Small molecule inhibition of DDAH1 significantly attenuates triple negative breast cancer cell vasculogenic mimicry in vitro

Recent advances in DDAH1 inhibitor design and discovery: insights from structure-activity relationships and X-ray crystal structures

Nitric oxide (NO) is an important signalling molecule which modulates several biological and pathological processes. Dimethylarginine dimethylaminohydrolase 1 (DDAH1) plays a key role indirectly regulating NO concentrations in the body. It has been shown that DDAH1 inhibition may be an effective therapeutic strategy in certain pathological states in which excessive NO is produced. In recent years, specific DDAH1 inhibitors have shown promise in suppressing abnormal neovascularization in cancer. However, the available DDAH1 inhibitors lack potency and selectivity and are mostly arginine-based. Further, these inhibitors display unfavourable pharmacokinetics and have not been tested in humans. Thus, the development of potent, selective, and chemically diverse DDAH1 inhibitors is essential. In this review, we examine the structure activity relationships (SARs) and X-ray crystal structures of known DDAH1 inhibitors. Then, we discuss current challenges in the design and development of novel DDAH1 inhibitors and provide future directions for developing potent and chemically diverse compounds.

Development of a HPLC-MS/MS Method to Assess the Pharmacokinetics and Tumour Distribution of the Dimethylarginine Dimethylaminohydrolase 1 Inhibitors ZST316 and L-257 in a Xenograft Model of Triple-Negative Breast Cancer in Mice

We describe the development and validation of an HPLC-MS/MS method to assess the pharmacokinetics and tumour distribution of ZST316, an arginine analogue with inhibitory activity towards dimethylarginine dimethylaminohydrolase 1 (DDAH1) and vasculogenic mimicry, and its active metabolite L-257 in a xenograft model of triple-negative breast cancer (TNBC). The method proved to be reproducible, precise, and highly accurate for the measurement of both compounds in plasma and tumour tissue following acute and chronic (five days) intraperitoneal administration of ZST316 (30 mg/Kg daily) in six-week-old severe combined immunodeficiency disease (SCID) mice inoculated with MDA-MB-231 TNBC cells. ZST316 was detected in tumour tissue and plasma after 1 h (6.47 and 9.01 μM, respectively) and 24 h (0.13 and 0.16 μM, respectively) following acute administration, without accumulation during chronic treatment. Similarly, the metabolite L-257 was found in tumour tissue and plasma after 1 h (15.06 and 8.72 μM, respectively) and 24 h (0.17 and 0.17 μM, respectively) following acute administration of ZST316, without accumulation during chronic treatment. The half-life after acute and chronic treatment ranged between 4.4-7.1 h (plasma) and 4.5-5.0 h (tumour) for ZST316, and 4.2-5.3 h (plasma) and 3.6-4.9 h (tumour) for L-257. The results of our study demonstrate the (a) capacity to accurately measure ZST316 and L-257 concentrations in plasma and tumour tissue in mice using the newly developed HPLC-MS/MS method, (b) rapid conversion of ZST316 into L-257, (c) good intra-tumour penetration of both compounds, and (d) lack of accumulation of both ZST316 and L-257 in plasma and tumour tissue during chronic administration. Compared to a previous method developed by our group to investigate ZST316 in plasma, the main advantages of the new method include a wider range of linearity which reduces the need for dilutions and the combined assessment of ZST316 and L-257 in plasma and tumour tissue which limits the required amount of matrix. The new HPLC-MS/MS method is useful to investigate the in vivo effects of ZST316 and L-257 on vasculogenic mimicry, tumour mass, and metastatic burden in xenograft models of TNBC.

MicroRNA-1289 Functions as a Novel Tumor Suppressor in Oral Squamous Cell Carcinoma

Recently, numerous tumor-suppressive microRNAs (TS-miRs) have been identified in human malignancies. Here, we attempted to identify novel TS-miRs in oral squamous cell carcinoma (OSCC). First, we transfected human OSCC cells individually with 968 synthetic miRs mimicking human mature miRs individually, and the growth of these cells was evaluated using the WST-8 assay. Five miR mimics significantly reduced the cell growth rate by less than 30%, and the miR-1289 mimic had the most potent growth inhibitory effect among these miRs. Subsequently, we assessed the in vivo growth-inhibitory effects of miR-1289 using a mouse model. The administration of the miR-1289 mimic-atelocollagen complex significantly reduced the size of subcutaneously xenografted human OSCC tumors. Next, we investigated the expression of miR-1289 in OSCC tissues using reverse transcription-quantitative PCR. The expression level of miR-1289 was significantly lower in OSCC tissues than in the adjacent normal oral mucosa. Furthermore, 15 genes were identified as target genes of miR-1289 via microarray and Ingenuity Pathway Analysis (IPA) microRNA target filtering. Among these genes, the knockdown of magnesium transporter 1 (MAGT1) resulted in the most remarkable cell growth inhibition in human OSCC cells. These results suggested that miR-1289 functions as a novel TS-miR in OSCC and may be a useful therapeutic tool for patients with OSCC.

