Nitric Oxide and Its Gatekeeper Thrombospondin-1 in Tumor Angiogenesis: Fig. 1

The molecular mechanism of thrombospondin family members in cardiovascular diseases

Cardiovascular diseases have been identified as vital factors in global morbidity and mortality in recent years. The available evidence suggests that various cytokines and pathological proteins participate in these complicated and changeable diseases. The thrombospondin (TSP) family is a series of conserved, multidomain calcium-binding glycoproteins that cause cell-matrix and cell-cell effects via interactions with other extracellular matrix components and cell surface receptors. The TSP family has five members that can be divided into two groups (Group A and Group B) based on their different structures. TSP-1, TSP-2, and TSP-4 are the most studied proteins. Among recent studies and findings, we investigated the functions of several family members, especially TSP-5. We review the basic concepts of TSPs and summarize the relevant molecular mechanisms and cell interactions in the cardiovascular system. Targeting TSPs in CVD and other diseases has a remarkable therapeutic benefit.

A metabolic perspective on nitric oxide function in melanoma

Nitric oxide (NO) generated from nitric oxide synthase (NOS) exerts a dichotomous effect in melanoma, suppressing or promoting tumor progression. This dichotomy is thought to depend on the intracellular NO concentration and the cell type in which it is generated. Due to its central role in the metabolism of multiple critical constituents involved in signaling and stress, it is crucial to explore NO's contribution to the metabolic dysfunction of melanoma. This review will discuss many known metabolites linked to NO production in melanoma. We discuss the synthesis of these metabolites, their role in biochemical pathways, and how they alter the biological processes observed in the melanoma tumor microenvironment. The metabolic pathways altered by NO and the corresponding metabolites reinforce its dual role in melanoma and support investigating this effect for potential avenues of therapeutic intervention.

Multifunctional MXene-Based Bioactive Materials for Integrated Regeneration Therapy

The reconstruction engineering of tissue defects accompanied by major diseases including cancer, infection, and inflammation is one of the important challenges in clinical medicine. The development of innovative tissue engineering strategies such as multifunctional bioactive materials presents a great potential to overcome the challenge of disease-impaired tissue regeneration. As the major representative of two-dimensional nanomaterials, MXenes have shown multifunctional physicochemical properties and have been diffusely studied as multimodal nanoplatforms in the field of biomedicine. This review summarized the recent advances in the multifunctional properties of MXenes and integrated regeneration-therapy applications of MXene-based biomaterials, including tissue regeneration-tumor therapy, tissue regeneration-infection therapy, and tissue regeneration-inflammation therapy. MXenes have been recognized as good candidates for promoting tissue regeneration and treating diseases through photothermal therapy, regulating cell behavior, and drug and gene delivery. The current challenges and future perspectives of MXene-based biomaterials in integrated regeneration-therapy are also discussed well in this review. In summary, MXene-based biomaterials have shown promising potential for integrated tissue regeneration and disease treatment due to their favorable physicochemical properties and bioactive functions. However, there are still many obstacles and challenges that must be addressed for the regeneration-therapy applications of MXene-based biomaterials, including understanding the bioactive mechanism, ensuring long-term biosafety, and improving their targeting therapy capacity.

Why do humans need thrombospondin-1?

Matricellular proteins comprise several families of secreted proteins that function in higher animals at the interface between cells and their surrounding extracellular matrix. Targeted gene disruptions that result in loss of viability in mice have revealed critical roles for several matricellular proteins in murine embryonic development, including two members of the cellular communication network (CCN) gene family. In contrast, mice lacking single or multiple members of the thrombospondin (THBS) gene family remain viable and fertile. The frequency of loss of function mutants, identified using human deep exome sequencing data, provided evidence that some of the essential genes in mice, including Ccn1, are also essential genes in humans. However, a deficit in loss of function mutants in humans indicated that THBS1 is also highly loss-intolerant. In addition to roles in embryonic development or adult reproduction, genes may be loss-intolerant in humans because their function is needed to survive environmental stresses that are encountered between birth and reproduction. Laboratory mice live in a protected environment that lacks the exposures to pathogens and injury that humans routinely face. However, subjecting Thbs1-/- mice to defined stresses has provided valuable insights into functions of thrombospondin-1 that could account for the loss-intolerance of THBS1 in humans. Stress response models using transgenic mice have identified protective functions of thrombospondin-1 in the cardiovascular system (red) and immune defenses (blue) that could account for its intolerance to loss of function mutants in humans.

Inhaled Nitric Oxide Promotes Angiogenesis in the Rodent Developing Brain

Inhaled nitric oxide (iNO) is a therapy used in neonates with pulmonary hypertension. Some evidence of its neuroprotective properties has been reported in both mature and immature brains subjected to injury. NO is a key mediator of the VEGF pathway, and angiogenesis may be involved in the reduced vulnerability to injury of white matter and the cortex conferred by iNO. Here, we report the effect of iNO on angiogenesis in the developing brain and its potential effectors. We found that iNO promotes angiogenesis in the developing white matter and cortex during a critical window in P14 rat pups. This shift in the developmental program of brain angiogenesis was not related to a regulation of NO synthases by exogenous NO exposure, nor the VEGF pathway or other angiogenic factors. The effects of iNO on brain angiogenesis were found to be mimicked by circulating nitrate/nitrite, suggesting that these carriers may play a role in transporting NO to the brain. Finally, our data show that the soluble guanylate cyclase/cGMP signaling pathway is likely to be involved in the pro-angiogenetic effect of iNO through thrombospondin-1, a glycoprotein of the extracellular matrix, inhibiting soluble guanylate cyclase through CD42 and CD36. In conclusion, this study provides new insights into the biological basis of the effect of iNO in the developing brain.

Multifunctional 3D-printed bioceramic scaffolds: Recent strategies for osteosarcoma treatment

Osteosarcoma is the most prevalent bone malignant tumor in children and teenagers. The bone defect, recurrence, and metastasis after surgery severely affect the life quality of patients. Clinically, bone grafts are implanted. Primary bioceramic scaffolds show a monomodal osteogenesis function. With the advances in three-dimensional printing technology and materials science, while maintaining the osteogenesis ability, scaffolds become more patient-specific and obtain additional anti-tumor ability with functional agents being loaded. Anti-tumor therapies include photothermal, magnetothermal, old and novel chemo-, gas, and photodynamic therapy. These strategies kill tumors through novel mechanisms to treat refractory osteosarcoma due to drug resistance, and some have shown the potential to reverse drug resistance and inhibit metastasis. Therefore, multifunctional three-dimensional printed bioceramic scaffolds hold excellent promise for osteosarcoma treatments. To better understand, we review the background of osteosarcoma, primary 3D-printed bioceramic scaffolds, and different therapies and have a prospect for the future.

