Intrinsic Resistance of Solid Tumors to Immune Checkpoint Blockade Therapy

Enhancing the Anticancer Efficacy of Immunotherapy through Combination with Histone Modification Inhibitors

In the nucleus of each cell, the DNA is wrapped around histone octamers, forming the so-called “nucleosomal core particles”. The histones undergo various modifications that influence chromatin structure and function, including methylation, acetylation, ubiquitination, phosphorylation, and SUMOylation. These modifications, known as epigenetic modifications (defined as heritable molecular determinants of phenotype that are independent of the DNA sequence), result in alterations of gene expression and changes in cell behavior. Recent work has shown that epigenetic drugs targeting histone deacetylation or methylation modulate the immune response and overcome acquired resistance to immunotherapy. A number of combination therapies involving immunotherapy and epigenetic drugs, which target histone deacetylation or methylation, are currently under various clinical/pre-clinical investigations and have shown promising anticancer efficacy. These combination therapies may provide a new strategy for achieving sustained anticancer efficacy and overcoming resistance.

Identification of discrepancy between CTLA4 expression and CTLA4 activation in gastric cancer

Objective: Recently, immune checkpoints blockers showed higher anti-tumor activity for advanced gastric cancer (GC). The purpose of the study is to find out predictive biomarkers related to anti-cytotoxic lymphocyte antigen 4 (CTLA4) therapy. Materials and methods: Datasets of gene expression omnibus (GEO), the cancer genome atlas (TCGA), and gene set enrichment analysis (GESA) were extracted. Differential expression of CTLA4 between cancer tissues and normal mucosa, enrichment of WT (wild type) vs. CTLA4_KO (knockout) upregulated gene set and clinical significance were analyzed. The expression of CTLA4, CD3, and granzyme A (GZMA) were validated on 30 cases of Chinese GC. Microsatellite instability (MSI) marker MLH1 and Epstein-Barr virus (EBV) marker EBER were examined on 30 cases of Chinese GC by immunohistochemistry and in situ hybridization. Results: CTLA4 was upregulated in GC tissue relative to normal mucosa in datasets of GSE27342 (fold change = 1.586, p < .001) and GSE63089 (fold change = 1.365, p < .001). Increased CTLA4 expression was positively related to CTLA4 activation. EBV-associated GC (EBVaGC) and microsatellite instability GC (MSIGC) disclosed higher CTLA4 levels than other GCs. Genomic stability GC (GSGC) also showed higher enrichment score of CTLA4 activation. CTLA4 activation resulted in shorter overall survival in GC. The expression level of CTLA4 was well correlated to expression levels of GZMA (R = 0.701, p < .001) and CD3 (R = 0.750, p < .001). Conclusions: Based on bioinformatics analysis, GSGC should be worth noticed as a potential GC subtypes responsive to anti-CTLA4 treatment.

The promising immune checkpoint LAG-3: from tumor microenvironment to cancer immunotherapy

Cancer immunotherapy and tumor microenvironment have been at the forefront of research over the past decades. Targeting immune checkpoints especially programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1) has made a breakthrough in treating advanced malignancies. However, the low response rate brings a daunting challenge, changing the focus to dig deeply into the tumor microenvironment for alternative therapeutic targets. Strikingly, the inhibitory immune checkpoint lymphocyte activation gene-3 (LAG-3) holds considerable potential. LAG-3 suppresses T cells activation and cytokines secretion, thereby ensuring immune homeostasis. It exerts differential inhibitory impacts on various types of lymphocytes and shows a remarkable synergy with PD-1 to inhibit immune responses. Targeting LAG-3 immunotherapy is moving forward in active clinical trials, and combination immunotherapy of anti-LAG-3 and anti-PD-1 has shown exciting efficacy in fighting PD-1 resistance. Herein, we shed light on the significance of LAG-3 in the tumor microenvironment, highlight its role to regulate different lymphocytes, interplay with other immune checkpoints especially PD-1, and emphasize new advances in LAG-3-targeted immunotherapy.

