Antiphosphatidylserine antibody combined with irradiation damages tumor blood vessels and induces tumor immunity in a rat model of glioblastoma

Deletion of the TMEM30A gene enables leukemic cell evasion of NK cell cytotoxicity

Natural killer (NK) cell immunotherapy has gained attention as a promising strategy for treatment of various malignancies. In this study, we used a genome-wide CRISPR screen to identify genes that provide protection or susceptibility to NK cell cytotoxicity. The screen confirmed the role of several genes in NK cell regulation, such as genes involved in interferon-γ signaling and antigen presentation, as well as genes encoding the NK cell receptor ligands B7-H6 and CD58. Notably, the gene TMEM30A, encoding CDC50A-beta-subunit of the flippase shuttling phospholipids in the plasma membrane, emerged as crucial for NK cell killing. Accordingly, a broad range of TMEM30A knock-out (KO) leukemia and lymphoma cells displayed increased surface levels of phosphatidylserine (PtdSer). TMEM30A KO cells triggered less NK cell degranulation, cytokine production and displayed lower susceptibility to NK cell cytotoxicity. Blockade of PtdSer or the inhibitory receptor TIM-3, restored the NK cell ability to eliminate TMEM30A-mutated cells. The key role of the TIM-3 - PtdSer interaction for NK cell regulation was further substantiated by disruption of the receptor gene in primary NK cells, which significantly reduced the impact of elevated PtdSer in TMEM30A KO leukemic cells. Our study underscores the potential significance of agents targeting the interaction between PtdSer and TIM-3 in the realm of cancer immunotherapy.

Potential roles for efferocytosis in glioblastoma immune evasion

Glioblastoma is an aggressive and incurable brain cancer. This cancer establishes both local and systemic immunosuppression that creates a major obstacle to effective immunotherapies. Many studies point to tumor-resident myeloid cells (primarily microglia and macrophages) as key mediators of this immunosuppression. Myeloid cells exhibit a high level of plasticity with respect to their phenotype and are capable of both stimulating and repressing immune responses. How glioblastomas recruit myeloid cells and exploit them to avoid the immune system is an active area of research. Macrophages can acquire an immunosuppressive phenotype as a consequence of exposure to cytokines such as TGFB1 or IL4; in addition, macrophages can acquire an immunosuppressive phenotype as a consequence of the engulfment of apoptotic cells, a process referred to as efferocytosis. There is substantial evidence that glioblastoma cells are able to secrete cytokines and other factors that induce an immunosuppressive phenotype in macrophages and microglia. However, less is known about the contribution of efferocytosis to immunosuppression in glioblastoma. Here I review the literature in this area and discuss the potential of efferocytosis inhibition to improve glioblastoma response to immunotherapy.

The Role of Antibody-Based Therapies in Neuro-Oncology

This review explores the evolving landscape of antibody-based therapies in neuro-oncology, in particular, immune checkpoint inhibitors and immunomodulatory antibodies. We discuss their mechanisms of action, blood-brain barrier (BBB) penetration, and experience in neuro-oncological conditions. Evidence from recent trials indicates that while these therapies can modulate the tumor immune microenvironment, their clinical benefits remain uncertain, largely due to challenges with BBB penetration and tumor-derived immunosuppression. This review also examines emerging targets such as TIGIT and LAG3, the potential of antibodies in modulating the myeloid compartment, and tumor-specific targets for monoclonal antibody therapy. We further delve into advanced strategies such as antibody-drug conjugates and bispecific T cell engagers. Lastly, we explore innovative techniques being investigated to enhance antibody delivery, including CAR T cell therapy. Despite current limitations, these therapies hold significant therapeutic potential for neuro-oncology. Future research should focus on optimizing antibody delivery to the CNS, identifying novel biological targets, and discovering combination therapies to address the hostile tumor microenvironment.

Bidirectional crosstalk between therapeutic cancer vaccines and the tumor microenvironment: Beyond tumor antigens

Immunotherapy has rejuvenated cancer therapy, especially after anti-PD-(L)1 came onto the scene. Among the many therapeutic options, therapeutic cancer vaccines are one of the most essential players. Although great progress has been made in research on tumor antigen vaccines, few phase III trials have shown clinical benefits. One of the reasons lies in obstruction from the tumor microenvironment (TME). Meanwhile, the therapeutic cancer vaccine reshapes the TME in an ambivalent way, leading to immune stimulation or immune escape. In this review, we summarize recent progress on the interaction between therapeutic cancer vaccines and the TME. With respect to vaccine resistance, innate immunosuppressive TME components and acquired resistance caused by vaccination are both involved. Understanding the underlying mechanism of this crosstalk provides insight into the treatment of cancer by directly targeting the TME or synergizing with other therapeutics.

Bavituximab Decreases Immunosuppressive Myeloid-Derived Suppressor Cells in Newly Diagnosed Glioblastoma Patients

PURPOSE

We evaluated the efficacy of bavituximab-a mAb with anti-angiogenic and immunomodulatory properties-in newly diagnosed patients with glioblastoma (GBM) who also received radiotherapy and temozolomide. Perfusion MRI and myeloid-related gene transcription and inflammatory infiltrates in pre-and post-treatment tumor specimens were studied to evaluate on-target effects (NCT03139916).

PATIENTS AND METHODS

Thirty-three adults with IDH--wild-type GBM received 6 weeks of concurrent chemoradiotherapy, followed by 6 cycles of temozolomide (C1-C6). Bavituximab was given weekly, starting week 1 of chemoradiotherapy, for at least 18 weeks. The primary endpoint was proportion of patients alive at 12 months (OS-12). The null hypothesis would be rejected if OS-12 was ≥72%. Relative cerebral blood flow (rCBF) and vascular permeability (Ktrans) were calculated from perfusion MRIs. Peripheral blood mononuclear cells and tumor tissue were analyzed pre-treatment and at disease progression using RNA transcriptomics and multispectral immunofluorescence for myeloid-derived suppressor cells (MDSC) and macrophages.

RESULTS

The study met its primary endpoint with an OS-12 of 73% (95% confidence interval, 59%-90%). Decreased pre-C1 rCBF (HR, 4.63; P = 0.029) and increased pre-C1 Ktrans were associated with improved overall survival (HR, 0.09; P = 0.005). Pre-treatment overexpression of myeloid-related genes in tumor tissue was associated with longer survival. Post-treatment tumor specimens contained fewer immunosuppressive MDSCs (P = 0.01).

CONCLUSIONS

Bavituximab has activity in newly diagnosed GBM and resulted in on-target depletion of intratumoral immunosuppressive MDSCs. Elevated pre-treatment expression of myeloid-related transcripts in GBM may predict response to bavituximab.

