Cytosolic phospholipase A2: targeting cancer through the tumor vasculature

Smart Nanoplatforms Responding to the Tumor Microenvironment for Precise Drug Delivery in Cancer Therapy

The tumor microenvironment (TME) is a complex and dynamic entity, comprising stromal cells, immune cells, blood vessels and extracellular matrix, which is intimately associated with the occurrence and development of cancers, as well as their therapy. Utilizing the shared characteristics of tumors, such as an acidic environment, enzymes and hypoxia, researchers have developed a promising cancer therapy strategy known as responsive release of nano-loaded drugs, specifically targeted at tumor tissues or cells. In this comprehensive review, we provide an in-depth overview of the current fundamentals and state-of-the-art intelligent strategies of TME-responsive nanoplatforms, which include acidic pH, high GSH levels, high-level adenosine triphosphate, overexpressed enzymes, hypoxia and reductive environment. Additionally, we showcase the latest advancements in TME-responsive nanoparticles. In conclusion, we thoroughly examine the immediate challenges and prospects of TME-responsive nanopharmaceuticals, with the expectation that the progress of these targeted nanoformulations will enable the exploitation, overcoming or modulation of the TME, ultimately leading to significantly more effective cancer therapy.

cPLA2 blockade attenuates S100A7-mediated breast tumorigenicity by inhibiting the immunosuppressive tumor microenvironment

BACKGROUND

Molecular mechanisms underlying inflammation-associated breast tumor growth are poorly studied. S100A7, a pro-inflammatory molecule has been shown to enhance breast cancer growth and metastasis. However, the S100A7-mediated molecular mechanisms in enhancing tumor growth and metastasis are unclear.

METHODS

Human breast cancer tissue and plasma samples were used to analyze the expression of S100A7, cPLA2, and PGE2. S100A7-overexpressing or downregulated human metastatic breast cancer cells were used to evaluate the S100A7-mediated downstream signaling mechanisms. Bi-transgenic mS100a7a15 overexpression, TNBC C3 (1)/Tag transgenic, and humanized patient-derived xenograft mouse models and cPLA2 inhibitor (AACOCF3) were used to investigate the role of S100A7/cPLA2/PGE2 signaling in tumor growth and metastasis. Additionally, CODEX, a highly advanced multiplexed imaging was employed to delineate the effects of S100A7/cPLA2 inhibition on the recruitment of various immune cells.

RESULTS

In this study, we found that S100A7 and cPLA2 are highly expressed and correlate with decreased overall survival in breast cancer patients. Further mechanistic studies revealed that S100A7/RAGE signaling promotes the expression of cPLA2 to mediate its oncogenic effects. Pharmacological inhibition of cPLA2 suppressed S100A7-mediated tumor growth and metastasis in multiple pre-clinical models including transgenic and humanized patient-derived xenograft (PDX) mouse models. The attenuation of cPLA2 signaling reduced S100A7-mediated recruitment of immune-suppressive myeloid cells in the tumor microenvironment (TME). Interestingly, we discovered that the S100A7/cPLA2 axis enhances the immunosuppressive microenvironment by increasing prostaglandin E2 (PGE2). Furthermore, CO-Detection by indEXing (CODEX) imaging-based analyses revealed that cPLA2 inhibition increased the infiltration of activated and proliferating CD4⁺ and CD8⁺ T cells in the TME. In addition, CD163⁺ tumor associated-macrophages were positively associated with S100A7 and cPLA2 expression in malignant breast cancer patients.

CONCLUSIONS

Our study provides new mechanistic insights on the cross-talk between S100A7/cPLA2 in enhancing breast tumor growth and metastasis by generating an immunosuppressive TME that inhibits the infiltration of cytotoxic T cells. Furthermore, our studies indicate that S100A7/cPLA2 could be used as novel prognostic marker and cPLA2 inhibitors as promising drugs against S100A7-overexpressing aggressive breast cancer.

Inhibition of Cytosolic Phospholipase A2α Induces Apoptosis in Multiple Myeloma Cells

Cytosolic phospholipase A2α (cPLA2α) is the rate-limiting enzyme in releasing arachidonic acid and biosynthesis of its derivative eicosanoids. Thus, the catalytic activity of cPLA2α plays an important role in cellular metabolism in healthy as well as cancer cells. There is mounting evidence suggesting that cPLA2α is an interesting target for cancer treatment; however, it is unclear which cancers are most relevant for further investigation. Here we report the relative expression of cPLA2α in a variety of cancers and cancer cell lines using publicly available datasets. The profiling of a panel of cancer cell lines representing different tissue origins suggests that hematological malignancies are particularly sensitive to the growth inhibitory effect of cPLA2α inhibition. Several hematological cancers and cancer cell lines overexpressed cPLA2α, including multiple myeloma. Multiple myeloma is an incurable hematological cancer of plasma cells in the bone marrow with an emerging requirement of therapeutic approaches. We show here that two cPLA2α inhibitors AVX420 and AVX002, significantly and dose-dependently reduced the viability of multiple myeloma cells and induced apoptosis in vitro. Our findings implicate cPLA2α activity in the survival of multiple myeloma cells and support further studies into cPLA2α as a potential target for treating hematological cancers, including multiple myeloma.