WEE1 kinase inhibition reverses G2/M cell cycle checkpoint activation to sensitize cancer cells to immunotherapy

Intrinsic resistance to cytotoxic T-lymphocyte (CTL) killing limits responses to immune activating anti-cancer therapies. Here, we established that activation of the G2/M cell cycle checkpoint results in tumor cell cycle pause and protection from granzyme B-induced cell death. This was reversed with WEE1 kinase inhibition, leading to enhanced CTL killing of antigen-positive tumor cells. Similarly, but at a later time point, cell cycle pause following TNFα exposure was reversed with WEE1 kinase inhibition, leading to CTL transmembrane TNFα-dependent induction of apoptosis and necroptosis in bystander antigen-negative tumor cells. Results were reproducible in models of oral cavity carcinoma, melanoma and colon adenocarcinoma harboring variable Tp53 genomic alterations. WEE1 kinase inhibition sensitized tumors to PD-1 mAb immune checkpoint blockade in vivo, resulting in CD8⁺-dependent rejection of established tumors harboring antigen-positive or mixed antigen-positive and negative tumor cells. Together, these data describe activation of the G2/M cell cycle checkpoint in response to early and late CTL products as a mechanism of resistance to CTL killing, and provide pre-clinical rationale for the clinical combination of agents that inhibit cell cycle checkpoints and activate anti-tumor immunity.

Adverse Effects of Immune Checkpoint Therapy in Cancer Patients Visiting the Emergency Department of a Comprehensive Cancer Center

STUDY OBJECTIVE

Cancer immunotherapy is evolving rapidly and is transforming cancer care. During the last decade, immune checkpoint therapies have been developed to enhance the immune response; however, specific adverse effects related to autoimmunity are increasingly apparent. This study aims to fill the knowledge gap related to the spectrum of immune-related adverse effects among cancer patients visiting emergency departments (EDs).

METHODS

We performed a retrospective review of patients treated with immune checkpoint therapy who visited the ED of a comprehensive cancer center between March 1, 2011, and February 29, 2016. Immune-related adverse effects from the ED visits were identified and profiled. We analyzed the association of each immune-related adverse effect with overall survival from the ED visit to death.

RESULTS

We identified 1,026 visits for 628 unique patients; of these, 257 visits (25.0%) were related to one or more immune-related adverse effects. Diarrhea was the most common one leading to an ED visit. The proportions of ED visits associated with diarrhea, hypophysitis, thyroiditis, pancreatitis, or hepatitis varied significantly by immune checkpoint therapy agent. Colitis was significantly associated with better prognosis, whereas pneumonitis was significantly associated with worse survival.

CONCLUSION

Cancer patients treated with ipilimumab, nivolumab, or pembrolizumab may have a spectrum of immune-related adverse effects that require emergency care. Future studies will need to update this profile as further novel immunotherapeutic agents are added.

Regulation of PD-L1: Emerging Routes for Targeting Tumor Immune Evasion

Immune checkpoint blockade therapies (ICBTs) targeting programmed cell death 1 (PD-1) and its ligand programmed death ligand-1 (PD-L1/B7-H1/CD274) have exhibited momentous clinical benefits and durable responses in multiple tumor types. However, primary resistance is found in considerable number of cancer patients, and most responders eventually develop acquired resistance to ICBT. To tackle these challenges, it is essential to understand how PD-L1 is controlled by cancer cells to evade immune surveillance. Recent research has shed new light into the mechanisms of PD-L1 regulation at genetic, epigenetic, transcriptional, translational, and posttranslational levels. In this work, we systematically discuss the mechanisms that control the gene amplification, epigenetic alteration, transcription, subcellular transportation and posttranscriptional modification of PD-L1 in cancer cells. We further categorize posttranscriptional PD-L1 regulations by the molecular modification of PD-L1, including glycosylation, phosphorylation, ubiquitination, deubiquitination, and lysosomal degradation. These findings may provide new routes for targeting tumor immune escape and catalyze the development of small molecular inhibitors of PD-L1 in addition to existing antibody drugs.

Immune signatures predicting responses to immunomodulatory antibody therapy

Since the first immunomodulatory antibody was licensed by the FDA in 2011 for treating melanoma it has remained the case that only a certain proportion of cancer patients respond favourably to a particular therapy. Recent results from combining two or more different antibodies each targeting a different immune checkpoint indicate that the proportion of responding patients can be increased, but thus far there are no such therapies routinely yielding clinical benefit in 100% of patients in any cancer type. Therefore, predicting which patients will respond to a particular therapy remains of the utmost importance in order to maximise treatment efficacy and minimise side-effects and costs. Moreover, determining biomarkers predicting responses may provide insight into the mechanisms responsible for success or failure of that therapy. This article reviews seminal papers mostly from the past two years of progress in this area of intense investigation, and mostly in melanoma, the tumour type for which the largest body of data exists thus far.

