Regulation of aminopeptidase A in human brain tumor vasculature: evidence for a role of transforming growth factor-beta

Current Strategies to Enhance Delivery of Drugs across the Blood–Brain Barrier

The blood–brain barrier (BBB) has shown to be a significant obstacle to brain medication delivery. The BBB in a healthy brain is a diffusion barrier that prevents most substances from passing from the blood to the brain; only tiny molecules can pass across the BBB. The BBB is disturbed in specific pathological illnesses such as stroke, diabetes, seizures, multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease. The goal of this study is to offer a general overview of current brain medication delivery techniques and associated topics from the last five years. It is anticipated that this review will stimulate readers to look into new ways to deliver medications to the brain. Following an introduction of the construction and function of the BBB in both healthy and pathological conditions, this review revisits certain contested questions, such as whether nanoparticles may cross the BBB on their own and if medications are selectively delivered to the brain by deliberately targeted nanoparticles. Current non-nanoparticle options are also discussed, including drug delivery via the permeable BBB under pathological circumstances and the use of non-invasive approaches to improve brain medication absorption.

Sex differences exist in brain renin-angiotensin system-regulating aminopeptidase activities in transplacental ethyl-nitrosourea-induced gliomas

INTRODUCTION

The renin angiotensin system (RAS) is emerging as an important target for the treatment of glioma. We had described that the local RAS is involved in vivo in tumor growth in the rat model of experimental C6 glioma implanted at the subcutaneous region, through the modification of several proteolytic regulatory enzymes of aminopeptidase type.

METHODS

We analyze RAS-regulating aminopeptidase activities in plasma and brain tissue of control male and female rats and rats with transplacental ethylnitrosourea-induced gliomas.

RESULTS

No differences were found either the mean total number of tumors per animal or the tumor volume between male and female animals. However, we have found increased levels in aspartyl aminopeptidase in both males and females and of aminopeptidase B only in males. On the contrary, decreased levels were found in aminopeptidase N and insulin-regulated aminopeptidase activities in both males and females, whereas aminopeptidase A only decreased in females. Decreased levels of aminopeptidase N, aminopeptidase B and insulin-regulated aminopeptidase were also shown in plasma of only female rats.

CONCLUSIONS

Under the complexity of RAS cascade, the changes found suggest the predominant actions of angiotensin III against a decreased action of angiotensin II and angiotensin IV. We conclude that angiotensin peptides are involved in tumor growth in this rat model of glioma and that their role in tumor growth can be analyzed through their corresponding proteolytic regulatory enzymes, which make them new and attractive therapeutic targets beyond the use or angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs).

Differential Effects of the Mitochondria-Active Tetrapeptide SS-31 (D-Arg-dimethylTyr-Lys-Phe-NH2) and Its Peptidase-Targeted Prodrugs in Experimental Acute Kidney Injury

The mitochondria-active tetrapeptide SS-31 can control oxidative tissue damage in kidney diseases. To investigate other potential beneficial nephroprotective effects of SS-31, in vivo murine models of acute tubular injury and glomerular damage were developed. Reduction of acute kidney injury was demonstrated in mice treated with SS-31. The expression of mRNAs involved in acute inflammatory and oxidative stress responses in the diseased kidneys confirmed that SS-31 could regulate these pathways in our in vivo models. Furthermore, ex vivo histoenzymography of mouse kidneys showed that aminopeptidase A (APA), the enzyme involved in the processing of angiotensin (Ang) II to Ang III, was induced in the diseased kidneys, and its activity was inhibited by SS-31. As the renin–angiotensin system (RAS) is a main regulator of kidney functions, the modulation of Ang receptors (ATR) and APA by SS-31 was further investigated using mRNAs extracted from diseased kidneys. Following acute tubular and/or glomerular damage, the expression of the AT₁R mRNA was upregulated, which could be selectively downregulated upon SS-31 administration to the animals. At the same time, SS-31 was able to increase the expression of the AT₂R, which may contribute to limit renal damage. Consequently, SS-31-based prodrugs were developed as substrates and/or inhibitors for APA and were screened using cells expressing high levels of APA, showing its selective regulation by α-Glu-SS-31. Thus, a link between SS-31 and the RAS opens new therapeutic implications for SS-31 in kidney diseases.

