DDR1-targeted therapies: current limitations and future potential

Discoidin domain receptor (DDR)-1 has a crucial role in regulating vital processes, including cell differentiation, proliferation, adhesion, migration, invasion, and matrix remodeling. Overexpression or activation of DDR1 in various pathological scenarios makes it a potential therapeutic target for the treatment of cancer, fibrosis, atherosclerosis, and neuropsychiatric, psychiatric, and neurodegenerative disorders. In this review, we summarize current therapeutic approaches targeting DDR1 from a medicinal chemistry perspective. Furthermore, we analyze factors other than issues of low selectivity and risk of resistance, contributing to the infrequent success of DDR1 inhibitors. The complex interplay between DDR1 and the extracellular matrix (ECM) necessitates additional validation, given that DDR1 might exhibit complex and synergistic interactions with other signaling molecules during ECM regulation. The mechanisms involved in DDR1 regulation in cancer and inflammation-related diseases also remain unknown.

Corneal Infantile Myofibromatosis Caused by Novel Activating Imatinib-Responsive Variants in PDGFRB

Purpose

To investigate the genetic cause, clinical characteristics, and potential therapeutic targets of infantile corneal myofibromatosis.

Design

Case series with genetic and functional in vitro analyses.

Participants

Four individuals from 2 unrelated families with clinical signs of corneal myofibromatosis were investigated.

Methods

Exome-based panel sequencing for platelet-derived growth factor receptor beta gene (PDGFRB) and notch homolog protein 3 gene (NOTCH3) was performed in the respective index patients. One clinically affected member of each family was tested for the pathogenic variant detected in the respective index by Sanger sequencing. Immunohistochemical staining on excised corneal tissue was conducted. Functional analysis of the individual PDGFRB variants was performed in vitro by luciferase reporter assays on transfected porcine aortic endothelial cells using tyrosine kinase inhibitors. Protein expression analysis of mutated PDGFRB was analyzed by Western blot.

Main Outcome Measures

Sequencing data, immunohistochemical stainings, functional analysis of PDGFRB variants, and protein expression analysis.

Results

We identified 2 novel, heterozygous gain-of-function variants in PDGFRB in 4 individuals from 2 unrelated families with corneal myofibromatosis. Immunohistochemistry demonstrated positivity for alpha-smooth muscle actin and β-catenin, a low proliferation rate in Ki-67 (< 5%), marginal positivity for Desmin, and negative staining for Caldesmon and CD34. In all patients, recurrence of disease occurred after corneal surgery. When transfected in cultured cells, the PDGFRB variants conferred a constitutive activity to the receptor in the absence of its ligand and were sensitive to the tyrosine kinase inhibitor imatinib. The variants can both be classified as likely pathogenic regarding the American College of Medical Genetics and Genomics classification criteria.

Conclusions

We describe 4 cases of corneal myofibromatosis caused by novel PDGFRB variants with autosomal dominant transmission. Imatinib sensitivity in vitro suggests perspectives for targeted therapy preventing recurrences in the future.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Research progress of DDR1 inhibitors in the treatment of multiple human diseases

Discoidin domain receptor 1 (DDR1) is a collagen-activated receptor tyrosine kinase (RTK) and plays pivotal roles in regulating cellular functions such as proliferation, differentiation, invasion, migration, and matrix remodeling. DDR1 is involved in the occurrence and progression of many human diseases, including cancer, fibrosis, and inflammation. Therefore, DDR1 represents a highly promising therapeutic target. Although no selective small-molecule inhibitors have reached clinical trials to date, many molecules have shown therapeutic effects in preclinical studies. For example, BK40143 has demonstrated significant promise in the therapy of neurodegenerative diseases. In this context, our perspective aims to provide an in-depth exploration of DDR1, encompassing its structure characteristics, biological functions, and disease relevance. Furthermore, we emphasize the importance of understanding the structure-activity relationship of DDR1 inhibitors and highlight the unique advantages of dual-target or multitarget inhibitors. We anticipate offering valuable insights into the development of more efficacious DDR1-targeted drugs.