Targeting the eicosanoid pathway in hepatocellular carcinoma

Liver cancer has variable incidence worldwide and high mortality. Histologically, the most common subtype of liver cancer is hepatocellular carcinoma (HCC). Approximately 30-40% of HCC patients are diagnosed at an advanced stage, and at present, there are limited treatment options for such patients. The current first-line therapy with tyrosine kinase inhibitors, sorafenib or lenvatinib, prolongs survival by a median of about 2.5-3 months after which the disease normally progresses. Additionally, many patients discontinue the use of tyrosine kinase inhibitors due to toxicity or may not be suitable candidates due to co-morbidity or frailty. It is, therefore, imperative to identify novel therapeutic targets for advanced HCC patients. Persistent injury to the liver as a result of insults such as hepatitis B or C viral (HBV or HCV) infections, alcohol abuse, and non-alcoholic fatty liver disease (NAFLD), results in chronic inflammation, which progresses to hepatic fibrosis and later, cirrhosis, provides the conditions for initiation of HCC. One of the key pathways studied for its role in inflammation and carcinogenesis is the eicosanoid pathway. In this review, we briefly outline the eicosanoid pathway, describe the mechanisms by which some pathway members either facilitate or counter the development of liver diseases, with the focus on NAFLD/hepatic fibrosis/cirrhosis, and HCC. We describe the link between the eicosanoid pathway, inflammation and these liver diseases, and identify components of the eicosanoid pathway that may be used as potential therapeutic targets in HCC.

Protein sulfenic acid-mediated anchoring of gold nanoparticles for enhanced CT imaging and radiotherapy of tumors in vivo

Radiotherapy (RT) has become one of the most widely used treatments for malignant tumors in clinics. Developing a novel radiosensitizer for the integration of precise diagnosis and effective radiotherapy against hypoxic tumors is desirable but remains a great challenge. Herein, protein sulfenic acid reactive gold nanoparticles as effective radiosensitizers were for the first time reported for enhanced X-ray computed tomography (CT) imaging and radiotherapy of tumors in vivo. The gold nanoparticles were decorated with biocompatible poly(ethylene glycol), folic acid (FA), and sulfenic acid reactive groups 1,3-cyclohexanedione (CHD). Such a nanostructure enables on-site immobilization within tumors under oxidative stress through the specific reaction between CHD and endogenous protein sulfenic acids resulting in enhanced accumulation and retention of gold nanoparticles within tumors, which remarkably improves the sensitivity of CT imaging and the radiotherapeutic efficacy of tumors in living mice. This study thus is the first to demonstrate that protein sulfenic acid reactive gold nanoparticles with a tumor anchoring function may serve as effective radiosensitizers for clinical X-ray theranostic application in the future.

Phospholipase A2 superfamily in cancer

Phospholipase A2 enzymes (PLA₂s) comprise a superfamily that is generally divided into six subfamilies known as cytosolic PLA₂s (cPLA₂s), calcium-independent PLA₂s (iPLA₂s), secreted PLA₂s (sPLA₂s), lysosomal PLA₂s, platelet-activating factor (PAF) acetylhydrolases, and adipose specific PLA₂s. Each subfamily consists of several isozymes that possess PLA₂ activity. The first three PLA₂ subfamilies play important roles in inflammation-related diseases and cancer. In this review, the roles of well-studied enzymes sPLA₂-IIA, cPLA₂α and iPLA₂β in carcinogenesis and cancer development were discussed. sPLA₂-IIA seems to play conflicting roles and can act as a tumor suppressor or a tumor promoter according to the cancer type, but cPLA₂α and iPLA₂β play protumorigenic role in most cancers. The mechanisms of PLA₂-mediated signal transduction and crosstalk between cancer cells and endothelial cells in the tumor microenvironment are described. Moreover, the mechanisms by which PLA₂s mediate lipid reprogramming and glycerophospholipid remodeling in cancer cells are illustrated. PLA₂s as the upstream regulators of the arachidonic acid cascade are generally high expressed and activated in various cancers. Therefore, they can be considered as potential pharmacological targets and biomarkers in cancer. The detailed information summarized in this review may aid in understanding the roles of PLA₂s in cancer, and provide new clues for the development of novel agents and strategies for tumor prevention and treatment.