The immunogenic radiation and new players in immunotherapy and targeted therapy for head and neck cancer

Although treatment modalities for head and neck cancer have evolved considerably over the past decades, survival rates have plateaued. The treatment options remained limited to definitive surgery, surgery followed by fractionated radiotherapy with optional chemotherapy, and a definitive combination of fractionated radiotherapy and chemotherapy. Lately, immunotherapy has been introduced as the fourth modality of treatment, mainly administered as a single checkpoint inhibitor for recurrent or metastatic disease. While other regimens and combinations of immunotherapy and targeted therapy are being tested in clinical trials, adapting the appropriate regimens to patients and predicting their outcomes have yet to reach the clinical setting. Radiotherapy is mainly regarded as a means to target cancer cells while minimizing the unwanted peripheral effect. Radiotherapy regimens and fractionation are designed to serve this purpose, while the systemic effect of radiation on the immune response is rarely considered a factor while designing treatment. To bridge this gap, this review will highlight the effect of radiotherapy on the tumor microenvironment locally, and the immune response systemically. We will review the methodology to identify potential targets for therapy in the tumor microenvironment and the scientific basis for combining targeted therapy and radiotherapy. We will describe a current experience in preclinical models to test these combinations and propose how challenges in this realm may be faced. We will review new players in targeted therapy and their utilization to drive immunogenic response against head and neck cancer. We will outline the factors contributing to head and neck cancer heterogeneity and their effect on the response to radiotherapy. We will review in-silico methods to decipher intertumoral and intratumoral heterogeneity and how these algorithms can predict treatment outcomes. We propose that (a) the sequence of surgery, radiotherapy, chemotherapy, and targeted therapy should be designed not only to annul cancer directly, but to prime the immune response. (b) Fractionation of radiotherapy and the extent of the irradiated field should facilitate systemic immunity to develop. (c) New players in targeted therapy should be evaluated in translational studies toward clinical trials. (d) Head and neck cancer treatment should be personalized according to patients and tumor-specific factors.

Design, Synthesis and Anti-Melanoma Activity of Novel Annexin V Derivative with β3-Integrin Affinity

Tumor tissues often exhibit unique integrin receptor presentation during development, such as high exposures of α_vβ₃ and α_IIbβ₃ integrins. These features are not present in normal tissues. The induction of selective thrombosis and infarction in the tumor-feeding vessels, as well as specific antagonism of α_vβ₃ integrin on the surface of tumor endothelial cells, is a potential novel antitumor strategy. The Echistatin-Annexin V (EAV) fusion protein is a novel Annexin V (ANV) derivative that possesses a high degree of α_vβ₃ and α_IIbβ₃ integrin receptor recognition and binding characteristics while retaining the specific binding ability of the natural ANV molecule for phosphatidylserine (PS). We systematically investigated the biological effects of this novel molecule with superimposed functions on mouse melanoma. We found that EAV inhibited the viability and migration of B16F10 murine melanoma cells in a dose-dependent manner, exhibited good tumor suppressive effects in a xenograft mouse melanoma model, strongly induced tumor tissue necrosis in mice, and targeted the inhibition of angiogenesis in mouse melanoma tumor tissue. EAV exhibited stronger biological effects than natural ANV molecules in inhibiting melanoma in mice. The unique biological effects of EAV are based on its high β₃-type integrin receptor-specific recognition and binding ability, as well as its highly selective binding to PS molecules. Based on these findings, we propose that EAV-mediated tumor suppression is a novel and promising antitumor strategy that targets both PS- and integrin β₃-positive tumor neovascularization and the tumor cells themselves, thus providing a possible mechanism for the treatment of melanoma.

Advances in antibody-based drugs and their delivery through the blood-brain barrier for targeted therapy and immunotherapy of gliomas

Gliomas are highly invasive and are the most common type of primary malignant brain tumor. The routine treatments for glioma include surgical resection, radiotherapy, and chemotherapy. However, glioma recurrence and patient survival remain unsatisfactory after employing these traditional treatment approaches. With the rapid development of molecular immunology, significant breakthroughs have been made in targeted glioma therapy and immunotherapy. Antibody-based therapy has excellent advantages in treating gliomas due to its high specificity and sensitivity. This article reviewed various targeted antibody drugs for gliomas, including anti-glioma surface marker antibodies, anti-angiogenesis antibodies, and anti-immunosuppressive signal antibodies. Notably, many antibodies have been validated clinically, such as bevacizumab, cetuximab, panitumumab, and anti-PD-1 antibodies. These antibodies can improve the targeting of glioma therapy, enhance anti-tumor immunity, reduce the proliferation and invasion of glioma, and thus prolong the survival time of patients. However, the existence of the blood-brain barrier (BBB) has caused significant difficulties in drug delivery for gliomas. Therefore, this paper also summarized drug delivery methods through the BBB, including receptor-mediated transportation, nano-based carriers, and some physical and chemical methods for drug delivery. With these exciting advancements, more antibody-based therapies will likely enter clinical practice and allow more successful control of malignant gliomas.

Mertk: An emerging target in cancer biology and immuno-oncology

Mertk, a type I Receptor Tyrosine Kinase (RTK) and member of the TAM (Tyro3, Axl, and Mertk) family of homologous tyrosine kinases, has important roles in signal transduction both homeostatically on normal cells as well as patho-physiologically on both tumor-associated macrophages and malignant cells by its overexpression in a wide array of cancers. The main ligands of Mertk are Vitamin K-modified endogenous proteins Gas6 and Protein S (ProS1), heterobifunctional modular proteins that bind Mertk via two carboxyl-terminal laminin-like globular (LG) domains, and an N-terminal Gla domain that binds anionic phospholipids, whereby externalized phosphatidylserine (PS) on stressed viable and caspase-activated apoptotic cells is most emblematic. Recent studies indicate that Vitamin K-dependent γ-carboxylation on the N-terminal Gla domain of Gas6 and Protein S is necessary for PS binding and Mertk activation, implying that Mertk is preferentially active in tissues where there is high externalized PS, such as the tumor microenvironment (TME) and acute virally infected tissues. Once stimulated, activated Mertk can provide a survival advantage for cancer cells as well as drive compensatory proliferation. On monocytes and tumor-associated macrophages, Mertk promotes efferocytosis and acts as an inhibitory receptor that impairs host anti-tumor immunity, functioning akin to a myeloid checkpoint inhibitor. In recent years, inhibition of Mertk has been implicated in a dual role to enhance the sensitivity of cancer cells to cytotoxic agents along with improving host anti-tumor immunity with anti-PD-1/PD-L1 immunotherapy. Here, we examine the rationale of Mertk-targeted immunotherapies, the current and potential therapeutic strategies, the clinical status of Mertk-specific therapies, and potential challenges and obstacles for Mertk-focused therapies.

SapC-DOPS as a Novel Therapeutic and Diagnostic Agent for Glioblastoma Therapy and Detection: Alternative to Old Drugs and Agents

Glioblastoma multiforme (GBM), the most common type of brain cancer, is extremely aggressive and has a dreadful prognosis. GBM comprises 60% of adult brain tumors and the 5 year survival rate of GBM patients is only 4.3%. Standard-of-care treatment includes maximal surgical removal of the tumor in combination with radiation and temozolomide (TMZ) chemotherapy. TMZ is the "gold-standard" chemotherapy for patients suffering from GBM. However, the median survival is only about 12 to 18 months with this protocol. Consequently, there is a critical need to develop new therapeutic options for treatment of GBM. Nanomaterials have unique properties as multifunctional platforms for brain tumor therapy and diagnosis. As one of the nanomaterials, lipid-based nanocarriers are capable of delivering chemotherapeutics and imaging agents to tumor sites by enhancing the permeability of the compound through the blood-brain barrier, which makes them ideal for GBM therapy and imaging. Nanocarriers also can be used for delivery of radiosensitizers to the tumor to enhance the efficacy of the radiation therapy. Previously, high-atomic-number element-containing particles such as gold nanoparticles and liposomes have been used as radiosensitizers. SapC-DOPS, a protein-based liposomal drug comprising the lipid, dioleoylphosphatidylserine (DOPS), and the protein, saposin C (SapC), has been shown to be effective for treatment of a variety of cancers in small animals, including GBM. SapC-DOPS also has the unique ability to be used as a carrier for delivery of radiotheranostic agents for nuclear imaging and radiotherapeutic purposes. These unique properties make tumor-targeting proteo-liposome nanocarriers novel therapeutic and diagnostic alternatives to traditional chemotherapeutics and imaging agents. This article reviews various treatment modalities including nanolipid-based delivery and therapeutic systems used in preclinical and clinical trial settings for GBM treatment and detection.

