Increased exposure of phosphatidylethanolamine on the surface of tumor vascular endothelium

Anticancer and toxic properties of cyclotides are dependent on phosphatidylethanolamine phospholipid targeting

Cyclotides, ultrastable disulfide-rich cyclic peptides, can be engineered to bind and inhibit specific cancer targets. In addition, some cyclotides are toxic to cancer cells, though not much is known about their mechanisms of action. Here we delineated the potential mode of action of cyclotides towards cancer cells. A novel set of analogues of kalata B1 (the prototypic cyclotide) and kalata B2 and cycloviolacin O2 were examined for their membrane-binding affinity and selectivity towards cancer cells. By using solution-state NMR, surface plasmon resonance, flow cytometry and bioassays we show that cyclotides are toxic against cancer and non-cancerous cells and their toxicity correlates with their ability to target and disrupt lipid bilayers that contain phosphatidylethanolamine phospholipids. Our results suggest that the potential of cyclotides as anticancer therapeutics might best be realised by combining their amenability to epitope engineering with their ability to bind cancer cell membranes.

Estrogen promotes Leydig cell engulfment by macrophages in male infertility

Male infertility accounts for almost half of infertility cases worldwide. A subset of infertile men exhibit reduced testosterone and enhanced levels of estradiol (E2), though it is unclear how increased E2 promotes deterioration of male fertility. Here, we utilized a transgenic mouse strain that overexpresses human CYP19, which encodes aromatase (AROM+ mice), and mice with knockout of Esr1, encoding estrogen receptor α (ERαKO mice), to analyze interactions between viable Leydig cells (LCs) and testicular macrophages that may lead to male infertility. In AROM+ males, enhanced E2 promoted LC hyperplasia and macrophage activation via ERα signaling. E2 stimulated LCs to produce growth arrest-specific 6 (GAS6), which mediates phagocytosis of apoptotic cells by bridging cells with surface exposed phosphatidylserine (PS) to macrophage receptors, including the tyrosine kinases TYRO3, AXL, and MER. Overproduction of E2 increased apoptosis-independent extrusion of PS on LCs, which in turn promoted engulfment by E2/ERα-activated macrophages that was mediated by AXL-GAS6-PS interaction. We further confirmed E2-dependant engulfment of LCs by real-time 3D imaging. Furthermore, evaluation of molecular markers in the testes of patients with nonobstructive azoospermia (NOA) revealed enhanced expression of CYP19, GAS6, and AXL, which suggests that the AROM+ mouse model reflects human infertility. Together, these results suggest that GAS6 has a potential as a clinical biomarker and therapeutic target for male infertility.

Phosphatidylserine-targeted bimodal liposomal nanoparticles for in vivo imaging of breast cancer in mice

Phosphatidylserine (PS) that is normally constrained to the inner plasma membrane becomes exposed on the surface of endothelial cells (ECs) in tumor vasculature. In the present study, we report the development of a novel tumor vasculature-targeted liposomal nanoprobe by conjugating a human monoclonal antibody, PGN635 that specifically targets PS to polyethylene glycol-coated liposomes. MR contrast, superparamagnetic iron oxide nanoparticles (SPIO) were packed into the core of liposomes, while near-infrared dye, DiR was incorporated into the lipophilic bilayer. The liposomal nanoprobe PGN-L-IO/DiR was fully characterized, and its binding specificity and subsequent internalization into PS-exposed vascular ECs was confirmed by in vitro MRI and histological staining. In vivo longitudinal MRI and optical imaging were performed after i.v. injection of the liposomal nanoprobes into mice bearing breast MDA-MB231 tumors. At 9.4T, T2-weighted MRI detected drastic reduction on signal intensity and T2 values of tumors at 24h. Ionizing radiation significantly increased PS exposure on tumor vascular ECs, resulting in a further MRI signal loss of tumors. Concurrent with MRI, optical imaging revealed a clear tumor contrast at 24h. Intriguingly, PGN-L-IO/DiR exhibited distinct pharmacokinetics and biodistribution with significantly reduced accumulations in liver or spleen. Localization of PGN-L-IO/DiR to tumor was antigen specific, since a control probe of irrelevant specificity showed minimal accumulation in the tumors. Our studies indicate that PS-targeted liposomes may provide a useful platform for tumor-targeted delivery of imaging contrast agents or potentially anti-cancer drugs for cancer theranostics.