Differential Effects of Doxazosin on Renin-Angiotensin-System- Regulating Aminopeptidase Activities in Neuroblastoma and Glioma Tumoral Cells

Background:

It has been described that doxazosin, an antihypertensive drug, also promotes glioblastoma cells death by inhibiting cell proliferation, arresting cell cycle and inducing apoptosis. Doxazosin has also demonstrated several modulator effects on renin-angiotensin system (RAS)- regulating aminopeptidase activities, which are highly involved in tumor growth in experimental glioma. Therefore, it remains to elucidate if the anti-tumoral effects of doxazosin could also be mediated by the proteolytic regulatory components of the RAS.

Objective:

To analyze the effects of doxazosin on cell growth and on RAS-regulating proteolytic regulatory aspartyl aminopeptidase (ASAP), aminopeptidase A (APA), aminopeptidase N (APN), aminopeptidase B (APB) and insulin-regulated aminopeptidase (IRAP) specific activities in the human neuroblastoma NB69 and astroglioma U373-MG tumoral cell lines.

Methods:

Human neuroblastoma NB69 and astroglioma U373-MG cell lines were treated with doxazosin 50-500 μM for 24h or 48h. The effects on cell growth and on RAS-regulating aminopeptidase specific activities were analyzed.

Results:

Doxazosin treatments promote a concentration-dependent inhibition on cell growth in both NB69 and U373-MG cells, being NB69 cells more sensitive to the drug than U373-MG cells. However, its effects on RAS-regulating aminopeptidase specific activities depend on the concentration used, the duration of the treatment and the cell type. These data confirm the existence of a different dynamic progression of RAS cascade in each tumoral cell line as a consequence of the treatment with doxazosin and time of action, which also implies a very dynamic metabolism of the peptides which participate in each step of RAS cascade.

Conclusion:

Our results indicate that doxazosin modifies the proteolytic regulatory enzymes of RAS cascade, modulating the bioactive efficacy of the different angiotensin peptides, and therefore, of their functional roles as initiators/promoters of cell proliferation as autocrine/paracrine mediators.

Renin angiotensin system and its role in biomarkers and treatment in gliomas

Gliomas are the most common primary intrinsic tumor in the brain and are classified as low- or high-grade according to the World Health Organization (WHO). Patients with high-grade gliomas (HGG) who undergo surgical resection with adjuvant therapy have a mean overall survival of 15 months and 100% recurrence. The renin-angiotensin system (RAS), the primary regulator of cardiovascular circulation, exhibits local action and works as a paracrine system. In the context of this local regulation, the expression of RAS peptides and receptors has been detected in different kinds of tumors, including gliomas. The dysregulation of RAS components plays a significant role in the proliferation, angiogenesis, and invasion of these tumors, and therefore in their outcomes. The study and potential application of RAS peptides and receptors as biomarkers in gliomas could bring advantages against the limitations of current tumoral markers and should be considered in the future. The targeting of RAS components by RAS blockers has shown potential of being protective against cancer and improving immunotherapy. In gliomas, RAS blockers have shown a broad spectrum for beneficial effects and are being considered for use in treatment protocols. This review aims to summarize the background behind how RAS plays a role in gliomagenesis and explore the evidence that could lead to their use as biomarkers and treatment adjuvants.