Regulation of pleiotropic physiological roles of nitric oxide signaling

Nitric Oxide (NO) is a highly diffusible, ubiquitous signaling molecule and a free radical that is naturally synthesized by our body. The pleiotropic effects of NO in biological systems are due to its reactivity with different molecules, such as molecular oxygen (O₂), superoxide anion, DNA, lipids, and proteins. There are several contradictory findings in the literature pertaining to its role in oncology. NO is a Janus-faced molecule shown to have both tumor promoting and tumoricidal effects, which depend on its concentration, duration of exposure, and location. A high concentration is shown to have cytotoxic effects by triggering apoptosis, and at a low concentration, NO promotes angiogenesis, metastasis, and tumor progression. Upregulated NO synthesis has been implicated as a causal factor in several pathophysiological conditions including cancer. This dichotomous effect makes it highly challenging to discover its true potential in cancer biology. Understanding the mechanisms by which NO acts in different cancers helps to develop NO based therapeutic strategies for cancer treatment. This review addresses the physiological role of this molecule, with a focus on its bimodal action in various types of cancers.

The RAGE/multiligand axis: a new actor in tumor biology

The receptor for advanced glycation end-products (RAGE) is a multiligand binding and single-pass transmembrane protein which actively participates in several chronic inflammation-related diseases. RAGE, in addition to AGEs, has a wide repertoire of ligands, including several damage-associated molecular pattern molecules or alarmins such as HMGB1 and members of the S100 family proteins.

Over the last years, a large and compelling body of evidence has revealed the active participation of the RAGE axis in tumor biology based on its active involvement in several crucial mechanisms involved in tumor growth, immune evasion, dissemination, as well as by sculpturing of the tumor microenvironment as a tumor-supportive niche. In the present review, we will detail the consequences of the RAGE axis activation to fuel essential mechanisms to guarantee tumor growth and spreading.

Engineering 2D Mesoporous Silica@MXene-Integrated 3D-Printing Scaffolds for Combinatory Osteosarcoma Therapy and NO-Augmented Bone Regeneration

The rising concerns of the recurrence and bone deficiency in surgical treatment of malignant bone tumors have raised an urgent need of the advance of multifunctional therapeutic platforms for efficient tumor therapy and bone regeneration. Herein, the construction of a multifunctional biomaterial system is reported by the integration of 2D Nb₂ C MXene wrapped with S-nitrosothiol (RSNO)-grafted mesoporous silica with 3D-printing bioactive glass (BG) scaffolds (MBS). The near infrared (NIR)-triggered photonic hyperthermia of MXene in the NIR-II biowindow and precisely controlled nitric oxide (NO) release are coordinated for multitarget ablation of bone tumors to enhance localized osteosarcoma treatment. The in situ formed phosphorus and calcium components degraded from BG scaffold promote bone-regeneration bioactivity, augmented by sufficient blood supply triggered by on-demand NO release. The tunable NO generation plays a crucial role in sequential adjuvant tumor ablation, combinatory promotion of coupled vascularization, and bone regeneration. This study demonstrates a combinatory osteosarcoma ablation and a full osseous regeneration as enabled by the implantation of MBS. The design of multifunctional scaffolds with the specific features of controllable NO release, highly efficient photothermal conversion, and stimulatory bone regeneration provides an intriguing biomaterial platform for the diversified treatment of bone tumors.

Nitric oxide synthase inhibitors 1400W and L-NIO inhibit angiogenesis pathway of colorectal cancer

BACKGROUND

It has been widely accepted that angiogenesis plays fundamental roles in colorectal cancer development, and therapeutic targeting of this pathway has achieved promising outcome. Recent reports have highlighted the involvement of nitric oxide synthases (NOS) in the development of angiogenesis in cancer; however, the mechanism and therapeutic value of NOS inhibitors in colon cancer are largely unknown.

OBJECTIVE

In this study, we investigated the effects and mechanism of the NOS inhibitors 1400W and L-NIO on the angiogenesis pathway in colorectal cancer cells.

METHODS

Two colorectal cancer cell lines, HT 29 and HCT 116, were used for in vitro study. The expression of iNOS and eNOS in cells was knocked down via shRNA transfection. MTS assays and wound healing assays were performed to assess cell proliferation and migration after shRNA transfection or treatment with 1400W, L-NIO, and 5-fluorouracil. Human angiogenesis PCR arrays and proteome profiler human angiogenesis arrays were used to detect changes in key genes/proteins involved in modulating angiogenesis after 1400W and L-NIO treatment.

RESULTS

Knockdown of iNOS and eNOS significantly inhibited colorectal cancer cell growth. Treatment with NOS inhibitors inhibited colorectal cancer cell growth and migration, and was associated with suppression of the expression of key genes/proteins involved in the angiogenesis pathway. In addition, the combined use of NOS inhibitors with 5-fluorouracil showed enhanced inhibition of cell proliferation and migration.

CONCLUSION

NOS inhibitors could suppress colorectal cancer cell growth and migration, likely via suppressing the angiogenesis pathway.

Multiple Tumor Marker Elevation in Androgen Ablation-Refractory Prostate Cancer with Long-Term Response to Metronomic Chemotherapy: A Case Report

Outcomes in hormone-refractory prostate cancer are very poor. The time from progression to death is only 12–19 months. We present the case of a 69-year-old man with hormone-refractory prostate cancer and bone metastases treated with metronomic chemotherapy (cyclophosphamide based). He had had a colon adenocarcinoma ten years before. The atypical features of this case were an unusually long-lasting response to metronomic chemotherapy and an increase in serum levels of some non-prostate-specific tumor markers (CEA and CA 19–9) that was not related to a relapse of colon cancer. We hypothesize a potential role of hypoxia inducing CA 19–9 and CEA expression in tumor cells, which may predict the development of progressive resistance to antiangiogenic therapies.

RBP4 and THBS2 are serum biomarkers for diagnosis of colorectal cancer

The potential role of serum RBP4 and THBS2 as biomarker in colorectal cancer (CRC) diagnosis has never been studied. We investigated in large sample using quantitative ELISA method to explore whether serum RBP4 and THBS2 can act as biomarkers for CRC diagnosis. The concentration of RBP4 and THBS2 was measured in 402 CRC patients' serum samples and 218 normal controls' serum samples. The results showed that the average RBP4 and THBS2 concentrations in normal controls were significantly higher than in CRC patients (36.5±11.4μg/mL vs 21.8±8.7μg/mL and 20.5±6.1ng/mL vs 14.5±7.3ng/mL, respectively), both p<0.001. RBP4 distinguished CRC patients from normal individuals with the area under the receiver operating characteristic curve (AUC) performing at 0.852, with sensitivity of 74.9% and specificity of 81.7%. While THBS2 distinguished CRC patients performing AUC at 0.794, with sensitivity of 64.9% and specificity of 87.1%. The ability of RBP4 and THBS2 serum concentration distinguishing CRC from normal controls showed better than that of serum CEA (AUC=0.818) or CA19-9 (AUC=0.650) concentration. This is the first study to report RBP4 and THBS2 as diagnosis serum biomarkers for CRC, which might be a good supplement for CEA or CA19-9 for clinical diagnosis.