Bioassays in natural product research - strategies and methods in the search for anti-inflammatory and antimicrobial activity

INTRODUCTION

Identifying bioactive molecules from complex biomasses requires careful selection and execution of relevant bioassays in the various stages of the discovery process of potential leads and targets.

OBJECTIVE

The aim of this review is to share our long-term experience in bioassay-guided isolation, and mechanistic studies, of bioactive compounds from different organisms in nature with emphasis on anti-inflammatory and antimicrobial activity.

METHODS

In the search for anti-inflammatory activity, in vivo and in vitro model combinations with enzymes and cells involved in the inflammatory process have been used, such as cyclooxygenases, human neutrophils and human cancer cell lines. Methods concerning adsorption and perforation of bacteria, fungi, human cells and model membranes, have been developed and optimised, with emphasis on antimicrobial peptides and their interaction with the membrane target, in particular their ability to distinguish host from pathogen.

RESULTS

A long-term research has provided experience of selection and combination of bioassay models, which has led to an increased understanding of ethnopharmacological and ecological observations, together with in-depth knowledge of mode of action of isolated compounds.

CONCLUSION

A more multidisciplinary approach and a higher degree of fundamental research in development of bioassays are often necessary to identify and to fully understand the mode of action of bioactive molecules with novel structure-activity relationships from natural sources.

Highly specific PET imaging of prostate tumors in mice with an iodine-124-labeled antibody fragment that targets phosphatidylserine

Phosphatidylserine (PS) is an attractive target for imaging agents that identify tumors and assess their response to therapy. PS is absent from the surface of most cell types, but becomes exposed on tumor cells and tumor vasculature in response to oxidative stresses in the tumor microenvironment and increases in response to therapy. To image exposed PS, we used a fully human PS-targeting antibody fragment, PGN635 F(ab’)_2, that binds to complexes of PS and β2-glycoprotein I. PGN635 F(ab’)₂ was labeled with the positron-emitting isotope iodine-124 (¹²⁴I) and the resulting probe was injected into nude mice bearing subcutaneous or orthotopic human PC3 prostate tumors. Biodistribution studies showed that ¹²⁴I-PGN635 F(ab’)₂ localized with remarkable specificity to the tumors with little uptake in other organs, including the liver and kidneys. Clear delineation of the tumors was achieved by PET 48 hours after injection. Radiation of the tumors with 15 Gy or systemic treatment of the mice with 10 mg/kg docetaxel increased localization in the tumors. Tumor-to-normal (T/N) ratios were inversely correlated with tumor growth measured over 28 days. These data indicate that ¹²⁴I-PGN635 F(ab’)₂ is a promising new imaging agent for predicting tumor response to therapy.

Liposomal encapsulation enhances in vivo near infrared imaging of exposed phosphatidylserine in a mouse glioma model