The Biomarker Like the Correlation between Vasculogenic Mimicry, Vascular Endothelial Cadherin, Sex-DeterminingRegion on Y-Box Transcription Factor 17, and Cyclin D1 in Oesophageal Squamous Cell Carcinoma

Background

This study aimed to explore the relationships between the sex-determining region on Y (SRY) box transcription factor 17 (SOX17), Cyclin D1, vascular endothelial cadherin (VE-cadherin), and vasculogenic mimicry (VM) in the occurrence and development of esophageal squamous cell carcinoma (ESCC).

Methods

The expressions of SOX17, Cyclin D1, and VE-cadherin, as well as VM, in tissues, were determined using immunohistochemistry. SOX17, Cyclin D1, and VE-cadherin mRNA in ESCC and their corresponding adjacent normal tissues were quantified using quantitative reverse transcription polymerase chain reaction analysis. Cell invasion, migration, and proliferation were determined after the silencing of VE-cadherin. SOX17, Cyclin D1, and VE-cadherin protein were quantified using Western blotting.

Results

The expression levels of SOX17, Cyclin D1, and VE-cadherin significantly correlated with the clinical characteristics of ESCC. After the VE-cadherin silencing, cell invasion, migration, and proliferation decreased, along with the Cyclin D1 levels, while the SOX17 levels increased.

Conclusion

SOX17, Cyclin D1, and VE-cadherin are involved in the development of ESCC.

On the kinetic mechanism of dimethylarginine dimethylaminohydrolase

Dimethylarginine dimethylaminohydrolase (DDAH, EC 3.5.3.18) catalyzes the hydrolysis of asymmetric N^ω,N^ω-dimethyl-l-arginine (ADMA), an endogenous inhibitor of human nitric oxide synthases. The active-site cysteine residue has been proposed to serve as the catalytic nucleophile, forming an S-alkylthiourea reaction intermediate, and serving as a target for covalent inhibitors. Inhibition can lead to ADMA accumulation and downstream inhibition of nitric oxide production. Prior studies have provided experimental evidence for formation of this covalent adduct but have not characterized it kinetically. Here, rapid quench-flow is used with ADMA and the DDAH from Pseudomonas aeruginosa to determine the rate constants for formation (k₂ = 17 ± 2 s^-1) and decay (k₃ = 1.5 ± 0.1 s^-1) of the covalent S-alkylthiourea adduct. A minimal kinetic mechanism for DDAH is proposed that supports the kinetic competence of this species as a covalent reaction intermediate and assigns the rate-limiting step in substrate turnover as hydrolysis of this intermediate. This work helps elucidate the different reactivities of S-alkylthiourea intermediates found among the mechanistically diverse pentein superfamily of guanidine-modifying enzymes and provides information useful for inhibitor development.

3D Collagen Fiber Concentration Regulates Treg Cell Infiltration in Triple Negative Breast Cancer

Background

Triple negative breast cancer (TNBC) is characterized by poor prognosis and a lack of effective therapeutic agents owing to the absence of biomarkers. A high abundance of tumor-infiltrating regulatory T cells (Tregs) was associated with worse prognosis in malignant disease. Exploring the association between Treg cell infiltration and TNBC will provide new insights for understanding TNBC immunosuppression and may pave the way for developing novel immune-based treatments.

Materials and Methods

Patients from TCGA were divided into Treg-high (Treg-H) and Treg-low (Treg-L) groups based on the abundance of Tregs according to CIBERSORT analysis. The association between expression level of Tregs and the clinical characteristics as well as prognosis of breast cancer were evaluated. Next, a Treg-related prognostic model was established after survival-dependent univariate Cox and LASSO regression analysis, companied with an external GEO cohort validation. Then, GO, KEGG and GSEA analyses were performed between the Treg-H and Treg-L groups. Masson and Sirius red/Fast Green staining were applied for ECM characterization. Accordingly, Jurkat T cells were encapsulated in 3D collagen to mimic the ECM microenvironment, and the expression levels of CD4, FOXP3 and CD25 were quantified according to immunofluorescence staining.