Inducible Nitric Oxide Synthase in the Carcinogenesis of Gastrointestinal Cancers

SIGNIFICANCE

Gastrointestinal (GI) cancer taken together constitutes one of the most common cancers worldwide with a broad range of etiological mechanisms. In this review, we have examined the impact of nitric oxide (NO) on the etiology of colon, colorectal, gastric, esophageal, and liver cancers. Recent Advances: Despite differences in etiology, initiation, and progression, chronic inflammation has been shown to be a common element within these cancers showing interactions of numerous pathways. NO generated at the inflammatory site contributes to the initiation and progression of disease. The amount of NO generated, time, and site vary and are an important determinant of the biological effects initiated. Among the nitric oxide synthase enzymes, the inducible isoform has the most diverse range, participating in numerous carcinogenic processes. There is emerging evidence showing that inducible nitric oxide synthase (NOS2) plays a central role in the process of tumor initiation and/or development.

CRITICAL ISSUES

Redox inflammation through NOS2 and cyclooxygenase-2 participates in driving the mechanisms of initiation and progression in GI cancers.

FUTURE DIRECTIONS

Understanding the underlying mechanism involved in NOS2 activation can provide new insights into important prevention and treatment strategies. Antioxid. Redox Signal. 26, 1059-1077.

Molecular pathway activation features linked with transition from normal skin to primary and metastatic melanomas in human

Melanoma is the most aggressive and dangerous type of skin cancer, but its molecular mechanisms remain largely unclear. For transcriptomic data of 478 primary and metastatic melanoma, nevi and normal skin samples, we performed high-throughput analysis of intracellular molecular networks including 592 signaling and metabolic pathways. We showed that at the molecular pathway level, the formation of nevi largely resembles transition from normal skin to primary melanoma. Using a combination of bioinformatic machine learning algorithms, we identified 44 characteristic signaling and metabolic pathways connected with the formation of nevi, development of primary melanoma, and its metastases. We created a model describing formation and progression of melanoma at the level of molecular pathway activation. We discovered six novel associations between activation of metabolic molecular pathways and progression of melanoma: for allopregnanolone biosynthesis, L-carnitine biosynthesis, zymosterol biosynthesis (inhibited in melanoma), fructose 2, 6-bisphosphate synthesis and dephosphorylation, resolvin D biosynthesis (activated in melanoma), D-myo-inositol hexakisphosphate biosynthesis (activated in primary, inhibited in metastatic melanoma). Finally, we discovered fourteen tightly coordinated functional clusters of molecular pathways. This study helps to decode molecular mechanisms underlying the development of melanoma.

Role of thrombospondin-1 expression in colorectal liver metastasis and its molecular mechanism

BACKGROUND

Thrombospondin-1 (THBS-1), a glycoprotein, is an endogenous inhibitor of angiogenesis and tumor growth. In this study, we investigated the clinical role and mechanism of THBS-1 expression in colorectal liver metastases, focusing on the relationships between its expression and tumor growth, epithelial-mesenchymal transition (EMT), and expression of other relevant molecules.

METHODS

Ninety-four patients who initially underwent curative hepatic resection were enrolled in this study and correlations between expression of THBS-1 (THBS-1 high [n = 35] and THBS-1 low [n = 59]) and tumor growth, Ki-67 labeling index (Ki-67 LI), expression of other relevant molecules, and microvessel density (MVD) investigated.

RESULTS

THBS-1 low expression correlated with more advanced grade of liver and lymph node metastases and significantly worse overall survival than strong THBS-1 expression (3-year survival: 96.7% vs. 65.4%, P < 0.01). Multivariate analysis identified THBS-1 low expression as an independent prognostic factor (HR 2.82, 95% CI 1.21-7.71, P = 0.01). THBS-1 low expression correlated positively with high Ki-67 LI (P < 0.05) and inversely with E-cadherin (P < 0.05) and hypoxia inducible factor-1α (HIF-1α) expression (P < 0.05); THBS-1 expression and MVD were not significantly correlated.

CONCLUSIONS

Low THBS-1 expression may be an independent poor prognostic factor that affects tumor growth and EMT acquisition. Additionally, THBS-1 may be regulated by the HIF-1 pathway.

Angiogenic factors are increased in circulating granulocytes and CD34+ cells of myeloproliferative neoplasms

It has been shown that angiogenesis and inflammation play an important role in development of most hematological malignancies including the myeloproliferative neoplasm (MPN). The aim of this study was to investigate and correlate the levels of key angiogenic molecules such as hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS) in peripheral blood and bone marrow cells of MPN patients, along with JAK2V617F mutation allele burden and effects of therapy. HIF-1α and VEGF gene expression were decreased, while eNOS mRNA levels were increased in granulocytes of MPN patients. Furthermore, positively correlated and increased VEGF and eNOS protein levels were in negative correlation with HIF-1α levels in granulocytes of MPN patients. According to immunoblotting, the generally augmented angiogenic factors demonstrated JAK2V617F allele burden dependence only in granulocytes of PMF. The angiogenic factors were largely reduced after hydroxyurea therapy in granulocytes of MPN patients. Levels of eNOS protein expression were stimulated by Calreticulin mutations in granulocytes of essential thrombocythemia. Immunocytochemical analyses of CD34⁺ cells showed a more pronounced enhancement of angiogenic factors than in granulocytes. Increased gene expression linked to the proinflammatory TGFβ and MAPK signaling pathways were detected in CD34⁺ cells of MPN patients. In conclusion, the angiogenesis is increased in several cell types of MPN patients supported by the transcriptional activation of inflammation-related target genes, and is not limited to bone marrow stroma cells. It also appears that some of the benefit of hydroxyurea therapy of the MPN is mediated by effects on angiogenic factors. © 2016 Wiley Periodicals, Inc.

Arginine dependence of tumor cells: targeting a chink in cancer's armor

Arginine, one among the 20 most common natural amino acids, has a pivotal role in cellular physiology as it is being involved in numerous cellular metabolic and signaling pathways. Dependence on arginine is diverse for both tumor and normal cells. Because of decreased expression of argininosuccinate synthetase and/or ornithine transcarbamoylase, several types of tumor are auxotrophic for arginine. Deprivation of arginine exploits a significant vulnerability of these tumor cells and leads to their rapid demise. Hence, enzyme-mediated arginine depletion is a potential strategy for the selective destruction of tumor cells. Arginase, arginine deiminase and arginine decarboxylase are potential enzymes that may be used for arginine deprivation therapy. These arginine catabolizing enzymes not only reduce tumor growth but also make them susceptible to concomitantly administered anti-cancer therapeutics. Most of these enzymes are currently under clinical investigations and if successful will potentially be advanced as anti-cancer modalities.

