Antibody-Mediated Blockade of Phosphatidylserine Enhances the Antitumor Effect of Sorafenib in Hepatocellular Carcinomas Xenografts

Development of betabodies: the next generation of phosphatidylserine targeting agents

Externalized phosphatidylserine (PS) is a phospholipid and a selective marker of the tumor microenvironment (TME). It is exposed on the outer leaflet of the plasma membrane of tumor-associated endothelial cells, apoptotic tumor cells, and some viable tumor cells, where it functions in part to suppress immune responses by binding to PS receptors expressed on tumor-infiltrating myeloid cells. PS has been targeted with antibodies, such as bavituximab, that bind the phospholipid via a cofactor, β2-glycoprotein 1 (β2GP1); these antibodies showed excellent specificity for tumor vasculature and induce an immune stimulatory environment. We have advanced this concept by developing the next generation of PS targeting agent, a fusion protein (betabody) constructed by linking PS-binding domain V of β2GP1 to the Fc of an IgG2a. Betabodies bind to externalized PS with high affinity (∼1 nM), without the requirement of a co-factor and localize robustly to the TME. We demonstrate that betabodies are a direct PS-targeting agent that have the potential to be used as anti-tumor therapy, drug delivery vehicles, and tools for imaging the TME.

Macrophage metabolism, phenotype, function, and therapy in hepatocellular carcinoma (HCC)

The pivotal role of the tumor microenvironment (TME) in the initiation and advancement of hepatocellular carcinoma (HCC) is widely acknowledged, as it fosters the proliferation and metastasis of HCC cells. Within the intricate TME of HCC, tumor-associated macrophages (TAMs) represent a significant constituent of non-malignant cells. TAMs engage in direct communication with cancer cells in HCC, while also exerting influence on other immune cells to adopt a tumor-supportive phenotype that facilitates tumor progression. Among the multifaceted mechanisms at play, the metabolic reprogramming of both tumor cells and macrophages leads to phenotypic alterations and functional modifications in macrophages. This comprehensive review elucidates the intricate interplay between cellular metabolism and macrophage phenotype/polarization, while also providing an overview of the associated signaling molecules and potential therapeutic strategies for HCC.

Phospholipid isotope tracing reveals β-catenin-driven suppression of phosphatidylcholine metabolism in hepatocellular carcinoma

Background and Aims

Activating mutations in the CTNNB1 gene encoding β-catenin are among the most frequently observed oncogenic alterations in hepatocellular carcinoma (HCC). HCC with CTNNB1 mutations show profound alterations in lipid metabolism including increases in fatty acid oxidation and transformation of the phospholipidome, but it is unclear how these changes arise and whether they contribute to the oncogenic program in HCC.

Methods

We employed untargeted lipidomics and targeted isotope tracing to quantify phospholipid production fluxes in an inducible human liver cell line expressing mutant β-catenin, as well as in transgenic zebrafish with activated β-catenin-driven HCC.

Results

In both models, activated β-catenin expression was associated with large changes in the lipidome including conserved increases in acylcarnitines and ceramides and decreases in triglycerides. Lipid flux analysis in human cells revealed a large reduction in phosphatidylcholine (PC) production rates as assayed by choline tracer incorporation. We developed isotope tracing lipid flux analysis for zebrafish and observed similar reductions in phosphatidylcholine synthesis flux accomplished by sex-specific mechanisms.

Conclusions

The integration of isotope tracing with lipid abundances highlights specific lipid class transformations downstream of β-catenin signaling in HCC and suggests future HCC-specific lipid metabolic targets.

