing (RNA-seq) on IRAK4-deleted PDAC cells, and single-cell RNA-seq on autochthonous KPC (p48-Cre/TP53^f/f/LSL-KRAS^G12D) mice treated with an IRAK4 inhibitor. We generated conditional IRAK4-deleted KPC mice and complementarily used IRAK4 inhibitors to determine the impact of IRAK4 on T cell immunity.

RESULTS

We found positive correlation between NF-κB activity, IRAK4 and T cell exhaustion from The Cancer Genome Atlas. We observed inverse correlation between phosphorylated IRAK4 and CD8⁺ T cell abundance in a PDAC tissue microarray. Loss of IRAK4 abrogates NF-κB activity, several immunosuppressive factors, checkpoint ligands, and hyaluronan synthase 2, all of which drive T cell dysfunction. Accordingly, conditional deletion or pharmacologic inhibition of IRAK4 markedly decreased tumor desmoplasia and increased the abundance and activity of infiltrative CD4⁺ and CD8⁺ T cells in KPC tumors. Single-cell RNA-seq showed myeloid and fibroblast reprogramming toward acute inflammatory responses following IRAK4 inhibition. These changes set the stage for successful combination of IRAK4 inhibitors with checkpoint immunotherapy, resulting in excellent tumor control and markedly prolonged survival of KPC mice.

CONCLUSION

IRAK4 drives T cell dysfunction in PDAC and is a novel, promising immunotherapeutic target.

Single-cell profiling of human dura and meningioma reveals cellular meningeal landscape and insights into meningioma immune response

BACKGROUND

Recent investigations of the meninges have highlighted the importance of the dura layer in central nervous system immune surveillance beyond a purely structural role. However, our understanding of the meninges largely stems from the use of pre-clinical models rather than human samples.

METHODS

Single-cell RNA sequencing of seven non-tumor-associated human dura samples and six primary meningioma tumor samples (4 matched and 2 non-matched) was performed. Cell type identities, gene expression profiles, and T cell receptor expression were analyzed. Copy number variant (CNV) analysis was performed to identify putative tumor cells and analyze intratumoral CNV heterogeneity. Immunohistochemistry and imaging mass cytometry was performed on selected samples to validate protein expression and reveal spatial localization of select protein markers.

RESULTS

In this study, we use single-cell RNA sequencing to perform the first characterization of both non-tumor-associated human dura and primary meningioma samples. First, we reveal a complex immune microenvironment in human dura that is transcriptionally distinct from that of meningioma. In addition, we characterize a functionally diverse and heterogenous landscape of non-immune cells including endothelial cells and fibroblasts. Through imaging mass cytometry, we highlight the spatial relationship among immune cell types and vasculature in non-tumor-associated dura. Utilizing T cell receptor sequencing, we show significant TCR overlap between matched dura and meningioma samples. Finally, we report copy number variant heterogeneity within our meningioma samples.

CONCLUSIONS

Our comprehensive investigation of both the immune and non-immune cellular landscapes of human dura and meningioma at single-cell resolution builds upon previously published data in murine models and provides new insight into previously uncharacterized roles of human dura.

Stromal architecture directs early dissemination in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is an extremely metastatic and lethal disease. Here, in both murine and human PDA, we demonstrate that extracellular matrix architecture regulates cell extrusion and subsequent invasion from intact ductal structures through tumor-associated collagen signatures (TACS). This results in early dissemination from histologically premalignant lesions and continual invasion from well-differentiated disease, and it suggests TACS as a biomarker to aid in the pathologic assessment of early disease. Furthermore, we show that pancreatitis results in invasion-conducive architectures, thus priming the stroma prior to malignant disease. Analysis in potentially novel microfluidic-derived microtissues and in vivo demonstrates decreased extrusion and invasion following focal adhesion kinase (FAK) inhibition, consistent with decreased metastasis. Thus, data suggest that targeting FAK or strategies to reengineer and normalize tumor microenvironments may have roles not only in very early disease, but also for limiting continued dissemination from unresectable disease. Likewise, it may be beneficial to employ stroma-targeting strategies to resolve precursor diseases such as pancreatitis in order to remove stromal architectures that increase risk for early dissemination.

Neoadjuvant FOLFIRINOX Therapy Is Associated with Increased Effector T Cells and Reduced Suppressor Cells in Patients with Pancreatic Cancer

PURPOSE

FOLFIRINOX has demonstrated promising results for patients with pancreatic ductal adenocarcinoma (PDAC). Chemotherapy-induced immunogenic cell death can prime antitumor immune responses. We therefore performed high-dimensional profiling of immune cell subsets in peripheral blood to evaluate the impact of FOLFIRINOX on the immune system.

EXPERIMENTAL DESIGN

Peripheral blood mononuclear cells (PBMC) were obtained from treatment-naïve (n = 20) and FOLFIRINOX-treated patients (n = 19) with primary PDAC tumors at the time of resection. PBMCs were characterized by 36 markers using mass cytometry by time of flight (CyTOF).

