Disruption of CXCR2-mediated MDSC tumor trafficking enhances anti-PD1 efficacy

Small Molecular Immune Modulators as Anticancer Agents

After decades of intense effort, immune checkpoint inhibitors have been conclusively demonstrated to be effective in cancer treatments and thus are revolutionizing the concepts in the treatment of cancers. Immuno-oncology has arrived and will play a key role in cancer treatment in the foreseeable future. However, efforts to find novel methods to improve the immune response to cancer have not ceased. Small-molecule approaches offer inherent advantages over biologic immunotherapies since they can cross cell membranes, penetrate into tumor tissue and tumor microenvironment more easily, and are amenable to be finely controlled than biological agents, which may help reduce immune-related adverse events seen with biologic therapies and provide more flexibility for the combination use with other therapies and superior clinical benefit. On the one hand, small-molecule therapies can modulate the immune response to cancer by restoring the antitumor immunity, promoting more effective cytotoxic lymphocyte responses, and regulating tumor microenvironment, either directly or epigenetically. On the other hand, the combination of different mechanisms of small molecules with antibodies and other biologics demonstrated admirable synergistic effect in clinical settings for cancer treatment and may expand antibodies' usefulness for broader clinical applications. This chapter provides an overview of small-molecule immunotherapeutic approaches either as monotherapy or in combination for the treatment of cancer.

CXCR1 and CXCR2 Chemokine Receptor Agonists Produced by Tumors Induce Neutrophil Extracellular Traps that Interfere with Immune Cytotoxicity

Neutrophils are expanded and abundant in cancer-bearing hosts. Under the influence of CXCR1 and CXCR2 chemokine receptor agonists and other chemotactic factors produced by tumors, neutrophils, and granulocytic myeloid-derived suppressor cells (MDSCs) from cancer patients extrude their neutrophil extracellular traps (NETs). In our hands, CXCR1 and CXCR2 agonists proved to be the major mediators of cancer-promoted NETosis. NETs wrap and coat tumor cells and shield them from cytotoxicity, as mediated by CD8⁺ T cells and natural killer (NK) cells, by obstructing contact between immune cells and the surrounding target cells. Tumor cells protected from cytotoxicity by NETs underlie successful cancer metastases in mice and the immunotherapeutic synergy of protein arginine deiminase 4 (PAD4) inhibitors, which curtail NETosis with immune checkpoint inhibitors. Intravital microscopy provides evidence of neutrophil NETs interfering cytolytic cytotoxic T lymphocytes (CTLs) and NK cell contacts with tumor cells.

The interplay between innate and adaptive immunity in cancer shapes the productivity of cancer immunosurveillance

The immune system is a vital determinant of cancer and shapes its trajectory. Notably, the immune reaction to cancer harbors dual potential for suppressing or promoting cancer development and progression. This polarity of the immune response is determined, in part, by the character of the interplay between innate and adaptive immunity. On the one hand, the innate immune compartment is a necessary proponent of cancer immunity by supporting an immunostimulatory state that enables T cell immunosurveillance. However, in the setting of cancer, innate immune cells are commonly polarized with immune-suppressive properties and as a result, orchestrate a tolerogenic niche that interferes with the cytotoxic potential of tumor antigen-specific T cells. Here, we discuss the role of innate immunity as a positive and negative regulator of adaptive immunosurveillance; moreover, we highlight how tumor cells may skew leukocytes toward an immunosuppressive state and, as such, subvert the phenotypic plasticity of the immune compartment to advance disease progression. These observations establish the precedent for novel therapeutic strategies that aim to restore the tumor microenvironment to an immunoreactive state and, in doing so, condition and maintain the immunogenicity of tumors to yield deep and durable responses to immunotherapy.

Melanoma immunotherapy: strategies to overcome pharmacological resistance

Introduction: Although checkpoint inhibitors have provided a breakthrough in how melanoma is treated, about half of patients still do not respond due to primary or acquired resistance. New strategies are, therefore, required to increase the number of patients benefiting from immunotherapy. This systematic review investigates novel combinations that may overcome immune resistance in patients with melanoma.Areas covered: We provide an overview of immune-related resistance mechanisms and the various therapeutic strategies that can be considered in attempting to overcome these barriers, including combined immunotherapy approaches and combinations with chemotherapy, radiotherapy, and targeted therapy.Expert opinion: The immune response is a dynamic process in which the tumor microenvironment and immune cells interact in a variety of ways. New treatment approaches aim to enrich the tumor microenvironment with immune-infiltrate and increase response to immune checkpoint inhibitors.

Dietary Choline Supplementation Attenuates High-Fat-Diet-Induced Hepatocellular Carcinoma in Mice

BACKGROUND

Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related death in the world. Choline deficiency has been well studied in the context of liver disease; however, less is known about the effects of choline supplementation in HCC.

OBJECTIVE

The objective of this study was to test whether choline supplementation could influence the progression of HCC in a high-fat-diet (HFD)-driven mouse model.

METHODS

Four-day-old male C57BL/6J mice were treated with the chemical carcinogen, 7,12-dimethylbenz[a]anthracene, and were randomly assigned at weaning to a cohort fed an HFD (60% kcal fat) or an HFD with supplemental choline (60% kcal fat, 1.2% choline; HFD+C) for 30 wk. Blood was isolated at 15 and 30 wk to measure immune cells by flow cytometry, and glucose-tolerance tests were performed 2 wk prior to killing. Overall tumor burden was quantified, hepatic lipids were measured enzymatically, and phosphatidylcholine species were measured by targeted MS methods. Gene expression and mitochondrial DNA were quantified by quantitative PCR.

RESULTS

HFD+C mice exhibited a 50-90% increase in both circulating choline and betaine concentrations in the fed state (P ≤ 0.05). Choline supplementation resulted in a 55% decrease in total tumor numbers, a 67% decrease in tumor surface area, and a 50% decrease in hepatic steatosis after 30 wk of diet (P ≤ 0.05). Choline supplementation increased the abundance of mitochondria and the relative expression of β-oxidation genes by 21% and ∼75-100%, respectively, in the liver. HFD+C attenuated circulating myeloid-derived suppressor cells at 15 wk of feeding (P ≤ 0.05).

CONCLUSIONS

Choline supplementation attenuated HFD-induced HCC and hepatic steatosis in male C57BL/6J mice. These results suggest a therapeutic benefit of choline supplementation in blunting HCC progression.

Immune Cell Types and Secreted Factors Contributing to Inflammation-to-Cancer Transition and Immune Therapy Response

Although chronic inflammation increases many cancers' risk, how inflammation facilitates cancer development is still not well studied. Recognizing whether and when inflamed tissues transition to cancerous tissues is of utmost importance. To unbiasedly infer molecular events, immune cell types, and secreted factors contributing to the inflammation-to-cancer (I2C) transition, we develop a computational package called "SwitchDetector" based on liver, gastric, and colon cancer I2C data. Using it, we identify angiogenesis associated with a common critical transition stage for multiple I2C events. Furthermore, we infer infiltrated immune cell type composition and their secreted or suppressed extracellular proteins to predict expression of important transition stage genes. This identifies extracellular proteins that may serve as early-detection biomarkers for pre-cancer and early-cancer stages. They alone or together with I2C hallmark angiogenesis genes are significantly related to cancer prognosis and can predict immune therapy response. The SwitchDetector and I2C database are publicly available at www.inflammation2cancer.org.