The Evolution of Safe and Effective Coaguligands for Vascular Targeting and Precision Thrombosis of Solid Tumors and Vascular Malformations

In cardiovascular and cerebrovascular biology, control of thrombosis and the coagulation cascade in ischemic stroke, myocardial infarction, and other coagulopathies is the focus of significant research around the world. Ischemic stroke remains one of the largest causes of death and disability in developed countries. Preventing thrombosis and protecting vessel patency is the primary goal. However, utilization of the body’s natural coagulation cascades as an approach for targeted destruction of abnormal, disease-associated vessels and tissues has been increasing over the last 30 years. This vascular targeting approach, often termed “vascular infarction”, describes the deliberate, targeted delivery of a thrombogenic effector to diseased blood vessels with the aim to induce localized activation of the coagulation cascade and stable thrombus formation, leading to vessel occlusion and ablation. As systemic delivery of pro-thrombotic agents may cause consternation amongst traditional stroke researchers, proponents of the approach must suitably establish both efficacy and safety to take this field forward. In this review, we describe the evolution of this field and, with a focus on thrombogenic effectors, summarize the current literature with respect to emerging trends in “coaguligand” development, in targeted tumor vessel destruction, and in expansion of the approach to the treatment of brain vascular malformations.

The complex roles of efferocytosis in cancer development, metastasis, and treatment

When tumor cells are killed by targeted therapy, radiotherapy, or chemotherapy, they trigger their primary tumor by releasing pro-inflammatory cytokines. Microenvironmental interactions can also promote tumor heterogeneity and development. In this line, several immune cells within the tumor microenvironment, including macrophages, dendritic cells, regulatory T-cells, and CD8⁺ and CD4⁺ T cells, are involved in the clearance of apoptotic tumor cells through a process called efferocytosis. Although the efficiency of apoptotic tumor cell efferocytosis is positive under physiological conditions, there are controversies regarding its usefulness in treatment-induced apoptotic tumor cells (ATCs). Efferocytosis can show the limitation of cytotoxic treatments, such as chemotherapy and radiotherapy. Since cytotoxic treatments lead to extensive cell mortality, efferocytosis, and macrophage polarization toward an M2 phenotype, the immune response may get involved in tumor recurrence and metastasis. Tumor cells can use the anti-inflammatory effect of apoptotic tumor cell efferocytosis to induce an immunosuppressive condition that is tumor-tolerant. Since M2 polarization and efferocytosis are tumor-promoting processes, the receptors on macrophages act as potential targets for cancer therapy. Moreover, researchers have shown that efferocytosis-related molecules/pathways are potential targets for cancer therapy. These include phosphatidylserine and calreticulin, Tyro3, Axl, and Mer tyrosine kinase (MerTK), receptors of tyrosine kinase, indoleamine-2,3-dioxygenase 1, annexin V, CD47, TGF-β, IL-10, and macrophage phenotype switch are combined with conventional therapy, which can be more effective in cancer treatment. Thus, we set out to investigate the advantages and disadvantages of efferocytosis in treatment-induced apoptotic tumor cells.

Research and application of hydrostatic high pressure in tumor vaccines (Review)

It is well known that hydrostatic pressure (HP) is a physical parameter that is now regarded as an important variable for life. High hydrostatic pressure (HHP) technology has influenced biological systems for more than 100 years. Food and bioscience researchers have shown great interest in HHP technology over the past few decades. The development of knowledge related to this area can better facilitate the application of HHP in the life sciences. Furthermore, new applications for HHP may come from these current studies, particularly in tumor vaccines. Currently, cancer recurrence and metastasis continue to pose a serious threat to human health. The limited efficacy of conventional treatments has led to the need for breakthroughs in immunotherapy and other related areas. Research into tumor vaccines is providing new insights for cancer treatment. The purpose of this review is to present the main findings reported thus far in the relevant scientific literature, focusing on knowledge related to HHP technology and tumor vaccines, and to demonstrate the potential of applying HHP technology to tumor vaccine development.

Molecular underpinning of intracellular pH regulation on TMEM16F

TMEM16F, a dual-function phospholipid scramblase and ion channel, is important in blood coagulation, skeleton development, HIV infection, and cell fusion. Despite advances in understanding its structure and activation mechanism, how TMEM16F is regulated by intracellular factors remains largely elusive. Here we report that TMEM16F lipid scrambling and ion channel activities are strongly influenced by intracellular pH (pHi). We found that low pHi attenuates, whereas high pHi potentiates, TMEM16F channel and scramblase activation under physiological concentrations of intracellular Ca2+ ([Ca2+]i). We further demonstrate that TMEM16F pHi sensitivity depends on [Ca2+]i and exhibits a bell-shaped relationship with [Ca2+]i: TMEM16F channel activation becomes increasingly pHi sensitive from resting [Ca2+]i to micromolar [Ca2+]i, but when [Ca2+]i increases beyond 15 µM, pHi sensitivity gradually diminishes. The mutation of a Ca2+-binding residue that markedly reduces TMEM16F Ca2+ sensitivity (E667Q) maintains the bell-shaped relationship between pHi sensitivity and Ca2+ but causes a dramatic shift of the peak [Ca2+]i from 15 µM to 3 mM. Our biophysical characterizations thus pinpoint that the pHi regulatory effects on TMEM16F stem from the competition between Ca2+ and protons for the primary Ca2+-binding residues in the pore. Within the physiological [Ca2+]i range, the protonation state of the primary Ca2+-binding sites influences Ca2+ binding and regulates TMEM16F activation. Our findings thus uncover a regulatory mechanism of TMEM16F by pHi and shine light on our understanding of the pathophysiological roles of TMEM16F in diseases with dysregulated pHi, including cancer.

Macrophage-Mediated Tumor Cell Phagocytosis: Opportunity for Nanomedicine Intervention

Macrophages are one of the most abundant non-malignant cells in the tumor microenvironment, playing critical roles in mediating tumor immunity. As important innate immune cells, macrophages possess the potential to engulf tumor cells and present tumor-specific antigens for adaptive antitumor immunity induction, leading to growing interest in targeting macrophage phagocytosis for cancer immunotherapy. Nevertheless, live tumor cells have evolved to evade phagocytosis by macrophages via the extensive expression of anti-phagocytic molecules, such as CD47. In addition, macrophages also rapidly recognize and engulf apoptotic cells (efferocytosis) in the tumor microenvironment, which inhibits inflammatory responses and facilitates immune escape of tumor cells. Thus, intervention of macrophage phagocytosis by blocking anti-phagocytic signals on live tumor cells or inhibiting tumor efferocytosis presents a promising strategy for the development of cancer immunotherapies. Here, the regulation of macrophage-mediated tumor cell phagocytosis is first summarized, followed by an overview of strategies targeting macrophage phagocytosis for the development of antitumor therapies. Given the potential off-target effects associated with the administration of traditional therapeutics (for example, monoclonal antibodies, small molecule inhibitors), we highlight the opportunity for nanomedicine in macrophage phagocytosis intervention.