A network map of discoidin domain receptor 1(DDR1)-mediated signaling in pathological conditions

Discoidin domain receptor 1 (DDR1) is one of the receptors that belong to a family of non-integrin collagen receptors. In common, DDR1 is predominantly found in epithelial and smooth muscle cells and its mainly involved in organogenesis during embryonic development. However, it's also overexpressed in several pathological conditions, including cancer and inflammation. The DDR1 is reported in numerous cancers, including breast, prostate, pancreatic, bladder, lung, liver, pituitary, colorectal, skin, gastric, glioblastoma, and inflammation. DDR1 activates through the collagen I, IV, IGF-1/IGF1R, and IGF2/IR, regulating downstream signaling molecules such as MAPKs, PI3K/Akt, and NF-kB in diseases. Despite its biomedical importance, there is a lack of consolidated network map of the DDR1 signaling pathway, which prompted us for curation of literature data pertaining to the DDR1 system following the NetPath criteria. We present here the compiled pathway map comprises 39 activation/inhibition events, 17 catalysis events, 22 molecular associations, 65 gene regulation events, 35 types of protein expression, and two protein translocation events. The detailed DDR1 signaling pathway map is made freely accessible through the WikiPathways Database ( https://www.wikipathways.org/index.php/ Pathway: https://www.wikipathways.org/index.php/Pathway:WP5288 ).

Focusing on discoidin domain receptors in premalignant and malignant liver diseases

Discoidin domain receptors (DDRs) are receptor tyrosine kinases on the membrane surface that bind to extracellular collagens, but they are rarely expressed in normal liver tissues. Recent studies have demonstrated that DDRs participate in and influence the processes underlying premalignant and malignant liver diseases. A brief overview of the potential roles of DDR1 and DDR2 in premalignant and malignant liver diseases is presented. DDR1 has proinflammatory and profibrotic benefits and promotes the invasion, migration and liver metastasis of tumour cells. However, DDR2 may play a pathogenic role in early-stage liver injury (prefibrotic stage) and a different role in chronic liver fibrosis and in metastatic liver cancer. These views are critically significant and first described in detail in this review. The main purpose of this review was to describe how DDRs act in premalignant and malignant liver diseases and their potential mechanisms through an in-depth summary of preclinical in vitro and in vivo studies. Our work aims to provide new ideas for cancer treatment and accelerate translation from bench to bedside.

Effects of Expression of Matrix Metalloproteinases and Discoidin Domain Receptors in Ligamentum Flavum Fibrosis in Patients with Degenerative Lumbar Canal Stenosis

STUDY DESIGN

This is a retrospective cohort study.

PURPOSE

This study aimed to clarify the role of crosstalk between discoidin domain receptors (DDRs) and matrix metalloproteinases (MMPs) in the ligamentum flavum (LF) fibrosis obtained from patients with degenerative lumbar canal stenosis (DLCS).

OVERVIEW OF LITERATURE

The DDRs, DDR1 and DDR2, are cell surface receptors and have an essential role in collagen fiber accumulation in several fibrotic diseases. MMPs are one of the critical factors in extracellular matrix remodeling and elastic fiber degradation in LF tissues. However, the crosstalk between DDRs and MMPs and the role of this molecular signal in LF fibrosis remain unclear.

METHODS

A total of 35 patients were divided into two groups in this study. Spinal surgery was performed in 23 of these patients with the diagnosis of DLCS. Twelve patients with lumbar disk herniation (LDH) were included in the control group. On axial T2-weighted magnetic resonance imaging, LF thickness was measured bilaterally at the level of the facet joint. Histology, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blot analyses were performed on LF tissue samples. LF tissues were stained with hematoxylin and eosin. In addition, the grade of fibrosis was histologically assessed using Masson trichrome triple staining. DDR1 and DDR2 Western blot analyses were performed. DDR1, DDR2, MMP2, MMP3, MMP9, and MMP13 expression levels were measured using qRT-PCR analysis.

RESULTS

The grade of fibrosis and LF thickness were significantly higher in the DLCS patients than in the LDH patients. DDR1 and DDR2 gene expression and protein levels in LF tissues are significantly greater in DLCS samples than in control samples, according to both qRT-PCR and Western blot analyses. In addition, we detected a significant expression of the MMP3, MMP9, and MMP13, which are known to have important roles in extracellular matrix remodeling in DLCS. Furthermore, we discovered a link between DDR protein levels and LF thickness, fibrosis, and MMP3/MMP9.