Myeloid-derived suppressor cells are essential partners for immune checkpoint inhibitors in the treatment of cisplatin-resistant bladder cancer

Myeloid-derived suppressor cells (MDSCs) are one of the key players that contribute to immune evasion. The purpose of the present study was to investigate whether MDSCs could be a novel target for the treatment of cisplatin-resistant bladder cancer. We established cisplatin-resistant bladder cancer cell lines (MB49R, MBT-2R, and T24R) and evaluated chemokine expression and MDSC expansion. We also assessed the antitumor effect by depleting MDSCs with or without a α-PD-L1 antibody using MB49R xenograft models. The chemokine expression of CXCL1, CXCL2, and CCL2 increased in cisplatin-resistant cells compared to those in their parent strains. Monocytic MDSCs (Mo-MDSCs) were observed more frequently compared to polymorphonuclear MDSCs (PMN-MDSCs) in MB49R tumors. The immunosuppressive genes arginase 1 and iNOS were comparably expressed in each MDSC subtype. In vivo, combination therapy targeting both PMN- and Mo-MDSCs using α-Gr1 and α-Ly6C antibodies significantly reduced tumor volume with increased infiltration of CD8 T cells in the tumor. Finally, co-targeting pan-MDSCs and PD-L1 remarkably reduced the tumor growth. These findings suggest that targeting MDSCs might enhance the therapeutic effect of immune checkpoint inhibitors in cisplatin-resistant bladder cancers.

Tumor immune microenvironment in cancer patients with leukocytosis

Tumor-related leukocytosis (TRL) is correlated with poor survival in various types of cancers, but the microenvironment of TRL-associated human tumors has not been fully elucidated. Here, we aimed to characterize the immune microenvironment of cancer patients with TRL. The transcriptional signatures of tumor tissues obtained from cervical cancer patients with (TRL^pos) and without TRL (TRL^neg) were compared. As a surrogate for TRL diagnosis, a leukocytosis signature (LS) score was derived using genes differentially expressed between TRL^pos and TRL^neg tumors. The immunological profiles of patients in the TCGA database with high (LS^high) or low LS scores were compared. TRL^pos tumors were transcriptionally distinct from TRL^neg tumors, exhibiting up-regulation of radioresistance and down-regulation of adaptive immune response-related genes. In the TCGA cervical cancer cohort (n = 303), patients with high LS had inferior survival rates compared to those with low LS (P = 0.023). LS^high tumors were enriched in radioresistance, wound healing, and myeloid-derived suppressor cell (MDSC) signatures and had a higher infiltration of M2 macrophages and a lower infiltration of M1 macrophages and lymphocytes. LS^high tumors also expressed higher levels of CXCR2 chemokines, CSF2, and CSF3. In the pan-cancer cohort (n = 9984), LS^high tumors also exhibited poor survival, signatures of a suppressive immune microenvironment, and higher expression of CXCR2 chemokines. Our data provide evidence for a suppressive immune microenvironment in patients with TRL and suggest promising targets, such as the CXCR2 axis, for its therapeutic intervention.

Simultaneous inhibition of CXCR1/2, TGF-β, and PD-L1 remodels the tumor and its microenvironment to drive antitumor immunity

BACKGROUND

Despite the success of immune checkpoint blockade therapy in the treatment of certain cancer types, only a small percentage of patients with solid malignancies achieve a durable response. Consequently, there is a need to develop novel approaches that could overcome mechanisms of tumor resistance to checkpoint inhibition. Emerging evidence has implicated the phenomenon of cancer plasticity or acquisition of mesenchymal features by epithelial tumor cells, as an immune resistance mechanism.

METHODS

Two soluble factors that mediate tumor cell plasticity in the context of epithelial-mesenchymal transition are interleukin 8 (IL-8) and transforming growth factor beta (TGF-β). In an attempt to overcome escape mechanisms mediated by these cytokines, here we investigated the use of a small molecule inhibitor of the IL-8 receptors CXCR1/2, and a bifunctional agent that simultaneously blocks programmed death ligand 1 (PD-L1) and traps soluble TGF-β.

RESULTS

We demonstrate that simultaneous inhibition of CXCR1/2, TGF-β, and PD-L1 signaling synergizes to reduce mesenchymal tumor features in murine models of breast and lung cancer, and to markedly increase expression of tumor epithelial E-cadherin while reducing infiltration with suppressive granulocytic myeloid-derived suppressor cells, significantly enhancing T-cell infiltration and activation in tumors, and leading to improved antitumor activity.

CONCLUSIONS

This study highlights the potential benefit of combined blockade of CXCR1/2 and TGF-β signaling for modulation of tumor plasticity and potential enhancement of tumor responses to PD-L1 blockade. The data provide rationale for the evaluation of this novel approach in the clinic.

The emerging role of myeloid-derived suppressor cells in radiotherapy

Radiotherapy (RT) has been used for decades as one of the main treatment modalities for cancer patients. The therapeutic effect of RT has been primarily ascribed to DNA damage leading to tumor cell death. Besides direct tumoricidal effect, RT affects antitumor responses through immune-mediated mechanism, which provides a rationale for combining RT and immunotherapy for cancer treatment. Thus far, for the combined treatment with RT, numerous studies have focused on the immune checkpoint inhibitors and have shown promising results. However, treatment resistance is still common, and one of the main resistance mechanisms is thought to be due to the immunosuppressive tumor microenvironment where myeloid-derived suppressor cells (MDSCs) play a crucial role. MDSCs are immature myeloid cells with a strong immunosuppressive activity. MDSC frequency is correlated with tumor progression, recurrence, negative clinical outcome, and reduced efficacy of immunotherapy. Therefore, increasing efforts to target MDSCs have been made to overcome the resistance in cancer treatments. In this review, we focus on the role of MDSCs in RT and highlight growing evidence for targeting MDSCs in combination with RT to improve cancer treatment.

Myeloid-Derived Suppressor Cells as a Therapeutic Target for Cancer

The emergence of immunotherapy has been an astounding breakthrough in cancer treatments. In particular, immune checkpoint inhibitors, targeting PD-1 and CTLA-4, have shown remarkable therapeutic outcomes. However, response rates from immunotherapy have been reported to be varied, with some having pronounced success and others with minimal to no clinical benefit. An important aspect associated with this discrepancy in patient response is the immune-suppressive effects elicited by the tumour microenvironment (TME). Immune suppression plays a pivotal role in regulating cancer progression, metastasis, and reducing immunotherapy success. Most notably, myeloid-derived suppressor cells (MDSC), a heterogeneous population of immature myeloid cells, have potent mechanisms to inhibit T-cell and NK-cell activity to promote tumour growth, development of the pre-metastatic niche, and contribute to resistance to immunotherapy. Accumulating research indicates that MDSC can be a therapeutic target to alleviate their pro-tumourigenic functions and immunosuppressive activities to bolster the efficacy of checkpoint inhibitors. In this review, we provide an overview of the general immunotherapeutic approaches and discuss the characterisation, expansion, and activities of MDSCs with the current treatments used to target them either as a single therapeutic target or synergistically in combination with immunotherapy.