RESULTS

Compared with treatment-naïve patients, FOLFIRINOX-treated patients showed distinct immune profiles, including significantly decreased inflammatory monocytes and regulatory T cells (Treg), increased Th1 cells, and decreased Th2 cells. Notably, both monocytes and Treg expressed high levels of immune suppression-associated CD39, and the total CD39⁺ cell population was significantly lower in FOLFIRINOX-treated patients compared with untreated patients. Cellular alterations observed in responders to FOLFIRINOX included a significantly decreased frequency of Treg, an increased frequency of total CD8 T cells, and an increased frequency of CD27^-Tbet⁺ effector/effector memory subsets of CD4 and CD8 T cells.

CONCLUSIONS

Our study reveals that neoadjuvant chemotherapy with FOLFIRINOX enhances effector T cells and downregulates suppressor cells. These data indicate that FOLFIRINOX neoadjuvant therapy may improve immune therapy and clinical outcome in patients with PDAC.

Abstract PO-112: Stromal reprogramming by FAK inhibition overcomes radiation resistance to allow for immune priming and response to checkpoint blockade

Pancreatic Ductal Adenocarcinoma (PDAC) is one of the most lethal malignancies. While checkpoint immunotherapies are effective therapies in many solid malignancies, these same regimens have not been effective in PDAC. Furthermore, clinical trials combining checkpoint immunotherapies with standard of care chemotherapy or radiation therapy (RT), which should be able to prime anti-tumor immunity and unlock immunotherapies, have not been successful. Thus, understanding why the combinations of RT and immunotherapy fail in PDAC is critical. To better understand why RT and checkpoint immunotherapies fail, we studied the impact of stereotactic body radiotherapy (SBRT), an RT regimen which delivers precise and intense doses of radiation into tumor cells, on antigen specific T cell responses in both human PDAC tissues and genetically engineered mouse models of PDAC. In human PDAC tumors, we found no increase in the number of CD8 tumor infiltrating T cells in the tumor stroma compared to a control group, which gives us no evidence of T cell priming following SBRT. Using the p48-Cre/LSL-KrasG12D/p53Flox/Flox/OVA-GFP+ (KPC-OG) mice, RT alone, despite inducing temporary tumor control did not prime new antigen specific T cell responses, similar to what we found in the human PDAC tissues. We postulated that the unique PDAC tumor microenvironment (TME), which is characterized by a fibrotic desmoplastic stroma, might play a role in limiting immune priming by SBRT. To study the role of PDAC’s TME to RT response, we developed a 3D organoid in vitro co-culture system. We found that fibroblasts and collagen work synergistically to cause RT resistance, which is mediated in part through the hyperactivation of Focal Adhesion Kinase (FAK). In KPC mice, FAK inhibitor (FAKi) rescues RT resistance leading to significant tumor regression and enhances long-term survival. Associated with this regression, we found enhanced anti-tumor immunity in the form of increased conventional dendritic cells and tumor specific CD8 T cells. Single cell RNA sequencing data revealed that this treatment combination enhances antigen processing and presentation and T cell activation in the immune myeloid compartment and alters the composition of cancer associated fibroblasts in the PDAC stroma. Based on these data, we initiated a phase Ib study in which FAKi (VS-6063) will be given in combination with SBRT to patients with locally advanced PDAC (NCT04331041). This trial is currently underway. With this human trial underway, we next hypothesized the combination of RT and FAKi would render immunotherapy effective. Pre-clinical studies in mouse PDAC models showed that while RT and checkpoint blockade was ineffective at tumor control, the triple combination of FAKi, RT, and checkpoint blockade led to extended long-term survival. Overall, these data suggest that stromal modulation can be used to allow RT to prime anti-tumor immunity in PDAC and unlock checkpoint immunotherapy efficacy.

Citation Format: Varintra E. Lander, Jad I. Belle, Brett L. Knolhoff, John M. Herndon, Cedric Mpoy, Buck E. Rogers, Julie K. Schwarz, David G. DeNardo. Stromal reprogramming by FAK inhibition overcomes radiation resistance to allow for immune priming and response to checkpoint blockade [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-112.

Abstract IA-002: Dendritic cell corner stone of tumor immunity in PDAC

T cell-directed immunotherapies have not been effective for the majority of pancreatic cancer patients, in part, due to our limited understanding of how T cell immunity is subverted in this disease. We sought to identify mechanisms for this failure using spontaneous mouse models. We report that endogenous antigen-specific responses in PDAC are aberrant due to a scarcity of dendritic cells, which favors the expansion of tumor-promoting TH17 immunity. Restoring cDCs in pancreatic cancer can enhance CD8+ T cell and TH1 activity to ultimately help control disease. These findings expand our understanding of T cell ineffectiveness in pancreatic cancer, and propose combinatorial strategies to modulate cDCs in conjunction with existing therapies for pancreatic cancer and similar solid malignancies.

Citation Format: David G. DeNardo. Dendritic cell corner stone of tumor immunity in PDAC [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr IA-002.