Targeting Phosphatidylserine Enhances the Anti-tumor Response to Tumor-Directed Radiation Therapy in a Preclinical Model of Melanoma

Phosphatidylserine (PS) is exposed on the surface of apoptotic cells and is known to promote immunosuppressive signals in the tumor microenvironment (TME). Antibodies that block PS interaction with its receptors have been shown to repolarize the TME into a proinflammatory state. Radiation therapy (RT) is an effective focal treatment of isolated solid tumors but is less effective at controlling metastatic cancers. We found that tumor-directed RT caused an increase in expression of PS on the surface of viable immune infiltrates in mouse B16 melanoma. We hypothesize that PS expression on immune cells may provide negative feedback to immune cells in the TME. Treatment with an antibody that targets PS (mch1N11) enhanced the anti-tumor efficacy of tumor-directed RT and improved overall survival. This combination led to an increase in proinflammatory tumor-associated macrophages. The addition of anti-PD-1 to RT and mch1N11 led to even greater anti-tumor efficacy and overall survival. We found increased PS expression on several immune subsets in the blood of patients with metastatic melanoma after receiving tumor-directed RT. These findings highlight the potential of combining PS targeting with RT and PD-1 pathway blockade to improve outcomes in patients with advanced-stage cancers.

Budhu et al. show that tumor-directed irradiation of murine B16 melanoma causes an increase in PS on the surface of infiltrating immune cells. Blocking PS and RT improves the anti-tumor efficacy and overall survival, which can be further improved with the addition of anti-PD-1. Melanoma patients exhibit increased PS on their PBMCs after RT.

Serine Incorporator 2 (SERINC2) Expression Predicts an Unfavorable Prognosis of Low-Grade Glioma (LGG): Evidence from Bioinformatics Analysis

Serine Incorporator 2 (SERINC2) is a transmembrane protein that incorporates serine into membrane lipids. The function of SERINC2 in tumors has been reported, but the role of SERINC2 in gliomas is not fully understood. RNA-sequencing data from The Cancer Genome Atlas (TCGA) (530 cases of low-grade glioma (LGG) and 173 cases of glioblastoma multiforme (GBM)) and microarray data from Gene Expression Omnibus (GEO) (Accession No. GSE16011, 284 cases gliomas were included) were acquired. Bioinformatics analysis was performed as the primary method to examine the function of SERINC2 and its correlated genes in glioma. SERINC2 was highly expressed in GBM compared with LGG and normal brain tissues. Elevated SERINC2 expression predicted shorter 5-, 10-, and 15-year overall survival (OS) of LGG patients and isocitrate dehydrogenase-1 (IDH-1) mutation-type LGG patients but had no effect on the OS of GBM patients. Cox regression analysis showed that SERINC2 was an independent factor in LGG OS. Methylation analysis found that 13 CpG methylation sites (methylation450k) correlated with SERINC2 expression in LGG. The mRNA expression level of SERINC2 was significant lower in the DNA deletion group than in the intact and amplification groups. A total of 390 copositive and 244 conegative correlation genes with SERINC2 were obtained from LGG in TCGA-LGG and GSE16011. Gene ontology (GO) category and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that the copositive correlation genes were primarily enriched in the mitotic process and cell cycle. Combining the results from the protein-protein interaction (PPI) network of SERINC2 correlation genes and CytoHubba led to the selection of 10 hub genes (CDC20, FN1, AURKB, AURKA, KIF2C, BIRC5, CCNB2, UBE2C, CCNA2, and CENPE). OncoLnc analysis confirmed that high expression levels of these hub genes were associated with poor OS in LGG. Our results suggested that aberrant SERINC2 expression existed in glioma and that its expression might be a potential prognostic marker in LGG patients. CDC20, FN1, AURKB, AURKA, KIF2C, BIRC5, CCNB2, UBE2C, CCNA2, and CENPE may be potential biomarkers and therapeutic targets for LGG.

Targeting of externalized αB-crystallin on irradiated endothelial cells with pro-thrombotic vascular targeting agents: Potential applications for brain arteriovenous malformations

BACKGROUND

Vascular targeting uses molecular markers on the surface of diseased vasculature for ligand-directed drug delivery to induce vessel occlusion or destruction. In the absence of discriminatory markers, such as in brain arteriovenous malformations (AVMs), stereotactic radiosurgery may be used to prime molecular changes on the endothelial surface. This study explored αB-crystallin (CRYAB) as a radiation induced target and pre-tested the specificity and efficacy of a CRYAB-targeting coaguligand for in vitro thrombus induction.

METHODS

A parallel-plate flow system was established to circulate human whole blood over a layer of human brain endothelial cells. A conjugate of anti-CRYAB antibody and thrombin was injected into the circuit to compare binding and thrombus formation on cells with or without prior radiation treatment (0-25 Gy).

RESULTS

Radiation increased CRYAB expression and surface exposure in human brain endothelial cells. In the parallel-plate flow system, the targeted anti-CRYAB-thrombin conjugate increased thrombus formation on the surface of irradiated cells relative to non-irradiated cells and to a non-targeting IgG-thrombin conjugate. Fibrin deposition and accumulation of fibrinogen degradation products increased significantly at radiation doses at or above 15 Gy with conjugate concentrations of 1.25 and 2.5 μg/mL.

CONCLUSIONS

CRYAB exposure can be detected at the surface of human brain endothelial cells in response to irradiation. Pro-thrombotic CRYAB-targeting conjugates can bind under high flow conditions and in the presence of whole blood induce stable thrombus formation with high specificity and efficacy on irradiated surfaces. CRYAB provides a novel radiation marker for potential vascular targeting in irradiated brain AVMs.

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.

Occlusion of Animal Model Arteriovenous Malformations Using Vascular Targeting

Brain arteriovenous malformations (AVMs) are a significant cause of intracerebral hemorrhage in children and young adults. Currently, one third of patients have no viable treatment options. Vascular targeting agents (VTAs) are being designed to deliver pro-thrombotic molecules to the abnormal AVM vessels for rapid occlusion and cure. This study assessed the efficacy of a pro-thrombotic VTA targeting phosphatidylserine (PS) in a radiation-primed AVM animal model. The model AVM was surgically created in rats by anastomosis of the left external jugular vein to the adjacent common carotid artery. After 6 weeks, the AVM was irradiated (20 Gy) using gamma knife surgery (GKS). A PS-targeting VTA was created by conjugation of annexin V with human thrombin and administered intravenously 3 weeks post-GKS or sham. Unconjugated thrombin was used as a non-targeting control. AVM thrombosis and occlusion was monitored 3 weeks later by angiography and histology. Preliminary experiments established a safe dose of active thrombin for systemic administration. Subsequently, a single dose of annexin V-thrombin conjugate (0.77 mg/kg) resulted in angiographic AVM occlusion in sham (75%) and irradiated (63%) animals, while non-targeted thrombin did not. Lowering the conjugate dose (0.38 mg/kg) decreased angiographic AVM occlusion in sham (13%) relative to irradiated (80%) animals (p = 0.03) as did delivery of two consecutive doses of 0.38 mg/kg, 2 days apart (sham (0%); irradiated (78%); p = 0.003). These findings demonstrate efficacy of the PS-targeting VTA and the feasibility of a vascular targeting approach for occlusion of high-flow AVMs. Targeting specificity can be enhanced by radiation-sensitization and VTA dose modification.