Epigenetic therapy inhibits metastases by disrupting premetastatic niches

Cancer recurrence after surgery remains an unresolved clinical problem^1-3. Myeloid cells derived from bone marrow contribute to the formation of the premetastatic microenvironment, which is required for disseminating tumour cells to engraft distant sites^4-6. There are currently no effective interventions that prevent the formation of the premetastatic microenvironment^6,7. Here we show that, after surgical removal of primary lung, breast and oesophageal cancers, low-dose adjuvant epigenetic therapy disrupts the premetastatic microenvironment and inhibits both the formation and growth of lung metastases through its selective effect on myeloid-derived suppressor cells (MDSCs). In mouse models of pulmonary metastases, MDSCs are key factors in the formation of the premetastatic microenvironment after resection of primary tumours. Adjuvant epigenetic therapy that uses low-dose DNA methyltransferase and histone deacetylase inhibitors, 5-azacytidine and entinostat, disrupts the premetastatic niche by inhibiting the trafficking of MDSCs through the downregulation of CCR2 and CXCR2, and by promoting MDSC differentiation into a more-interstitial macrophage-like phenotype. A decreased accumulation of MDSCs in the premetastatic lung produces longer periods of disease-free survival and increased overall survival, compared with chemotherapy. Our data demonstrate that, even after removal of the primary tumour, MDSCs contribute to the development of premetastatic niches and settlement of residual tumour cells. A combination of low-dose adjuvant epigenetic modifiers that disrupts this premetastatic microenvironment and inhibits metastases may permit an adjuvant approach to cancer therapy.

Sensitizing the Tumor Microenvironment to Immune Checkpoint Therapy

Immune checkpoint blockade (ICB) has revolutionized cancer treatment, providing remarkable clinical responses in some patients. However, the majority of patients do not respond. It is therefore crucial both to identify predictive biomarkers of response and to increase the response rates to immune checkpoint therapy. In this review we explore the current literature about the predictive characteristics of the tumor microenvironment and discuss therapeutic approaches that aim to change this toward a milieu that is conducive to response. We propose a personalized biomarker-based adaptive approach to immunotherapy, whereby a sensitizing therapy is tailored to the patient's specific tumor microenvironment, followed by on-treatment verification of a change in the targeted biomarker, followed by immune checkpoint therapy. By incorporating detailed knowledge of the immunological tumor microenvironment, we may be able to sensitize currently non-responsive tumors to respond to immune checkpoint therapy.

Emergency myelopoiesis contributes to immune cell exhaustion and pulmonary vascular remodelling

BACKGROUND AND PURPOSE

Pulmonary hypertension (PH) secondary to chronic lung disease (World Health Organization Group 3 PH) is deadly, with lung transplant being the only available long-term treatment option. Myeloid-derived cells are known to affect progression of both pulmonary fibrosis and PH, although the mechanism of action is unknown. Therefore, we investigated the effect of myeloid cell proliferation induced by emergency myelopoiesis on development of PH and therapy directed against programmed death-ligand 1 (PD-L1), expressed by myeloid cells in prevention of pulmonary vascular remodelling.

EXPERIMENTAL APPROACH

LysM.Cre-DTR ("mDTR") mice were injected with bleomycin (0.018 U·g^-1 , i.p.) while receiving either vehicle or diphtheria toxin (DT; 100 ng, i.p.) to induce severe PH. Approximately 4 weeks after initiation of bleomycin protocol, right ventricular pressure measurements were performed and tissue samples collected for histologic assessment. In a separate experiment, DT-treated mice were given anti-PD-L1 antibody (αPD-L1; 500 μg, i.p.) preventive treatment before bleomycin administration.

KEY RESULTS

Mice undergoing induction of emergency myelopoiesis displayed more severe PH, right ventricular remodelling and pulmonary vascular muscularization compared to controls, without a change in lung fibrosis. This worsening of PH was associated with increased pulmonary myeloid-derived suppressor cell (MDSC), particularly polymorphonuclear MDSC (PMN-MDSC). Treatment with αPD-L1 normalized pulmonary pressures. PD-L1 expression was likewise found to be elevated on circulating PMN-MDSC from patients with interstitial lung disease and PH.

CONCLUSIONS AND IMPLICATIONS

PD-L1 is a viable therapeutic target in PH, acting through a signalling axis involving MDSC.

LINKED ARTICLES

This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.1/issuetoc.

Predictive biomarkers and mechanisms underlying resistance to PD1/PD-L1 blockade cancer immunotherapy

Immune checkpoint blockade targeting PD-1/PD-L1 has promising therapeutic efficacy in a variety of tumors, but resistance during treatment is a major issue. In this review, we describe the utility of PD-L1 expression levels, mutation burden, immune cell infiltration, and immune cell function for predicting the efficacy of PD-1/PD-L1 blockade therapy. Furthermore, we explore the mechanisms underlying immunotherapy resistance caused by PD-L1 expression on tumor cells, T cell dysfunction, and T cell exhaustion. Based on these mechanisms, we propose combination therapeutic strategies. We emphasize the importance of patient-specific treatment plans to reduce the economic burden and prolong the life of patients. The predictive indicators, resistance mechanisms, and combination therapies described in this review provide a basis for improved precision medicine.

Overcoming immunotherapeutic resistance by targeting the cancer inflammation cycle

Inflammation is a hallmark of cancer and supports tumor growth, proliferation, and metastasis, but also inhibits T cell immunosurveillance and the efficacy of immunotherapy. The biology of cancer inflammation is defined by a cycle of distinct immunological steps that begins during disease conception with the release of inflammatory soluble factors. These factors communicate with host organs to trigger bone marrow mobilization of myeloid cells, trafficking of myeloid cells to the tumor, and differentiation of myeloid cells within the tumor bed. Tumor-infiltrating myeloid cells then orchestrate an immunosuppressive microenvironment and assist in sustaining a vicious cycle of inflammation that co-evolves with tumor cells. This Cancer-Inflammation Cycle acts as a rheostat or "inflammostat" that impinges upon T cell immunosurveillance and prevents the development of productive anti-tumor immunity. Here, we define the major nodes of the Cancer-Inflammation Cycle and describe their impact on T cell immunosurveillance in cancer. Additionally, we discuss emerging pre-clinical and clinical data suggesting that intervening upon the Cancer-Inflammation Cycle will be a necessary step for broadening the potential of immunotherapy in cancer.