Targeting tumor-associated macrophages in hepatocellular carcinoma: biology, strategy, and immunotherapy

Hepatocellular carcinoma (HCC), one of the most malignant tumors, is characterized by its stubborn immunosuppressive microenvironment. As one of the main members of the tumor microenvironment (TME) of HCC, tumor-associated macrophages (TAMs) play a critical role in its occurrence and development, including stimulating angiogenesis, enhancing immunosuppression, and promoting the drug resistance and cancer metastasis. This review describes the origin as well as phenotypic heterogeneity of TAMs and their potential effects on the occurrence and development of HCC and also discusses about various adjuvant therapy based strategies that can be used for targeting TAMs. In addition, we have highlighted different treatment modalities for TAMs based on immunotherapy, including small molecular inhibitors, immune checkpoint inhibitors, antibodies, tumor vaccines, adoptive cellular immunotherapy, and nanocarriers for drug delivery, to explore novel combination therapies and provide feasible therapeutic options for clinically improving the prognosis and quality of life of HCC patients.

Differential Plasma Metabolites between High- and Low-Grade Meningioma Cases

Meningiomas (MGMs) are currently classified into grades I, II, and III. High-grade tumors are correlated with decreased survival rates and increased recurrence rates. The current grading classification is based on histological criteria and determined only after surgical tumor sampling. This study aimed to identify plasma metabolic alterations in meningiomas of different grades, which would aid surgeons in predefining the ideal surgical strategy. Plasma samples were collected from 51 patients with meningioma and classified into low-grade (LG) (grade I; n = 43), and high-grade (HG) samples (grade II, n = 5; grade III, n = 3). An untargeted metabolomic approach was used to analyze plasma metabolites. Statistical analyses were performed to select differential biomarkers among HG and LG groups. Metabolites were identified using tandem mass spectrometry along with database verification. Five and four differential biomarkers were identified for HG and LG meningiomas, respectively. To evaluate the potential of HG MGM metabolites to differentiate between HG and LG tumors, a receiving operating characteristic curve was constructed, which revealed an area under the curve of 95.7%. This indicates that the five HG MGM metabolites represent metabolic alterations that can differentiate between LG and HG meningiomas. These metabolites may indicate tumor grade even before the appearance of histological features.

Noncoding RNA-mediated macrophage and cancer cell crosstalk in hepatocellular carcinoma

The tumor microenvironment (TME) is a well-recognized system that plays an essential role in tumor initiation, development, and progression. Intense intercellular communication between tumor cells and other cells (especially macrophages) occurs in the TME and is mediated by cell-to-cell contact and/or soluble messengers. Emerging evidence indicates that noncoding RNAs (ncRNAs) are critical regulators of the relationship between cells within the TME. In this review, we provide an update on the regulation of ncRNAs (primarily micro RNAs [miRNAs], long ncRNAs [lncRNAs], and circular RNAs [circRNAs]) in the crosstalk between macrophages and tumor cells in hepatocellular carcinoma (HCC). These ncRNAs are derived from macrophages or tumor cells and act as oncogenes or tumor suppressors, contributing to tumor progression not only by regulating the physiological and pathological processes of tumor cells but also by controlling macrophage infiltration, activation, polarization, and function. Herein, we also explore the options available for clinical therapeutic strategies targeting crosstalk-related ncRNAs to treat HCC. A better understanding of the relationship between macrophages and tumor cells mediated by ncRNAs will uncover new diagnostic biomarkers and pharmacological targets in cancer.

The Apoptosis Paradox in Cancer

Cancer growth represents a dysregulated imbalance between cell gain and cell loss, where the rate of proliferating mutant tumour cells exceeds the rate of those that die. Apoptosis, the most renowned form of programmed cell death, operates as a key physiological mechanism that limits cell population expansion, either to maintain tissue homeostasis or to remove potentially harmful cells, such as those that have sustained DNA damage. Paradoxically, high-grade cancers are generally associated with high constitutive levels of apoptosis. In cancer, cell-autonomous apoptosis constitutes a common tumour suppressor mechanism, a property which is exploited in cancer therapy. By contrast, limited apoptosis in the tumour-cell population also has the potential to promote cell survival and resistance to therapy by conditioning the tumour microenvironment (TME)-including phagocytes and viable tumour cells-and engendering pro-oncogenic effects. Notably, the constitutive apoptosis-mediated activation of cells of the innate immune system can help orchestrate a pro-oncogenic TME and may also effect evasion of cancer treatment. Here, we present an overview of the implications of cell death programmes in tumour biology, with particular focus on apoptosis as a process with "double-edged" consequences: on the one hand, being tumour suppressive through deletion of malignant or pre-malignant cells, while, on the other, being tumour progressive through stimulation of reparatory and regenerative responses in the TME.