Radiation-Stimulated Translocation of CD166 and CRYAB to the Endothelial Surface Provides Potential Vascular Targets on Irradiated Brain Arteriovenous Malformations

Vascular targeting with pro-thrombotic antibody-conjugates is a promising biological treatment for brain arteriovenous malformations (bAVMs). However, targeted drug delivery relies on the identification of unique or overexpressed markers on the surface of a target cell. In the absence of inherent biological markers, stereotactic radiosurgery may be used to prime induction of site-specific and targetable molecular changes on the endothelial surface. To investigate lumen-accessible, endothelial targets induced by radiation, we combined Gamma knife surgery in an AVM animal model with in vivo biotin-labeling and comparative proteomics. Two proteins, αB-crystallin (CRYAB)-a small heat shock protein that normally acts as an intracellular chaperone to misfolded proteins-and activated leukocyte cell adhesion molecule CD166, were further validated for endothelial surface expression after irradiation. Immunostaining of endothelial cells in vitro and rat AVM tissue ex vivo confirmed de novo induction of CRYAB following irradiation (20 Gy). Western analysis demonstrated that CRYAB accumulated intracellularly as a 20 kDa monomer, but, at the cell surface, a novel 65 kDa protein was observed, suggesting radiation stimulates translocation of an atypical CRYAB isoform. In contrast, CD166 had relatively high expression in non-irradiated cells, localized predominantly to the lateral surfaces. Radiation increased CD166 surface exposure by inducing translocation from intercellular junctions to the apical surface without significantly altering total protein levels. These findings reinforce the dynamic molecular changes induced by radiation exposure, particularly at the cell surface, and support further investigation of radiation as a priming mechanism and these molecules as putative targets for focused drug delivery in irradiated tissue.

Randomized phase III study of docetaxel plus bavituximab in previously treated advanced non-squamous non-small-cell lung cancer

Background

Bavituximab is a monoclonal antibody that targets phosphatidylserine in the presence of β2 glycoprotein 1 (β2GP1) to exert an antitumor immune response. This phase III trial determined the efficacy of bavituximab combined with docetaxel in patients with previously treated advanced non-small-cell lung cancer (NSCLC).

Patients and methods

Key eligibility criteria included advanced non-squamous NSCLC with disease progression after treatment with platinum-based doublet chemotherapy, evidence of disease control after at least two cycles of first-line therapy, presence of measurable disease, ECOG performance status 0 or 1, adequate bone marrow and organ function, and no recent history of clinically significant bleeding. Eligible patients were randomized 1 : 1 to receive up to six 21-day cycles of docetaxel plus either weekly bavituximab 3 mg/kg or placebo until progression or toxicity. The primary end point was overall survival (OS).

Results

A total of 597 patients were enrolled. Median OS was 10.5 months in the docetaxel + bavituximab arm and was 10.9 months in the docetaxel + placebo arm (HR 1.06; 95% CI 0.88-1.29; P = 0.533). There was no difference in progression-free survival (HR 1.00; 95% CI 0.82-1.22; P = 0.990). Toxicities were manageable and similar between arms. In subset analysis, among patients with high baseline serum β2GP1 levels ≥200 µg/ml, a nonsignificant OS trend favored the bavituximab arm (HR 0.82; 95% CI 0.63-1.06; P = 0.134). Among patients who received post-study immune checkpoint inhibitor therapy, OS favored the bavituximab arm (HR 0.46; 95% CI 0.26-0.81; P = 0.006).

Conclusions

The combination of bavituximab plus docetaxel is not superior to docetaxel in patients with previously treated advanced NSCLC. The addition of bavituximab to docetaxel does not meaningfully increase toxicity. The potential benefit of bavituximab observed in patients with high β2GP1 levels and in patients subsequently treated with immune checkpoint inhibitors requires further investigation.

Clinical trial number

NCT01999673.

A Model of Indirect Cell Death Caused by Tumor Vascular Damage after High-Dose Radiotherapy

There is increasing evidence that high doses of radiotherapy, like those delivered in stereotactic body radiotherapy (SBRT), trigger indirect mechanisms of cell death. Such effect seems to be two-fold. High doses may trigger an immune response and may cause vascular damage, leading to cell starvation and death. Development of mathematical response models, including indirect death, may help clinicians to design SBRT optimal schedules. Despite increasing experimental literature on indirect tumor cell death caused by vascular damage, efforts on modeling this effect have been limited. In this work, we present a biomathematical model of this effect. In our model, tumor oxygenation is obtained by solving the reaction-diffusion equation; radiotherapy kills tumor cells according to the linear-quadratic model, and also endothelial cells (EC), which can trigger loss of functionality of capillaries. Capillary death will affect tumor oxygenation, driving nearby tumor cells into severe hypoxia. Capillaries can recover functionality due to EC proliferation. Tumor cells entering a predetermined severe hypoxia status die according to a hypoxia-death model. This model fits recently published experimental data showing the effect of vascular damage on surviving fractions. It fits surviving fraction curves and qualitatively reproduces experimental values of percentages of functional capillaries 48 hours postirradiation, and hypoxic cells pre- and 48 hours postirradiation. This model is useful for exploring aspects of tumor and EC response to radiotherapy and constitutes a stepping stone toward modeling indirect tumor cell death caused by vascular damage and accounting for this effect during SBRT planning. SIGNIFICANCE: A novel biomathematical model of indirect tumor cell death caused by vascular radiation damage could potentially help clinicians interpret experimental data and design better radiotherapy schedules.

Acoustic feedback enables safe and reliable carboplatin delivery across the blood-brain barrier with a clinical focused ultrasound system and improves survival in a rat glioma model

The blood-brain barrier (BBB) restricts delivery of most chemotherapy agents to brain tumors. Here, we investigated a clinical focused ultrasound (FUS) device to disrupt the BBB in rats and enhance carboplatin delivery to the brain using the F98 glioma model.

Methods: In each rat, 2-3 volumetric sonications (5 ms bursts at 1.1 Hz for 75s) targeted 18-27 locations in one hemisphere. Sonication was combined with Definity microbubbles (10 µl/kg) and followed by intravenous carboplatin (50 mg/kg). Closed-loop feedback control was performed based on acoustic emissions analysis.

Results: Safety and reliability were established in healthy rats after three sessions with carboplatin; BBB disruption was induced in every target without significant damage evident in MRI or histology. In tumor-bearing rats, concentrations of MRI contrast agent (Gadavist) were 1.7 and 3.3 times higher in the tumor center and margin, respectively, than non-sonicated tumors (P<0.001). Tissue-to-plasma ratios of intact carboplatin concentrations were increased by 7.3 and 2.9 times in brain and tumor respectively, at one hour after FUS and 4.2 and 2.4 times at four hours. Tumor volume doubling time in rats receiving FUS and carboplatin increased by 96% and 126% compared to rats that received carboplatin alone and non-sonicated controls, respectively (P<0.05); corresponding increases in median survival were 48% and 66% (P<0.01).

Conclusion: Overall, this work demonstrates that actively-controlled BBB disruption with a clinical device can enhance carboplatin delivery without neurotoxicity at level that reduces tumor growth and improves survival in an aggressive and infiltrative rat glioma model.

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.

Apoptotic cell clearance in the tumor microenvironment: a potential cancer therapeutic target

Millions of cells in the human body undergo apoptosis not only under normal physiological conditions but also under pathological conditions such as infection or other diseases related to acute tissue injury. Swift apoptotic cell clearance is essential for tissue homeostasis. Defective clearance of dead cells is linked to pathogenesis of diseases such as inflammatory diseases, atherosclerosis, neurological disease, and cancer. Significance of apoptotic cell clearance has been emerging as an interesting field for disease treatment. Efficient apoptotic cell clearance plays an important role in reducing inflammation through the suppression of inappropriate inflammatory responses under healthy and diseased conditions. However, apoptotic cell clearance related to cancer pathogenesis is more complex in tumor microenvironments. Chronic inflammation resulting from the failure of apoptotic cell clearance can contribute to tumor progression. Conversely, tumor cells can exploit the anti-inflammatory effect of apoptotic cell clearance to generate an immunosuppressive tumor microenvironment. In this review, focus is on the current understanding of apoptotic cell clearance in the tumor microenvironment. Furthermore, we discuss how signaling molecules (PtdSer and PtdSer recognition receptor) mediating apoptotic cell clearance are aberrantly expressed in the tumor microenvironment and their current development state as potential therapeutic targets for clinical cancer therapy.