Original insights on thrombospondin-1-related antireceptor strategies in cancer

Thrombospondin-1 (TSP-1) is a large matricellular glycoprotein known to be overexpressed within tumor stroma in several cancer types. While mainly considered as an endogenous angiogenesis inhibitor, TSP-1 exhibits multifaceted functionalities in a tumor context depending both on TSP-1 concentration as well as differential receptor expression by cancer cells and on tumor-associated stromal cells. Besides, the complex modular structure of TSP-1 along with the wide variety of its soluble ligands and membrane receptors considerably increases the complexity of therapeutically targeting interactions involving TSP-1 ligation of cell-surface receptors. Despite the pleiotropic nature of TSP-1, many different antireceptor strategies have been developed giving promising results in preclinical models. However, transition to clinical trials often led to nuanced outcomes mainly due to frequent severe adverse effects. In this review, we will first expose the intricate and even sometimes opposite effects of TSP-1-related signaling on tumor progression by paying particular attention to modulation of angiogenesis and tumor immunity. Then, we will provide an overview of current developments and prospects by focusing particularly on the cell-surface molecules CD47 and CD36 that function as TSP-1 receptors; including antibody-based approaches, therapeutic gene modulation and the use of peptidomimetics. Finally, we will discuss original approaches specifically targeting TSP-1 domains, as well as innovative combination strategies with a view to producing an overall anticancer response.

Signaling and stress: The redox landscape in NOS2 biology

Nitric oxide (NO) has a highly diverse range of biological functions from physiological signaling and maintenance of homeostasis to serving as an effector molecule in the immune system. However, deleterious as well as beneficial roles of NO have been reported. Many of the dichotomous effects of NO and derivative reactive nitrogen species (RNS) can be explained by invoking precise interactions with different targets as a result of concentration and temporal constraints. Endogenous concentrations of NO span five orders of magnitude, with levels near the high picomolar range typically occurring in short bursts as compared to sustained production of low micromolar levels of NO during immune response. This article provides an overview of the redox landscape as it relates to increasing NO concentrations, which incrementally govern physiological signaling, nitrosative signaling and nitrosative stress-related signaling. Physiological signaling by NO primarily occurs upon interaction with the heme protein soluble guanylyl cyclase. As NO concentrations rise, interactions with nonheme iron complexes as well as indirect modification of thiols can stimulate additional signaling processes. At the highest levels of NO, production of a broader range of RNS, which subsequently interact with more diverse targets, can lead to chemical stress. However, even under such conditions, there is evidence that stress-related signaling mechanisms are triggered to protect cells or even resolve the stress. This review therefore also addresses the fundamental reactions and kinetics that initiate signaling through NO-dependent pathways, including processes that lead to interconversion of RNS and interactions with molecular targets.

Differential role of gene hypermethylation in adenocarcinomas, squamous cell carcinomas and cervical intraepithelial lesions of the uterine cervix

Cervical cancer is the third most common cancer in women worldwide. The hypermethylation of P16, TSLC-1 and TSP-1 genes was analyzed in squamous cell carcinomas (SCC), cervical intraepithelial lesions (CIN) and adenocarcinomas (ADC) of the uterine cervix (total 181 lesions). Additionally human papillomavirus (HPV) type, EPB41L3, RASSF1 and RASSF2 hypermethylation were tested in ADC and the results were compared with those obtained previously by our group in SCC. P16, TSLC-1 and TSP-1 hypermethylation was more frequent in SCCs than in CINs. These percentages and the corresponding ones for EPB41L3, RASSF1 and RASSF2 genes were also higher in SCCs than in ADCs, except for P16. The presence of HPV in ADCs was lower than reported previously in SCC and CIN. Patients with RASSF1A hypermethylation showed significantly longer disease-free survival (P = 0.015) and overall survival periods (P = 0.009) in ADC patients. To our knowledge, this is the first description of the EPB41L3 and RASSF2 hypermethylation in ADCs. These results suggest that the involvement of DNA hypermethylation in cervical cancer varies depending on the histological type, which might contribute to explaining the different prognosis of patients with these types of tumors.

Insights into the diverse effects of nitric oxide on tumor biology

Among its many roles in cellular biology, nitric oxide (·NO) has long been associated with cancers both as a protumorigenic and as an antitumorigenic agent. The dual nature of this signaling molecule in varied settings is attributable to its temporal and concentration-dependent effects that produce different phenotypes. The steady-state ·NO concentration within the cell is a balance between its rate of enzymatic synthesis from the three nitric oxide synthase (NOS) isoforms and consumption via numerous metabolic pathways and demonstrates strong dependence on the tissue oxygen concentration. NOS expression and ·NO production are often deregulated and associated with numerous types of cancers with dissimilar prognostic outcomes. ·NO influences several facets of tumor initiation and progression including DNA damage, chronic inflammation, angiogenesis, epithelial-mesenchymal transition, and metastasis, to name a few. The role of ·NO as an epigenetic modulator has also recently emerged and has potentially important mechanistic implications in regulating transcription of oncogenes and tumor-suppressor genes. ·NO-derived cellular adducts such as dinitrosyliron complexes and the formation of higher nitrogen oxides further alter its cellular behavior. Among anticancer strategies, the use of NOS as a prognostic biomarker and modulation of ·NO production for therapeutic benefit have gained importance over the past decade. Numerous ·NO-releasing drugs and NOS inhibitors have been evaluated in preclinical and clinical settings to arrest tumor growth. Taken together, ·NO affects various arms of cancer signaling networks. An overview of this complex interplay is provided in this chapter.

Cancer cell metabolism and the modulating effects of nitric oxide

Altered metabolic phenotype has been recognized as a hallmark of tumor cells for many years, but this aspect of the cancer phenotype has come into greater focus in recent years. NOS2 (inducible nitric oxide synthase of iNOS) has been implicated as a component in many aggressive tumor phenotypes, including melanoma, glioblastoma, and breast cancer. Nitric oxide has been well established as a modulator of cellular bioenergetics pathways, in many ways similar to the alteration of cellular metabolism observed in aggressive tumors. In this review we attempt to bring these concepts together with the general hypothesis that one function of NOS2 and NO in cancer is to modulate metabolic processes to facilitate increased tumor aggression. There are many mechanisms by which NO can modulate tumor metabolism, including direct inhibition of respiration, alterations in mitochondrial mass, oxidative inhibition of bioenergetic enzymes, and the stimulation of secondary signaling pathways. Here we review metabolic alterations in the context of cancer cells and discuss the role of NO as a potential mediator of these changes.