Macrophages M1-Related Prognostic Signature in Hepatocellular Carcinoma

A large number of studies have found that macrophages M1 play an important role in the occurrence and development of tumors. The aim of our study is to explore the causes of differential infiltration of macrophages M1 in hepatocellular carcinoma from the perspective of transcriptome and establish a prognostic model of hepatocellular carcinoma. We downloaded gene expression and clinical data from the public database, estimated the content of macrophages M1 in different samples with R software, and found the different genes between high- and low-infiltration groups. Using differentially expressed genes, we constructed a model composed of 7 genes. The risk score of the model has a good ability to predict the prognosis, has a positive correlation with immune checkpoints, and is closely related to other immune cells and immune function. Our model shows good prognostic function and has wide application value.

Bringing Macrophages to the Frontline against Cancer: Current Immunotherapies Targeting Macrophages

Macrophages are found in all tissues and display outstanding functional diversity. From embryo to birth and throughout adult life, they play critical roles in development, homeostasis, tissue repair, immunity, and, importantly, in the control of cancer growth. In this review, we will briefly detail the multi-functional, protumoral, and antitumoral roles of macrophages in the tumor microenvironment. Our objective is to focus on the ever-growing therapeutic opportunities, with promising preclinical and clinical results developed in recent years, to modulate the contribution of macrophages in oncologic diseases. While the majority of cancer immunotherapies target T cells, we believe that macrophages have a promising therapeutic potential as tumoricidal effectors and in mobilizing their surroundings towards antitumor immunity to efficiently limit cancer progression.

Axl and Mertk Receptors Cooperate to Promote Breast Cancer Progression by Combined Oncogenic Signaling and Evasion of Host Antitumor Immunity

Despite the promising clinical benefit of targeted and immune checkpoint blocking therapeutics, current strategies have limited success in breast cancer, indicating that additional inhibitory pathways are required to complement existing therapeutics. TAM receptors (Tyro-3, Axl, and Mertk) are often correlated with poor prognosis because of their capacities to sustain an immunosuppressive environment. Here, we ablate Axl on tumor cells using CRISPR/Cas9 gene editing, and by targeting Mertk in the tumor microenvironment (TME), we observed distinct functions of TAM as oncogenic kinases, as well as inhibitory immune receptors. Depletion of Axl suppressed cell intrinsic oncogenic properties, decreased tumor growth, reduced the incidence of lung metastasis and increased overall survival of mice when injected into mammary fat pad of syngeneic mice, and demonstrated synergy when combined with anti-PD-1 therapy. Blockade of Mertk function on macrophages decreased efferocytosis, altered the cytokine milieu, and resulted in suppressed macrophage gene expression patterns. Mertk-knockout mice or treatment with anti-Mertk-neutralizing mAb also altered the cellular immune profile, resulting in a more inflamed tumor environment with enhanced T-cell infiltration into tumors and T-cell-mediated cytotoxicity. The antitumor activity from Mertk inhibition was abrogated by depletion of cytotoxic CD8α T cells by using anti-CD8α mAb or by transplantation of tumor cells into B6.CB17-Prkdc SCID mice. Our data indicate that targeting Axl expressed on tumor cells and Mertk in the TME is predicted to have a combinatorial benefit to enhance current immunotherapies and that Axl and Mertk have distinct functional activities that impair host antitumor response. SIGNIFICANCE: This study demonstrates how TAM receptors act both as oncogenic tyrosine kinases and as receptors that mediate immune evasion in cancer progression.