We have previously demonstrated that exposed phosphatidylserine (PS) on tumor vascular endothelial cells is highly tumor specific, and development of the PS targeted near infrared (NIR) optical probe enables successful in vivo optical imaging of U87 gliomas in a mouse model. Liposomes have been widely used as a nanovector for delivery of chemotherapeutics and imaging contrast agents due to their high payload and longer circulation time. In the current study, we have fabricated PS-targeted liposomal nanoprobes encapsulating a NIR dye, IRDye^® 800CW, aiming to enhance PS-targeted tumor imaging. Hydrophilic 800CW dye was packed into the core of polyethylene glycol (PEG)-coated liposomes functionalized with F(ab’)₂ fragments of PGN635, a fully human monoclonal antibody that binds PS. As expected, in vivo dynamic NIR imaging revealed significantly improved tumor/normal contrast (TNR = 20 ± 3; p < 0.01) of subcutaneous U87 gliomas in mice after injection of the liposomal nanoprobes. Markedly enhanced TNR was observed after the tumors were irradiated to increase PS exposure (TNR = 48 ± 6; p < 0.05). Intriguingly, the liposomal nanoprobes, PGN-L-800CW showed distinct biodistribution and pharmacokinetics compared to the 800CW-PGN probes used in our previous study. Our data further suggest the usefulness of PS-targeted imaging probes for sensitive tumor detection and the potential of utilizing liposomal platform for glioma theranostics.

Identification of CD300a as a new hypoxia-inducible gene and a regulator of CCL20 and VEGF production by human monocytes and macrophages

Peripheral blood monocytes are recruited to inflammatory and tumor lesions where they undergo terminal differentiation into macrophages. Monocytes/macrophages integrate stimulatory and inhibitory signals present in the pathologic microenvironment through a defined repertoire of cell surface receptors, and deregulated expression of these molecules may result in amplification of inflammation or establishment of immune escape mechanisms. Characterization of the expression and function of these receptors is required for a better understanding of the regulation of monocyte/macrophage activity at pathologic sites. Hypoxia is a common feature of many pathological situations and an important regulator of monocyte/macrophage pro-inflammatory responses. In this study, we identify the leukocyte membrane antigen, CD300a, a member of the CD300 superfamily of immunoregulatory receptors, as a new hypoxia-inducible gene in primary human monocytes and monocyte-derived macrophages. CD300a mRNA up-regulation by hypoxia was rapid and reversible, paralleled by increased surface protein expression, and mediated by hypoxia-inducible factor-1α. CD300a induction was also triggered by the hypoxia-mimetic agent, desferrioxamine. CD300a exhibited both activating and inhibitory potential, differentially regulating CCL20 and vascular endothelial growth factor pro-inflammatory cytokine production by monocytes/macrophages upon triggering by an agonist Ab. These results suggest that CD300a induction by the hypoxic environment represents a mechanism of regulation of monocyte/macrophage pro-inflammatory responses at pathologic sites.

Overcoming intratumor heterogeneity of polygenic cancer drug resistance with improved biomarker integration

Improvements in technology and resources are helping to advance our understanding of cancer-initiating events as well as factors involved with tumor progression, adaptation, and evasion of therapy. Tumors are well known to contain diverse cell populations and intratumor heterogeneity affords neoplasms with a diverse set of biologic characteristics that can be used to evolve and adapt. Intratumor heterogeneity has emerged as a major hindrance to improving cancer patient care. Polygenic cancer drug resistance necessitates reconsidering drug designs to include polypharmacology in pursuit of novel combinatorial agents having multitarget activity to overcome the diverse and compensatory signaling pathways in which cancer cells use to survive and evade therapy. Advances will require integration of different biomarkers such as genomics and imaging to provide for more adequate elucidation of the spatially varying location, type, and extent of diverse intratumor signaling molecules to provide for a rationale-based personalized cancer medicine strategy.

Endothelial cell heterogeneity

The endothelial lining of blood vessels shows remarkable heterogeneity in structure and function, in time and space, and in health and disease. An understanding of the molecular basis for phenotypic heterogeneity may provide important insights into vascular bed-specific therapies. First, we review the scope of endothelial heterogeneity and discuss its proximate and evolutionary mechanisms. Second, we apply these principles, together with their therapeutic implications, to a representative vascular bed in disease, namely, tumor endothelium.