A Phase I study of the novel immunomodulatory agent PG545 (pixatimod) in subjects with advanced solid tumours

Background

PG545 (pixatimod) is a novel immunomodulatory agent, which has been demonstrated to stimulate innate immune responses against tumours in preclinical cancer models.

Methods

This Phase I study investigated the safety, tolerability, pharmacokinetics, pharmacodynamics and preliminary efficacy of PG545 monotherapy. Escalating doses of PG545 were administered to patients with advanced solid malignancies as a weekly 1-h intravenous infusion.

Results

Twenty-three subjects were enrolled across four cohorts (25, 50, 100 and 150 mg). Three dose-limiting toxicities (DLTs)—hypertension (2), epistaxis (1)—occurred in the 150 mg cohort. No DLTs were noted in the 100 mg cohort, which was identified as the maximum-tolerated dose. No objective responses were reported. Best response was stable disease up to 24 weeks, with the disease control rate in evaluable subjects of 38%. Exposure was proportional up to 100 mg and mean half-life was 141 h. The pharmacodynamic data revealed increases in innate immune cell activation, plasma IFNγ, TNFα, IP-10 and MCP-1.

Conclusion

PG545 demonstrated a tolerable safety profile, proportional PK, evidence of immune cell stimulation and disease control in some subjects. Taken together, these data support the proposed mechanism of action, which represents a promising approach for use in combination with existing therapies.

High Number of Circulating Tumor Cells Predicts Poor Survival of Cutaneous Melanoma Patients in China

BACKGROUND Melanoma is an aggressive cancer with complex etiology and poor prognosis. Surgical resection is still the primary treatment of melanoma, but shows limited efficacy in late-stage patients. Additionally, reliable prognostic markers of skin melanoma patients are still lacking. Circulating tumor cells (CTCs) have shown promise in predicting prognosis of multiple cancers. Evaluating the prognostic value of CTC number in melanoma patients. MATERIAL AND METHODS CTCs were isolated by immunomagnetic capture from 7.5-mL samples of blood from 100 patients with cutaneous melanoma. Baseline CTC number (pre-treatment) and post-treatment CTC number were measured. Baseline CTC number and CTC number alteration were correlated with clinicopathological features and survival. RESULTS Forty-three (43%) patients had more than 6 CTCs, whereas 57 (57%) had 6 cells or less. High baseline CTC count was associated with deep local invasion, lymph node metastasis, and distance metastasis, with P value of 0.003, 0.047, and 0.034, respectively. High baseline CTC count was also correlated with short overall survival time and was considered as an independent prognostic factor (P value=0.012, hazard ratio=2.262). CTC cell alteration was associated with progression-free survival and disease-specific survival (with P values of 0.012 and 0.009, respectively). CONCLUSIONS Baseline CTC count was correlated with adverse pathological features and was predictive of survival in melanoma patients. Alteration of CTC count before and after treatment was an indicator of therapy response and prognosis. Measuring the baseline and post-treatment CTC counts is a powerful tool in monitoring melanoma progression, drug response, and survival.

Identification of pyrrolopyrimidine derivative PP-13 as a novel microtubule-destabilizing agent with promising anticancer properties

Despite the emergence of targeted therapies and immunotherapy, chemotherapy remains the gold-standard for the treatment of most patients with solid malignancies. Spindle poisons that interfere with microtubule dynamics are commonly used in chemotherapy drug combinations. However, their troublesome side effects and the emergence of chemoresistance highlight the need for identifying alternative agents. We performed a high throughput cell-based screening and selected a pyrrolopyrimidine molecule (named PP-13). In the present study, we evaluated its anticancer properties in vitro and in vivo. We showed that PP-13 exerted cytotoxic effects on various cancer cells, including those resistant to current targeted therapies and chemotherapies. PP-13 induced a transient mitotic blockade by interfering with both mitotic spindle organization and microtubule dynamics and finally led to mitotic slippage, aneuploidy and direct apoptotic death. PP-13 was identified as a microtubule-targeting agent that binds directly to the colchicine site in β-tubulin. Interestingly, PP-13 overcame the multidrug-resistant cancer cell phenotype and significantly reduced tumour growth and metastatic invasiveness without any noticeable toxicity for the chicken embryo in vivo. Overall, PP-13 appears to be a novel synthetic microtubule inhibitor with interesting anticancer properties and could be further investigated as a potent alternative for the management of malignancies including chemoresistant ones.