Targeting phosphatidylserine for Cancer therapy: prospects and challenges

Cancer is a leading cause of mortality and morbidity worldwide. Despite major improvements in current therapeutic methods, ideal therapeutic strategies for improved tumor elimination are still lacking. Recently, immunotherapy has attracted much attention, and many immune-active agents have been approved for clinical use alone or in combination with other cancer drugs. However, some patients have a poor response to these agents. New agents and strategies are needed to overcome such deficiencies. Phosphatidylserine (PS) is an essential component of bilayer cell membranes and is normally present in the inner leaflet. In the physiological state, PS exposure on the external leaflet not only acts as an engulfment signal for phagocytosis in apoptotic cells but also participates in blood coagulation, myoblast fusion and immune regulation in nonapoptotic cells. In the tumor microenvironment, PS exposure is significantly increased on the surface of tumor cells or tumor cell-derived microvesicles, which have innate immunosuppressive properties and facilitate tumor growth and metastasis. To date, agents targeting PS have been developed, some of which are under investigation in clinical trials as combination drugs for various cancers. However, controversial results are emerging in laboratory research as well as in clinical trials, and the efficiency of PS-targeting agents remains uncertain. In this review, we summarize recent progress in our understanding of the physiological and pathological roles of PS, with a focus on immune suppressive features. In addition, we discuss current drug developments that are based on PS-targeting strategies in both experimental and clinical studies. We hope to provide a future research direction for the development of new agents for cancer therapy.

TIMs, TAMs, and PS- antibody targeting: implications for cancer immunotherapy

Immunotherapy for cancer is making impressive strides at improving survival of a subset of cancer patients. To increase the breadth of patients that benefit from immunotherapy, new strategies that combat the immunosuppressive microenvironment of tumors are needed. Phosphatidylserine (PS) signaling is exploited by tumors to enhance tumor immune evasion and thus strategies to inhibit PS-mediated immune suppression have potential to increase the efficacy of immunotherapy. PS is a membrane lipid that flips to the outer surface of the cell membrane during apoptosis and/or cell stress. Externalized PS can drive efferocytosis or engage PS receptors (PSRs) to promote local immune suppression. In the tumor microenvironment (TME) PS-mediated immune suppression is often termed apoptotic mimicry. Monoclonal antibodies (mAbs) targeting PS or PSRs have been developed and are in preclinical and clinical testing. The TIM (T-cell/transmembrane, immunoglobulin, and mucin) and TAM (Tyro3, AXL, and MerTK) family of receptors are PSRs that have been shown to drive PS-mediated immune suppression in tumors. This review will highlight the development of mAbs targeting PS, TIM-3 and the TAM receptors.

APR-246 alone and in combination with a phosphatidylserine-targeting antibody inhibits lung metastasis of human triple-negative breast cancer cells in nude mice

Background

Approximately 15–20% of all human breast cancers are classified as triple-negative because they lack estrogen and progesterone receptors and Her-2-neu, which are commonly targeted by chemotherapeutic drugs. New treatment strategies are therefore urgently needed to combat triple-negative breast cancers (TNBCs). Almost 80% of the triple-negative tumors express mutant p53 (mtp5), a functionally defective tumor suppressor protein. Whereas wild-type p53 (wtp53) promotes cell-cycle arrest and apoptosis and inhibits vascular endothelial growth factor-dependent angiogenesis, mtp53 fails to regulate these functions, resulting in tumor vascularization, growth, resistance to chemotherapy, and metastasis. Restoration of p53 function is therefore a promising drug-targeted strategy for suppressing TNBC metastasis.