The G protein coupled receptor CCR5 in cancer

The G coupled protein receptor CC chemokine receptor type 5 (CCR5) has the unusual characteristic in humans of being a developmentally non-essential gene that participates in several pathological processes including infection with HIV (Dean et al., 1996; Gupta et al., 2019; Samson et al., 1996), progression of stroke (Joy et al., 2019), osteoporosis (Xie et al., 2019) and the metastasis of cancer (Jiao et al., 2018; Velasco-Velazquez et al., 2012, 2014) (Reviewed in: Jiao, Nawab, et al., 2019; Jiao, Wang, & Pestell, 2019). The importance of CCR5 in HIV led to recent genetic engineering of humans to recreate a non-functional CCR5 gene. Thus, although the application of gene-editing tools, to manipulate human embryos is prohibited in the United States, and China. at the Second International Summit on Human Genome Editing in Hong Kong (http://www.nationalacademies.org/), it was claimed that CRISPR-Cas9 systems had been used to edit the CCR5 gene in twin baby girls. The importance of CCR5 in stroke has led to clinical trials using maraviroc (NCT03172026). The key function of CCR5 in cancer metastasis and homing (Jiao et al., 2018; Jiao, Nawab, et al., 2019; Velasco-Velazquez et al., 2012, 2014) has led to three active clinical trials for metastatic cancer using CCR5 antagonists (Jiao, Nawab, et al., 2019; Jiao, Wang, & Pestell, 2019). Thus, it was surprising to find that the all-cause mortality rate in individuals who are homozygous for the CCR5△32 allele in the United Kingdom normal population was increased >20% increase, with an almost 2 year reduction overall lifespan (Wei & Nielsen, 2019). The current review herein discusses the distinct functions of CCR5 in human disease and potential avenues for further research.

Pseudoneutrophil Cytokine Sponges Disrupt Myeloid Expansion and Tumor Trafficking to Improve Cancer Immunotherapy

Myeloid-derived suppressor cells (MDSCs) promote tumor immune escape through multiple mechanisms including suppressing antitumor activities of T lymphocytes. However, therapeutic abrogation of MDSCs often causes severe adverse effects, compensatory recruitment of alternative cell populations, and the multiplicity and complexity of relevant cytokines/receptors. Alternatively, suppressing the expansion and tumor trafficking of MDSCs may be a proficient and safe way for cancer treatment. Here we report that pseudoneutrophil cytokine sponges (pCSs) can disrupt expansion and tumor trafficking of MDSCs and reverse immune tolerance. Coated with plasma membranes of neutrophils phenotypically and morphologically similar to polymorphonuclear MDSCs (PMN-MDSCs), the nanosized pCSs inherited most membrane receptors from the "parental" neutrophils, enabling the neutralization of MDSC-related cytokines. Upon pCSs administration, the expansion of MDSCs and their enrichment in peripheral lymphoid organs and tumors were reduced without the compensatory influx of alternative myeloid subsets. In murine breast cancer and melanoma syngeneic models, pCSs treatment dramatically increased the number of tumor-infiltrating T lymphocytes and restored their antitumor functions. In addition, when pCSs were combined with the programmed cell death protein 1 (PD-1), the immune checkpoint blockade synergistically suppressed tumor progression and prolonged animal survival. Overall, the pseudocell nanoplatform opens up new paths toward effective cancer immunotherapy.

RNA Nanotechnology-Mediated Cancer Immunotherapy

RNA molecules (e.g., siRNA, microRNA, and mRNA) have shown tremendous potential for immunomodulation and cancer immunotherapy. They can activate both innate and adaptive immune system responses by silencing or upregulating immune-relevant genes. In addition, mRNA-based vaccines have recently been actively pursued and tested in cancer patients, as a form of treatment. Meanwhile, various nanomaterials have been developed to enhance RNA delivery to the tumor and immune cells. In this review article, we summarize recent advances in the development of RNA-based therapeutics and their applications in cancer immunotherapy. We also highlight the variety of nanoparticle platforms that have been used for RNA delivery to elicit anti-tumor immune responses. Finally, we provide our perspectives of potential challenges and opportunities of RNA-based nanotherapeutics in clinical translation towards cancer immunotherapy.

Myeloid-driven mechanisms as barriers to antitumor CD8+ T cell activity

The adaptive immune system is essential for host defense against pathogenic challenges, and a major constituent is the CD8⁺ cytotoxic T cell. Ordinarily, CD8⁺ T cells are endowed with a unique ability to specifically recognize and destroy their targets. However, in cases where disease emerges, especially in cancer, the efficacy of the CD8⁺ T cell response is frequently counterbalanced in a 'tug-of-war' by networks of tumor-driven mechanisms of immune suppression. As a result, antitumor CD8⁺ T cell activity is hampered, which contributes to clinical manifestations of disease. It is now well-recognized that prominent elements of that network include myeloid-derived suppressor cells (MDSC) and macrophages which assume tumor-supportive phenotypes. Both myeloid populations are thought to arise as consequences of chronic inflammatory cues produced during the neoplastic process. Numerous preclinical studies have now shown that inhibiting the production, trafficking and/or function of these immune suppressive myeloid populations restore antitumor CD8⁺ T cell responses during both immune surveillance or in response to immune-targeted interventions. Correlative studies in cancer patients support these preclinical findings and, thus, have laid the foundation for ongoing clinical trials in patients receiving novel agents that target such myeloid elements alone or in combination with immunotherapy to potentially improve cancer patient outcomes. Accordingly, this review focuses on how and why it is important to study the myeloid-T cell interplay as an innovative strategy to boost or reinvigorate the CD8⁺ T cell response as a critical weapon in the battle against malignancy.

Chemokines and their receptors promoting the recruitment of myeloid-derived suppressor cells into the tumor

Myeloid-derived suppressor cells (MDSCs) expand in tumor-bearing host. They suppress anti-tumor immune response and promote tumor growth. Chemokines play a vital role in recruiting MDSCs into tumor tissue. They can also induce the generation of MDSCs in the bone marrow, maintain their suppressive activity, and promote their proliferation and differentiation. Here, we review CCL2/CCL12-CCR2, CCL3/4/5-CCR5, CCL15-CCR1, CX3CL1/CCL26-CX3CR1, CXCL5/2/1-CXCR2, CXCL8-CXCR1/2, CCL21-CCR7, CXCL13-CXCR5 signaling pathways, their role in MDSCs recruitment to tumor tissue, and their correlation with tumor development, metastasis and prognosis. Targeting chemokines and their receptors may serve as a promising strategy in immunotherapy, especially combined with other strategies such as chemotherapy, cyclin-dependent kinase or immune checkpoints inhibitors.

Inflammation induced by incomplete radiofrequency ablation accelerates tumor progression and hinders PD-1 immunotherapy

Radiofrequency ablation (RFA) promotes tumor antigen-specific T cell responses and enhances the effect of immunotherapy in preclinical settings. Here we report that the existence of remnant tumor masses due to incomplete RFA (iRFA) is associated with earlier new metastases and poor survival in patients with colorectal cancer liver metastases (CRCLM). Using mouse models, we demonstrate that iRFA promotes tumor progression and hinders the efficacy of anti-PD-1 therapy. Immune analysis reveals that iRFA induces sustained local inflammation with predominant myeloid suppressor cells, which inhibit T cell function in tumors. Mechanistically, tumor cell-derived CCL2 is critical for the accumulation of monocytes and tumor-associated macrophages (TAMs). The crosstalk between TAMs and tumor cells enhances the CCL2 production by tumor cells. Furthermore, we find that administration of a CCR2 antagonist or the loss of CCL2 expression in tumor cells enhances the antitumor activity of PD-1 blockade, providing a salvage alternative for residual tumors after iRFA.