High expression of CD47 predicts adverse prognosis in Chinese patients and suppresses immune response in melanoma

BACKGROUND

Cluster of differentiation 47 (CD47) negatively regulates macrophage phagocytosis and is correlated with adverse survival of multiple cancers. In melanoma patients, especially in Chinese melanoma patients, its prognostic value is unclear. In this study, we aim to study the prognostic value of CD47 in a Chinse melanoma patient cohort and its immunomodulation roles in mouse model.

METHOD

164 melanoma tissue specimens were collected. The expression of CD47 in these clinical samples was examined by immunohistochemistry staining (IHC). The correlation between CD47 expression and clinicopathological parameters was assessed by statistical analysis. Prognostic values CD47 expression were also investigated. In an animal model, effects of CD47 expression on immune infiltration were examined.

RESULTS

CD47 expression was positively correlated with TNM stage, distant metastasis, and death of melanoma patients with the P value of 0.008, 0.018, and 0.032 respectively. High expression of CD47 was an independent prognostic marker of overall survival (HR=1.563, 95% CI: 1.069-2.285) and progression free survival (HR=1.542, 95% CI: 1.053-2.258) of Chinese melanoma patients.

CONCLUSION

In conclusion, high expression of CD47 predicted poor survival in a Chinese melanoma patient cohort and impaired antitumor immune response in the animal model. Targeting CD47 might be a novel option for melanoma patients.

Tumor location impacts immune response in mouse models of colon cancer

Existing preclinical models of human colorectal cancer (CRC) that rely on syngeneic subcutaneous grafts are problematic, because of increasing evidence that the immune microenvironment in subcutaneous tissue is significantly different from the gastrointestinal tract. Similarly, existing orthotopic models that use a laparotomy for establishing grafts are also problematic, because the surgical procedure results in extensive inflammation, thereby creating a nonphysiologic tumor microenvironment. To facilitate the bench-to-bedside translation of CRC immunotherapy strategies, we developed a novel orthotopic model in mice that uses endoscopy-guided microinjection of syngeneic cancer cells. When we compared immune system infiltration, we found that tumors in the subcutaneous model had fewer T cells, B cells, and natural killer (NK) cells, but more immunosuppressive myeloid cells; in contrast, tumors in our orthotopic model had a higher number of tumor-infiltrating T cells, B cells, and NK cells, with fewer immunosuppressive myeloid cells. The number of immune-stimulating cytokines, such as interleukin (IL)-2, IL-6, interferon (IFN)-gamma, and granzyme B, was also higher in tumors in our model, as compared with the subcutaneous model. Those differences resulted in heightened sensitivity to immune checkpoint blockade therapy in our endoscopy-guided orthotopic CRC model. Our study indicates that tumor location affects immune response in CRC mouse models; choosing the appropriate preclinical model is important when testing immunotherapy in CRC.

Constitutive and acquired mechanisms of resistance to immune checkpoint blockade in human cancer

Cancer immunotherapy with monoclonal antibodies directed against regulatory pathways in T lymphocytes has been revolutionizing medical oncology, and the clinical success of monoclonal antibodies targeting either cytotoxic T lymphocyte antigen-4 (CTLA-4) or program death-1 (PD-1) in patients affected by melanoma, Hodgkin's lymphoma, Merkel cell carcinoma, and head and neck, bladder, renal cell or non-small cell lung cancer is way beyond the most optimistic expectation. However, immune checkpoint blockade (ICB) has failed to arrest progression in a consistent amount of patients affected by those tumors, and various histological types, including breast, colon and prostate cancer, are less sensitive to this therapeutic approach. Such clinical findings have fueled massive research efforts in the attempt to identify pre-existing and acquired mechanisms of resistance to ICB. Here we focus on evidences emerging from studies in humans on how tumor cells and the tumor microenvironment contribute to the heterogeneous clinical responses, and we propose strategies stemming from pre-clinical models that might improve clinical outcomes for patients.

Current status and perspectives of patient-derived xenograft models in cancer research

Cancers remain a major public health problem worldwide, which still require profound research in both the basic and preclinical fields. Patient-derived xenograft (PDX) models are created when cancerous cells or tissues from patients' primary tumors are implanted into immunodeficient mice to simulate human tumor biology in vivo, which have been extensively used in cancer research. The routes of implantation appeared to affect the outcome of PDX research, and there has been increasing applications of patient-derived orthotopic xenograft (PDOX) models. In this review, we firstly summarize the methodology to establish PDX models and then go over recent application and function of PDX models in basic cancer research on the areas of cancer characterization, initiation, proliferation, metastasis, and tumor microenvironment and in preclinical explorations of anti-cancer targets, drugs, and therapeutic strategies and finally give our perspectives on the future prospects of PDX models.