Functional link between plasma membrane spatiotemporal dynamics, cancer biology, and dietary membrane-altering agents

The cell plasma membrane serves as a nexus integrating extra- and intracellular components, which together enable many of the fundamental cellular signaling processes that sustain life. In order to perform this key function, plasma membrane components assemble into well-defined domains exhibiting distinct biochemical and biophysical properties that modulate various signaling events. Dysregulation of these highly dynamic membrane domains can promote oncogenic signaling. Recently, it has been demonstrated that select membrane-targeted dietary bioactives (MTDBs) have the ability to remodel plasma membrane domains and subsequently reduce cancer risk. In this review, we focus on the importance of plasma membrane domain structural and signaling functionalities as well as how loss of membrane homeostasis can drive aberrant signaling. Additionally, we discuss the intricacies associated with the investigation of these membrane domain features and their associations with cancer biology. Lastly, we describe the current literature focusing on MTDBs, including mechanisms of chemoprevention and therapeutics in order to establish a functional link between these membrane-altering biomolecules, tuning of plasma membrane hierarchal organization, and their implications in cancer prevention.

Enhanced phosphatidylserine-selective cancer therapy with irradiation and SapC-DOPS nanovesicles

Normal living cells exhibit phosphatidylserine (PS) primarily within the intracellular leaflet of the plasma membrane. In contrast, viable cancer cells have high levels of PS on the external surface, and exhibit a broad range of surface PS, even within specific types of cancer. Agents that target surface PS have recently been developed to treat tumors and are expected to be more effective with higher surface PS levels. In this context, we examined whether surface PS is increased with irradiation. In vitro irradiation of cancer cell lines selected surviving cells that had higher surface PS in a dose- and time-dependent manner. This was more pronounced if surface PS was initially in the lower range for cancer cells. Radiation also increased the surface PS of tumor cells in subcutaneous xenografts in nude mice. We found an inverse relationship between steady state surface PS level of cancer cell lines and their sensitivity to radiation-induced cell death. In addition, serial irradiation, which selected surviving cells with higher surface PS, also increased resistance to radiation and to some chemotherapeutic drugs, suggesting a PS-dependent mechanism for development of resistance to therapy. On the other hand, fractionated radiation enhanced the effect of a novel anti-cancer, PS-targeting drug, SapC-DOPS, in some cancer cell lines. Our data suggest that we can group cancer cells into cells with low surface PS, which are sensitive to radiation, and high surface PS, which are sensitive to SapC-DOPS. Combination of these interventions may provide a potential new combination therapy.

Efferocytosis in the tumor microenvironment

Within the course of a single minute, millions of cells in the human body will undergo programmed cell death in response to physiological or pathological cues. The diminished energetic capacity of an apoptotic cell renders the cell incapable of sustaining plasma membrane integrity. Under these circumstances, intracellular contents that might leak into the surrounding tissue microenvironment, a process referred to as secondary necrosis, could induce inflammation and tissue damage. Remarkably, in most cases of physiologically rendered apoptotic cell death, inflammation is avoided because a mechanism to swiftly remove apoptotic cells from the tissue prior to their secondary necrosis becomes activated. This mechanism, referred to as efferocytosis, uses phagocytes to precisely identify and engulf neighboring apoptotic cells. In doing so, efferocytosis mantains tissue homeostasis that would otherwise be disrupted by normal cellular turnover and exacerbated further when the burden of apoptotic cells becomes elevated due to disease or insult. Efferocytosis also supports the resolution of inflammation, restoring tissue homesostasis. The importance of efferocytosis in health and disease underlies the increasing research efforts to understand the mechanisms by which efferocytosis occurs, and how a failure in the efferocytic machinery contributes to diseases, or conversely, how cancers effectively use the existing efferocytic machinery to generate a tumor-tolerant, immunosuppressive tumor microenvironment. We discuss herein the molecular mechanisms of efferocytosis, how the process of efferocytosis might support a tumor ‘wound healing’ phenotype, and efforts to target efferocytosis as an adjunct to existing tumor treatments.

Efferocytosis of dying cells differentially modulate immunological outcomes in tumor microenvironment

Programmed cell death (apoptosis) is an integral part of tissue homeostasis in complex organisms, allowing for tissue turnover, repair, and renewal while simultaneously inhibiting the release of self antigens and danger signals from apoptotic cell-derived constituents that can result in immune activation, inflammation, and autoimmunity. Unlike cells in culture, the physiological fate of cells that die by apoptosis in vivo is their rapid recognition and engulfment by phagocytic cells (a process called efferocytosis). To this end, apoptotic cells express specific eat-me signals, such as externalized phosphatidylserine (PS), that are recognized in a specific context by receptors to initiate signaling pathways for engulfment. The importance of carefully regulated recognition and clearance pathways is evident in the spectrum of inflammatory and autoimmune disorders caused by defects in PS receptors and signaling molecules. However, in recent years, several additional cell death pathways have emerged, including immunogenic cell death, necroptosis, pyroptosis, and netosis that interweave different cell death pathways with distinct innate and adaptive responses from classical apoptosis that can shape long-term host immunity. In this review, we discuss the role of different cell death pathways in terms of their immune potential outcomes specifically resulting in specific cell corpse/phagocyte interactions (phagocytic synapses) that impinge on host immunity, with a main emphasis on tolerance and cancer immunotherapy.

Oral NaHCO3 Activates a Splenic Anti-Inflammatory Pathway: Evidence That Cholinergic Signals Are Transmitted via Mesothelial Cells

We tested the hypothesis that oral NaHCO₃ intake stimulates splenic anti-inflammatory pathways. Following oral NaHCO₃ loading, macrophage polarization was shifted from predominantly M1 (inflammatory) to M2 (regulatory) phenotypes, and FOXP3⁺CD4⁺ T-lymphocytes increased in the spleen, blood, and kidneys of rats. Similar anti-inflammatory changes in macrophage polarization were observed in the blood of human subjects following NaHCO₃ ingestion. Surprisingly, we found that gentle manipulation to visualize the spleen at midline during surgical laparotomy (sham splenectomy) was sufficient to abolish the response in rats and resulted in hypertrophy/hyperplasia of the capsular mesothelial cells. Thin collagenous connections lined by mesothelial cells were found to connect to the capsular mesothelium. Mesothelial cells in these connections stained positive for the pan-neuronal marker PGP9.5 and acetylcholine esterase and contained many ultrastructural elements, which visually resembled neuronal structures. Both disruption of the fragile mesothelial connections or transection of the vagal nerves resulted in the loss of capsular mesothelial acetylcholine esterase staining and reduced splenic mass. Our data indicate that oral NaHCO₃ activates a splenic anti-inflammatory pathway and provides evidence that the signals that mediate this response are transmitted to the spleen via a novel neuronal-like function of mesothelial cells.

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.