cPLA2α reversibly regulates different subsets of cancer stem cells transformation in cervical cancer

Cervical cancer stem cells (CCSCs) are considered major causes of chemoresistance/radioresistance and metastasis. Although several cell surface antigens have been identified in CCSCs, these markers vary among tumors because of CSC heterogeneity. However, whether these markers specifically distinguish CCSCs with different functions is unclear. Here, we demonstrated that CCSCs exist in two biologically distinct phenotypes characterized by different levels of cytosolic phospholipase A2α (cPLA2α) expression. Overexpression of cPLA2α results in a CD44⁺ CD24^- phenotype associated with mesenchymal traits, including increased invasive and migration abilities, whereas CCSCs with cPLA2α downregulation express CD133 and show quiescent epithelial characteristics. In addition, cPLA2α regulates the reversible transition between mesenchymal and epithelial CCSC states through PKCζ, an atypical protein kinase C, which governs cancer cell state changes and the maintenance of various embryonic stem cell characteristics, further inhibiting β-catenin-E-cadherin interaction in membrane and promoting β-catenin translocation into the nucleus to affect the transcriptional regulation of stemness signals. We propose that reversible transitions between mesenchymal and epithelial CCSC states regulated by cPLA2α are necessary for cervical cancer metastasis and recurrence. Thus, cPLA2α might be an attractive therapeutic target for eradicating different states of CCSCs to eliminate tumors more effectively.

Tissue and serum metabolite profiling reveals potential biomarkers of human hepatocellular carcinoma

BACKGROUND AND AIMS

Metabolomics serves as an important tool in distinguishing changes in metabolic pathways and the diagnosis of human disease. Hepatocellular carcinoma (HCC) is a malignance present of heterogeneous metabolic disorder and lack of effective biomarker for surveillance and diagnosis. In this study, we searched for potential metabolite biomarkers of HCC using tissue and serum metabolomics approach.

METHODS

A total of 30 pairs of matched liver tissue samples from HCC patients and 90 serum samples (30 HCC patients, 30 liver cirrhosis patients, and 30 healthy individuals) were assessed. Metabolomics was performed through ultra performance liquid chromatography-mass spectrometry in conjunction with multivariate and univariate statistical analyses.

RESULTS

A total of six differential metabolites including chenodeoxycholic acid (CDCA), glycocholic acid (GCA), LPC20:5, LPE18:0, succinyladenosine and uridine were present in HCC tissue and serum samples. CDCA, LPC20:5, succinyladenosine and uridine were used to construct a diagnostic model based on logistic regression. The four-metabolite panel discriminated HCC from liver cirrhosis with an AUC score of 0.938, sensitivity of 93.3% and specificity of 86.7%. For all HCC and cirrhosis patients, the diagnostic accuracy increased to 96.7% and 90.0%, respectively.

CONCLUSION

The combination of CDCA, LPC20:5, succinyladenosine and uridine can be used as a biomarker panel to improve HCC sensitivity and specificity. This panel significantly benefits HCC diagnostics and reveals new insight into HCC pathogenesis.

cPLA2α activates PI3K/AKT and inhibits Smad2/3 during epithelial-mesenchymal transition of hepatocellular carcinoma cells

Cytosolic phospholipase A2α (cPLA2α), a key phospholipase that regulates lipid metabolism, plays an important role in tumor progression. In the present study of hepatocellular carcinoma (HCC), cPLA2α was overexpressed in highly metastatic HCC cell lines. Immunohistochemical staining showed increased levels of cPLA2α at the invasive edges of HCC, and a clinicopathological analysis of samples from 111 patients revealed that its expression level was linked with micro-vascular invasion and cirrhosis. Knockdown of cPLA2α inhibited migration, probably due to its role in actin polymerization. Overexpression of cPLA2α promoted cell migration and invasion. Based on the mechanistic analysis, our data suggested that cPLA2α mediate epidermal growth factor (EGF) induced epithelial-mesenchymal transition (EMT) through PI3K/AKT/ERK pathway. cPLA2α activity was required for the transforming growth factor-(TGF)-β-induced EMT. However, cPLA2α inhibited Smad2/3 activation and promoted the activation of the PI3K/AKT/ERK pathway. A xenograft tumor transplant model confirmed the role of cPLA2α in HCC invasion and metastasis. Based on the mechanistic analysis, cPLA2α mediated both EGF- and TGF-β-induced EMT, which are essential for HCC metastasis. cPLA2α is a potentially target for novel therapies of HCC.