Breast cancer-derived GM-CSF regulates arginase 1 in myeloid cells to promote an immunosuppressive microenvironment

Tumor-infiltrating myeloid cells contribute to the development of the immunosuppressive tumor microenvironment. Myeloid cell expression of arginase 1 (ARG1) promotes a protumor phenotype by inhibiting T cell function and depleting extracellular l-arginine, but the mechanism underlying this expression, especially in breast cancer, is poorly understood. In breast cancer clinical samples and in our mouse models, we identified tumor-derived GM-CSF as the primary regulator of myeloid cell ARG1 expression and local immune suppression through a gene-KO screen of breast tumor cell-produced factors. The induction of myeloid cell ARG1 required GM-CSF and a low pH environment. GM-CSF signaling through STAT3 and p38 MAPK and acid signaling through cAMP were required to activate myeloid cell ARG1 expression in a STAT6-independent manner. Importantly, breast tumor cell-derived GM-CSF promoted tumor progression by inhibiting host antitumor immunity, driving a significant accumulation of ARG1-expressing myeloid cells compared with lung and melanoma tumors with minimal GM-CSF expression. Blockade of tumoral GM-CSF enhanced the efficacy of tumor-specific adoptive T cell therapy and immune checkpoint blockade. Taken together, we show that breast tumor cell-derived GM-CSF contributes to the development of the immunosuppressive breast cancer microenvironment by regulating myeloid cell ARG1 expression and can be targeted to enhance breast cancer immunotherapy.

GB1275, a first-in-class CD11b modulator: rationale for immunotherapeutic combinations in solid tumors

Resistance to immune checkpoint inhibitors (ICI) and other anticancer therapies is often associated with the accumulation of myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) in the tumor microenvironment (TME). Therefore, targeting MDSC recruitment or function is of significant interest as a strategy to treat patients with ICI-resistant cancer. The migration and recruitment of MDSCs to the TME is mediated in part by the CD11b/CD18 integrin heterodimer (Mac-1; α_Mβ₂), expressed on both MDSCs and TAMs. However, inhibition or blockade of CD11b/CD18 has had limited success in clinical trials to date, likely since saturation of CD11b requires doses that are not clinically tolerable with the agents tested so far. Interestingly, activation of CD11b with leukadherin-1 was found to reduce macrophage and neutrophil migration in animal models of inflammatory conditions. Preclinical studies with GB1275, a salt form of leukadherin-1, demonstrated that activation of CD11b improves the antitumor immune response and enhances the response to immunotherapy in mouse models of pancreatic adenocarcinoma, breast cancer and lung cancer. Based on the promising results from preclinical studies, a phase 1/2 clinical study (NCT04060342) of GB1275 in patients with advanced solid tumor types known to be resistant or less likely responsive to immuno-oncology therapies, including pancreatic, breast, prostate, and microsatellite-stable colorectal cancer, is ongoing. In this review, we examine targeting MDSCs as a therapeutic approach in cancer therapy, with a special focus on GB1275 preclinical studies laying the rationale for the phase 1/2 clinical study.

Metabolic modulation by CDK4/6 inhibitor promotes chemokine-mediated recruitment of T cells into mammary tumors

Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) delay progression of metastatic breast cancer. However, complete responses are uncommon and tumors eventually relapse. Here, we show that CDK4/6i can enhance efficacy of T cell-based therapies, such as adoptive T cell transfer or T cell-activating antibodies anti-OX40/anti-4-1BB, in murine breast cancer models. This effect is driven by the induction of chemokines CCL5, CXCL9, and CXCL10 in CDK4/6i-treated tumor cells facilitating recruitment of activated CD8+ T cells, but not Tregs, into the tumor. Mechanistically, chemokine induction is associated with metabolic stress that CDK4/6i treatment induces in breast cancer cells. Despite the cell cycle arrest, CDK4/6i-treated cells retain high metabolic activity driven by deregulated PI3K/mTOR pathway. This causes cell hypertrophy and increases mitochondrial content/activity associated with oxidative stress and inflammatory stress response. Our findings uncover a link between tumor metabolic vulnerabilities and anti-tumor immunity and support further development of CDK4/6i and immunotherapy combinations.

Abstract IA011: Conventional dendritic cells as regulators of therapeutic response in pancreas cancer

In these studies, we utilized spontaneous models of pancreatic and lung cancer to examine how neo-antigenicity shapes tumor immunity and progression. As expected, neoantigen expression during lung adenocarcinoma development leads to T cell-mediated immunity and disease restraint. By contrast, neoantigen expression in pancreatic ductal adenocarcinoma (PDAC) resulted in exacerbation of the inflammatory and fibrotic tumor microenvironment that drives disease progression and metastasis. Pathogenic TH17 responses are responsible for this neoantigen-induced tumor progression in PDAC. Underlying these divergent T cell responses in pancreas and lung cancer are differences in infiltrating conventional dendritic cells (cDCs). Overcoming cDC deficiency in early- stage PDAC leads to disease restraint, while restoration of cDC function thru treatment with both CD40 agonists and FLT3L in advanced PDAC restores tumor-restraining immunity and enhances responsiveness to radiation therapy.