Effect and mechanism of thrombospondin-1 on the angiogenesis potential in human endothelial progenitor cells: an in vitro study

Objective

Coronary collateral circulation plays a protective role in patients with coronary artery disease (CAD). We investigated whether thrombospondin-1(TSP-1) has an inhibitory effect on angiogenesis potential in endothelial progenitor cells(EPCs) and tested whether TSP-1 are altered in plasma of patients who had chronic total occlusion (CTO) in at least one coronary artery and with different collateral stages(according to Rentrop grading system).

Methods and Results

We isolated early and late EPCs from human cord blood and investigated a dose-dependent effect of TSP-1 on their angiogenesis potential by Matrigel angiogenesis assay. We found that TSP-1 (5 µg/ml) inhibited early EPCs incorporation into tubules after pretreatment for 1, 6 and 12 hours, respectively (83.3±11.9 versus 50.0±10.1 per field for 1 hour,161.7±12.6 versus 124.0±14.4 for 6 hours, 118.3±12.6 versus 68.0±20.1 for 12 hours, p<0.05). TSP-1 also inhibited late EPCs tubule formation at 1 µg/ml (6653.4±422.0 µm/HPFversus 5552.8±136.0 µm/HPF, p<0.05), and the inhibition was further enhanced at 5 µg/ml (6653.4±422.0 µm/HPF versus 2118.6±915.0 µm/HPF p<0.01). To explore the mechanism involved, a small interfering RNA was used. In vitro, CD47 siRNA significantly attenuated TSP-1's inhibition of angiogenesis on late EPCs and similar results were obtained after functional blocking by anti-CD47 antibody. Then we investigated pathways downstream of CD47 and found TSP-1 regulated VEGF-induced VEGFR2 phosphorylation via CD47. Furthermore, we examined plasma TSP-1 levels in patients with CTO who developed different stages of collaterals and found a paradoxical higher level of TSP-1 in patients with good collaterals compared with bad ones (612.9±554.0 ng/ml versus 224.4±132.4 ng/ml, p<0.05).

Conclusion

TSP-1 inhibited angiogenesis potential of early and late EPCs in vitro. This inhibition may be regulated by TSP-1's interaction with CD47, resulting in down regulation of VEGFR2 phosphorylation. In patients with CTO, there may be a self-adjustment mechanism in bad collaterals which is shown as low level of angiogenesis inhibitor TSP-1, and thus favoring collateral formation.

Physiological and pathological angiogenesis in the adult pulmonary circulation

Angiogenesis occurs during growth and physiological adaptation in many systemic organs, for example, exercise-induced skeletal and cardiac muscle hypertrophy, ovulation, and tissue repair. Disordered angiogenesis contributes to chronic inflammatory disease processes and to tumor growth and metastasis. Although it was previously thought that the adult pulmonary circulation was incapable of supporting new vessel growth, over that past 10 years new data have shown that angiogenesis within this circulation occurs both during physiological adaptive processes and as part of the pathogenic mechanisms of lung diseases. Here we review the expression of vascular growth factors in the adult lung, their essential role in pulmonary vascular homeostasis and the changes in their expression that occur in response to physiological challenges and in disease. We consider the evidence for adaptive neovascularization in the pulmonary circulation in response to alveolar hypoxia and during lung growth following pneumonectomy in the adult lung. In addition, we review the role of disordered angiogenesis in specific lung diseases including idiopathic pulmonary fibrosis, acute adult distress syndrome and both primary and metastatic tumors of the lung. Finally, we examine recent experimental data showing that therapeutic enhancement of pulmonary angiogenesis has the potential to treat lung diseases characterized by vessel loss.

Molecular basis for the regulation of angiogenesis by thrombospondin-1 and -2

Thrombospondins TSP-1 and TSP-2 are potent endogenous inhibitors of angiogenesis. They inhibit angiogenesis through direct effects on endothelial cell migration, proliferation, survival, and apoptosis and by antagonizing the activity of VEGF. Several of the membrane receptor systems and signal transduction molecules that mediate the effects of TSP-1 and TSP-2 have been elucidated. TSP-1 and TSP-2 exert their direct effects through CD36, CD47, and integrins. Recent data indicate that CD36 and β1 integrins collaborate to transmit the signals that are initiated by TSP-1 and TSP-2. Furthermore, these receptors appear to associate with VEGFR2 to form a platform for the integration of positive and negative signals for angiogenesis. Cross talk between pro- and antiangiogenic signal transduction pathways may enable TSP-1 and TSP-2 to inhibit angiogenesis by antagonizing survival pathways while also activating apoptotic pathways. CD36 and CD47 are both involved in the suppression of nitric oxide (NO). Advances in understanding of the molecular regulation of angiogenesis by TSP have paved the way for innovations in experimental treatment of cancers and will likely continue to offer vast avenues for discovery in other disease processes as well.

Role of endothelial nitric oxide synthase (eNOS) in chronic stress-promoted tumour growth

Accumulating evidence suggests that chronic stress can be a cofactor for the initiation and progression of cancer. Here we evaluated the role of endothelial nitric oxide synthase (eNOS) in stress-promoted tumour growth of murine B16F10 melanoma cell line in C57BL/6 mice. Animals subjected to restraint stress showed increased levels adrenocorticotropic hormone, enlarged adrenal glands, reduced thymus weight and a 3.61-fold increase in tumour growth in respect to no-stressed animals. Tumour growth was significantly reduced in mice treated with the β-antagonist propranolol. Tumour samples obtained from stressed mice displayed high levels of vascular endothelial growth factor (VEGF) protein in immunohistochemistry. Because VEGF can induce eNOS increase, and nitric oxide is a relevant factor in angiogenesis, we assessed the levels of eNOS protein by Western blot analysis. We found a significant increase in eNOS levels in tumour samples from stressed mice, indicating an involvement of this enzyme in stress-induced tumour growth. Accordingly, chronic stress did not promote tumour growth in eNOS^−/− mice. These results disclose for the first time a pivotal role for eNOS in chronic stress-induced initiation and promotion of tumour growth.