CONCLUSIONS

Our results indicate that DDR1, DDR2, and MMP3 and MMP9 signals can be correlated with each other in LF tissues and be promoted LF fibrosis leading to spinal canal narrowing in patients with DLCS.

Discoidin domain receptor 1 may be involved in biological barrier homeostasis

WHAT IS KNOWN AND OBJECTIVE

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase involved in the pathological processes of several diseases, such as keloid formation, renal fibrosis, atherosclerosis, tumours, and inflammatory processes. The biological barrier is the first line of defence against pathogens, and its disruption is closely related to diseases. In this review, we attempt to elucidate the relationship between DDR1 and the biological barrier, explore the potential biological value of DDR1, and review the current research status and clinical potential of DDR1-selective inhibitors.

METHODS

We conducted an extensive literature search on PubMed to collect studies on the relevance of DDR1 to biological barriers and DDR1-selective inhibitors. With these studies, we explored the relationship between DDR1 and biological barriers and briefly reviewed representative DDR1-selective inhibitors that have been reported in recent years.

RESULTS AND DISCUSSION

First, the review of the potential mechanisms by which DDR1 regulates biological barriers, including the epithelial, vascular, glomerular filtration, blood-labyrinth, and blood-brain barriers. In the body, DDR1 dysfunction and aberrant expression may be involved in the homeostasis of the biological barrier. Secondly, the review of DDR1 inhibitors reported in recent years shows that DDR1-targeted inhibition is an attractive and promising pharmacological intervention.

WHAT IS NEW AND CONCLUSIONS

This review shows that DDR1 is involved in various physiological and pathological processes and in the regulation of biological barrier homeostasis. However, studies on DDR1 and biological barriers are still scarce, and further studies are needed to elucidate their specific mechanisms. The development of targeted inhibitors provides a new direction and idea to study the mechanism of DDR1.

In Silico Analysis of Collagens Missense SNPs and Human Abnormalities

Collagens are the most abundant proteins in the extra cellular matrix/ECM of human tissues that are encoded by different genes. There are single nucleotide polymorphisms/SNPs which are considered as the most useful biomarkers for some disease diagnosis or prognosis. The aim of this study is screening and identifying the functional missense SNPs of human ECM-collagens and investigating their correlation with human abnormalities. All of the missense SNPs were retrieved from the NCBI SNP database and screened for a global frequency of more than 0.1. Seventy missense SNPs that met the screening criteria were characterized for functional and stability impact using six and three protein analysis tools, respectively. Next, HOPE and geneMANIA analysis tools were used to show the effect of SNPs on three-dimensional structure (3D) and physical interaction of proteins. Results showed that 13 missense SNPs (rs2070739, rs28381984, rs13424243, rs1800517, rs73868680, rs12488457, rs1353613, rs59021909, rs9830253, rs2228547, rs3753841, rs2855430, and rs970547), which are in nine different collagen genes, affect the structure and function of different collagen proteins. Among these polymorphisms, COL4A3-rs13424243 and COL6A6-rs59021909 were predicted as the most effective ones. On the other hand, designed mutated and native 3D of rs13424243 variant illustrated that it can disturb the protein motifs. Also, geneMANIA predicted that COL4A3 and COL6A6 are interacting with some proteins including: DDR1, COL6A1, COL11A2 and so on. Based on our findings, ECM-collagens functional SNPs are important and may be considered as a risk factor or molecular marker for human disorders in the future studies.

CSF MicroRNAs Reveal Impairment of Angiogenesis and Autophagy in Parkinson Disease

Background and Objectives

We assessed longitudinal changes in CSF microRNAs (miRNAs) in patients with moderately severe Parkinson disease.

Methods

We used next-generation whole-genome miRNA sequencing to determine CSF miRNA expression in 75 patients with Parkinson disease after single random ascending doses of nilotinib and longitudinal miRNA expression after daily nilotinib, 150 and 300 mg, vs placebo for 1 year.