Citation Format: David G. DeNardo. Conventional dendritic cells as regulators of therapeutic response in pancreas cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr IA011.

Rethinking immune checkpoint blockade: 'Beyond the T cell'

The clinical success of immune checkpoint inhibitors has highlighted the central role of the immune system in cancer control. Immune checkpoint inhibitors can reinvigorate anti-cancer immunity and are now the standard of care in a number of malignancies. However, research on immune checkpoint blockade has largely been framed with the central dogma that checkpoint therapies intrinsically target the T cell, triggering the tumoricidal potential of the adaptive immune system. Although T cells undoubtedly remain a critical piece of the story, mounting evidence, reviewed herein, indicates that much of the efficacy of checkpoint therapies may be attributable to the innate immune system. Emerging research suggests that T cell-directed checkpoint antibodies such as anti-programmed cell death protein-1 (PD-1) or programmed death-ligand-1 (PD-L1) can impact innate immunity by both direct and indirect pathways, which may ultimately shape clinical efficacy. However, the mechanisms and impacts of these activities have yet to be fully elucidated, and checkpoint therapies have potentially beneficial and detrimental effects on innate antitumor immunity. Further research into the role of innate subsets during checkpoint blockade may be critical for developing combination therapies to help overcome checkpoint resistance. The potential of checkpoint therapies to amplify innate antitumor immunity represents a promising new field that can be translated into innovative immunotherapies for patients fighting refractory malignancies.

Abstract PO-017: Targeting NF-kB pathway through IRAK4 renders immune checkpoint blockade effective in pancreatic cancer

Effective immunotherapy in pancreatic ductal adenocarcinoma (PDAC) is impeded by multiple barriers in the tumor microenvironment. These include the dense extracellular matrix (ECM), excessive inhibitory myeloid cells, cytokines and chemokines, which collectively incapacitate anti-tumour T cells. Constitutive activation the NF-kB pathway is a mechanism that drives intrinsic survival of PDAC cells and stromal fibrosis, but its impact on anti-tumour immunity has not been investigated. Using The Cancer Genome Atlas database, we found that expression of RELA, a canonical NF-kB factor, in PDAC samples is associated with activated stroma and lower cytotoxic T cell signatures. In a PDAC tissue microarray, the staining intensity of activated IRAK4, the innate immune kinase that drives NF-kB signaling, negatively correlates with T cell abundance. Based on these findings, we investigated the immunological impact role of IRAK4 in PDAC. Transcriptomic analysis showed that ablation of IRAK4 in PDAC cells downregulates NF-kB and inflammatory signatures, and markedly decreases transcription of hyaluronan synthase 2 (HAS2). Accordingly, pharmacologic inhibition of IRAK4 significantly decreased intratumoral hyaluronan, as well as collagen, in autochthonous PDAC mice and potentiated standard chemotherapy. Furthermore, IRAK4 inhibition also significantly reduced production of several suppressive chemokines and checkpoint ligands PD-L1 and Nectin2, leading to revitalization of infiltrative CD4+ and CD8+ T cells. These effects were partly mediated through reduction of intratumoural hyaluronan, which we recapitulated with HAS inhibitor, 4-MU. Accordingly, combined IRAK4 inhibitors with immune checkpoint blockade (ICB) especially anti-CTLA4, were highly efficacious in abrogating tumour growth in autochthonous PDAC mice and doubling their survival. In summary, we showed that targeting the NF-kB pathway through IRAK4 renders ICB effective via multiple mechanisms and should be tested in clinical trials for PDAC patients.

Citation Format: Daoxiang Zhang, Vikas Somani, Paarth B. Dodhiawala, Patrick M. Grierson, Lin Li, Kuljeet Seehra, Xiuting Liu, Brett L. Knolhoff, Marianna B. Ruzinova, David G. DeNardo, Kian-Huat Lim. Targeting NF-kB pathway through IRAK4 renders immune checkpoint blockade effective in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-017.

Tumor Microenvironment as a Regulator of Radiation Therapy: New Insights into Stromal-Mediated Radioresistance

Simple Summary

Cancer is multifaceted and consists of more than just a collection of mutated cells. These cancerous cells reside along with other non-mutated cells in an extracellular matrix which together make up the tumor microenvironment or tumor stroma. The composition of the tumor microenvironment plays an integral role in cancer initiation, progression, and response to treatments. In this review, we discuss how the tumor microenvironment regulates the response and resistance to radiation therapy and what targeted agents have been used to combat stromal-mediated radiation resistance.

Abstract

A tumor is a complex “organ” composed of malignant cancer cells harboring genetic aberrations surrounded by a stroma comprised of non-malignant cells and an extracellular matrix. Considerable evidence has demonstrated that components of the genetically “normal” tumor stroma contribute to tumor progression and resistance to a wide array of treatment modalities, including radiotherapy. Cancer-associated fibroblasts can promote radioresistance through their secreted factors, contact-mediated signaling, downstream pro-survival signaling pathways, immunomodulatory effects, and cancer stem cell-generating role. The extracellular matrix can govern radiation responsiveness by influencing oxygen availability and controlling the stability and bioavailability of growth factors and cytokines. Immune status regarding the presence of pro- and anti-tumor immune cells can regulate how tumors respond to radiation therapy. Furthermore, stromal cells including endothelial cells and adipocytes can modulate radiosensitivity through their roles in angiogenesis and vasculogenesis, and their secreted adipokines, respectively. Thus, to successfully eradicate cancers, it is important to consider how tumor stroma components interact with and regulate the response to radiation. Detailed knowledge of these interactions will help build a preclinical rationale to support the use of stromal-targeting agents in combination with radiotherapy to increase radiosensitivity.