Results

The expression level of Tregs is significantly associated with the clinical characteristics of breast cancer patients, and a high level of Treg cell expression indicates a poor prognosis in TNBC. To further evaluate this, a Treg-related prognostic model was established that accurately predicted outcomes in both TCGA training and GEO validation cohorts of TNBC patients. Subsequently, ECM-associated signaling pathways were identified between the Treg-H and Treg-L groups, indicating the role of ECM in Treg infiltration. Since we found increasing collagen concentrations in TNBC patients with distant migration, we encapsulated Jurkat T cells within a 3D matrix with different collagen concentrations and observed that increasing collagen concentrations promoted the expression of Treg biomarkers, supporting the regulatory role of ECM in Treg infiltration.

Conclusion

Our results support the association between Treg expression and breast cancer progression as well as prognosis in the TNBC subtype. Moreover, increasing collagen density may promote Treg infiltration, and thus induce an immunosuppressed TME.

The Potential Role of Exosomal Proteins in Prostate Cancer

Prostate cancer is the most prevalent malignant tumor in men across developed countries. Traditional diagnostic and therapeutic methods for this tumor have become increasingly difficult to adapt to today’s medical philosophy, thus compromising early detection, diagnosis, and treatment. Prospecting for new diagnostic markers and therapeutic targets has become a hot topic in today’s research. Notably, exosomes, small vesicles characterized by a phospholipid bilayer structure released by cells that is capable of delivering different types of cargo that target specific cells to regulate biological properties, have been extensively studied. Exosomes composition, coupled with their interactions with cells make them multifaceted regulators in cancer development. Numerous studies have described the role of prostate cancer-derived exosomal proteins in diagnosis and treatment of prostate cancer. However, so far, there is no relevant literature to systematically summarize its role in tumors, which brings obstacles to the later research of related proteins. In this review, we summarize exosomal proteins derived from prostate cancer from different sources and summarize their roles in tumor development and drug resistance.

Pharmacokinetic Characterization of the DDAH1 Inhibitors ZST316 and ZST152 in Mice Using a HPLC-MS/MS Method

The pharmacokinetic profile of ZST316 and ZST152, arginine analogues with inhibitory activity towards human dimethylarginine dimethylaminohydrolase-1 (DDAH1), was investigated in mice using a newly developed HPLC-MS/MS method. The method proved to be reproducible, precise, and accurate for the measurement of the compounds in plasma and urine. Four-week-old female FVB mice received a single dose of ZST316 and ZST152 by intravenous bolus (30 mg/Kg) and oral gavage (60 mg/Kg). ZST316 Cmax was 67.4 µg/mL (intravenous) and 1.02 µg/mL (oral), with a half-life of 6 h and bioavailability of 4.7%. ZST152 Cmax was 24.9 µg/mL (intravenous) and 1.65 µg/mL (oral), with a half-life of 1.2 h and bioavailability of 33.3%. Urinary excretion of ZST152 and ZST316 was 12.5%–22.2% and 2.3%–7.5%, respectively. At least eight urinary metabolites were identified. After chronic intraperitoneal treatment with the more potent DDAH1 inhibitor, ZST316 (30 mg/Kg/day for three weeks), the bioavailability was 59% and no accumulation was observed. Treatment was well tolerated with no changes in body weight vs. untreated animals and no clinical signs of toxicity or distress. The results of this study show that ZST316 has a favorable pharmacokinetic profile, following intraperitoneal administration, to investigate the effects of DDAH1 inhibition in mice.

Dissecting VEGF-induced acute versus chronic vascular hyperpermeability: Essential roles of dimethylarginine dimethylaminohydrolase-1

Vascular endothelial cell growth factor (VEGF) is a key regulator of vascular permeability. Herein we aim to understand how acute and chronic exposures of VEGF induce different levels of vascular permeability. We demonstrate that chronic VEGF exposure leads to decreased phosphorylation of VEGFR2 and c-Src as well as steady increases of nitric oxide (NO) as compared to that of acute exposure. Utilizing heat-inducible VEGF transgenic zebrafish (Danio rerio) and establishing an algorithm incorporating segmentation techniques for quantification, we monitored acute and chronic VEGF-induced vascular hyperpermeability in real time. Importantly, dimethylarginine dimethylaminohydrolase-1 (DDAH1), an enzyme essential for NO generation, was shown to play essential roles in both acute and chronic vascular permeability in cultured human cells, zebrafish model, and Miles assay. Taken together, our data reveal acute and chronic VEGF exposures induce divergent signaling pathways and identify DDAH1 as a critical player and potentially a therapeutic target of vascular hyperpermeability-mediated pathogenesis.