The interaction between CD300a and phosphatidylserine inhibits tumor cell killing by NK cells

The activity of NK cells is controlled by inhibitory and activating receptors. The inhibitory receptors interact mostly with MHC class I proteins, however, inhibitory receptors such as CD300a, which bind to non-MHC class I ligands, also exist. Recently, it was discovered that phosphatidylserine (PS) is a ligand for CD300a and that the interaction between PS expressed on apoptotic cells and CD300a inhibits the uptake of apoptotic cells by phagocytic cells. Whether PS can inhibit NK-cell activity through CD300a is unknown. Here, we have generated specific antibodies directed against CD300a and we used these mAbs to demonstrate that various NK-cell clones express different levels of CD300a. We further demonstrated that both CD300a and its highly homologous molecule CD300c bind to the tumor cells equally well and that they recognize PS and additional unknown ligand(s) expressed by tumor cells. Finally, we showed that blocking the PS-CD300a interaction resulted in increased NK-cell killing of tumor cells. Collectively, we demonstrate a new tumor immune evasion mechanism that is mediated through the interaction between PS and CD300a and we suggest that CD300c, similarly to CD300a, also interacts with PS.

Measuring response to therapy by near-infrared imaging of tumors using a phosphatidylserine-targeting antibody fragment

Imaging tumors and their response to treatment could be a valuable biomarker toward early assessment of therapy in patients with cancer. Phosphatidylserine (PS) is confined to the inner leaflet of the plasma membrane in normal cells but is externalized on tumor vascular endothelial cells (ECs) and tumor cells, and PS exposure is further enhanced in response to radiation and chemotherapy. In the present study, we evaluated the potential of a PS-targeting human F(ab')2 antibody fragment, PGN650, to detect exposure of PS in tumor-bearing mice. Tumor uptake of PGN650 was measured by near-infrared optical imaging in human tumor xenografts in immunodeficient mice. PGN650 specifically targeted tumors and was shown to target CD31-positive ECs and tumor cells. Tumor uptake of PGN650 was significantly higher in animals pretreated with docetaxel. The peak tumor to normal tissue (T/N) ratio of probe was observed at 24 hours postinjection of probe, and tumor binding was detected for at least 120 hours. In repeat dose studies, PGN650 uptake in tumors was significantly higher following pretreatment with docetaxel compared to baseline uptake prior to treatment. PGN650 may be a useful probe to detect PS exposed in tumors and to monitor enhanced PS exposure to optimize therapeutic agents to treat tumors.

Duramycin exhibits antiproliferative properties and induces apoptosis in tumour cells

Duramycin is a polypeptide that binds specifically to phosphatidylethanolamine (PE) on cell surfaces with high affinity, and has been shown to disrupt tumour cell surface-based coagulation and exhibit weak antimicrobial activity. The aim of the present study was to characterize the effect of duramycin on tumour cell proliferation and viability. Duramycin was used to detect phosphatidylethanolamine expression on cell lines by flow cytometry. Cells were cultured in the presence of duramycin and proliferation and cell viability assessed. Electron microscopy and confocal microscopy were utilized to investigate cell membrane structure after duramycin treatment. Pancreatic tumour cells were shown to express phosphatidylethanolamine on their cell surfaces by specific labelling with duramycin. Phosphatidylethanolamine expression was generally increased in apoptotic cells and more so in necrotic cells. Cells cultured in the presence of duramycin showed increasing levels of apoptosis and ultimately necrosis with increasing duramycin concentrations, and cell proliferation was reduced in a duramycin dose-dependent manner between 0.125 and 12.5 μmol/l. Tissue factor expression was also reduced when cells were cultured in the presence of duramycin. Cells imaged by electron microscopy were fragile, suggesting that membrane integrity was compromised by duramycin, although no obvious differences in membrane structure were observed by live cell confocal imaging. Duramycin induced apoptosis and exhibited antiproliferative and anticoagulant effects on pancreatic tumour cells, most probably by disrupting cell membrane structure and/or function.