Avenues to molecular imaging of dying cells: Focus on cancer

Successful treatment of cancer patients requires balancing of the dose, timing, and type of therapeutic regimen. Detection of increased cell death may serve as a predictor of the eventual therapeutic success. Imaging of cell death may thus lead to early identification of treatment responders and nonresponders, and to “patient‐tailored therapy.” Cell death in organs and tissues of the human body can be visualized, using positron emission tomography or single‐photon emission computed tomography, although unsolved problems remain concerning target selection, tracer pharmacokinetics, target‐to‐nontarget ratio, and spatial and temporal resolution of the scans. Phosphatidylserine exposure by dying cells has been the most extensively studied imaging target. However, visualization of this process with radiolabeled Annexin A5 has not become routine in the clinical setting. Classification of death modes is no longer based only on cell morphology but also on biochemistry, and apoptosis is no longer found to be the preponderant mechanism of cell death after antitumor therapy, as was earlier believed. These conceptual changes have affected radiochemical efforts. Novel probes targeting changes in membrane permeability, cytoplasmic pH, mitochondrial membrane potential, or caspase activation have recently been explored. In this review, we discuss molecular changes in tumors which can be targeted to visualize cell death and we propose promising biomarkers for future exploration.

Mertk on tumor macrophages is a therapeutic target to prevent tumor recurrence following radiation therapy

Radiation therapy provides a means to kill large numbers of cancer cells in a controlled location resulting in the release of tumor-specific antigens and endogenous adjuvants. However, by activating pathways involved in apoptotic cell recognition and phagocytosis, irradiated cancer cells engender suppressive phenotypes in macrophages. We demonstrate that the macrophage-specific phagocytic receptor, Mertk is upregulated in macrophages in the tumor following radiation therapy. Ligation of Mertk on macrophages results in anti-inflammatory cytokine responses via NF-kB p50 upregulation, which in turn limits tumor control following radiation therapy. We demonstrate that in immunogenic tumors, loss of Mertk is sufficient to permit tumor cure following radiation therapy. However, in poorly immunogenic tumors, TGFβ inhibition is also required to result in tumor cure following radiation therapy. These data demonstrate that Mertk is a highly specific target whose absence permits tumor control in combination with radiation therapy.

Anti-cancer vaccine therapy for hematologic malignancies: An evolving era

The potential promise of therapeutic vaccination as effective therapy for hematologic malignancies is supported by the observation that allogeneic hematopoietic cell transplantation is curative for a subset of patients due to the graft-versus-tumor effect mediated by alloreactive lymphocytes. Tumor vaccines are being explored as a therapeutic strategy to re-educate host immunity to recognize and target malignant cells through the activation and expansion of effector cell populations. Via several mechanisms, tumor cells induce T cell dysfunction and senescence, amplifying and maintaining tumor cell immunosuppressive effects, resulting in failure of clinical trials of tumor vaccines and adoptive T cell therapies. The fundamental premise of successful vaccine design involves the introduction of tumor-associated antigens in the context of effective antigen presentation so that tolerance can be reversed and a productive response can be generated. With the increasing understanding of the role of both the tumor and tumor microenvironment in fostering immune tolerance, vaccine therapy is being explored in the context of immunomodulatory therapies. The most effective strategy may be to use combination therapies such as anti-cancer vaccines with checkpoint blockade to target critical aspects of this environment in an effort to prevent the re-establishment of tumor tolerance while limiting toxicity associated with autoimmunity.

HIV antivirals: targeting the functional organization of the lipid envelope

Most of the surface of the lipid bilayer covering the human immunodeficiency virus type 1 (HIV-1) particle is directly accessible from the aqueous medium. Its peculiar chemical composition and physical properties appear to be critical for infection and, therefore, may comprise a target for selective antiviral activity. The HIV-1 membrane is enriched in raft-type lipids and also displays aminophospholipids on its external leaflet. We contend here that a great deal of membrane-active compounds described to block HIV-1 infection can do so by following a common mechanism of action: alteration of the lateral heterogeneity that supports the functional organization of the lipid envelope. The confirmation of this hypothesis could lay new foundations for the rational development of compounds with anti-HIV activity.

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.

Phosphatidylserine-targeted liposome for enhanced glioma-selective imaging

Phosphatidylserine (PS), which is normally intracellular, becomes exposed on the outer surface of viable endothelial cells (ECs) of tumor vasculature. Utilizing a PS-targeting antibody, we have recently established a PS-targeted liposomal (PS-L) nanoplatform that has demonstrated to be highly tumor-selective. Because of the vascular lumen-exposed PS that is immediately accessible without a need to penetrate the intact blood brain barrier (BBB), we hypothesize that the systemically administered PS-L binds specifically to tumor vascular ECs, becomes subsequently internalized into the cells and then enables its cargos to be efficiently delivered to glioma parenchyma. To test this, we exploited the dual MRI/optical imaging contrast agents-loaded PS-L and injected it intravenously into mice bearing intracranial U87 glioma. At 24 h, both in vivo optical imaging and MRI depicted enhanced tumor contrast, distinct from the surrounding normal brain. Intriguingly, longitudinal MRI revealed temporal and spatial intratumoral distribution of the PS-L by following MRI contrast changes, which appeared punctate in tumor periphery at an earlier time point (4 h), but became clustering and disseminated throughout the tumor at 24 h post injection. Importantly, glioma-targeting specificity of the PS-L was antigen specific, since a control probe of irrelevant specificity showed minimal accumulation in the glioma. Together, these results indicate that the PS-L nanoplatform enables the enhanced, glioma-targeted delivery of imaging contrast agents by crossing the tumor BBB efficiently, which may also serve as a useful nanoplatform for anti-glioma drugs.

Identification of lipid-phosphatidylserine (PS) as the target of unbiasedly selected cancer specific peptide-peptoid hybrid PPS1

Phosphatidylserine (PS) is an anionic phospholipid maintained on the inner-leaflet of the cell membrane and is externalized in malignant cells. We previously launched a careful unbiased selection targeting biomolecules (e.g. protein, lipid or carbohydrate) distinct to cancer cells by exploiting HCC4017 lung cancer and HBEC30KT normal epithelial cells derived from the same patient, identifying HCC4017 specific peptide-peptoid hybrid PPS1. In this current study, we identified PS as the target of PPS1. We validated direct PPS1 binding to PS using ELISA-like assays, lipid dot blot and liposome based binding assays. In addition, PPS1 recognized other negatively charged and cancer specific lipids such as phosphatidic acid, phosphatidylinositol and phosphatidylglycerol. PPS1 did not bind to neutral lipids such as phosphatidylethanolamine found in cancer and phosphatidylcholine and sphingomyelin found in normal cells. Further we found that the dimeric version of PPS1 (PPS1D1) displayed strong cytotoxicity towards lung cancer cell lines that externalize PS, but not normal cells. PPS1D1 showed potent single agent anti-tumor activity and enhanced the efficacy of docetaxel in mice bearing H460 lung cancer xenografts. Since PS and anionic phospholipid externalization is common across many cancer types, PPS1 may be an alternative to overcome limitations of protein targeted agents.

The TAM family as a therapeutic target in combination with radiation therapy

Radiation therapy is primarily a modality to kill cancer cells in the treatment field. It is becoming increasingly clear that radiation therapy can also be used to direct immune responses that have the potential to clear residual local or distant disease outside the treatment field. We believe that cancer cell death is the critical link between these processes. Understanding the handling of dying cancer cells by immune cells in the tumor environment is crucial to facilitate immune responses following radiation therapy. We review the role of the TAM (Tyro3 Axl Mertk) group of receptor tyrosine kinases and their role following radiation-induced cancer cell death in the tumor environment.

Resolvins suppress tumor growth and enhance cancer therapy

Cancer therapy reduces tumor burden by killing tumor cells, yet it simultaneously creates tumor cell debris that may stimulate inflammation and tumor growth. Sulciner et al. demonstrate that specific resolvins (RvD1, RvD2, and RvE1) inhibit tumor growth and enhance cancer therapy through the clearance of tumor cell debris.