Radiofrequency ablation is used to treat metastatic colorectal cancer. In this study, the authors show that incomplete ablation of tumours results in metastases and show in mouse models that the chemokine CCL2 recruits myeloid cells to the partially ablated tumours, which can block T cell function.

Unmasking the Many Faces of Tumor-Associated Neutrophils and Macrophages: Considerations for Targeting Innate Immune Cells in Cancer

Immunotherapy has emerged at the forefront of cancer therapy; however, patient survival remains low for many cancer types. In consideration of this, non-T cell immune populations, such as innate immune cells, have been identified as potential immunotherapeutic targets. In noncancerous settings, neutrophils are first responders to injury and infection, and work in a partnership with macrophages to regulate inflammation. However, the diversity of tumor-associated neutrophils (TANs) remains elusive. Furthermore, it is likely that TANs and tumor-associated macrophages (TAMs) act in tandem within tumors and contribute both contrasting and synergistic roles in tumor progression. In this Opinion, we discuss the complexity of TAN and TAM functions, the interplay between TANs and TAMs, and major considerations required for implementing TAN/TAM-based therapies.

The Crucial Role of CXCL8 and Its Receptors in Colorectal Liver Metastasis

CXCL8 (also known as IL-8) can produce different biological effects by binding to its receptors: CXCR1, CXCR2, and the Duffy antigen receptor for chemokines (DARC). CXCL8 and its receptors are associated with the development of various tumor types, especially colorectal cancer and its liver metastases. In addition to promoting angiogenesis, proliferation, invasion, migration, and the survival of colorectal cancer (CRC) cells, CXCL8 and its receptors have also been known to induce the epithelial-mesenchymal transition (EMT) of CRC cells, to help them to escape host immunosurveillance as well as to enhance resistance to anoikis, which promotes the formation of circulating tumor cells (CTCs) and their colonization of distant organs. In this paper, we will review the established roles of CXCL8 signaling in CRC and discuss the possible strategies of targeting CXCL8 signaling for overcoming CRC drug resistance and cancer progression, including direct targeting of CXCL8/CXCR1/2 or indirect targeting through the inhibition of CXCL8-CXCR1/2 signaling.

Immune cells within the tumor microenvironment: Biological functions and roles in cancer immunotherapy

The immune cells within the tumor microenvironment (TME) play important roles in tumorigenesis. It has been known that these tumor associated immune cells may possess tumor-antagonizing or tumor-promoting functions. Although the tumor-antagonizing immune cells within TME tend to target and kill the cancer cells in the early stage of tumorigenesis, the cancer cells seems to eventually escape from immune surveillance and even inhibit the cytotoxic function of tumor-antagonizing immune cells through a variety of mechanisms. The immune evasion capability, as a new hallmark of cancer, accidently provides opportunities for new strategies of cancer therapy, namely harnessing the immune cells to battle the cancer cells. Recently, the administrations of immune checkpoint modulators (represented by anti-CTLA4 and anti-PD antibodies) and adoptive immune cells (represented by CAR-T) have exhibited unexpected antitumor effect in multiple types of cancer, bringing a new era for cancer therapy. Here, we review the biological functions of immune cells within TME and their roles in cancer immunotherapy, and discuss the perspectives of the basic studies for improving the effectiveness of the clinical use.

Targeting CXCR1/2: The medicinal potential as cancer immunotherapy agents, antagonists research highlights and challenges ahead

Immune suppression in the tumor microenvironment (TME) is an intractable issue in anti-cancer immunotherapy. The chemokine receptors CXCR1 and CXCR2 recruit immune suppressive cells such as the myeloid derived suppressor cells (MDSCs) to the TME. Therefore, CXCR1/2 antagonists have aroused pharmaceutical interest in recent years. In this review, the medicinal chemistry of CXCR1/2 antagonists and their relevance in cancer immunotherapy have been summarized. The development of the drug candidates, along with their design rationale, clinical status and current challenges have also been discussed.

Myeloid-Derived Suppressor Cells and Pancreatic Cancer: Implications in Novel Therapeutic Approaches

Pancreatic ductal adenocarcinoma (PDAC) remains a devastating human malignancy with poor prognosis and low survival rates. Several cellular mechanisms have been linked with pancreatic carcinogenesis and also implicated in inducing tumor resistance to known therapeutic regimens. Of various factors, immune evasion mechanisms play critical roles in tumor progression and impeding the efficacy of cancer therapies including PDAC. Among immunosuppressive cell types, myeloid-derived suppressor cells (MDSCs) have been extensively studied and demonstrated to not only support PDAC development but also hamper the anti-tumor immune responses elicited by therapeutic agents. Notably, recent efforts have been directed in devising novel approaches to target MDSCs to limit their effects. Multiple strategies including immune-based approaches have been explored either alone or in combination with therapeutic agents to target MDSCs in preclinical and clinical settings of PDAC. The current review highlights the roles and mechanisms of MDSCs as well as the implications of this immunomodulatory cell type as a potential target to improve the efficacy of therapeutic regimens for PDAC.

Activated hepatic stellate cells regulate MDSC migration through the SDF-1/CXCR4 axis in an orthotopic mouse model of hepatocellular carcinoma

Hepatic stellate cells (HSCs) are important stromal cells and pivotal mediators involved in the pathogenesis and immunosuppression of hepatocellular carcinoma (HCC). The liver has been demonstrated to be a site for accumulation of tumor-induced myeloid-derived suppressor cells (MDSCs). We previously reported that HSCs induced an increase in the number of MDSCs in HCC. However, how MDSCs are recruited in HCC remains largely unclear. In the present study, we found that HSC-conditioned medium (HSC-CM) induced bone marrow-derived cell and splenocyte migration, especially MDSC migration. Using chemokine-neutralizing antibodies and chemokine receptor inhibitors, we found that HSCs promoted MDSC migration through the SDF-1/CXCR4 axis. Subsequently, we used an orthotopic mouse liver tumor model to determine how HSCs mediated MDSC migration to HCC in vivo. The in vivo results indicated that pretreatment of MDSCs with a CXCR4 inhibitor or injection with SDF-1-knocked down HSCs inhibited MDSC migration to the spleen and liver of the tumor-bearing mice. Together, our findings indicate a central role for HSCs in MDSC migration mediated by the SDF-1/CXCR4 axis, thus revealing a potentially effective approach for modulating the tumor microenvironment by targeting HSCs in HCC.

Small molecules as theranostic agents in cancer immunology

With further research into the molecular mechanisms and roles linking immune suppression and restraint of (pre)malignancies, immunotherapies have revolutionized clinical strategies in the treatment of cancer. However, nearly 70% of patients who received immune checkpoint therapeutics showed no response. Complementary and/or synergistic effects may occur when extracellular checkpoint antibody blockades combine with small molecules targeting intracellular signal pathways up/downstream of immune checkpoints or regulating the innate and adaptive immune response. After radiolabeling with radionuclides, small molecules can also be used for estimating treatment efficacy of immune checkpoint blockades. This review not only highlights some significant intracellular pathways and immune-related targets such as the kynurenine pathway, purinergic signaling, the kinase signaling axis, chemokines, etc., but also summarizes some attractive and potentially immunosuppression-related small molecule agents, which may be synergistic with extracellular immune checkpoint blockade. In addition, opportunities for small molecule-based theranostics in cancer immunology will be discussed.