Targeting arachidonic acid pathway by natural products for cancer prevention and therapy

Arachidonic acid (AA) pathway, a metabolic process, plays a key role in carcinogenesis. Hence, AA pathway metabolic enzymes phospholipase A₂s (PLA₂s), cyclooxygenases (COXs) and lipoxygenases (LOXs) and their metabolic products, such as prostaglandins and leukotrienes, have been considered novel preventive and therapeutic targets in cancer. Bioactive natural products are a good source for development of novel cancer preventive and therapeutic drugs, which have been widely used in clinical practice due to their safety profiles. AA pathway inhibitory natural products have been developed as chemopreventive and therapeutic agents against several cancers. Curcumin, resveratrol, apigenin, anthocyans, berberine, ellagic acid, eugenol, fisetin, ursolic acid, [6]-gingerol, guggulsteone, lycopene and genistein are well known cancer chemopreventive agents which act by targeting multiple pathways, including COX-2. Nordihydroguaiaretic acid and baicalein can be chemopreventive molecules against various cancers by inhibiting LOXs. Several PLA₂s inhibitory natural products have been identified with chemopreventive and therapeutic potentials against various cancers. In this review, we critically discuss the possible utility of natural products as preventive and therapeutic agents against various oncologic diseases, including prostate, pancreatic, lung, skin, gastric, oral, blood, head and neck, colorectal, liver, cervical and breast cancers, by targeting AA pathway. Further, the current status of clinical studies evaluating AA pathway inhibitory natural products in cancer is reviewed. In addition, various emerging issues, including bioavailability, toxicity and explorability of combination therapy, for the development of AA pathway inhibitory natural products as chemopreventive and therapeutic agents against human malignancy are also discussed.

Anti-vascular effects of the cytosolic phospholipase A2 inhibitor AVX235 in a patient-derived basal-like breast cancer model

BACKGROUND

Group IVA cytosolic phospholipase A2 (cPLA2α) plays an important role in tumorigenesis and angiogenesis. It is overexpressed in basal-like breast cancer (BLBC), which is aggressive and usually triple-negative, making it unresponsive to current targeted therapies. Here, we evaluated the anti-angiogenic effects of a specific cPLA2α inhibitor, AVX235, in a patient-derived triple-negative BLBC model.

METHODS

Mice bearing orthotopic xenografts received i.p. injections of AVX235 or DMSO vehicle daily for 1 week and then every other day for up to 19 days. Six treated and six control mice were terminated after 2 days of treatment, and the tumors excised for high resolution magic angle spinning magnetic resonance spectroscopy (HR MAS MRS) and prostaglandin E2 (PGE2) enzyme immunoassay (EIA) analysis. A 1-week imaging study was performed on a separate cohort of mice. Longitudinal dynamic contrast enhanced (DCE)-MRI was performed before, after 4 days, and after 1 week of treatment. The mice were then perfused with a radiopaque vascular casting agent, and the tumors excised for micro-CT angiography. Subsequently, tumors were sectioned and stained with lectin and for Ki67 or α-smooth muscle actin to quantify endothelial cell proliferation and vessel maturity, respectively. Partial least squares discriminant analysis was performed on the multivariate HR MAS MRS data, and non-parametric univariate analyses using Mann-Whitney U tests (α = 0.05) were performed on all other data.

RESULTS

Glycerophosphocholine and PGE2 levels, measured by HR MAS MRS and EIA, respectively, were lower in treated tumors after 2 days of treatment. These molecular changes are expected downstream effects of cPLA2α inhibition and were followed by significant tumor growth inhibition after 8 days of treatment. DCE-MRI revealed that AVX235 treatment caused a decrease in tumor perfusion. Concordantly, micro-CT angiography showed that vessel volume fraction, density, and caliber were reduced in treated tumors. Moreover, histology showed decreased endothelial cell proliferation and fewer immature vessels in treated tumors.

CONCLUSIONS

These results demonstrate that cPLA2α inhibition with AVX235 resulted in decreased vascularization and perfusion and subsequent inhibition of tumor growth. Thus, cPLA2α inhibition may be a potential new therapeutic option for triple-negative basal-like breast cancer.