Targeting CD47 Enhances the Efficacy of Anti-PD-1 and CTLA-4 in an Esophageal Squamous Cell Cancer Preclinical Model

Esophageal squamous cell cancer is a highly aggressive cancer with a dismal 5-year survival rate. CD47 is a cell transmembrane protein that is involved in cell apoptosis, proliferation, adhesion, migration, and antigen presentation in the immune system. By interacting with signal regulatory protein-α expressed in antigen-presenting cells (APCs), CD47 acts as an antiphagocytic mechanism to inhibit APC-dependent antigen presentation. Overexpression of CD47 was found in various types of cancer. However, its role in esophageal squamous cell cancer is not yet clear. Anti-CD47 is an antagonist of CD47 signaling pathways by competing with its ligand. In the current study, we investigated the effects of anti-CD47 treatment on the antitumor immune response in an esophageal squamous cell cancer preclinical model. We found that anti-CD47 treatment enhanced proinflammatory responses and increased CD8+ T-cell infiltration in tumor tissue in the animal model. T cells in anti-CD47-treated tumors showed higher PD-1 and CTLA-4 expression, indicating T-cell activation and the rationale of combining anti-CD47 with anti-PD-1 and CLTA-4. The combinatory treatment showed the best antitumor response, implying a novel treatment strategy. The effects of anti-CD47 depended on dendritic cell function. In patient samples, expression of CD47 was negatively correlated with CD8+ T-cell infiltration in esophageal squamous cell cancer patients. Taken together, CD47 might be a novel target to enhance anti-PD-1 and CLTA-4 efficacy in esophageal squamous cell cancer.

FAP positive fibroblasts induce immune checkpoint blockade resistance in colorectal cancer via promoting immunosuppression

Immune checkpoint blockades that significantly prolonged survival of melanoma patients have been less effective on colorectal cancer (CRC) patients. Growing evidence suggested that fibroblast activation protein-alpha (FAP) on cancer associate fibroblasts (CAFs) has critical roles in regulating antitumor immune response by inducing tumor-promoting inflammation. In this study, we explored the roles of FAP in regulating the tumor immunity and immune checkpoint blockades resistance in CRC experimental systems. We found that CAFs with high FAP expression could induce immune checkpoint blockade resistance in CRC mouse model. Mechanistically, CAFs with high FAP expression promoted immunosuppression in the CRC tumor immune microenvironment by up-regulating CCL2 secretion, recruiting myeloid cells, and decreasing T-cell activity. In human CRC samples, FAP expression was proportional to myeloid cells number, but inversely related to T-cell number. High FAP expression also predicted poor survival of CRC patients. Taken together, our study suggested that high FAP expression in CAFs is one reason leading to immune checkpoint blockades resistance in CRC patients and FAP is an optional target for reversing immune checkpoint blockades resistance.

IL-6 and PD-L1 blockade combination inhibits hepatocellular carcinoma cancer development in mouse model

Limited efficacy of immune checkpoint inhibitors in hepatocellular carcinoma (HCC) was observed in clinical trials, thus prompting investigation into combination therapy. Interleukin-6 (IL-6) has important roles in modeling immune responses in cancers. Here, we hypothesized that IL-6 blockade would enhance antitumor immunity of HCC and synergize with anti-programmed death-1-ligand 1 (PD-L1) checkpoint inhibitor in treating HCC. The sources and immune modulating effects of IL-6 were investigated in HCC models. Combination of anti-IL-6 and anti-PD-L1 was tested in HCC bearing mice. We found that IL-6 is mainly secreted by cancer associated fibroblast (CAFs), but not tumor cells in HCC. High IL-6 expression CAFs could induce strong immunosuppression in HCC microenvironment by recruiting immunosuppressive cells, such as myeloid derived suppressive cells. In addition, high IL-6 expression CAFs also impaired tumor infiltrating T-cell function via upregulating inhibitory immune checkpoints. Using IL-6 blockade could reverse anti-PD-L1 resistance in HCC tumor model. In conclusion, our study indicates that targeted inhibition of IL-6 may enhance the efficacy of anti-PD-L1 in HCC, providing a potential strategy to overcoming anti-PD-L1 resistance in HCC.