Anti-Inflammatory and Antitumor Effects of Hydroxytyrosol but Not Oleuropein on Experimental Glioma In Vivo. A Putative Role for the Renin-Angiotensin System

Functional roles of the angiotensin peptides of the renin-angiotensin system (RAS) cascade can be analyzed through their corresponding proteolytic regulatory enzymes aspartyl aminopeptidase (ASAP), aminopeptidase A (APA), aminopeptidase B (APB), aminopeptidase N (APN) and insulin-regulated aminopeptidase (IRAP). These enzyme activities generate active or inactive angiotensin peptides that alter the ratios between their bioactive forms, regulating several important processes such as the regulation of cardiovascular functions, body water regulation, normal memory consolidation and retrieval, but also cell growth, differentiation and apoptosis or the inflammatory response. We have previously described that the treatment with hydroxytyrosol but not with oleuropein or with the mixture of both compounds led to the significant inhibition of tumor growth in an in vivo glioma model by mechanisms not only related to redox balance. Using this glioma model, here we analyze the effects of the phenolic compounds oleuropein and hydroxytyrosol in circulating RAS-regulating ASAP, APA, APN, APB and IRAP specific activities and the pro-inflammatory cytokines IL-6 and TNFα to understand the relationship between the antitumor and anti-inflammatory effects of hydroxytyrosol, but not oleuropein, and the components of the RAS. We found that oleuropein increased all the activities analyzed and promoted a pro-inflammatory status, whereas hydroxytyrosol only modified ASAP and IRAP activities and promotes an anti-inflammatory status. When administrated together, oleuropein overrode the effects of hydroxytyrosol. Our results suggest a role for angiotensin III and angiotensin 1-7 in both tumor growth inhibition and anti-inflammatory response promoted by hydroxytyrosol.

Structural and theoretical studies on rhodium and iridium complexes with 5-nitrosopyrimidines. Effects on the proteolytic regulatory enzymes of the renin-angiotensin system in human tumoral brain cells

The reactions of [RhCl(CO)(PPh3)2], [RhCl(CO)2]2 and [IrCl(CO)(PPh3)2] with different 5-nitrosopyrimidines afforded sixteen complexes which have been structurally characterized by elemental analysis, IR and NMR ((1)H and (13)C) spectral methods and luminescence spectroscopy. The crystal and molecular structures of [Rh(III)Cl(VIOH-1)2(PPh3)], [Rh(III)Cl(DVIOH-1)2(PPh3)] and [Rh(II)(DVIOH-1)2(PPh3)2] have been established from single crystal x-ray structure analyses. The three complexes are six-coordinated with both violurato ligands into an equatorial N5,O4-bidentate fashion, but with different mutually arrangements. Theoretical studies were driven on the molecular structure of [Rh(III)Cl(VIOH-1)2(PPh3)] to assess the nature of the metal-ligand interaction as well as the foundations of the cis-trans (3L-2L) isomerism. An assortment of density functional (SOGGA11-X, B1LYP, B3LYP, B3LYP-D3 and wB97XD) has been used, all of them leading to a similar description of the target system. Thus, a topological analysis of the electronic density within AIM scheme and the study of the Mulliken charges yield a metal-ligand link of ionic character. Likewise, it has been proved that the cis-trans isomerism is mainly founded on that metal-ligand interaction with the relativistic effects playing a significant role. Although most of the compounds showed low direct toxicity against the human cell lines NB69 (neuroblastoma) and U373-MG (astroglioma), they differently modify in several ways the renin-angiotensin system (RAS)-regulating proteolytic regulatory enzymes aminopeptidase A (APA), aminopeptidase N (APN) and insulin-regulated aminopeptidase (IRAP). Therefore, these complexes could exert antitumor activity against both brain tumor types, acting through the paracrine regulating system mediated by tissue RAS rather than exerting a direct cytotoxic effect on tumor cells.

Computational tools for the interactive exploration of proteomic and structural data

Linking proteomics and structural data is critical to our understanding of cellular processes, and interactive exploration of these complementary data sets can be extremely valuable for developing or confirming hypotheses in silico. However, few computational tools facilitate linking these types of data interactively. In addition, the tools that do exist are neither well understood nor widely used by the proteomics or structural biology communities. We briefly describe several relevant tools, and then, using three scenarios, we present in depth two tools for the integrated exploration of proteomics and structural data.