Diagnostic imaging advances in murine models of colitis

Inflammatory bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis are chronic-remittent inflammatory disorders of the gastrointestinal tract still evoking challenging clinical diagnostic and therapeutic situations. Murine models of experimental colitis are a vital component of research into human IBD concerning questions of its complex pathogenesis or the evaluation of potential new drugs. To monitor the course of colitis, to the present day, classical parameters like histological tissue alterations or analysis of mucosal cytokine/chemokine expression often require euthanasia of animals. Recent advances mean revolutionary non-invasive imaging techniques for in vivo murine colitis diagnostics are increasingly available. These novel and emerging imaging techniques not only allow direct visualization of intestinal inflammation, but also enable molecular imaging and targeting of specific alterations of the inflamed murine mucosa. For the first time, in vivo imaging techniques allow for longitudinal examinations and evaluation of intra-individual therapeutic response. This review discusses the latest developments in the different fields of ultrasound, molecularly targeted contrast agent ultrasound, fluorescence endoscopy, confocal laser endomicroscopy as well as tomographic imaging with magnetic resonance imaging, computed tomography and fluorescence-mediated tomography, discussing their individual limitations and potential future diagnostic applications in the management of human patients with IBD.

Cytosolic phospholipase A₂: physiological function and role in disease

The group IV phospholipase A2 (PLA2) family is comprised of six intracellular enzymes (GIVA, -B, -C, -D, -E, and -F) commonly referred to as cytosolic PLA2 (cPLA2)α, -β, -γ, -δ, -ε, and -ζ. They contain a Ser-Asp catalytic dyad and all except cPLA2γ have a C2 domain, but differences in their catalytic activities and subcellular localization suggest unique regulation and function. With the exception of cPLA2α, the focus of this review, little is known about the in vivo function of group IV enzymes. cPLA2α catalyzes the hydrolysis of phospholipids to arachidonic acid and lysophospholipids that are precursors of numerous bioactive lipids. The regulation of cPLA2α is complex, involving transcriptional and posttranslational processes, particularly increases in calcium and phosphorylation. cPLA2α is a highly conserved widely expressed enzyme that promotes lipid mediator production in human and rodent cells from a variety of tissues. The diverse bioactive lipids produced as a result of cPLA2α activation regulate normal physiological processes and disease pathogenesis in many organ systems, as shown using cPLA2α KO mice. However, humans recently identified with cPLA2α deficiency exhibit more pronounced effects on health than observed in mice lacking cPLA2α, indicating that much remains to be learned about this interesting enzyme.

Membrane phospholipids, EML4-ALK, and Hsp90 as novel targets in lung cancer treatment

Approximately one third of patients with non-small cell lung cancer have unresectable stage IIIA or stage IIIB disease; combined cytotoxic chemotherapy and radiation therapy delivered concurrently has been established as the standard treatment for such patients. Despite many clinical trials that tested several different radiochemotherapy combinations, it seems that a plateau of efficiencies at the acceptable risk of complications has been reached. Clinical studies indicate that the improved efficacy of radiochemotherapy is associated with the radiosensitizing effects of chemotherapy. Improvement of outcomes of this combined modality by developing novel radiosensitizers is a viable therapeutic strategy. In addition to causing cell death, ionizing radiation also induces a many-faceted signaling response, which activates numerous prosurvival pathways that lead to enhanced proliferation in the endothelial cells and increased vascularization in tumors. Radiation at doses used in the clinic activates cytoplasmic phospholipase A2, leading to increased production of arachidonic acid and lysophosphatidylcholine. The former is the initial step in the generation of eicosanoids, while the later is the initial step in the formation of lysophosphatidic acid, leading to the activation of inflammatory pathways. The echinoderm microtubule-associated protein-like 4 anaplastic lymphoma kinase (EML4-ALK) is member of the insulin superfamily of receptor tyrosine kinases. The EML4-ALK fusion gene appears unique to lung cancer and signals through extracellular signal regulated kinase and phosphoinositide 3-kinase. Heat shock protein 90 (Hsp90) is often overexpressed and present in an activated multichaperone complex in cancer cells, and it is now regarded as essential for malignant transformation and progression. In this review we focus on radiosensitizing strategies involving the targeting of membrane phospholipids, EML4-ALK, and Hsp90 with specific inhibitors and briefly discuss the combination of radiation with antivascular agents.

Autotaxin Inhibition with PF-8380 Enhances the Radiosensitivity of Human and Murine Glioblastoma Cell Lines

Purpose: Glioblastoma multiforme (GBM) is an aggressive primary brain tumor that is radio-resistant and recurs despite aggressive surgery, chemo, and radiotherapy. Autotaxin (ATX) is over expressed in various cancers including GBM and is implicated in tumor progression, invasion, and angiogenesis. Using the ATX specific inhibitor, PF-8380, we studied ATX as a potential target to enhance radiosensitivity in GBM.