Alternative Vascularization Mechanisms in Tumor Resistance to Therapy

Simple Summary

Tumors rely on blood vessels to grow and metastasize. Malignant tumors can employ different strategies to create a functional vascular network. Tumor cells can use normal processes of vessel formation but can also employ cancer-specific mechanisms, by co-opting normal vessels present in tissues or by turning themselves into vascular cells. These different types of tumor vessels have specific molecular and functional characteristics that profoundly affect tumor behavior and response to therapies, including drugs targeting the tumor vasculature (antiangiogenic therapies). In this review, we discuss how vessels formed by different mechanisms affect the intrinsic sensitivity of tumors to therapy and, on the other hand, how therapies can affect tumor vessel formation, leading to resistance to drugs, cancer recurrence, and treatment failure. Potential strategies to avoid vessel-mediated resistance to antineoplastic therapies will be discussed.

Abstract

Blood vessels in tumors are formed through a variety of different mechanisms, each generating vessels with peculiar structural, molecular, and functional properties. This heterogeneity has a major impact on tumor response or resistance to antineoplastic therapies and is now emerging as a promising target for strategies to prevent drug resistance and improve the distribution and efficacy of antineoplastic treatments. This review presents evidence of how different mechanisms of tumor vessel formation (vasculogenesis, glomeruloid proliferation, intussusceptive angiogenesis, vasculogenic mimicry, and vessel co-option) affect tumor responses to antiangiogenic and antineoplastic therapies, but also how therapies can promote alternative mechanisms of vessel formation, contributing to tumor recurrence, malignant progression, and acquired drug resistance. We discuss the possibility of tailoring treatment strategies to overcome vasculature-mediated drug resistance or to improve drug distribution and efficacy.

SIO: A Spatioimageomics Pipeline to Identify Prognostic Biomarkers Associated with the Ovarian Tumor Microenvironment

Stromal and immune cells in the tumor microenvironment (TME) have been shown to directly affect high-grade serous ovarian cancer (HGSC) malignant phenotypes, however, how these cells interact to influence HGSC patients' survival remains largely unknown. To investigate the cell-cell communication in such a complex TME, we developed a SpatioImageOmics (SIO) pipeline that combines imaging mass cytometry (IMC), location-specific transcriptomics, and deep learning to identify the distribution of various stromal, tumor and immune cells as well as their spatial relationship in TME. The SIO pipeline automatically and accurately segments cells and extracts salient cellular features to identify biomarkers, and multiple nearest-neighbor interactions among tumor, immune, and stromal cells that coordinate to influence overall survival rates in HGSC patients. In addition, SIO integrates IMC data with microdissected tumor and stromal transcriptomes from the same patients to identify novel signaling networks, which would lead to the discovery of novel survival rate-modulating mechanisms in HGSC patients.

Circ_0004771 Accelerates Cell Carcinogenic Phenotypes via Suppressing miR-1253-Mediated DDAH1 Inhibition in Breast Cancer

Background

Circ_0004771 was demonstrated to mediate cell growth promotion and apoptosis suppression in breast cancer (BC). Herein, the precise functions and mechanism of circ_0004771 in the biological property of BC cells were investigated.

Methods

The expression of circ_0004771, microRNA (miR)-1253 and dimethylarginine dimethylaminohydrolase 1 (DDAH1) mRNA was analyzed using quantitative real-time polymerase chain reaction. The proliferation, apoptosis, migration, invasion, adhesion, Western blot and in vivo tumorigenesis assays were employed to evaluate the roles of circ_0004771 and DDAH1 in BC tumorigenesis. The interaction between miR-1253 and circ_0004771 or DDAH1 was validated by dual-luciferase reporter, pull-down and RNA immunoprecipitation (RIP) assay. Exosomes were isolated by Exoquick-TC^® methods, and qualified using Nanosight™ technology and Western blot.

Results

Circ_0004771 or DDAH1 expression was elevated in BC, and silencing either of them suppressed cell malignant phenotypes, thus impeding BC progression. Importantly, circ_0004771 up-regulation attenuated the anticancer action of DDAH1-knockdown in BC. Additionally, we confirmed that circ_0004771 functioned as a sponge of miR-1253 to up-regulate DDAH1 expression. Moreover, xenograft assay exhibited that circ_0004771 knockdown also hindered tumor growth in vivo via regulating DDAH1 and miR-1253. Besides that, it was found that circ_0004771 was packaged into exosomes isolated from the serum of BC.