Opportunities and challenges in tumor angiogenesis research: back and forth between bench and bed

Angiogenesis is essential for tumor growth and metastasis. Many signaling pathways are involved in regulating tumor angiogenesis, with the vascular endothelial growth factor pathway being of particular interest. The recognition of the heterogeneity in tumor vasculature has led to better predictions of prognosis through differential analyses of the vasculature. However, the clinical benefits from antiangiogenic therapy are limited, because many antiangiogenic agents cannot provide long-term survival benefits, suggesting the development of drug resistance. Activation of the hypoxia and c-Met pathways, as well as other proangiogenic factors, has been shown to be responsible for such resistance. Vessel co-option could be another important mechanism. For future development, research to improve the efficacy of antiangiogenic therapy includes (a) using tumor-derived endothelial cells for drug screening; (b) developing the drugs focusing on specific tumor types; (c) developing a better preclinical model for drug study; (d) developing more accurate biomarkers for patient selection; (e) targeting the c-Met pathway or other pathways; and (f) optimizing the dose and schedule of antiangiogenic therapy. In summary, the future of antiangiogenic therapy for cancer patients depends on our efforts to develop the right drugs, select the right patients, and optimize the treatment conditions.

The role of thrombospondin 1 on intestinal inflammation and carcinogenesis

Crohn’s disease and ulcerative colitis are inflammatory bowel diseases (IBD) quite common in the United States and other Western countries. Patients suffering IBD are at greater risk of developing colorectal adenocarcinoma than the general population. Both, the adenomacarcinoma and the inflammation-carcinogenesis processes are characterized by active angiogenesis. Recent studies also have shown that anti-angiogenesis might be a novel therapeutic approach for IBD. Thrombospondin 1 (TSP1) is an extracellular protein well known for its anti-angiogenic properties. TSP1 also has key functions in inflammation, which is assumed to be the primary cause for carcinogenesis in IBD. This review is focused on the role of TSP1 in colorectal carcinogenesis. The therapeutic effects of TSP derived-peptides on inhibiting the inflammation-carcinogenesis progression are also discussed.

Transplantable subcutaneous hepatoma 22a affects functional activity of resident tissue macrophages in periphery

Tumors spontaneously develop central necroses due to inadequate blood supply. Recent data indicate that dead cells and their products are immunogenic to the host. We hypothesized that macrophage tumor-dependent reactions can be mediated differentially by factors released from live or dead tumor cells. In this study, functional activity of resident peritoneal macrophages was investigated in parallel with tumor morphology during the growth of syngeneic nonimmunogenic hepatoma 22a. Morphometrical analysis of tumor necroses, mitoses and leukocyte infiltration was performed in histological sections. We found that inflammatory potential of peritoneal macrophages in tumor-bearing mice significantly varied depending on the stage of tumor growth and exhibited two peaks of activation as assessed by nitroxide and superoxide anion production, 5'-nucleotidase activity and pinocytosis. Increased inflammatory reactions were not followed by the enhancement of angiogenic potential as assessed by Vascular Endothelial Growth Factor mRNA expression. Phases of macrophage activity corresponded to the stages of tumor growth characterized by high proliferative potential. The appearance and further development of necrotic tissue inside the tumor did not coincide with changes in macrophage behavior and therefore indirectly indicated that activation of macrophages was a reaction mostly to the signals produced by live tumor cells.

Vasculopathy in type 2 diabetes mellitus: role of specific angiogenic modulators

Type 2 diabetes mellitus (T2DM) is largely defined by hyperglycemia that promotes vascular complications. Abnormal angiogenesis has been claimed to have a role in this disease. This study aimed to investigate serum levels of both conventional and other markers of angiogenesis not well studied before in diabetes, and to correlate findings with age of the patients, glycemic control, presence of microvascular complications, and oxidative stress. Thirty-eight patients with T2DM and 13 age- and sex-matched healthy persons representing controls were recruited. Serum levels of basic fibroblast growth factor (b-FGF) was measured by immunosorbent assay kit; advanced glycosylation end products, platelet-derived endothelial cell growth factor (PD-ECGF), cathepsin-D (CD), gangliosides, hyaluronic acid (HA), nitric oxide (NO), lipid peroxides (LPER), superoxide dismutase, and total thiols by chemical methods; and copper (Cu) by atomic absorption flame photometry. Advanced glycosylation end products and angiogenic factors (b-FGF, PD-ECGF, CD, gangliosides, HA, and Cu) were significantly higher in patients than controls. Oxidative stress markers, NO, and LPER were significantly higher while total thiols were significantly lower in patients than controls. These changes were more pronounced with age, poor glycemic control, and presence of microvascular complications. Angiogenesis dysfunction coinciding with elevated levels of many angiogenic growth factors may point to their malfunctioning due to oxidative stress and/or protein glycation at the factor and the receptor levels. This necessitates further investigations.

Nitric oxide physiology and pathology

Nitric oxide (NO) is just one member of a new class of gaseous signalling molecules with fundamental actions in biology. In higher vertebrates it has key roles in maintaining haemostasis and in smooth muscle (especially vascular smooth muscle), neurons and the gastrointestinal tract. It is intimately involved in regulating all aspects of our lives from waking, digestion, sexual function, perception of pain and pleasure, memory recall and sleeping. Finally, the way it continues to function in our bodies will influence how we degenerate with age. It will likely play a role in our deaths through cardiovascular disease, stroke, diabetes and cancer. Our ability to control NO signalling and to use NO effectively in therapy must therefore have a major bearing on the future quality and duration of human life.

A role for thrombospondin-1 deficits in astrocyte-mediated spine and synaptic pathology in Down's syndrome

BACKGROUND

Down's syndrome (DS) is the most common genetic cause of mental retardation. Reduced number and aberrant architecture of dendritic spines are common features of DS neuropathology. However, the mechanisms involved in DS spine alterations are not known. In addition to a relevant role in synapse formation and maintenance, astrocytes can regulate spine dynamics by releasing soluble factors or by physical contact with neurons. We have previously shown impaired mitochondrial function in DS astrocytes leading to metabolic alterations in protein processing and secretion. In this study, we investigated whether deficits in astrocyte function contribute to DS spine pathology.

METHODOLOGY/PRINCIPAL FINDINGS

Using a human astrocyte/rat hippocampal neuron coculture, we found that DS astrocytes are directly involved in the development of spine malformations and reduced synaptic density. We also show that thrombospondin 1 (TSP-1), an astrocyte-secreted protein, possesses a potent modulatory effect on spine number and morphology, and that both DS brains and DS astrocytes exhibit marked deficits in TSP-1 protein expression. Depletion of TSP-1 from normal astrocytes resulted in dramatic changes in spine morphology, while restoration of TSP-1 levels prevented DS astrocyte-mediated spine and synaptic alterations. Astrocyte cultures derived from TSP-1 KO mice exhibited similar deficits to support spine formation and structure than DS astrocytes.

CONCLUSIONS/SIGNIFICANCE

These results indicate that human astrocytes promote spine and synapse formation, identify astrocyte dysfunction as a significant factor of spine and synaptic pathology in the DS brain, and provide a mechanistic rationale for the exploration of TSP-1-based therapies to treat spine and synaptic pathology in DS and other neurological conditions.