The targeted delivery of cancer drugs across the blood-brain barrier: chemical modifications of drugs or drug-nanoparticles?

One of the most challenging problems, if not the most challenging, in drug development is not to develop drugs to treat diseases of the central nervous system (CNS), but to manage to distribute them to the CNS across the blood-brain barrier (BBB) using transvascular routes following intravenous administration. The development of BBB targeting technologies is a very active field of research and development. One goal is to develop chemically modified derivatives of drugs or chemically modified nanoparticulate vectors of drugs, capable of crossing biological barriers, in particular the BBB. This manuscript will review the approaches that have been explored to achieve these goals, using chemical functionalization of drugs or of drug vector systems and endogenous transporters at the BBB.

Derivatives of 5-Aminolevulinic Acid for Photodynamic Therapy

Photodynamic therapy (PDT) is a clinical treatment that combines the effects of visible light irradiation with subsequent biochemical events that arise from the presence of a photosensitising drug (possessing no dark toxicity) to cause destruction of selected cells. Today, the most common agent used in dermatological PDT is 5-aminolevulinic acid (ALA). As a result of its hydrophilic character, ALA penetrates skin lesions poorly when applied topically. Its systemic bioavailability is limited and it is known to cause significant side effects when given orally or intravenously. Numerous chemical derivatives of ALA have been synthesised with the aims of either improving topical penetration or enhancing systemic bioavailability, while reducing side effects. In vitro cell culture experiments with ALA derivatives have yielded promising results. However, if ALA derivatives are to demonstrate meaningful clinical benefits, a rational approach to topical formulation design is required, along with a systematic study aimed at uncovering the true potential of ALA derivatives in photodynamic therapy. With respect to systemic ALA delivery, more study is required in the developing area of ALA-containing dendrons and dendrimers.

Chemical modification of therapeutic drugs or drug vector systems to achieve targeted therapy: looking for the grail

Most therapeutic drugs distribute to the whole body, which results in general toxicity and poor acceptance of the treatments by patients. The targeted delivery of chemotherapeutics to defined cells, either stromal or cancer cells in cancer lesions, or defined inflammatory cells in immunological disorders, is one of the main challenges and a very active field of research in the development of treatment strategies to minimize side-effects of drugs. Disease-associated cells express molecules, including proteases, receptors, or adhesion molecules, that are different or differently expressed than their normal counterparts. Therefore one goal in the field of targeted therapies is to develop chemically derivatized drugs or drug vectors able to target defined cells via specific recognition mechanisms and also able to overcome biological barriers. This article will review the approaches which have been explored to achieve these goals and will discuss in more detail three examples (i) the use of nanostructures to take advantage of increased vascular permeability in some human diseases, (ii) the targeting of therapeutic drugs to an organ, the brain, protected against foreign molecules by the blood-brain barrier, and (iii) the use of the folate receptor to target either tumor cells or activated macrophages.

Manipulating the angiotensin system--new approaches to the treatment of solid tumours

Angiotensin II (Ang II), a main effector peptide in the renin-angiotensin system (RAS), plays a fundamental role as a vasoconstrictor in controlling cardiovascular function and renal homeostasis. Ang II also acts as a growth promoter or angiogenic factor via type 1 angiotensin II receptors (AT1Rs) in certain tumour cell lines. Recent studies have shown the activation of the local RAS in various tumour tissues, including the abundant generation of Ang II by angiotensin-converting enzyme (ACE) and the upregulation of AT1R expression. Thus, considerable attention has been paid to the role of the RAS in cancer and its blockade as a new approach to the treatment of cancer. There is increasing evidence that the Ang II-AT1R system is involved in tumour growth, angiogenesis and metastasis in experimental models, suggesting the therapeutic potential of an ACE inhibitor and AT1R blocker, both of which have been used as antihypertensive drugs. In addition, specific Ang II-degrading enzymes are expressed in tumours and play a regulatory role in cell proliferation and invasion. This review focuses on the role of the Ang II-AT1R system in solid tumours, particularly in the progression of gynaecological cancer, and presents the clinical potential of manipulating the angiotensin system as a novel and promising strategy for cancer treatment.