Methods and Materials: Mouse GL261 and Human U87-MG cells were used as GBM cell models. Clonogenic survival assays and tumor transwell invasion assays were performed using PF-8380 to evaluate role of ATX in survival and invasion. Radiation dependent activation of Akt was analyzed by immunoblotting. Tumor induced angiogenesis was studied using the dorsal skin fold model in GL261. Heterotopic mouse GL261 tumors were used to evaluate the efficacy of PF-8380 as a radiosensitizer.

Results: Pre-treatment of GL261 and U87-MG cells with 1 μM PF-8380 followed by 4 Gy irradiation resulted in decreased clonogenic survival, decreased migration (33% in GL261; P = 0.002 and 17.9% in U87-MG; P = 0.012), decreased invasion (35.6% in GL261; P = 0.0037 and 31.8% in U87-MG; P = 0.002), and attenuated radiation-induced Akt phosphorylation. In the tumor window model, inhibition of ATX abrogated radiation induced tumor neovascularization (65%; P = 0.011). In a heterotopic mouse GL261 tumors untreated mice took 11.2 days to reach a tumor volume of 7000 mm³, however combination of PF-8380 (10 mg/kg) with irradiation (five fractions of 2 Gy) took more than 32 days to reach a tumor volume of 7000 mm³.

Conclusion: Inhibition of ATX by PF-8380 led to decreased invasion and enhanced radiosensitization of GBM cells. Radiation-induced activation of Akt was abrogated by inhibition of ATX. Furthermore, inhibition of ATX led to diminished tumor vascularity and delayed tumor growth. These results suggest that inhibition of ATX may ameliorate GBM response to radiotherapy.

Cytosolic phospholipaseA2 inhibition with PLA-695 radiosensitizes tumors in lung cancer animal models

Lung cancer remains the leading cause of cancer deaths in the United States and the rest of the world. The advent of molecularly directed therapies holds promise for improvement in therapeutic efficacy. Cytosolic phospholipase A2 (cPLA₂) is associated with tumor progression and radioresistance in mouse tumor models. Utilizing the cPLA₂ specific inhibitor PLA-695, we determined if cPLA2 inhibition radiosensitizes non small cell lung cancer (NSCLC) cells and tumors. Treatment with PLA-695 attenuated radiation induced increases of phospho-ERK and phospho-Akt in endothelial cells. NSCLC cells (LLC and A549) co-cultured with endothelial cells (bEND3 and HUVEC) and pre-treated with PLA-695 showed radiosensitization. PLA-695 in combination with irradiation (IR) significantly reduced migration and proliferation in endothelial cells (HUVEC & bEND3) and induced cell death and attenuated invasion by tumor cells (LLC &A549). In a heterotopic tumor model, the combination of PLA-695 and radiation delayed growth in both LLC and A549 tumors. LLC and A549 tumors treated with a combination of PLA-695 and radiation displayed reduced tumor vasculature. In a dorsal skin fold model of LLC tumors, inhibition of cPLA₂ in combination with radiation led to enhanced destruction of tumor blood vessels. The anti-angiogenic effects of PLA-695 and its enhancement of the efficacy of radiotherapy in mouse models of NSCLC suggest that clinical trials for its capacity to improve radiotherapy outcomes are warranted.

A VE-cadherin-PAR3-α-catenin complex regulates the Golgi localization and activity of cytosolic phospholipase A(2)α in endothelial cells

The rapid regulation of phospholipase A₂ activity is essential for vascular function. Evidence is found for a VE-cadherin–α-catenin–PAR3 complex regulating the reversible association of cPLA₂α with the Golgi apparatus in confluent endothelial cells. This regulation is important for controlling both cPLA₂α activity and angiogenesis.

Phospholipase A₂ enzymes hydrolyze phospholipids to liberate arachidonic acid for the biosynthesis of prostaglandins and leukotrienes. In the vascular endothelium, group IV phospholipase A₂α (cPLA₂α) enzyme activity is regulated by reversible association with the Golgi apparatus. Here we provide evidence for a plasma membrane cell adhesion complex that regulates endothelial cell confluence and simultaneously controls cPLA₂α localization and enzymatic activity. Confluent endothelial cells display pronounced accumulation of vascular endothelial cadherin (VE-cadherin) at cell–cell junctions, and mechanical wounding of the monolayer stimulates VE-cadherin complex disassembly and cPLA₂α release from the Golgi apparatus. VE-cadherin depletion inhibits both recruitment of cPLA₂α to the Golgi and formation of tubules by endothelial cells. Perturbing VE-cadherin and increasing the soluble cPLA₂α fraction also stimulated arachidonic acid and prostaglandin production. Of importance, reverse genetics shows that α-catenin and δ-catenin, but not β-catenin, regulates cPLA₂α Golgi localization linked to cell confluence. Furthermore, cPLA₂α Golgi localization also required partitioning defective protein 3 (PAR3) and annexin A1. Disruption of F-actin internalizes VE-cadherin and releases cPLA₂α from the adhesion complex and Golgi apparatus. Finally, depletion of either PAR3 or α-catenin promotes cPLA₂α-dependent endothelial tubule formation. Thus a VE-cadherin–PAR3–α-catenin adhesion complex regulates cPLA₂α recruitment to the Golgi apparatus, with functional consequences for vascular physiology.