Immunobiology of cholangiocarcinoma

Cholangiocarcinoma (CCA) represents a heterogeneous group of epithelial tumours that are classified according to anatomical location as intrahepatic (iCCA), perihilar (pCCA), or distal (dCCA). Although surgical resection and liver transplantation following neoadjuvant therapy are potentially curative options for a subset of patients with early-stage disease, the currently available medical therapies for CCA have limited efficacy. Immunotherapeutic strategies such as immune checkpoint blockade (ICB) harness the host immune system to unleash an effective and durable antitumour response in a subset of patients with a variety of malignancies. However, response to ICB monotherapy has been relatively disappointing in CCA. CCAs are desmoplastic tumours with an abundant tumour immune microenvironment (TIME) that contains immunosuppressive innate immune cells such as tumour-associated macrophages and myeloid-derived suppressor cells. A subset of CCAs may be classified as immune 'hot' tumours with a high density of CD8+ T cells and enhanced expression of immune checkpoint molecules. Immune 'hot' tumour types are associated with higher response rates to ICB. However, the suboptimal response rates to ICB monotherapy in human clinical trials of CCA imply that the preponderance of CCAs are immune 'cold' tumours with a non-T cell infiltrated TIME. An enhanced comprehension of the immunobiology of CCA, particularly the innate immune response to CCA, is essential in the effort to develop effective combination immunotherapeutic strategies that can target a larger subset of CCAs.

Tumour-associated macrophages-derived CXCL8 determines immune evasion through autonomous PD-L1 expression in gastric cancer

OBJECTIVE

Our previous studies have identified CXCL8 as the crucial chemokine responsible for gastric cancer metastasis mediated by loss of RACK1. However, the regulatory effect of CXCL8 on immune surveillance in gastric cancer remains obscure.

DESIGN

Flow cytometry analyses were performed to examine major source of CXCL8 and phenotypes of immune cells in fresh tumour tissues from 76 patients with gastric cancer. Real-time PCR was performed to analyse CXCL8 mRNA level in gastric cancer tissues. For immunohistochemical analyses, a total of 420 patients with gastric cancer undergoing curative resection were enrolled. In vitro culture of fresh tumour tissue was performed to evaluate the potential therapeutic effect of blocking CXCL8 pathway in gastric cancer.

RESULTS

Increased level of CXCL8 indicates poor clinical outcome and tumour progression in patients with gastric cancer. In gastric cancer tissues, CXCL8 is predominantly secreted by macrophages and colony stimulating factor 2 (CSF-2) facilitates macrophage-derived CXCL8 secretion. High level of CXCL8 is associated with decreased CD8⁺ T cells infiltration and Ki67⁺ CD8⁺ T cells proportion. Moreover, CXCL8 also inhibits CD8⁺ T cells function by inducing the expression of PD-L1 on macrophages. Finally, we show that a small-molecule CXCR2 inhibitor, reparixin, drives the decreased programmed death-ligand 1 (PD-L1⁺) macrophages and promotes antitumour immunity. Accordingly, high levels of CXCL8⁺ macrophages are positively correlated with poor prognosis in patients with gastric cancer.

CONCLUSIONS

CXCL8 is predominantly secreted by macrophages and contributes to the immunosuppressive microenvironment by inducing PD-L1⁺ macrophages in gastric cancer. CXCL8 inhibitors may drive antitumour response, providing potential therapeutic effects for patients with gastric cancer.

Chemokine signaling axis between endothelial and myeloid cells regulates development of pulmonary hypertension associated with pulmonary fibrosis and hypoxia

Pulmonary hypertension complicates the care of many patients with chronic lung diseases (defined as Group 3 pulmonary hypertension), yet the mechanisms that mediate the development of pulmonary vascular disease are not clearly defined. Despite being the most prevalent form of pulmonary hypertension, to date there is no approved treatment for patients with disease. Myeloid-derived suppressor cells (MDSCs) and endothelial cells in the lung express the chemokine receptor CXCR2, implicated in the evolution of both neoplastic and pulmonary vascular remodeling. However, precise cellular contribution to lung disease is unknown. Therefore, we used mice with tissue-specific deletion of CXCR2 to investigate the role of this receptor in Group 3 pulmonary hypertension. Deletion of CXCR2 in myeloid cells attenuated the recruitment of polymorphonuclear MDSCs to the lungs, inhibited vascular remodeling, and protected against pulmonary hypertension. Conversely, loss of CXCR2 in endothelial cells resulted in worsened vascular remodeling, associated with increased MDSC migratory capacity attributable to increased ligand availability, consistent with analyzed patient sample data. Taken together, these data suggest that CXCR2 regulates MDSC activation, informing potential therapeutic application of MDSC-targeted treatments.

Recent Advances Targeting CCR5 for Cancer and Its Role in Immuno-Oncology

Experiments of nature have revealed the peculiar importance of the G-protein-coupled receptor, C-C chemokine receptor type 5 (CCR5), in human disease since ancient times. The resurgence of interest in heterotypic signals in the onset and progression of tumorigenesis has led to the current focus on CCR5 as an exciting new therapeutic target for metastatic cancer with clinical trials now targeting breast and colon cancer. The eutopic expression of CCR5 activates calcium signaling and thereby augments regulatory T cell (Treg) differentiation and migration to sites of inflammation. The misexpression of CCR5 in epithelial cells, induced upon oncogenic transformation, hijacks this migratory phenotype. CCR5 reexpression augments resistance to DNA-damaging agents and is sufficient to induce cancer metastasis and "stemness". Recent studies suggest important cross-talk between CCR5 signaling and immune checkpoint function. Because CCR5 on Tregs serves as the coreceptor for human immunodeficiency virus (HIV) entry, CCR5-targeted therapeutics used in HIV, [small molecules (maraviroc and vicriviroc) and a humanized mAb (leronlimab)], are now being repositioned in clinical trials as cancer therapeutics. As CCR5 is expressed on a broad array of tumors, the opportunity for therapeutic repositioning and the rationale for combination therapy approaches are reviewed herein.

A novel CXCL8 analog is effective in inhibiting the growth via cell cycle arrest and attenuating invasion of Lewis lung carcinoma

Purpose

Lung cancer and other solid tumors contain not only tumor cells but various types of stromal cells, such as fibroblasts and endothelial cells. In addition, tumors are infiltrated by inflammatory cells (neutrophils, macrophages, and lymphocytes). Tumor cells, stromal cells, and the tumor-associated leukocytes are responsible for the production of chemokines inside the tumor and the maintenance of systemic circulating chemokine levels. CXCL8 and its receptors, CXCR1 and CXCR2, were found to play important roles in tumor proliferation, migration, survival, and growth. We have developed a novel ELR-CXC chemokine antagonist CXCL8-IP10 based on the structure of CXCL8 and IP10.