JS-K, a nitric oxide-releasing prodrug, modulates ß-catenin/TCF signaling in leukemic Jurkat cells: evidence of an S-nitrosylated mechanism

β-Catenin is a central player of the Wnt signaling pathway that regulates cell-cell adhesion and may promote leukemia cell proliferation. We examined whether JS-K, an NO-donating prodrug, modulates the Wnt/β-catenin/TCF-4 signaling pathway in Jurkat T-Acute Lymphoblastic Leukemia cells. JS-K inhibited Jurkat T cell growth in a concentration and time-dependent manner. The IC(50)s for cell growth inhibition were 14±0.7 and 9±1.2μM at 24 and 48h, respectively. Treatment of the cells with JS-K for 24h, caused a dose-dependent increase in apoptosis from 16±3.3% at 10μM to 74.8±2% at 100μM and a decrease in proliferation. This growth inhibition was also due, in part, to alterations in the different phases of the cell cycle. JS-K exhibited a dose-dependent cytotoxicity as measured by LDH release at 24h. However, between 2 and 8h, LDH release was less than 20% for any indicated JS-K concentration. The β-catenin/TCF-4 transcriptional inhibitory activity was reduced by 32±8, 63±5, and 93±2% at 2, 10, and 25μM JS-K, respectively, based on luciferase reporter assays. JS-K reduced nuclear β-catenin and cyclin D1 protein levels, but cytosolic β-catenin expression did not change. Based on a time-course assay of S-nitrosylation of proteins by a biotin switch assay, S-nitrsolyation of nuclear β-catenin was determined to precede its degradation. A comparison of the S-nitrosylated nuclear β-catenin to the total nuclear β-catenin showed that β-catenin protein levels were degraded at 24h, while S-nitrosylation of β-catenin occurred earlier at 0-6h. The NO scavenger PTIO abrogated the JS-K mediated degradation of β-catenin demonstrating the need for NO.

Gene expression profiling for nitric oxide prodrug JS-K to kill HL-60 myeloid leukemia cells

The nitric oxide (NO) prodrug JS-K is shown to have anticancer activity. To profile the molecular events associated with the anticancer effects of JS-K, HL-60 leukemia cells were treated with JS-K and subjected to microarray and real-time RT-PCR analysis. JS-K induced concentration- and time-dependent gene expression changes in HL-60 cells corresponding to the cytolethality effects. The apoptotic genes (caspases, Bax, and TNF-alpha) were induced, and differentiation-related genes (CD14, ITGAM, and VIM) were increased. For acute phase protein genes, some were increased (TP53, JUN) while others were suppressed (c-myc, cyclin E). The expression of anti-angiogenesis genes THBS1 and CD36 and genes involved in tumor cell migration such as tissue inhibitors of metalloproteinases, were also increased by JS-K. Confocal analysis confirmed key gene changes at the protein levels. Thus, multiple molecular events are associated with JS-K effects in killing HL-60, which could be molecular targets for this novel anticancer NO prodrug.

L-Arginine promotes angiogenesis in the chronically hypoxic lung: a novel mechanism ameliorating pulmonary hypertension

Chronic alveolar hypoxia, whether due to residence at high altitude or lung disease, leads to a sustained increase in pulmonary vascular resistance and pulmonary hypertension (PH). Strategies that augment endogenous nitric oxide production or activity, including l-arginine supplementation, attenuate the development of PH. This action has been attributed to inhibition of vessel wall remodeling, thus preventing structural narrowing of the vascular lumen. However, more recent evidence suggests that structural changes are not responsible for the elevated vascular resistance observed in chronic hypoxic PH, calling into question the previous explanation for the action of l-arginine. We examined the effect of dietary l-arginine supplementation on pulmonary vasoconstriction, structurally determined maximum vascular lumen diameter, and vessel length in rats during 2 wk of exposure to hypoxia. l-Arginine attenuated the development of hypoxic PH by preventing increased arteriolar resistance. It did not alter mean maximal vascular lumen diameter, nor did it augment nitric oxide-mediated vasodilatation, in chronically hypoxic lungs. However, the total length of vessels within the gas exchange region of the hypoxic lungs was significantly increased after l-arginine supplementation. These findings suggest that dietary l-arginine ameliorated hypoxic PH, but not by an effect on the structurally determined lumen diameter of pulmonary blood vessels. l-Arginine enhanced angiogenesis in the hypoxic pulmonary circulation, which may attenuate hypoxic PH by producing new parallel vascular pathways through the lung.

Thrombospondin 1 and vasoactive agents indirectly alter tumor blood flow

Nitric oxide (NO) plays important physiological roles in the vasculature to regulate angiogenesis, blood flow, and hemostasis. In solid tumors, NO is generally acknowledged to mediate angiogenic responses to several growth factors. This contrasts with conflicting evidence that NO can acutely increase tumor perfusion through local vasodilation or diminish perfusion by preferential relaxation of peripheral vascular beds outside the tumor. Because thrombospondin 1 (TSP1) is an important physiological antagonist of NO in vascular cells, we examined whether, in addition to inhibiting tumor angiogenesis, TSP1 can acutely regulate tumor blood flow. We assessed this activity of TSP1 in the context of perfusion responses to NO as a vasodilator and epinephrine as a vasoconstrictor. Nitric oxide treatment of wild type and TSP1 null mice decreased perfusion of a syngeneic melanoma, whereas epinephrine transiently increased tumor perfusion. Acute vasoactive responses were also independent of the level of tumor-expressed TSP1 in a melanoma xenograft, but recovery of basal perfusion was modulated by TSP1 expression. In contrast, overexpression of truncated TSP1 lacking part of its CD47 binding domain lacked this modulating activity. These data indicate that TSP1 primarily regulates long-term vascular responses in tumors, in part, because the tumor vasculature has a limited capacity to acutely respond to vasoactive agents.

Molecular signatures associated with transformation and progression to breast cancer in the isogenic MCF10 model

Comparative microarray analyses provided insight into understanding transcript changes during cancer progression; however, a reproducible signature underlying breast carcinogenesis has yet to be little available. We utilized gene expression profiling to define molecular signatures associated with transformation and cancer progression in a series of isogenic human breast cancer cell lines including a normal, benign, noninvasive and invasive carcinoma. Clustering analysis revealed four distinct expression patterns based on upregulation or downregulation patterns. These profiles proved quite useful for describing breast cancer tumorigenesis and invasiveness. Downregulation of TNFSF7, S100A4, S100A7, S100A8, and S100A9 (calcium-binding protein family), and upregulation of kallikrein-5 and thrombospondin-1 were associated with transformation and progression of breast cancer cells. Importantly, downregulation of the genes was reversed by treatment with silencing inhibitors, implying the potential roles of epigenetic inactivation in breast carcinogenesis. Exogenous expressions of S100A8 and S100A9 inhibit growth in benign and noninvasive carcinoma cells, suggesting their negative role in cell proliferation. The data presented here may facilitate the identification and functional analyses of prognostic biomarkers for breast cancer.