Methods

APR-246 is a small-molecule drug that reactivates mtp53, thereby restoring p53 function. In this study, we sought to determine whether administration of APR-246, either alone or in combination with 2aG4, an antibody that targets phosphatidylserine residues on tumor blood vessels and disrupts tumor vasculature, effectively inhibits stem cell-like characteristics of tumor cells and migration in vitro, and metastasis of human mtp53-expressing TNBC cells to the lungs in mouse models.

Results

APR-246 reduced both the stem cell-like properties and migration of TNBC cells in vitro. In mouse models, administration of either APR-246 or 2aG4 reduced metastasis of TNBC cells to the lungs; a combination of the two diminished lung metastasis to the same extent as either agent alone. Combination treatment significantly reduced the incidence of lung metastasis compared either single agent alone.

Conclusion

Metastasis of human mtp53-expressing TNBC cells to the lungs of nude mice is inhibited by the treatment that combines activation of mtp53 with targeting of phosphatidylserine residues on tumor blood vessels. We contend therefore that our findings strongly support the use of combination treatment involving mtp53 activation and immunotherapy in patients with TNBC.

Molecular Repolarisation of Tumour-Associated Macrophages

The tumour microenvironment (TME) is composed of extracellular matrix and non-mutated cells supporting tumour growth and development. Tumour-associated macrophages (TAMs) are among the most abundant immune cells in the TME and are responsible for the onset of a smouldering inflammation. TAMs play a pivotal role in oncogenic processes as tumour proliferation, angiogenesis and metastasis, and they provide a barrier against the cytotoxic effector function of T lymphocytes and natural killer (NK) cells. However, TAMs are highly plastic cells that can adopt either pro- or anti-inflammatory roles in response to environmental cues. Consequently, TAMs represent an attractive target to recalibrate immune responses in the TME. Initial TAM-targeted strategies, such as macrophage depletion or disruption of TAM recruitment, have shown beneficial effects in preclinical models and clinical trials. Alternatively, reprogramming TAMs towards a proinflammatory and tumouricidal phenotype has become an attractive strategy in immunotherapy. This work summarises the molecular wheelwork of macrophage biology and presents an overview of molecular strategies to repolarise TAMs in immunotherapy.

Phosphatidylserine-Targeted Nanotheranostics for Brain Tumor Imaging and Therapeutic Potential

Phosphatidylserine (PS), the most abundant anionic phospholipid in cell membrane, is strictly confined to the inner leaflet in normal cells. However, this PS asymmetry is found disruptive in many tumor vascular endothelial cells. We discuss the underlying mechanisms for PS asymmetry maintenance in normal cells and its loss in tumor cells. The specificity of PS exposure in tumor vasculature but not normal blood vessels may establish it a useful biomarker for cancer molecular imaging. Indeed, utilizing PS-targeting antibodies, multiple imaging probes have been developed and multimodal imaging data have shown their high tumor-selective targeting in various cancers. There is a critical need for improved diagnosis and therapy for brain tumors. We have recently established PS-targeted nanoplatforms, aiming to enhance delivery of imaging contrast agents across the blood-brain barrier to facilitate imaging of brain tumors. Advantages of using the nanodelivery system, in particular, lipid-based nanocarriers, are discussed here. We also describe our recent research interest in developing PS-targeted nanotheranostics for potential image-guided drug delivery to treat brain tumors.

A combination of p53-activating APR-246 and phosphatidylserine-targeting antibody potently inhibits tumor development in hormone-dependent mutant p53-expressing breast cancer xenografts

Background

Between 30 and 40% of human breast cancers express a defective tumor suppressor p53 gene. Wild-type p53 tumor suppressor protein promotes cell-cycle arrest and apoptosis and inhibits vascular endothelial growth factor-dependent angiogenesis, whereas mutant p53 protein (mtp53) lacks these functions, resulting in tumor cell survival and metastasis. Restoration of p53 function is therefore a promising drug-targeted strategy for combating mtp53-expressing breast cancer.