Tumor-Endothelial Cell Three-dimensional Spheroids: New Aspects to Enhance Radiation and Drug Therapeutics

Classic cancer research for several decades has focused on understanding the biology of tumor cells in vitro. However, extending these findings to in vivo settings has been impeded owing to limited insights on the impact of microenvironment on tumor cells. We hypothesized that tumor cell biology and treatment response would be more informative when done in the presence of stromal components, like endothelial cells, which exist in the tumor microenvironment. To that end, we have developed a system to grow three-dimensional cultures of GFP-4T1 mouse mammary tumor and 2H11 murine endothelial cells in hanging drops of medium in vitro. The presence of 2H11 endothelial cells in these three-dimensional cocultures was found to sensitize 4T1-GFP tumor cells to chemotherapy (Taxol) and, at the same time, protect cells from ionizing radiation. These spheroidal cultures can also be implanted into the dorsal skinfold window chamber of mice for fluorescence imaging of vascularization and disease progression/treatment response. We observed rapid neovascularization of the tumor-endothelial spheroids in comparison to tumor spheroids grown in nude mice. Molecular analysis revealed pronounced up-regulation of several proangiogenic factors in the tumor tissue derived from the tumor-endothelial spheroids compared with tumor-only spheroids. Furthermore, the rate of tumor growth from tumor-endothelial spheroids in mice was faster than the tumor cell-only spheroids, resulting in greater metastasis to the lung. This three-dimensional coculture model presents an improved way to investigate more pertinent aspects of the therapeutic potential for radiation and/or chemotherapy alone and in combination with antiangiogenic agents.

Towards novel radiosensitizing agents: the role of cytosolic PLA2α in combined modality cancer therapy

The radioresistant nature of some tumors serves as an obstacle to curative therapy for several poor-prognosis malignancies. The radiosensitivity of a cancer is dependent not only on the intrinsic ability of tumor cells to recover from radiation-induced damage, but also the ability of stromal elements (e.g., vasculature) in the tumor microenvironment to survive and continue proliferating in the face of ionizing radiation. In this regard, it is important to understand the initial events activating radiation-induced signal transduction pathways. Among these events is the activation of cytosolic phospholipase A2 α and the subsequent production of the lipid second messengers. These events occur within minutes following exposure to ionizing radiation, and have been shown to enhance cell viability through a number of prosurvival signaling pathways. Furthermore, inhibition of cytosolic phospholipase A2 α has now been shown to reduce the viability of endothelial cells in culture after exposure to ionizing radiation, as well as slowing the growth of tumors in animal models of cancer.

Autotaxin and LPA receptors represent potential molecular targets for the radiosensitization of murine glioma through effects on tumor vasculature

Despite wide margins and high dose irradiation, unresectable malignant glioma (MG) is less responsive to radiation and is uniformly fatal. We previously found that cytosolic phospholipase A2 (cPLA₂) is a molecular target for radiosensitizing cancer through the vascular endothelium. Autotaxin (ATX) and lysophosphatidic acid (LPA) receptors are downstream from cPLA₂ and highly expressed in MG. Using the ATX and LPA receptor inhibitor, α-bromomethylene phosphonate LPA (BrP-LPA), we studied ATX and LPA receptors as potential molecular targets for the radiosensitization of tumor vasculature in MG. Treatment of Human Umbilical Endothelial cells (HUVEC) and mouse brain microvascular cells bEND.3 with 5 µmol/L BrP-LPA and 3 Gy irradiation showed decreased clonogenic survival, tubule formation, and migration. Exogenous addition of LPA showed radioprotection that was abrogated in the presence of BrP-LPA. In co-culture experiments using bEND.3 and mouse GL-261 glioma cells, treatment with BrP-LPA reduced Akt phosphorylation in both irradiated cell lines and decreased survival and migration of irradiated GL-261 cells. Using siRNA to knock down LPA receptors LPA1, LPA2 or LPA3 in HUVEC, we demonstrated that knockdown of LPA2 but neither LPA1 nor LPA3 led to increased viability and proliferation. However, knockdown of LPA1 and LPA3 but not LPA2 resulted in complete abrogation of tubule formation implying that LPA1 and LPA3 on endothelial cells are likely targets of BrP-LPA radiosensitizing effect. Using heterotopic tumor models of GL-261, mice treated with BrP-LPA and irradiation showed a tumor growth delay of 6.8 days compared to mice treated with irradiation alone indicating that inhibition of ATX and LPA receptors may significantly improve malignant glioma response to radiation therapy. These findings identify ATX and LPA receptors as molecular targets for the development of radiosensitizers for MG.