Patients and methods

We assessed the anticancer efficacies of the blockade of CXCL8-CXCR1/2 axis in the Lewis lung carcinoma (LL/2) model using CXCL8-IP10.

Results

We found that CXCL8-IP10 markedly reduced LL/2 cell anchorage-independent growth and invasion. Moreover, we demonstrated that CXCL8-IP10 could significantly suppress tumor growth and improve survival rate as well as lifespan of C57BL/6 mice inoculated with LL/2 cells.

Conclusion

Our results suggest that ELR-CXC chemokine antagonism would potentially be a useful therapeutic approach in patients with lung cancer.

Phase I trial of HuMax-IL8 (BMS-986253), an anti-IL-8 monoclonal antibody, in patients with metastatic or unresectable solid tumors

BACKGROUND

HuMax-IL8 (now known as BMS-986253) is a novel, fully human monoclonal antibody that inhibits interleukin-8 (IL-8), a chemokine that promotes tumor progression, immune escape, epithelial-mesenchymal transition, and recruitment of myeloid-derived suppressor cells. Studies have demonstrated that high serum IL-8 levels correlate with poor prognosis in many malignant tumors. Preclinical studies have shown that IL-8 blockade may reduce mesenchymal features in tumor cells, making them less resistant to treatment.

METHODS

Fifteen patients with metastatic or unresectable locally advanced solid tumors were enrolled in this 3 + 3 dose-escalation trial at four dose levels (4, 8, 16, or 32 mg/kg). HuMax-IL8 was given IV every 2 weeks, and patients were followed for safety and immune monitoring at defined intervals up to 52 weeks.

RESULTS

All enrolled patients (five chordoma, four colorectal, two prostate, and one each of ovarian, papillary thyroid, chondrosarcoma, and esophageal) received at least one dose of HuMax-IL8. Eight patients had received three or more prior lines of therapy and five patients had received prior immunotherapy. Treatment-related adverse events occurred in five patients (33%), mostly grade 1. Two patients receiving the 32 mg/kg dose had grade 2 fatigue, hypophosphatemia, and hypersomnia. No dose-limiting toxicities were observed, and maximum tolerated dose was not reached. Although no objective tumor responses were observed, 11 patients (73%) had stable disease with median treatment duration of 24 weeks (range, 4-54 weeks). Serum IL-8 was significantly reduced on day 3 of HuMax-IL8 treatment compared to baseline (p = 0.0004), with reductions in IL-8 seen at all dose levels.

CONCLUSIONS

HuMax-IL8 is safe and well-tolerated. Ongoing studies are evaluating the combination of IL-8 blockade and other immunotherapies.

TRIAL REGISTRATION

NCTN, NCT02536469. Registered 23 August 2015, https://clinicaltrials.gov/ct2/show/NCT02536469?term=NCT02536469&rank=1 .

Visualization and quantification of in vivo homing kinetics of myeloid-derived suppressor cells in primary and metastatic cancer

Myeloid-derived suppressor cells (MDSCs) are immunosuppressive cells of the myeloid compartment and major players in the tumor microenvironment (TME). With increasing numbers of studies describing MDSC involvement in cancer immune escape, cancer metastasis and the dampening of immunotherapy responses, MDSCs are of high interest in current cancer therapy research. Although heavily investigated in the last decades, the in vivo migration dynamics of MDSC subpopulations in tumor- or metastases-bearing mice have not yet been studied extensively. Therefore, we have modified our previously reported intracellular cell labeling method and applied it to in vitro generated MDSCs for the quantitative in vivo monitoring of MDSC migration in primary and metastatic cancer. MDSC migration to primary cancers was further correlated to the frequency of endogenous MDSCs. Methods: Utilizing a ⁶⁴Cu-labeled 1,4,7-triazacyclononane-triacetic acid (NOTA)-modified CD11b-specific monoclonal antibody (mAb) (clone M1/70), we were able to label in vitro generated polymorphonuclear (PMN-) and monocytic (M-) MDSCs for positron emission tomography (PET) imaging. Radiolabeled PMN- and M-MDSCs ([⁶⁴Cu]PMN-MDSCs and [⁶⁴Cu]M-MDSCs, respectively) were then adoptively transferred into primary and metastatic MMTV-PyMT-derived (PyMT-) breast cancer- and B16F10 melanoma-bearing experimental animals, and static PET and anatomical magnetic resonance (MR) images were acquired 3, 24 and 48 h post cell injection. Results: The internalization of the [⁶⁴Cu]NOTA-mAb-CD11b-complex was completed within 3 h, providing moderately stable radiolabeling with little detrimental effect on cell viability and function as determined by Annexin-V staining and T cell suppression in flow cytometric assays. Further, we could non-invasively and quantitatively monitor the migration and tumor homing of both [⁶⁴Cu]NOTA-αCD11b-mAb-labeled PMN- and M-MDSCs in mouse models of primary and metastatic breast cancer and melanoma by PET. We were able to visualize and quantify an increased migration of adoptively transferred [⁶⁴Cu]M-MDSCs than [⁶⁴Cu]PMN-MDSCs to primary breast cancer lesions. The frequency of endogenous MDSCs in the PyMT breast cancer and B16F10 melanoma model correlated to the uptake values of adoptively transferred MDSCs with higher frequencies of PMN- and M-MDSCs in the more aggressive B16F10 melanoma tumors. Moreover, aggressively growing melanomas and melanoma-metastatic lesions recruited higher percentages of both [⁶⁴Cu]PMN- and [⁶⁴Cu]M-MDSCs than primary and metastatic breast cancer lesions as early as 24 h post adoptive MDSC transfer, indicating an overall stronger recruitment of cancer-promoting immunosuppressive MDSCs. Conclusion: Targeting of the cell surface integrin CD11b with a radioactive mAb is feasible for labeling of murine MDSCs for PET imaging. Fast internalization of the [⁶⁴Cu]NOTA-αCD11b-mAb provides presumably enhanced stability while cell viability and functionality was not significantly affected. Moreover, utilization of the CD11b-specific mAb allows for straightforward adaptation of the labeling approach for in vivo molecular imaging of other myeloid cells of interest in cancer therapy, including monocytes, macrophages or neutrophils.

PD-1/PD-L1 blockade in paediatric cancers: What does the future hold?

Checkpoint blockade (CPB) immunotherapy has shown unprecedented success in a wide range of adult malignancies, and is increasingly being employed in the treatment of advanced cancers. However, the experience in the paediatric population remains limited and the small number of single agent studies reported have shown disappointing response rates. Paediatric cancers offer unique challenges that can hinder the translation of CPB into the paediatric clinic, and combinational therapies are likely to be needed to achieve therapeutic success. As the number of paediatric trials using CPB rapidly increases, understanding the challenges that these agents may encounter in this population is of special significance to allow the design of optimal combinatorial strategies for each tumour type. Here, we offer an overview of the unique biological and immunological features of paediatric cancers as compared to adult malignancies, and how these might impact the overall success of CPB in the paediatric population. We review the growing body of pre-clinical and clinical experiences to date, and discuss future strategies involving the combination of CPB with traditionally used therapies (chemotherapy and radiotherapy) or with other newly developed immunotherapies.