Phosphatidylserine synthase 2: high efficiency for synthesizing phosphatidylserine containing docosahexaenoic acid

Phosphatidylserine (PS), the major anionic phospholipid in eukaryotic cell membranes, is synthesized by the integral membrane enzymes PS synthase 1 (PSS1) and 2 (PSS2). PSS2 is highly expressed in specific tissues, such as brain and testis, where docosahexaenoic acid (DHA, 22:6n-3) is also highly enriched. The purpose of this work was to characterize the hydrocarbon-chain preference of PSS2 to gain insight on the specialized role of PSS2 in PS accumulation in the DHA-abundant tissues. Flag-tagged PSS2 was expressed in HEK cells and immunopurified in a functionally active form. Purified PSS2 utilized both PE plasmalogen and diacyl PE as substrates. Nevertheless, the latter was six times better utilized, indicating the importance of an ester linkage at the sn-1 position. Although no sn-1 fatty acyl preference was noted, PSS2 exhibited significant preference toward DHA compared with 18:1 or 20:4 at the sn-2 position. Preferential production of DHA-containing PS (DHA-PS) was consistently observed with PSS2 purified from a variety of cell lines as well as with microsomes from mutant cells in which PS synthesis relies primarily on PSS2. These findings suggest that PSS2 may play a key role in PS accumulation in brain and testis through high activity toward DHA-containing substrates that are abundant in these tissues.

Toward an animal model of the human tear film: biochemical comparison of the mouse, canine, rabbit, and human meibomian lipidomes

PURPOSE

Secretions that are produced by meibomian glands (also known as meibum) are a major source of lipids for the ocular surface of humans and animals alike. Many animal species have been evaluated for their meibomian lipidomes. However, there have been a very small number of studies in which the animals were compared with humans side by side. Therefore, the purpose of this study was to compare meibum collected from humans and three typical laboratory animals, canines, mice, and rabbits, for their meibomian lipid composition in order to determine which animal species most resembles humans.

METHODS

High pressure liquid chromatography (HPLC) and gas-liquid chromatography (GLC) in combination with mass spectrometry were used to evaluate lipidomes of all tested species.

RESULTS

Among three tested animal species, mice were found to be the closest match to humans in terms of their meibomian lipidomes, while canines were the second closest species. The lipids of these three species were close to each other structurally and, for most lipid classes, quantitatively. The rabbit meibomian lipidome, on the other hand, was vastly different from lipidomes of all other tested species. Interestingly, a previously described class of lipids, acylated omega-hydroxy fatty acids (OAHFA), was found to be present in every tested species as the major amphiphilic component of meibum.

CONCLUSIONS

Our side by side comparison of the rabbit and the human meibum demonstrated their vast differences. Thus, the rabbit seems to be a poor animal model of the human tear film, at least when studying its biochemistry and biophysics.

Biomarkers and molecular probes for cell death imaging and targeted therapeutics

Cell death is a critically important biological process. Disruption of homeostasis, either by excessive or deficient cell death, is a hallmark of many pathological conditions. Recent research advances have greatly increased our molecular understanding of cell death and its role in a range of diseases and therapeutic treatments. Central to these ongoing research and clinical efforts is the need for imaging technologies that can locate and identify cell death in a wide array of in vitro and in vivo biomedical samples with varied spatiotemporal requirements. This review article summarizes community efforts over the past five years to identify useful biomarkers for dead and dying cells, and to develop molecular probes that target these biomarkers for optical, radionuclear, or magnetic resonance imaging. Apoptosis biomarkers are classified as either intracellular (caspase enzymes, mitochondrial membrane potential, cytosolic proteins) or extracellular (plasma membrane phospholipids, membrane potential, surface exposed histones). Necrosis, autophagy, and senescence biomarkers are described, as well as unexplored cell death biomarkers. The article discusses possible chemotherapeutic and theranostic strategies, and concludes with a summary of current challenges and expected eventual rewards of clinical cell death imaging.