Abstract CT247: A phase 1/2 study of GB1275, a first-in-class CD11b modulator, as monotherapy and with an anti-PD-1 antibody in specified advanced solid tumors or with chemotherapy in metastatic pancreatic cancer (KEYNOTE-A36)

Background: Tumor influx of CD11b-expressing myeloid-derived suppressor cells (MDSCs) and M2 tumor-associated macrophages (TAMs) creates an immunosuppressive tumor microenvironment associated with resistance to anti-PD-1 antibody therapy. GB1275 is a novel, first-in-class, CD11b modulator that, in vivo, reduced MDSCs and TAMs at the tumor site, repolarized M2 immunosuppressive TAMs to an M1 phenotype, and increased tumor infiltration of activated CD8+ T cells. In combination with an anti-PD-1 antibody or chemotherapy, these immunomodulatory effects translated into potent anti-tumor effects and prolonged survival in orthotopic PDAC models. We hypothesize that GB1275-based therapy can alleviate myeloid cell-mediated immunosuppression and improve cancer treatment outcomes. Methods: This is an open-label, first-in-human study comprising phase 1 dose escalation of GB1275 monotherapy (Regimen A) and GB1275 plus pembrolizumab (Regimen B) in patients with previously treated, locally advanced or metastatic PDA, esophageal, gastric/GEJ, triple negative breast, castration-resistant prostate, or microsatellite-stable colorectal cancer (MSS CRC), and GB1275 plus nab-paclitaxel and gemcitabine (Nab-P+Gem) (Regimen C) in mPDAC. This is followed by phase 2 expansion in three disease cohorts: 1) newly diagnosed stage IV mPDAC (GB1275+Nab-P+Gem), 2) MSS CRC (GB1275+pembrolizumab), and 3) PD-L1+ gastric/GEJ cancer (GB1275+pembrolizumab). Patients are enrolled in Regimen A initially, with Regimen B commencing after completion of the first few cohorts of Regimen A. Regimen C will initiate when Regimen A is completed. Eligible patients are ≥18 years of age, with histologically confirmed locally advanced/metastatic tumor specified and ECOG 0-1 PS; prior immunotherapy is permissible during Regimen A and B dose escalation, but not Regimen C or during the expansion phase. Patients are excluded for untreated or symptomatic CNS metastasis, prior myeloid targeting treatment or other prohibited medications, or a history of clinically significant cardiovascular disease. Patients with active autoimmune disease requiring systemic therapy will be excluded from Regimen B and from expansion cohorts 2 and 3. Primary objectives for phase 1 are to determine the maximum tolerated dose/recommended phase dose and pharmacokinetic profile of GB1275 alone and combination with pembrolizumab, and safety in combination with Nab-P+Gem, and for phase 2, to assess efficacy.Statistical Considerations: A 3+3 design is used for the dose escalation phase and Simon's 2-stage design for the expansion phase. Adverse events are graded per CTCAE v5.0, responses per RECIST v1.1. This study is open for recruitment (NCT04060342).

Citation Format: Andrea Wang-Gillam, Drew W. Rasco, Wungki Park, Eileen O'Reilly, Wells Messersmith, David G. DeNardo, Vineet Gupta, Lei Zhou, Anna Galkin, Debbie Slee, Laura L. Carter, David Nickle, Rebecca Tran, Jack Li, Beatrice Ferguson, Marya F. Chaney, Luisa Salter-Cid, Jakob Dupont, Johanna C. Bendell. A phase 1/2 study of GB1275, a first-in-class CD11b modulator, as monotherapy and with an anti-PD-1 antibody in specified advanced solid tumors or with chemotherapy in metastatic pancreatic cancer (KEYNOTE-A36) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT247.

Agonism of CD11b reprograms innate immunity to sensitize pancreatic cancer to immunotherapies

Although checkpoint immunotherapies have revolutionized the treatment of cancer, not all tumor types have seen substantial benefit. Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy in which very limited responses to immunotherapy have been observed. Extensive immunosuppressive myeloid cell infiltration in PDAC tissues has been postulated as a major mechanism of resistance to immunotherapy. Strategies concomitantly targeting monocyte or granulocyte trafficking or macrophage survival, in combination with checkpoint immunotherapies, have shown promise in preclinical studies, and these studies have transitioned into ongoing clinical trials for the treatment of pancreatic and other cancer types. However, compensatory actions by untargeted monocytes, granulocytes, and/or tissue resident macrophages may limit the therapeutic efficacy of such strategies. CD11b/CD18 is an integrin molecule that is highly expressed on the cell surface of these myeloid cell subsets and plays an important role in their trafficking and cellular functions in inflamed tissues. Here, we demonstrate that the partial activation of CD11b by a small-molecule agonist (ADH-503) leads to the repolarization of tumor-associated macrophages, reduction in the number of tumor-infiltrating immunosuppressive myeloid cells, and enhanced dendritic cell responses. These actions, in turn, improve antitumor T cell immunity and render checkpoint inhibitors effective in previously unresponsive PDAC models. These data demonstrate that molecular agonism of CD11b reprograms immunosuppressive myeloid cell responses and potentially bypasses the limitations of current clinical strategies to overcome resistance to immunotherapy.