Methods

In this study, we sought to determine whether administration of APR-246, a small-molecule drug that restores p53 function, in combination with 2aG4, an antibody that targets phosphatidylserine residues on tumor blood vessels and disrupts tumor vasculature, effectively inhibits advanced hormone-dependent breast cancer tumor growth.

Results

APR-246 reduced cell viability in mtp53-expressing BT-474 and T47-D human breast cancer cells in vitro, and significantly induced apoptosis in a dose-dependent manner. However, APR-246 did not reduce cell viability in MCF-7 breast cancer cells, which express wild-type p53. We next examined APR-246's anti-tumor effects in vivo using BT-474 and T47-D tumor xenografts established in female nude mice. Tumor-bearing mice were treated with APR-246 and/or 2aG4 and tumor volume followed over time. Tumor growth was more effectively suppressed by combination treatment than by either agent alone, and combination therapy completely eradicated some tumors. Immunohistochemistry analysis of tumor tissue sections demonstrated that combination therapy more effectively induced apoptosis and reduced cell proliferation in tumor xenografts than either agent alone. Importantly, combination therapy dramatically reduced the density of blood vessels, which serve as the major route for tumor metastasis, in tumor xenografts compared with either agent alone.

Conclusion

Based on our findings, we contend that breast tumor growth might effectively be controlled by simultaneous targeting of mtp53 protein and tumor blood vessels in mtp53-expressing cancers.

Antibody targeting of phosphatidylserine for the detection and immunotherapy of cancer

Phosphatidylserine (PS) is a negatively charged phospholipid in all eukaryotic cells that is actively sequestered to the inner leaflet of the cell membrane. Exposure of PS on apoptotic cells is a normal physiological process that triggers their rapid removal by phagocytic engulfment under noninflammatory conditions via receptors primarily expressed on immune cells. PS is aberrantly exposed in the tumor microenvironment and contributes to the overall immunosuppressive signals that antagonize the development of local and systemic antitumor immune responses. PS-mediated immunosuppression in the tumor microenvironment is further exacerbated by chemotherapy and radiation treatments that result in increased levels of PS on dying cells and necrotic tissue. Antibodies targeting PS localize to tumors and block PS-mediated immunosuppression. Targeting exposed PS in the tumor microenvironment may be a novel approach to enhance immune responses to cancer.

Targeting Phosphatidylserine with Calcium-Dependent Protein-Drug Conjugates for the Treatment of Cancer

In response to cellular stress, phosphatidylserine is exposed on the outer membrane leaflet of tumor blood vessels and cancer cells, motivating the development of phosphatidylserine-specific therapies. The generation of drug-conjugated phosphatidylserine-targeting agents represents an unexplored therapeutic approach, for which antitumor effects are critically dependent on efficient internalization and lysosomal delivery of the cytotoxic drug. In the current study, we have generated phosphatidylserine-targeting agents by fusing phosphatidylserine-binding domains to a human IgG1-derived Fc fragment. The tumor localization and pharmacokinetics of several phosphatidylserine-specific Fc fusions have been analyzed in mice and demonstrate that Fc-Syt1, a fusion containing the synaptotagmin 1 C2A domain, effectively targets tumor tissue. Conjugation of Fc-Syt1 to the cytotoxic drug monomethyl auristatin E results in a protein-drug conjugate (PDC) that is internalized into target cells and, due to the Ca²⁺ dependence of phosphatidylserine binding, dissociates from phosphatidylserine in early endosomes. The released PDC is efficiently delivered to lysosomes and has potent antitumor effects in mouse xenograft tumor models. Interestingly, although an engineered, tetravalent Fc-Syt1 fusion shows increased binding to target cells, this higher avidity variant demonstrates reduced persistence and therapeutic effects compared with bivalent Fc-Syt1. Collectively, these studies show that finely tuned, Ca²⁺-switched phosphatidylserine-targeting agents can be therapeutically efficacious. Mol Cancer Ther; 17(1); 169-82. ©2017 AACR.