Tumor endothelial markers as a target in cancer

INTRODUCTION

Several anti-angiogenic agents have been developed and some of them have been clinically applied in the tumor therapy. Anti-angiogenic therapy faces some hurdles: inherent or acquired resistance, increased invasiveness, and lack of biomarkers. Characterization of tumor endothelial markers may help to target endothelium and to identify potential predictive factors of response to anti-angiogenic therapies. Numerous surrogates, angiogenic and endothelium markers have emerged from recent pre-clinical studies, including physiological and soluble molecules in plasma and from platelets, circulating cells, tumor tissue factors and imaging markers. However, no wholly validated biomarkers currently exist to predict the success or the failure of the anti-angiogenic therapy of cancer. Therefore, the research of suitable and validate biomarkers is currently ongoing.

AREAS COVERED

This review provides an overview of the status of our knowledge concerning tumor endothelial markers, therapeutics targeting, possible resistance mechanisms and predictive value of these biomarkers and discuss future strategies to use and identify them in the anti-angiogenic therapy.

EXPERT OPINION

Anti-angiogenesis is a milestone to improve the treatment of several types of cancer and predictive biomarkers for a response to anti-endothelium therapy are one of the most important challenges for anti-angiogenesis research.

Phosphatidylethanolamine binding is a conserved feature of cyclotide-membrane interactions

Cyclotides are bioactive cyclic peptides isolated from plants that are characterized by a topologically complex structure and exceptional resistance to enzymatic or thermal degradation. With their sequence diversity, ultra-stable core structural motif, and range of bioactivities, cyclotides are regarded as a combinatorial peptide template with potential applications in drug design. The mode of action of cyclotides remains elusive, but all reported biological activities are consistent with a mechanism involving membrane interactions. In this study, a diverse set of cyclotides from the two major subfamilies, Möbius and bracelet, and an all-d mirror image form, were examined to determine their mode of action. Their lipid selectivity and membrane affinity were determined, as were their toxicities against a range of targets (red blood cells, bacteria, and HIV particles). Although they had different membrane-binding affinities, all of the tested cyclotides targeted membranes through binding to phospholipids containing phosphatidylethanolamine headgroups. Furthermore, the biological potency of the tested cyclotides broadly correlated with their ability to target and disrupt cell membranes. The finding that a broad range of cyclotides target a specific lipid suggests their categorization as a new lipid-binding protein family. Knowledge of their membrane specificity has the potential to assist in the design of novel drugs based on the cyclotide framework, perhaps allowing the targeting of peptide drugs to specific cell types.

High resolution tumor targeting in living mice by means of multispectral optoacoustic tomography

Background

Tumor targeting is of high clinical and biological relevance, and major efforts have been made to develop molecular imaging technologies for visualization of the disease markers in tissue. Of particular interest is apoptosis which has a profound role within tumor development and has significant effect on cancer malignancy.

Methods

Herein, we report on targeting of phosphatidylserine-exposing cells within live tumor allograft models using a synthetic near infrared zinc(II)-dipicolylamine probe. Visualization of the probe biodistribution is performed with whole body multispectral optoacoustic tomography (MSOT) system and subsequently compared to results attained by planar and tomographic fluorescence imaging systems.

Results

Compared to whole body optical visualization methods, MSOT attains remarkably better imaging capacity by delivering high-resolution scans of both disease morphology and molecular function in real time. Enhanced resolution of MSOT clearly showed that the probe mainly localizes in the vessels surrounding the tumor, suggesting that its tumor selectivity is gained by targeting the phosphatidylserine exposed on the surface of tumor vessels.

Conclusions

The current study demonstrates the high potential of MSOT to broadly impact the fields of tumor diagnostics and preclinical drug development.