Tumor-insular Complex in Neoadjuvant Treated Pancreatic Ductal Adenocarcinoma Is Associated With Higher Residual Tumor

The tumor microenvironment in pancreatic ductal adenocarcinoma (PDAC) plays a vital role in treatment response, and therefore, patient survival. We and others have observed an intimate association of neoplastic ductal cells with non-neoplastic islet cells, recapitulating the ductoinsular complex. We define this phenomenon as tumor-insular complex (TIC). Herein, we describe the clinicopathologic characteristics of TIC in neoadjuvant treated PDAC cases for the first time. We retrospectively reviewed the pathology of 105 cases of neoadjuvant treated PDAC resected at our institution. TIC was noted in 35 cases (33.3%), the mean tumor bed size was 2.7±1.0 cm, mean percentage of residual tumor 40±28% and mean Residual Tumor Index (RTI) (an index previously established as a prognostic parameter by our group) was 1.1±1.0. TIC was significantly associated with perineural invasion (P=0.001), higher tumor bed size (P=0.007), percentage of residual tumor (P=0.009), RTI (P=0.001), ypT stage (P=0.045), and poor treatment response, grouped by a previously established criteria (P=0.010). Using our prior binary reported prognostic cutoff for RTI of ≤0.35 and >0.35, TIC was associated with a RTI >0.35 (P=0.002). Moreover, patients who did not receive neoadjuvant radiation were associated with a higher frequency of TIC (P=0.003). In this cohort, RTI but not TIC was also shown to be a significant independent prognosticator for recurrence-free survival and overall survival on multivariate analysis. In conclusion, TIC is significantly associated with a more aggressive neoplasm which shows a poor treatment response. Further studies will be needed to better understand the tumor biology of TICs.

Positive Allosteric Modulation of CD11b as a Novel Therapeutic Strategy Against Lung Cancer

Lung cancer is one of the leading causes of cancer-related deaths in the United States. A major hurdle for improved therapies is immune suppression mediated by the tumor and its microenvironment. The lung tumor microenvironment (TME) contains large numbers of tumor-associated macrophages (TAMs), which suppress the adaptive immune response, increase neo-vascularization of the tumor, and provide pro-tumor factors to promote tumor growth. CD11b is highly expressed on myeloid cells, including TAMs, where it forms a heterodimeric integrin receptor with CD18 (known as CD11b/CD18, Mac-1, CR3, and αMβ2), and plays an important role in recruitment and biological functions of these cells, and is a validated therapeutic target. Here, we describe our pre-clinical studies targeting CD11b in the context of lung cancer, using pharmacologic and genetic approaches that work via positive allosteric modulation of CD11b function. GB1275 is a novel small molecule modulator of CD11b that is currently in Phase 1/2 clinical development. We assess GB1275 treatment effects on tumor growth and immune infiltrates in the murine Lewis Lung Carcinoma (LLC) syngeneic tumor model. Additionally, as an orthogonal approach to determine mechanisms of action, we utilize our recently developed novel CD11b knock-in (KI) mouse that constitutively expresses CD11b containing an activating isoleucine to glycine substitution at residue 332 in the ligand binding CD11b A-domain (I332G) that acts as a positive allosteric modulator of CD11b activity. We report that pharmacologic modulation of CD11b with GB1275 significantly reduces LLC tumor growth. CD11b KI mice similarly show significant reduction in both the size and rate of LLC tumor growth, as compared to WT mice, mimicking our observed treatment effects with GB1275. Tumor profiling revealed a significant reduction in TAM infiltration in GB1275-treated and in CD11b KI mice, increase in the ratio of M1/M2-like TAMs, and concomitant increase in cytotoxic T cells. The profiling also showed a significant decrease in CCL2 levels and a concomitant reduction in Ly6C^hi monocytes in circulation in both groups. These findings suggest that positive allosteric modulation of CD11b reduces TAM density and reprograms them to enhance the adaptive immune response and is a novel therapeutic strategy against lung cancer.