Stimulation of iNOS expression and apoptosis resistance in B-cell chronic lymphocytic leukemia (B-CLL) cells through engagement of Toll-like receptor 7 (TLR-7) and NF-kappaB activation

B-CLL cells are characterized by in vivo resistance to apoptosis due, in part, to the presence of an inducible nitric oxide synthase, iNOS, as the NO released plays anti-apoptotic role, notably by inhibiting caspases. The mechanisms leading to spontaneous expression of iNOS in these cells are presently unknown. The restricted use of some V(H) sub-groups and the sequences of the monoclonal immunoglobulins of the B-cell receptor expressed by the leukemia cells suggested that the latter have encountered specific auto-antigens and/or microbial derived antigens. Their binding to the BCR provides an activation signal resulting in enhanced survival, hence could be involved in the aetiology of the disease. At the interface of innate and cognate immunity, Toll-like receptors, TLR, recognize PAMPs (pathogen-associated molecular patterns) expressed by various bacteria and virus as well as some self-antigens. We thus hypothesized that TLR were involved in the early steps of B-CLL oncogenesis, notably apoptosis resistance through the induction of iNOS expression and the production of NO. Our results show that B-CLL cells express TLR-7 and TLR-9. Incubation of B-CLL cells with TLR-7 agonists effectively resulted in an increased resistance to apoptosis that was reverted with the NOS inhibitor L-NMMA. This resistance was associated with enhanced iNOS expression (protein and mRNA) and NO release, stimulation of NF-kappaB activation, phosphorylation of I kappaB alpha, all these events being suppressed with wedelolactone or Bay 11-7085, two inhibitors of I kappaB alpha phosphorylation. Our present data thus suggest that TLR-7 signaling stimulates apoptosis resistance, notably through an NF-kappaB-dependent activation of the NO pathway.

Molecular mechanisms for discrete nitric oxide levels in cancer

Nitric oxide (NO) has been invoked in nearly every normal and pathological condition associated with human physiology. In tumor biology, nitrogen oxides have both positive and negative affects as they have been implicated in both promoting and preventing cancer. Our work has focused on NO chemistry and how it correlates with cytotoxicity and cancer. Toward this end, we have studied both concentration- and time-dependent NO regulation of specific signaling pathways in response to defined nitrosative stress levels that may occur within the tumor microenvironment. Threshold levels of NO required for activation and stabilization of key proteins involved in carcinogenesis including p53, ERK, Akt and HIF have been identified. Importantly, threshold NO levels are further influenced by reactive oxygen species (ROS) including superoxide, which can shift or attenuate NO-mediated signaling as observed in both tumor and endothelial cells. Our studies have been extended to determine levels of NO that are critical during angiogenic response through regulation of the anti-angiogenic agent thrombospondin-1 (TSP-1) and pro-angiogenic agent matrix metalloproteinase-9 (MMP-9). The quantification of redox events at the cellular level has revealed potential mechanisms that may either limit or potentiate tumor growth, and helped define the positive and negative function of nitric oxide in cancer.

Thrombospondins in cancer

The thrombospondins (TSPs) are a family of five proteins that are involved in the tissue remodeling that is associated with embryonic development, wound healing, synaptogenesis, and neoplasia. These proteins mediate the interaction of normal and neoplastic cells with the extracellular matrix and surrounding tissue. In the tumor microenvironment, TSP-1 has been shown to suppress tumor growth by inhibiting angiogenesis and by activating transforming growth factor beta. TSP-1 inhibits angiogenesis through direct effects on endothelial cell migration and survival, and through effects on vascular endothelial cell growth factor bioavailability. In addition, TSP-1 may affect tumor cell function through interaction with cell surface receptors and regulation of extracellular proteases. Whereas the role of TSP-1 in the tumor microenvironment is the best characterized, the other TSPs may have similar functions. (Part of a Multi-author Review).

Thrombospondin-1 Activates Medial Smooth Muscle Cells and Triggers Neointima Formation Upon Mouse Carotid Artery Ligation

OBJECTIVE

Thrombospondin-1 (TSP1) is described as a positive regulator of vascular smooth muscle growth in cell culture. However, insight into the in vivo effects of TSP1 on smooth muscle cell (SMC) function is lacking.

METHODS AND RESULTS

We analyzed wild-type (WT) and TSP1-deficient (Tsp1-/-) mice in a carotid artery ligation model, in which neointimal lesions form without overt mechanical damage to the endothelium. On ligation, the expression of TSP1 increased strongly in the matrix of neointima and adventitia. In the early phase after ligation (day 3 to 7), activation, proliferation, and migration of medial SMCs were delayed and impaired in Tsp1-/- mice, in parallel with defective upregulation of metalloproteinase (MMP)-2 activity. As a result, Tsp1-/- arteries developed smaller neointimal lesions, a thicker media but comparably attenuated patency as in WT arteries, 28 days after ligation. Furthermore, medial and neointimal SMCs in Tsp1-/- mice produced more collagen, more osteopontin, and displayed weaker smooth muscle actin staining than WT SMCs, indicative of a modified SMC phenotype in Tsp1-/- mice.

CONCLUSIONS

Arterial SMC activation in the absence of TSP1 is delayed and dysregulated, reducing neointima formation, on mild vascular injury.

Thrombospondin-based antiangiogenic therapy

Thrombospondins (TSPs) are a family of extracellular matrix proteins that regulate tissue genesis and remodeling. TSP-1 plays a pivotal role in the regulation of both physiological and pathological angiogenesis. The inhibitory effects of TSP-1 on angiogenesis have been established in numerous experimental models. Among other TSP members, TSP-2 has equivalent domain structure as TSP-1 and shares most functions of TSP-1. The mechanisms by which TSP-1 and -2 inhibit angiogenesis can be broadly characterized as direct effects on vascular endothelial cells and indirect effects on the various angiogenic regulators. The fact that TSP-1 and -2 are potent endogenous angiogenic inhibitors has prompted studies to explore their therapeutic applications, and detailed understanding of the mechanisms of action of TSP-1 and -2 has facilitated the design of therapeutic strategies to optimize these activities. The therapeutic effects can be achieved by up-regulation of endogenous TSPs, or by the delivery of recombinant proteins or synthetic peptides that contain sequences from the angiogenic domain of TSP-1. In this article, we review the progress in thrombospondin-based antiangiogenic therapy and discuss the perspectives on the significant challenges that remain.