Conclusion

Circ_0004771 accelerated cell carcinogenic phenotypes via up-regulating DDAH1 expression through absorbing miR-1253 in BC. Besides, circ_0004771 was packaged into exosomes isolated from the serum of BC. All these findings suggested a promising molecular target for BC treatment.

An Overview of Vasculogenic Mimicry in Breast Cancer

Vasculogenic mimicry (VM) is the formation of vascular channels lacking endothelial cells. These channels are lined by tumor cells with cancer stem cell features, positive for periodic acid-Schiff, and negative for CD31 staining. The term VM was introduced by Maniotis et al. (1), who reported this phenomenon in highly aggressive uveal melanomas; since then, VM has been associated with poor prognosis, tumor aggressiveness, metastasis, and drug resistance in several tumors, including breast cancer. It is proposed that VM and angiogenesis (the de novo formation of blood vessels from the established vasculature by endothelial cells, which is observed in several tumors) rely on some common mechanisms. Furthermore, it is also suggested that VM could constitute a means to circumvent anti-angiogenic treatment in cancer. Therefore, it is important to determinant the factors that dictate the onset of VM. In this review, we describe the current understanding of VM formation in breast cancer, including specific signaling pathways, and cancer stem cells. In addition, we discuss the clinical significance of VM in prognosis and new opportunities of VM as a target for breast cancer therapy.

RPV-modified epirubicin and dioscin co-delivery liposomes suppress non-small cell lung cancer growth by limiting nutrition supply

Chemotherapy for non‐small cell lung cancer (NSCLC) is far from satisfactory, mainly due to poor targeting of antitumor drugs and self‐adaptations of the tumors. Angiogenesis, vasculogenic mimicry (VM) channels, migration, and invasion are the main ways for tumors to obtain nutrition. Herein, RPV‐modified epirubicin and dioscin co‐delivery liposomes were successfully prepared. These liposomes showed ideal physicochemical properties, enhanced tumor targeting and accumulation in tumor sites, and inhibited VM channel formation, tumor angiogenesis, migration and invasion. The liposomes also downregulated VM‐related and angiogenesis‐related proteins in vitro. Furthermore, when tested in vivo, the targeted co‐delivery liposomes increased selective accumulation of drugs in tumor sites and showed extended stability in blood circulation. In conclusion, RPV‐modified epirubicin and dioscin co‐delivery liposomes showed strong antitumor efficacy in vivo and could thus be considered a promising strategy for NSCLC treatment.

Discovery of N-(4-Aminobutyl)-N'-(2-methoxyethyl)guanidine as the First Selective, Nonamino Acid, Catalytic Site Inhibitor of Human Dimethylarginine Dimethylaminohydrolase-1 (hDDAH-1)

N-(4-Aminobutyl)-N'-(2-methoxyethyl)guanidine (8a) is a potent inhibitor targeting the hDDAH-1 active site (K_i = 18 μM) and derived from a series of guanidine- and amidine-based inhibitors. Its nonamino acid nature leads to high selectivities toward other enzymes of the nitric oxide-modulating system. Crystallographic data of 8a-bound hDDAH-1 illuminated a unique binding mode. Together with its developed N-hydroxyguanidine prodrug 11, 8a will serve as a most widely applicable, pharmacological tool to target DDAH-1-associated diseases.

Inhibition of Dimethylarginine Dimethylaminohydrolase (DDAH) Enzymes as an Emerging Therapeutic Strategy to Target Angiogenesis and Vasculogenic Mimicry in Cancer

The small free radical gas nitric oxide (NO) plays a key role in various physiological and pathological processes through enhancement of endothelial cell survival and proliferation. In particular, NO has emerged as a molecule of interest in carcinogenesis and tumor progression due to its crucial role in various cancer-related events including cell invasion, metastasis, and angiogenesis. The dimethylarginine dimethylaminohydrolase (DDAH) family of enzymes metabolize the endogenous nitric oxide synthase (NOS) inhibitors, asymmetric dimethylarginine (ADMA) and monomethyl arginine (L-NMMA), and are thus key for maintaining homeostatic control of NO. Dysregulation of the DDAH/ADMA/NO pathway resulting in increased local NO availability often promotes tumor growth, angiogenesis, and vasculogenic mimicry. Recent literature has demonstrated increased DDAH expression in tumors of different origins and has also suggested a potential ADMA-independent role for DDAH enzymes in addition to their well-studied ADMA-mediated influence on NO. Inhibition of DDAH expression and/or activity in cell culture models and in vivo studies has indicated the potential therapeutic benefit of this pathway through inhibition of both angiogenesis and vasculogenic mimicry, and strategies for manipulating DDAH function in cancer are currently being actively pursued by several research groups. This review will thus provide a timely discussion on the expression, regulation, and function of DDAH enzymes in regard to angiogenesis and vasculogenic mimicry, and will offer insight into the therapeutic potential of DDAH inhibition in cancer based on preclinical studies.