Cytosolic phospholipase A2 as a molecular target for the radiosensitization of ovarian cancer

In ovarian cancer, the molecular targeted chemotherapeutics could increase the efficiency of low-dose radiotherapy while decreasing injury to adjusted organs. In irradiated A2780 human ovarian carcinoma cells, cytosolic phospholipase A2 (cPLA(2)) inhibitor AACOCF(3) prevented activation of pro-survival Akt signaling and enhanced cell death. The potential molecular mechanisms of this effect could involve signaling through lysophosphatidic acid receptors. In the heterotopic A2780 tumor model using nude mice, cPLA(2) inhibition significantly delayed tumor growth compared to treatment with radiation or vehicle alone. These results identify cPLA(2) as a molecular target to enhance the therapeutic ratio of radiation in ovarian cancer.

Cytosolic phospholipase A2 and lysophospholipids in tumor angiogenesis

Background

Lung cancer and glioblastoma multiforme are highly angiogenic and, despite advances in treatment, remain resistant to therapy. Cytosolic phospholipase A2 (cPLA₂) activation contributes to treatment resistance through transduction of prosurvival signals. We investigated cPLA₂ as a novel molecular target for antiangiogenesis therapy.

Methods

Glioblastoma (GL261) and Lewis lung carcinoma (LLC) heterotopic tumor models were used to study the effects of cPLA₂ expression on tumor growth and vascularity in C57/BL6 mice wild type for (cPLA₂α^+/+) or deficient in (cPLA₂α^−/−) cPLA₂α, the predominant isoform in endothelium (n = 6–7 mice per group). The effect of inhibiting cPLA₂ activity on GL261 and LLC tumor growth was studied in mice treated with the chemical cPLA₂ inhibitor 4-[2-[5-chloro-1-(diphenylmethyl)-2-methyl-1H-indol-3-yl]-ethoxy]benzoic acid (CDIBA). Endothelial cell proliferation and function were evaluated by Ki-67 immunofluorescence and migration assays in primary cultures of murine pulmonary microvascular endothelial cells (MPMEC) isolated from cPLA₂α^+/+ and cPLA₂α^−/− mice. Proliferation, invasive migration, and tubule formation were assayed in mouse vascular endothelial 3B-11 cells treated with CDIBA. Effects of lysophosphatidylcholine, arachidonic acid, and lysophosphatidic acid (lipid mediators of tumorigenesis and angiogenesis) on proliferation and migration were examined in 3B-11 cells and cPLA₂α^−/− MPMEC. All statistical tests were two-sided.

Results

GL261 tumor progression proceeded normally in cPLA₂α^+/+ mice, whereas no GL261 tumors formed in cPLA₂α^−/− mice. In the LLC tumor model, spontaneous tumor regression was observed in 50% of cPLA₂α^−/− mice. Immunohistochemical examination of the remaining tumors from cPLA₂α^−/− mice revealed attenuated vascularity (P ≤ .001) compared with tumors from cPLA₂α^+/+ mice. Inhibition of cPLA₂ activity by CDIBA resulted in a delay in tumor growth (eg, LLC model: average number of days to reach tumor volume of 700 mm³, CDIBA vs vehicle: 16.8 vs 11.8, difference = 5, 95% confidence interval = 3.6 to 6.4, P = .04) and a decrease in tumor size (eg, GL261 model: mean volume on day 21, CDIBA vs vehicle: 40.1 vs 247.4 mm³, difference = 207.3 mm³, 95% confidence interval = 20.9 to 293.7 mm³, P = .021). cPLA₂ deficiency statistically significantly reduced MPMEC proliferation and invasive migration (P = .002 and P = .004, respectively). Compared with untreated cells, cPLA₂α^−/− MPMEC treated with lysophosphatidylcholine and lysophosphatidic acid displayed increased cell proliferation (P = .011) and invasive migration (P < .001).

Conclusions

In these mouse models of brain and lung cancer, cPLA₂ and lysophospholipids have key regulatory roles in tumor angiogenesis. cPLA₂ inhibition may be a novel effective antiangiogenic therapy.