Cancer-Derived VEGF-C Increases Chemokine Production in Lymphatic Endothelial Cells to Promote CXCR2-Dependent Cancer Invasion and MDSC Recruitment

Breast cancer-derived vascular endothelial growth factor-C (VEGF-C) has been shown to enhance lymphangiogenesis in lymph nodes to accelerate cancer metastasis. However, the remodeling of lymph node microenvironments by VEGF-C remains elusive. By in vivo selection, we established a subline (named as “LC”) with strong lymphatic tropism and high VEGF-C expression from the human MDA-MB-231 breast cancer cell line. Co-culture with LC cells or treatment with LC-conditioned medium upregulated the expression of CXC chemokines in lymphatic endothelial cells (LECs), which could be inhibited by pre-incubation with VEGF-C-neutralizing antibodies and VEGFR3 inhibitors. The chemokines produced by LECs enhanced recruitment of myeloid-derived suppressor cells (MDSCs) to tumor-draining and distant lymph nodes in tumor-bearing mice. Treatment with a CXCR2 inhibitor after tumor cell inoculation dramatically decreased the number of MDSCs in lymph nodes, suggesting the importance of the chemokine/CXCR2 signaling axis in MDSC recruitment. In addition, LEC-released chemokines also stimulated the expression of serum amyloid A1 (SAA1) in cancer cells, enhancing their lymphatic invasion by increasing VE-cadherin phosphorylation, junction disruption, and vascular permeability of LECs. Clinical sample validation confirmed that SAA1 expression was associated with increased lymph node metastasis. Collectively, we reveal a novel mechanism by which cancer cell-derived VEGF-C remodels lymphovascular microenvironments by regulating chemokine production in LECs to promote cancer invasion and MDSC recruitment. Our results also suggest that inhibition of CXCR2 is effective in treating lymphatic metastasis.

Plasma Protein Binding as an Optimizable Parameter for Acidic Drugs

The low volume of distribution associated with acidic molecules means that clearance (CL) must also be very low to achieve an effective half-life commensurate with once or twice daily dosing. Plasma protein binding (PPB) should not usually be considered a parameter for optimization, but in the particular case of acidic molecules, raising the PPB above a certain level can result in distribution volume becoming a constant low value equal to the distribution volume of albumin while acting to reduce CL through restricting hepatic and renal access of unbound drug. Thus effective half-life can be increased. Here we detail the approaches and lessons learned at AstraZeneca during the optimization of acidic CXC chemokine receptor 2 (CXCR2) antagonists for the oral drug treatment of inflammatory diseases, resulting in discovery and clinical testing of N-[2-[(2,3-difluorophenyl)methylsulfanyl]-6-[(2R,3S)-3,4-dihydroxybutan-2-yl]oxypyrimidin-4-yl]azetidine-1-sulfonamide (AZD5069) and AZD4721, orally bioavailable acidic molecules with PPB of <1%, human hepatocyte intrinsic clearance values <5 µl/min per 106 cells and predicted human volume of distribution at steady state (V ss) <0.3 l/kg, resulting in effective half-lives in humans of 4 and 17 hours, respectively. SIGNIFICANCE STATEMENT: Provided that the pharmacologic potency is high enough, modulation of plasma protein binding can form part of a viable strategy in drug discovery to optimize the effective half-life of drug candidates in humans.

Targeting Myeloid Cells in Combination Treatments for Glioma and Other Tumors

Myeloid cells constitute a significant part of the immune system in the context of cancer, exhibiting both immunostimulatory effects, through their role as antigen presenting cells, and immunosuppressive effects, through their polarization to myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages. While they are rarely sufficient to generate potent anti-tumor effects on their own, myeloid cells have the ability to interact with a variety of immune populations to aid in mounting an appropriate anti-tumor immune response. Therefore, myeloid therapies have gained momentum as a potential adjunct to current therapies such as immune checkpoint inhibitors (ICIs), dendritic cell vaccines, oncolytic viruses, and traditional chemoradiation to enhance therapeutic response. In this review, we outline critical pathways involved in the recruitment of the myeloid population to the tumor microenvironment and in their polarization to immunostimulatory or immunosuppressive phenotypes. We also emphasize existing strategies of modulating myeloid recruitment and polarization to improve anti-tumor immune responses. We then summarize current preclinical and clinical studies that highlight treatment outcomes of combining myeloid targeted therapies with other immune-based and traditional therapies. Despite promising results from reports of limited clinical trials thus far, there remain challenges in optimally harnessing the myeloid compartment as an adjunct to enhancing anti-tumor immune responses. Further large Phase II and ultimately Phase III clinical trials are needed to elucidate the treatment benefit of combination therapies in the fight against cancer.

Distinct Spatio-Temporal Dynamics of Tumor-Associated Neutrophils in Small Tumor Lesions

Across a majority of cancer types tumor-associated neutrophils (TAN) are linked with poor prognosis. However, the underlying mechanisms, especially the intratumoral behavior of TAN, are largely unknown. Using intravital multiphoton imaging on a mouse model with neutrophil-specific fluorescence, we measured the migration of TAN in distinct compartments of solid tumor cell lesions in vivo. By longitudinally quantifying the infiltration and persistence of TAN into growing tumors in the same animals, we observed cells that either populated the peripheral stromal zone of the tumor (peritumoral TAN) or infiltrated into the tumor core (intratumoral TAN). Intratumoral TAN showed prolonged tumor-associated persistence and reduced motility compared to peritumoral TAN, whose velocity increased with tumor progression. Selective pharmacological blockade of CXCR2 receptors using AZD5069 profoundly inhibited recruitment of TAN into peritumoral regions, while intratumoral infiltration was only transiently attenuated and rebounded at later time points. Our findings unravel distinct spatial dynamics of TAN that are partially and differentially regulated via the CXCR2 signaling pathway.

CD163+ immune cell infiltrates and presence of CD54+ microvessels are prognostic markers for patients with embryonal rhabdomyosarcoma

Rhabdomyosarcomas (RMS) are rare and often lethal diseases. It is assumed that the tumor microenvironment (TME) of RMS exerts an immunosuppressive function, but there is currently no systematic analysis of the immune cells infiltrating sarcoma tissue. Focusing on two common types of RMS (alveolar [RMA] and embryonal [RME]), we performed a comprehensive immunohistochemical analysis of tumor-infiltrating immune cells in the TME. We performed a qualitative estimation of infiltrating immune cells in the tumor microenvironment by an experienced pathologist as well as a quantitative digital pathology analysis. We found that (1) manual and automatic quantification of tumor-infiltrating immune cells were consistent; (2) RME tumors showed a higher degree of immune cell infiltration than RMA tumors but (3) the number of tumor infiltrating lymphocytes was low compared to other solid tumor types; (4) microvascular density correlated with immune cell infiltration and (5) CD163 positive macrophages as well as CD54 positive microvessels were more often detected in RME than in RMA and correlated with patient overall and event free survival. Our systematic analysis provides a comprehensive view of the immune landscape of RMS which needs to be taken into account for developing immunotherapies for this rare type of cancer.