Genome-Wide Tiling Array Analysis of HPV-Induced Warts Reveals Aberrant Methylation of Protein-Coding and Non-Coding Regions

The human papillomaviruses (HPV) are a group of double-stranded DNA viruses that exhibit an exclusive tropism for squamous epithelia. HPV can either be low- or high-risk depending on its ability to cause benign lesions or cancer, respectively. Unsurprisingly, the majority of epigenetic research has focused on the high-risk HPV types, neglecting the low-risk types in the process. Therefore, the main objective of this study is to better understand the epigenetics of wart formation by investigating the differences in methylation between HPV-induced cutaneous warts and normal skin. A number of clear and very significant differences in methylation patterns were found between cutaneous warts and normal skin. Around 55% of the top-ranking 100 differentially methylated genes in warts were protein coding, including the EXOC4, KCNU, RTN1, LGI1, IRF2, and NRG1 genes. Additionally, non-coding RNA genes, such as the AZIN1-AS1, LINC02008, and MGC27382 genes, constituted 11% of the top-ranking 100 differentially methylated genes. Warts exhibited a unique pattern of methylation that is a possible explanation for their transient nature. Since the genetics of cutaneous wart formation are not completely known, the findings of the present study could contribute to a better understanding of how HPV infection modulates host methylation to give rise to warts in the skin.

Circ-EZH2 knockdown reverses DDAH1 and CBX3-mediated cell growth and invasion in glioma through miR-1265 sponge activity

Accumulating evidence has indicated the important roles of circular RNAs (circRNAs) in different tumors. However, their detailed regulatory mechanisms in glioma are not fully understood. In this study, the functional role of a novel circRNA, circ-EZH2, was investigated by cell counting kit-8 (CCK-8), colony formation, flow cytometry, and transwell experiments. The regulatory mechanism of circ-EZH2 was explored by bioinformatics analysis, quantitative real-time PCR (qRT-PCR), Western blot and dual-luciferase reporter assay. We identified that circ-EZH2 was overexpressed in glioma tissues and cell lines. Further studies revealed that ectopic expression of circ-EZH2 significantly promoted cell growth, migration and invasion but inhibited cell apoptosis. By contrast, silencing of circ-EZH2 induced the opposite effects. Additionally, we found circ-EZH2 served as a miRNA sponge for miR-1265 to release its suppression on DDAH1 and CBX3. Rescue assays further revealed that the oncogenic function of circ-EZH2 was partly dependent on its modulation of DDAH1 and CBX3. Our study unraveled a novel molecular pathway in glioma and may provide a new perspective for the treatment of glioma.

The Second Life of Methylarginines as Cardiovascular Targets

Endogenous methylarginines were proposed as cardiovascular risk factors more than two decades ago, however, so far, this knowledge has not led to the development of novel therapeutic approaches. The initial studies were primarily focused on the endogenous inhibitors of nitric oxide synthases asymmetric dimethylarginine (ADMA) and monomethylarginine (MMA) and the main enzyme regulating their clearance dimethylarginine dimethylaminohydrolase 1 (DDAH1). To date, all the screens for DDAH1 activators performed with the purified recombinant DDAH1 enzyme have not yielded any promising hits, which is probably the main reason why interest towards this research field has started to fade. The relative contribution of the second DDAH isoenzyme DDAH2 towards ADMA and MMA clearance is still a matter of controversy. ADMA, MMA and symmetric dimethylarginine (SDMA) are also metabolized by alanine: glyoxylate aminotransferase 2 (AGXT2), however, in addition to methylarginines, this enzyme also has several cardiovascular protective substrates, so the net effect of possible therapeutic targeting of AGXT2 is currently unclear. Recent studies on regulation and functions of the enzymes metabolizing methylarginines have given a second life to this research direction. Our review discusses the latest discoveries and controversies in the field and proposes novel directions for targeting methylarginines in clinical settings.