5-Aminolevulinic Acid Derivatives in Photomedicine: Characteristics, Application and Perspectives

The introduction of lipophilic derivatives of the naturally occurring heme precursor 5-aminolevulinic acid (5-ALA) into photomedicine has led to a true revival of this research area. 5-ALA-mediated photodynamic therapy (PDT) and fluorescence photodetection (FD) of neoplastic disease is probably one of the most selective cancer treatments currently known in oncology. To date, this method has been assessed experimentally for the treatment of various medical indications. However, the limited local bioavailability of 5-ALA has widely prevented its use in daily clinical practice. Although researchers were already aware of this drawback early during the development of 5-ALA-mediated PDT, only recently have well-established concepts in pharmaceutical science been adapted to investigate ways to overcome this drawback. Recently, two derivatives of 5-ALA, methylaminolevulinate (MAL) and hexylaminolevulinate (HAL), gained marketing authorization from the regulatory offices in Europe and Australia. MAL is marketed under the trade name Metvix for the treatment of actinic keratosis and difficult-to-treat basal cell carcinoma. HAL has recently been launched under the trade name Hexvix to improve the detection of superficial bladder cancer in Europe. This review will first present the fundamental concepts underlying the use of 5-ALA derivatives in PDT and FD from a chemical, biochemical and pharmaceutical point of view. Experimental evidences from preclinical data on the improvements and limits observed with 5-ALA derivatives will then be introduced. The state-of-the-art from clinical studies with 5-ALA esters will be discussed, with special emphasis placed on the process that led to the development of MAL in dermatology and to HAL in urology. Finally, we will discuss promising medical fields in which use of 5-ALA derivatives might potentially lead to further use of this methodology in photomedicine.

Endothelin-Converting Enzyme-1 Inhibition and Growth of Human Glioblastoma Cells

Endothelin-1 (ET-1) is mitogenic and/or antiapoptotic in human cancers, and antagonists to ET-1 receptors are under evaluation for cancer treatment. Inhibition of ET-1 activation by the endothelin-converting enzymes 1(a)(-)(d) (ECE-1(a)(-)(d); EC 3.4.24.71) represents another approach to block the ET-1 effect in cancer. To evaluate this potential, we synthesized and characterized a series of low nanomolar nonpeptidic thiol-containing ECE-1 inhibitors, and evaluated their effect, as well as the effect of inhibitors for the related metalloproteases neprilysin (NEP; EC 3.4.24.11) and angiotensin-converting enzyme (ACE; EC 3.4.15.1), on human glioblastoma cell growth. Only ECE-1 inhibitors inhibited DNA synthesis by human glioblastoma cells. Exogenous addition of ET-1 or bigET-1 to glioblastoma cells did not counterbalance the growth inhibition elicited by ECE-1 inhibitors, suggesting that ECE-1 inhibitors block the proliferation of human glioblastoma cells most likely via a mechanism not involving extracellular production of ET-1. This class of molecules may thus represent novel therapeutic agents for the potential treatment of human cancer.