Forms, crosstalks, and the role of phospholipid biosynthesis in autophagy

Autophagy is a highly conserved cellular process occurring during periods of stress to ensure a cell's survival by recycling cytosolic constituents and making products that can be used in energy generation and other essential processes. Three major forms of autophagy exist according to the specific mechanism through which cytoplasmic material is transported to a lysosome. Chaperone-mediated autophagy is a highly selective form of autophagy that delivers specific proteins for lysosomal degradation. Microautophagy is a less selective form of autophagy that occurs through lysosomal membrane invaginations, forming tubes and directly engulfing cytoplasm. Finally, macroautophagy involves formation of new membrane bilayers (autophagosomes) that engulf cytosolic material and deliver it to lysosomes. This review provides new insights on the crosstalks between different forms of autophagy and the significance of bilayer-forming phospholipid synthesis in autophagosomal membrane formation.

The interconnectedness of cancer cell signaling

The elegance of fundamental and applied research activities have begun to reveal a myriad of spatial and temporal alterations in downstream signaling networks affected by cell surface receptor stimulation including G protein-coupled receptors and receptor tyrosine kinases. Interconnected biochemical pathways serve to integrate and distribute the signaling information throughout the cell by orchestration of complex biochemical circuits consisting of protein interactions and covalent modification processes. It is clear that scientific literature summarizing results from both fundamental and applied scientific research activities has served to provide a broad foundational biologic database that has been instrumental in advancing our continued understanding of underlying cancer biology. This article reflects on historical advances and the role of innovation in the competitive world of grant-sponsored research.

Near-infrared Optical Imaging of Exposed Phosphatidylserine in a Mouse Glioma Model

Phosphatidylserine (PS) is normally intracellular but becomes exposed on the luminal surface of vascular endothelial cells in tumors. It also becomes exposed on tumors cells responding to therapy. In the present study, we optically imaged exposed PS in vivo using PGN635, a novel monoclonal antibody that binds PS. The F(ab')(2) fragment of PGN635 was labeled with the near-infrared (NIR) dye, IRDye800CW. In vivo dynamic NIR imaging was performed after injection of 800CW-PGN635 into mice bearing radiation-treated or untreated U87 glioma xenografts growing subcutaneously or orthotopically. NIR optical imaging revealed a clear tumor contrast in nonirradiated subcutaneous U87 gliomas after injection of 800CW-PGN635. The tumor contrast was visible as early as 4 hours later and was maximal 24 hours later (tumor-to-normal tissue ratio [TNR] = 2.8 ± 0.7). Irradiation enhanced the tumor contrast at 24 hours (TNR = 4.0 ± 0.3). Similar results were observed for orthotopic gliomas. Localization of 800CW-PGN635 to tumors was antigen specific because 800CW-Aurexis, a control probe of irrelevant specificity, did not localize to the tumors, and preadministration of unlabeled PGN635 blocked the uptake of 800CW-PGN635. Fluorescence microscopy confirmed that 800CW-PGN635 was binding to PS-positive vascular endothelial cells in nonirradiated gliomas. Irradiation of the gliomas increased PS exposure on both tumor vascular endothelial cells and tumor cells and gave rise to an increase in tumor contrast with 800CW-PGN635 that was predictive of the reduction in tumor growth. 800CW-PGN635 may be a useful new imaging probe for detection of exposed PS in tumors responding to therapy.

Transbilayer phospholipids molecular imaging

Nuclear medicine has become a key part of molecular imaging. In the present review article, we focus on the transbilayer phospholipids as exquisite targets for radiolabelled probes in molecular imaging. Asymmetry of phospholipid distribution is a characteristic of mammalian cell membranes. Phosphatidylcholine and sphyngomyelin cholinophospholipids are primarily located within the external leaflet of the cell membrane. Phosphatidylserine and phosphatidylethanolamine aminophospholipids, and also phosphatidylinositol are primarily located within the internal leaflet of the cell membrane. New radiolabelled tracers have been designed in preclinical and clinical research for PET-CT and SPECT-CT molecular imaging of transbilayer phospholipids.