Results

Significant changes in the expression of miRNAs that control genes and pathways that regulate angiogenesis, autophagy, and the blood-brain-barrier components, primarily collagen, were observed over 1 year, suggesting impairment of these pathways in Parkinson progression in these patients. Different miRNAs that indicate activation of genes associated with autophagy flux and clearance and angiogenesis were significantly altered in the nilotinib, 300 mg vs 150 mg, or placebo group, and these changes correlated with clinical outcomes. No changes were observed in miRNAs after a single dose of nilotinib vs placebo.

Discussion

This study suggests vascular and autophagy defects in Parkinson progression. Nilotinib, 300 mg, reverses these effects via alteration of miRNA expression, suggesting epigenomic changes that may underlie long-term disease-modifying effects.

Trial Registration Information

Clinical trial registration number: NCT02954978.

Inhibitors of Discoidin Domain Receptor (DDR) Kinases for Cancer and Inflammation

The discoidin domain receptor tyrosine kinases DDR1 and DDR2 are distinguished from other kinase enzymes by their extracellular domains, which interact with collagen rather than with peptidic growth factors, before initiating signaling via tyrosine phosphorylation. They share significant sequence and structural homology with both the c-Kit and Bcr-Abl kinases, and so many inhibitors of those kinases are also effective. Nevertheless, there has been an extensive research effort to develop potent and specific DDR inhibitors. A key interaction for many of these compounds is H-bonding to Met-704 in a hydrophobic pocket of the DDR enzyme. The most widespread use of DDR inhibitors has been for cancer therapy, but they have also shown effectiveness in animal models of inflammatory conditions such as Alzheimer’s and Parkinson’s diseases, and in chronic renal failure and glomerulonephritis.

Truncated Milk Fat Globule-EGF-like Factor 8 Ameliorates Liver Fibrosis via Inhibition of Integrin-TGFβ Receptor Interaction

Milk fat globule-EGF factor 8 (MFG-E8) protein is known as an immunomodulator in various diseases, and we previously demonstrated the anti-fibrotic role of MFG-E8 in liver disease. Here, we present a truncated form of MFG-E8 that provides an advanced therapeutic benefit in treating liver fibrosis. The enhanced therapeutic potential of the modified MFG-E8 was demonstrated in various liver fibrosis animal models, and the efficacy was further confirmed in human hepatic stellate cells and a liver spheroid model. In the subsequent analysis, we found that the modified MFG-E8 more efficiently suppressed transforming growth factor β (TGF-β) signaling than the original form of MFG-E8, and it deactivated the proliferation of hepatic stellate cells in the liver disease environment through interfering with the interactions between integrins (αvβ3 & αvβ5) and TGF-βRI. Furthermore, the protein preferentially delivered in the liver after administration, and the safety profiles of the protein were demonstrated in male and female rat models. Therefore, in conclusion, this modified MFG-E8 provides a promising new therapeutic strategy for treating fibrotic diseases.

Interplay between extracellular matrix components and cellular and molecular mechanisms in kidney fibrosis

Chronic kidney disease (CKD) is characterized by pathological accumulation of extracellular matrix (ECM) proteins in renal structures. Tubulointerstitial fibrosis is observed in glomerular diseases as well as in the regeneration failure of acute kidney injury (AKI). Therefore, finding antifibrotic therapies comprises an intensive research field in Nephrology. Nowadays, ECM is not only considered as a cellular scaffold, but also exerts important cellular functions. In this review, we describe the cellular and molecular mechanisms involved in kidney fibrosis, paying particular attention to ECM components, profibrotic factors and cell-matrix interactions. In response to kidney damage, activation of glomerular and/or tubular cells may induce aberrant phenotypes characterized by overproduction of proinflammatory and profibrotic factors, and thus contribute to CKD progression. Among ECM components, matricellular proteins can regulate cell-ECM interactions, as well as cellular phenotype changes. Regarding kidney fibrosis, one of the most studied matricellular proteins is cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), currently considered as a fibrotic marker and a potential therapeutic target. Integrins connect the ECM proteins to the actin cytoskeleton and several downstream signaling pathways that enable cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. In kidney fibrosis, there is an increase in ECM deposition, lower ECM degradation and ECM proteins cross-linking, leading to an alteration in the tissue mechanical properties and their responses to injurious stimuli. A better understanding of these complex cellular and molecular events could help us to improve the antifibrotic therapies for CKD.