Response to FOLFIRINOX neoadjuvant chemotherapy is associated with a high prevalence of Tbet expressing T cells in pancreatic cancer patients

FOLFIRINOX is the first line treatment option for patients with pancreatic ductal adenocarcinoma (PDAC). Neoadjuvant chemotherapy has a beneficial effect on overall survival in PDAC in comparison with upfront surgery and adjuvant therapy. However, chemotherapy has not yet been successfully combined with immune therapy in PDAC. Herein, we characterize the immunologic effect of FOLFIRINOX and thus provide a rationale for future combination with immune therapy in PDAC. Peripheral Blood Mononuclear Cells were obtained from treatment-naïve (n=20) and FOLFIRINOX-treated patients (n=15) with primary PDAC tumors. Immune cell subset composition was assessed by using mass cytometry (CyTOF). Response to FOLFIRINOX was defined as a reduction in tumor size by more than 30%. 8 of 15 patients were considered responders with a range from 32 to 60% reduction in tumor volume. Responders to FOLFIRINOX showed a significantly higher proportion of CD8+ T cells and lower proportion of monocytes in their peripheral blood compared to treatment naïve patients (both p<0.05). Responders to FOLFIRINOX treatment also showed a significantly lower percentage of CD39+ Treg cells and a significantly higher percentage of CXCR3+CCR6+ Th1/Th17 cells compared to treatment naïve patients (both p<0.05). Lastly, FOLFIRINOX responders showed significantly higher proportions of Tbet expressing CD4+ and CD8+ T cells compared to non-responder patients (both p<0.05). Taken together, our study reveals that neoadjuvant chemotherapy with FOLFIRINOX could enhance functional T cells and down-regulate suppressor cells in circulation. Thus, combination neoadjuvant FOLFIRINOX chemotherapy with immunotherapy may improve clinical outcome.

Dendritic Cell Paucity Leads to Dysfunctional Immune Surveillance in Pancreatic Cancer

Here, we utilized spontaneous models of pancreatic and lung cancer to examine how neoantigenicity shapes tumor immunity and progression. As expected, neoantigen expression during lung adenocarcinoma development leads to T cell-mediated immunity and disease restraint. By contrast, neoantigen expression in pancreatic ductal adenocarcinoma (PDAC) results in exacerbation of a fibro-inflammatory microenvironment that drives disease progression and metastasis. Pathogenic T_H17 responses are responsible for this neoantigen-induced tumor progression in PDAC. Underlying these divergent T cell responses in pancreas and lung cancer are differences in infiltrating conventional dendritic cells (cDCs). Overcoming cDC deficiency in early-stage PDAC leads to disease restraint, while restoration of cDC function in advanced PDAC restores tumor-restraining immunity and enhances responsiveness to radiation therapy.

A framework for advancing our understanding of cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs) are a key component of the tumour microenvironment with diverse functions, including matrix deposition and remodelling, extensive reciprocal signalling interactions with cancer cells and crosstalk with infiltrating leukocytes. As such, they are a potential target for optimizing therapeutic strategies against cancer. However, many challenges are present in ongoing attempts to modulate CAFs for therapeutic benefit. These include limitations in our understanding of the origin of CAFs and heterogeneity in CAF function, with it being desirable to retain some antitumorigenic functions. On the basis of a meeting of experts in the field of CAF biology, we summarize in this Consensus Statement our current knowledge and present a framework for advancing our understanding of this critical cell type within the tumour microenvironment.

B cell-Derived IL35 Drives STAT3-Dependent CD8+ T-cell Exclusion in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA) is an aggressive malignancy characterized by a paucity of tumor-proximal CD8+ T cells and resistance to immunotherapeutic interventions. Cancer-associated mechanisms that elicit CD8+ T-cell exclusion and resistance to immunotherapy are not well-known. Here, using a Kras- and p53-driven model of PDA, we describe a mechanism of action for the protumorigenic cytokine IL35 through STAT3 activation in CD8+ T cells. Distinct from its action on CD4+ T cells, IL35 signaling in gp130+CD8+ T cells activated the transcription factor STAT3, which antagonized intratumoral infiltration and effector function of CD8+ T cells via suppression of CXCR3, CCR5, and IFNγ expression. Inhibition of STAT3 signaling in tumor-educated CD8+ T cells improved PDA growth control upon adoptive transfer to tumor-bearing mice. We showed that activation of STAT3 in CD8+ T cells was driven by B cell- but not regulatory T cell-specific production of IL35. We also demonstrated that B cell-specific deletion of IL35 facilitated CD8+ T-cell activation independently of effector or regulatory CD4+ T cells and was sufficient to phenocopy therapeutic anti-IL35 blockade in overcoming resistance to anti-PD-1 immunotherapy. Finally, we identified a circulating IL35+ B-cell subset in patients with PDA and demonstrated that the presence of IL35+ cells predicted increased occurrence of phosphorylated (p)Stat3+CXCR3-CD8+ T cells in tumors and inversely correlated with a cytotoxic T-cell signature in patients. Together, these data identified B cell-mediated IL35/gp130/STAT3 signaling as an important direct link to CD8+ T-cell exclusion and immunotherapy resistance in PDA.

Development of resistance to FAK inhibition in pancreatic cancer is linked to stromal depletion

OBJECTIVE

We investigated how pancreatic cancer developed resistance to focal adhesion kinase (FAK) inhibition over time.