Regulation of aminopeptidase A expression in cervical carcinoma: role of tumor-stromal interaction and vascular endothelial growth factor

We previously demonstrated that aminopeptidase A (APA), a membrane-bound metallopeptidase degrading bioactive peptides such as angiotensin II (Ang II), is expressed in neoplastic lesions of the uterine cervix, and that its expression is upregulated as the lesion progresses from cervical intraepithelial neoplasms (CIN) toward invasive squamous cell carcinomas (SCC). The present study investigated the regulatory mechanisms involved in APA expression and its potential role in cervical carcinoma. Immunohistochemical staining in high-grade CIN and SCC tissues showed that APA was strongly expressed at the edge of lesions adjacent to cervical stromal cells. Fluorescence-activated cell sorting analysis demonstrated that cell surface APA expression was extremely low in three human SCC cell lines, SiHa, TCS and CaSki, under basal conditions. However, both contact and noncontact cocultures with human cervical fibroblasts resulted in the induction of APA expression in these SCC cells. APA expression was also induced in vivo when TCS cells were subcutaneously inoculated into nude mice. Furthermore, APA expression and enzymatic activity were enhanced by addition of the conditioned medium (CM) from fibroblast culture, but not by heat-treated CM. Among the various cytokines tested, vascular endothelial growth factor (VEGF) significantly increased APA activity, and induction of APA by the fibroblast CM was partly inhibited by anti-VEGF neutralizing antibody. Finally, APA cDNA-transfected APA-overexpressing TCS cells significantly reduced the Ang II-induced cell invasion ability as compared with parental or control vector-transfected TCS cells, although there was no significant difference in cellular proliferation among them. These results suggested the importance of tumor-stromal interaction for the regulation of APA expression in the microenvironment of cervical carcinoma and the potential role for this peptidase in regulating tumor invasion through inactivation of Ang II activity.

Renin and angiotensinogen expression and functions in growth and apoptosis of human glioblastoma

The expression and function in growth and apoptosis of the renin-angiotensin system (RAS) was evaluated in human glioblastoma. Renin and angiotensinogen (AGT) mRNAs and proteins were found by in situ hybridisation and immunohistochemistry in glioblastoma cells. Angiotensinogen was present in glioblastoma cystic fluids. Thus, human glioblastoma cells produce renin and AGT and secrete AGT. Human glioblastoma and glioblastoma cells expressed renin, AGT, renin receptor, AT(2) and/or AT(1) mRNAs and proteins determined by RT-PCR and/or Western blotting, respectively. The function of the RAS in glioblastoma was studied using human glioblastoma cells in culture. Angiotensinogen, des(Ang I)AGT, tetradecapaptide renin substrate (AGT1-14), Ang I, Ang II or Ang III, added to glioblastoma cells in culture, did not modulate their proliferation, survival or death. Angiotensin-converting enzyme inhibitors did not diminish glioblastoma cell proliferation. However, the addition of selective synthetic renin inhibitors to glioblastoma cells decreased DNA synthesis and viable tumour cell number, and induced apoptosis. This effect was not counterbalanced by concomitant addition of Ang II. In conclusion, the complete RAS is expressed by human glioblastomas and glioblastoma cells in culture. Inhibition of renin in glioblastoma cells may be a potential approach to control glioblastoma cell proliferation and survival, and glioblastoma progression in combination therapy.

Ethylene glycol and amino acid derivatives of 5-aminolevulinic acid as new photosensitizing precursors of protoporphyrin IX in cells

Protoporphyrin IX (PpIX) is used as a photosensitizing agent in photodynamic detection and therapy (PDT) of cancer and is synthesized intracellularly from aminolevulinic acid (ALA) precursors. To evaluate means to specifically target ALA derivatives to defined cells, we have synthesized and characterized ethylene glycol esters and amino acid pseudodipeptide derivatives of ALA as potential specific substrates for cellular esterases and aminopeptidases, respectively. The PpIX formation induced by these products was investigated using cultures of human and rat cell lines of carcinoma and endothelial origins. The cytotoxicity of these compounds in the absence of light was also controlled. The results have shown that ethylenglycol esters can induce high levels of PpIX and are useful at concentrations below their cytotoxicity threshold. From the ALA-amino acid derivatives which were evaluated, the highest PpIX production was obtained using ALA derivatives of neutral amino acids, as compared to acidic or basic amino acids.