Cancer therapy reduces tumor burden by killing tumor cells, yet it simultaneously creates tumor cell debris that may stimulate inflammation and tumor growth. Thus, conventional cancer therapy is inherently a double-edged sword. In this study, we show that tumor cells killed by chemotherapy or targeted therapy (“tumor cell debris”) stimulate primary tumor growth when coinjected with a subthreshold (nontumorigenic) inoculum of tumor cells by triggering macrophage proinflammatory cytokine release after phosphatidylserine exposure. Debris-stimulated tumors were inhibited by antiinflammatory and proresolving lipid autacoids, namely resolvin D1 (RvD1), RvD2, or RvE1. These mediators specifically inhibit debris-stimulated cancer progression by enhancing clearance of debris via macrophage phagocytosis in multiple tumor types. Resolvins counterregulate the release of cytokines/chemokines, including TNFα, IL-6, IL-8, CCL4, and CCL5, by human macrophages stimulated with cell debris. These results demonstrate that enhancing endogenous clearance of tumor cell debris is a new therapeutic target that may complement cytotoxic cancer therapies.

A Novel Therapeutic Strategy for Cancer Using Phosphatidylserine Targeting Stearylamine-Bearing Cationic Liposomes

There is a pressing need for a ubiquitously expressed antigen or receptor on the tumor surface for successful mitigation of the deleterious side effects of chemotherapy. Phosphatidylserine (PS), normally constrained to the intracellular surface, is exposed on the external surface of tumors and most tumorigenic cell lines. Here we report that a novel PS-targeting liposome, phosphatidylcholine-stearylamine (PC-SA), induced apoptosis and showed potent anticancer effects as a single agent against a majority of cancer cell lines. We experimentally proved that this was due to a strong affinity for and direct interaction of these liposomes with PS. Complexation of the chemotherapeutic drugs doxorubicin and camptothecin in these vesicles demonstrated a manyfold enhancement in the efficacies of the drugs both in vitro and across three advanced tumor models without any signs of toxicity. Both free and drug-loaded liposomes were maximally confined to the tumor site with low tissue concentration. These data indicate that PC-SA is a unique and promising liposome that, alone and as a combination therapy, has anticancer potential across a wide range of cancer types.

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.

A Phase I Clinical Trial of the Phosphatidylserine-targeting Antibody Bavituximab in Combination With Radiation Therapy and Capecitabine in the Preoperative Treatment of Rectal Adenocarcinoma

OBJECTIVES

There is interest in improving the tumoricidal effects of preoperative radiotherapy for rectal carcinoma by studying new radiosensitizers. The safety and toxicity profile of these combination regimens needs rigorous clinical evaluation. The primary objective of this study was to evaluate the toxicity of combining bavituximab, an antibody that targets exposed phosphatidylserine, with capecitabine and radiation therapy.

MATERIALS AND METHODS

Patients with stage II or III rectal adenocarcinoma were enrolled on a phase I study combining radiation therapy, capecitabine, and bavituximab. A standard 3+3 trial designed was used.

RESULTS

In general, bavituximab was safe and well tolerated in combination with radiation therapy and capecitabine in the treatment of rectal adenocarcinoma. One patient at the highest dose level experienced a grade III infusion reaction related to the bavituximab. One tumor demonstrated a complete pathologic response to the combination treatment.

CONCLUSIONS

Bavituximab is safe in combination with capecitabine and radiation therapy at the doses selected for the study. Further clinical investigation would be necessary to better define the efficacy of this combination.

TAM receptor tyrosine kinases as emerging targets of innate immune checkpoint blockade for cancer therapy

Cancer immunotherapy utilizing T-cell checkpoint inhibitors has shown tremendous clinical success. Yet, this mode of treatment is effective in only a subset of patients. Unresponsive patients tend to have non-T-cell-inflamed tumors that lack markers associated with the activation of adaptive anti-tumor immune responses. Notably, elimination of cancer cells by T cells is critically dependent on the optimal activity of innate immune cells. Therefore, identifying new targets that regulate innate immune cell function and promote the engagement of adaptive tumoricidal responses is likely to lead to the development of improved therapies against cancer. Here, we review the TAM receptor tyrosine kinases-TYRO3, AXL, and MERTK-as an emerging class of innate immune checkpoints that participate in key steps of anti-tumoral immunity. Namely, TAM-mediated efferocytosis, negative regulation of dendritic cell activity, and dysregulated production of chemokines collectively favor the escape of malignant cells. Hence, disabling TAM signaling may promote engagement of adaptive immunity and complement T-cell checkpoint blockade.

Phosphatidylserine Translocation after Radiosurgery in an Animal Model of Arteriovenous Malformation

Phosphatidylserine (PS) is asymmetrically distributed across the plasma membrane, located predominantly on the inner leaflet in healthy cells. Translocation of PS to the outer leaflet makes it available as a target for biological therapies. We examined PS translocation after radiosurgery in an animal model of brain arteriovenous malformation (AVM). An arteriovenous fistula was created by end-to-side anastomosis of the left external jugular vein to the common carotid artery in 6-week-old, male Sprague Dawley rats. Six weeks after AVM creation, 15 rats underwent Gamma Knife stereotactic radiosurgery receiving a single 15 Gy dose to the margin of the fistula; 15 rats received sham treatment. Externalization of PS was examined by intravenous injection of a PS-specific near-infrared probe, PSVue-794, and in vivo fluorescence optical imaging at 1, 7, 21, 42, 63 and 84 days postirradiation. Fluorescent signaling indicative of PS translocation to the luminal cell surface accumulated in the AVM region, in both irradiated and nonirradiated animals, at all time points. Fluorescence was localized specifically to the AVM region and was not present in any other anatomical sites. Translocated PS increased over time in irradiated rats (P < 0.001) but not in sham-irradiated rats and this difference reached statistical significance at day 84 (P < 0.05). In summary, vessels within the mature rat AVM demonstrate elevated PS externalization compared to normal vessels. A single dose of ionizing radiation can increase PS externalization in a time-dependent manner. Strict localization of PS externalization within the AVM region suggests that stereotactic radiosurgery can serve as an effective priming agent and PS may be a suitable candidate for vascular-targeting approaches to AVM treatment.

Identification of the minimum pharmacophore of lipid-phosphatidylserine (PS) binding peptide-peptoid hybrid PPS1D1

We previously reported a unique peptide-peptoid hybrid, PPS1 that specifically recognizes lipid-phosphatidylserine (PS) and a few other negatively charged phospholipids, but not neutral phospholipids, on the cell membrane. The dimeric version of PPS1, i.e., PPS1D1 triggers strong cancer cell cytotoxicity and has been validated in lung cancer models both in vitro and in vivo. Given that PS and other negatively charged phospholipids are abundant in almost all tumor microenvironments, PPS1D1 is an attractive drug lead that can be developed into a globally applicable anti-cancer agent. Therefore, it is extremely important to identify the minimum pharmacophore of PPS1D1. In this study, we have synthesized alanine/sarcosine derivatives as well as truncated derivatives of PPS1D1. We performed ELISA-like competitive binding assay to evaluate the PS-recognition potential and standard MTS cell viability assay on HCC4017 lung cancer cells to validate the cell cytotoxicity effects of these derivatives. Our studies indicate that positively charged residues at the second and third positions, as well as four hydrophobic residues at the fifth through eighth positions, are imperative for the binding and activity of PPS1D1. Methionine at the first position was not essential, whereas the positively charged Nlys at the fourth position was minimally needed, as two derivatives that were synthesized replacing this residue were almost as active as PPS1D1.