DESIGN

Pancreatic ductal adenocarcinoma (PDAC) tumours from KPC mice (p48-CRE; LSL-KRas^G12D/wt; p53^flox/wt) treated with FAK inhibitor were analysed for the activation of a compensatory survival pathway in resistant tumours. We identified pathways involved in the regulation of signal transducer and activator of transcription 3 (STAT3) signalling on FAK inhibition by gene set enrichment analysis and verified these outcomes by RNA interference studies. We also tested combinatorial approaches targeting FAK and STAT3 in syngeneic transplantable mouse models of PDAC and KPC mice.

RESULTS

In KPC mice, the expression levels of phosphorylated STAT3 (pSTAT3) were increased in PDAC cells as they progressed on FAK inhibitor therapy. This progression corresponded to decreased collagen density, lowered numbers of SMA⁺ fibroblasts and downregulation of the transforming growth factor beta (TGF-β)/SMAD signalling pathway in FAK inhibitor-treated PDAC tumours. Furthermore, TGF-β production by fibroblasts in vitro drives repression of STAT3 signalling and enhanced responsiveness to FAK inhibitor therapy. Knockdown of SMAD3 in pancreatic cancer cells abolished the inhibitory effects of TGF-β on pSTAT3. We further found that tumour-intrinsic STAT3 regulates the durability of the antiproliferative activity of FAK inhibitor, and combinatorial targeting of FAK and Janus kinase/STAT3 act synergistically to suppress pancreatic cancer progression in mouse models.

CONCLUSION

Stromal depletion by FAK inhibitor therapy leads to eventual treatment resistance through the activation of STAT3 signalling. These data suggest that, similar to tumour-targeted therapies, resistance mechanisms to therapies targeting stromal desmoplasia may be critical to treatment durability.

IRAK4 mediates colitis-induced tumorigenesis and chemoresistance in colorectal cancer

Aberrant activation of the NF-κB transcription factors underlies chemoresistance in various cancer types, including colorectal cancer (CRC). Targeting the activating mechanisms, particularly with inhibitors to the upstream IκB kinase (IKK) complex, is a promising strategy to augment the effect of chemotherapy. However, clinical success has been limited, largely because of low specificity and toxicities of tested compounds. In solid cancers, the IKKs are driven predominantly by the Toll-like receptor (TLR)/IL-1 receptor family members, which signal through the IL-1 receptor-associated kinases (IRAKs), with isoform 4 (IRAK4) being the most critical. The pathogenic role and therapeutic value of IRAK4 in CRC have not been investigated. We found that IRAK4 inhibition significantly abrogates colitis-induced neoplasm in APCMin/+ mice, and bone marrow transplant experiments showed an essential role of IRAK4 in immune cells during neoplastic progression. Chemotherapy significantly enhances IRAK4 and NF-κB activity in CRC cells through upregulating TLR9 expression, which can in turn be suppressed by IRAK4 and IKK inhibitors, suggesting a feed-forward pathway that protects CRC cells from chemotherapy. Lastly, increased tumor phospho-IRAK4 staining or IRAK4 mRNA expression is associated with significantly worse survival in CRC patients. Our results support targeting IRAK4 to improve the effects of chemotherapy and outcomes in CRC.

A Single-Cell Window into Pancreas Cancer Fibroblast Heterogeneity

Cancer-associated fibroblasts (CAF) have been implicated in diverse and sometimes divergent tumor modulatory processes that can be explained only by the existence of heterogeneous CAF subsets. In this issue of Cancer Discovery, Elyada and colleagues utilize single-cell transcriptomics to resolve CAF heterogeneity in pancreatic ductal adenocarcinoma and identify a novel antigen-presenting CAF population.See related article by Elyada et al., p. 1102.

Precision delivery of RAS-inhibiting siRNA to KRAS driven cancer via peptide-based nanoparticles

Over 95% of pancreatic adenocarcinomas (PDACs), as well as a large fraction of other tumor types, such as colorectal adenocarcinoma, are driven by KRAS activation. However, no direct RAS inhibitors exist for cancer therapy. Furthermore, the delivery of therapeutic agents of any kind to PDAC in particular has been hindered by the extensive desmoplasia and resultant drug delivery challenges that accompanies these tumors. Small interfering RNA (siRNA) is a promising modality for anti-neoplastic therapy due to its precision and wide range of potential therapeutic targets. Unfortunately, siRNA therapy is limited by low serum half-life, vulnerability to intracellular digestion, and transient therapeutic effect. We assessed the ability of a peptide based, oligonucleotide condensing, endosomolytic nanoparticle (NP) system to deliver siRNA to KRAS-driven cancers. We show that this peptide-based NP is avidly taken up by cancer cells in vitro, can deliver KRAS-specific siRNA, inhibit KRAS expression, and reduce cell viability. We further demonstrate that this system can deliver siRNA to the tumor microenvironment, reduce KRAS expression, and inhibit pancreatic cancer growth in vivo. In a spontaneous KPPC model of PDAC, this system effectively delivers siRNA to stroma-rich tumors. This model has the potential for translational relevance for patients with KRAS driven solid tumors.