Inhibition of discoidin domain receptors by imatinib prevented pancreatic fibrosis demonstrated in experimental chronic pancreatitis model

Discoidin domain receptors (DDR1 and DDR2) are the collagen receptors of the family tyrosine kinases, which play significant role in the diseases like inflammation, fibrosis and cancer. Chronic pancreatitis (CP) is a fibro-inflammatory disease in which recurrent pancreatic inflammation leads to pancreatic fibrosis. In the present study, we have investigated the role of DDR1 and DDR2 in CP. The induced expression of DDR1 and DDR2 was observed in primary pancreatic stellate cells (PSCs) and cerulein-induced CP. Subsequently, the protective effects of DDR1/DDR2 inhibitor, imatinib (IMT) were investigated. Pharmacological intervention with IMT effectively downregulated DDR1 and DDR2 expression. Further, IMT treatment reduced pancreatic injury, inflammation, extracellular matrix deposition and PSCs activation along with inhibition of TGF-β1/Smad signaling pathway. Taken together, these results suggest that inhibition of DDR1 and DDR2 controls pancreatic inflammation and fibrosis, which could represent an attractive and promising therapeutic strategy for the treatment of CP.

The Journey of DDR1 and DDR2 Kinase Inhibitors as Rising Stars in the Fight Against Cancer

Discoidin domain receptor (DDR) is a collagen-activated receptor tyrosine kinase that plays critical roles in regulating essential cellular processes such as morphogenesis, differentiation, proliferation, adhesion, migration, invasion, and matrix remodeling. As a result, DDR dysregulation has been attributed to a variety of human cancer disorders, for instance, non-small-cell lung carcinoma (NSCLC), ovarian cancer, glioblastoma, and breast cancer, in addition to some inflammatory and neurodegenerative disorders. Since the target identification in the early 1990s to date, a lot of efforts have been devoted to the development of DDR inhibitors. From a medicinal chemistry perspective, we attempted to reveal the progress in the development of the most promising DDR1 and DDR2 small molecule inhibitors covering their design approaches, structure-activity relationship (SAR), biological activity, and selectivity.

A story of fibers and stress: Matrix-embedded signals for fibroblast activation in the skin

Our skin is continuously exposed to mechanical challenge, including shear, stretch, and compression. The extracellular matrix of the dermis is perfectly suited to resist these challenges and maintain integrity of normal skin even upon large strains. Fibroblasts are the key cells that interpret mechanical and chemical cues in their environment to turnover matrix and maintain homeostasis in the skin of healthy adults. Upon tissue injury, fibroblasts and an exclusive selection of other cells become activated into myofibroblasts with the task to restore skin integrity by forming structurally imperfect but mechanically stable scar tissue. Failure of myofibroblasts to terminate their actions after successful repair or upon chronic inflammation results in dysregulated myofibroblast activities which can lead to hypertrophic scarring and/or skin fibrosis. After providing an overview on the major fibrillar matrix components in normal skin, we will interrogate the various origins of fibroblasts and myofibroblasts in the skin. We then examine the role of the matrix as signaling hub and how fibroblasts respond to mechanical matrix cues to restore order in the confusing environment of a healing wound.

Tyrosine kinases in the pathogenesis of tissue fibrosis in systemic sclerosis and potential therapeutic role of their inhibition

Systemic sclerosis (SSc) is an idiopathic autoimmune disease with a heterogeneous clinical phenotype ranging from limited cutaneous involvement to rapidly progressive diffuse SSc. The most severe SSc clinical and pathologic manifestations result from an uncontrolled fibrotic process involving the skin and various internal organs. The molecular mechanisms responsible for the initiation and progression of the SSc fibrotic process have not been fully elucidated. Recently it has been suggested that tyrosine protein kinases play a role. The implicated kinases include receptor-activated tyrosine kinases and nonreceptor tyrosine kinases. The receptor kinases are activated following specific binding of growth factors (platelet-derived growth factor, fibroblast growth factor, or vascular endothelial growth factor). Other receptor kinases are the discoidin domain receptors activated by binding of various collagens, the ephrin receptors that are activated by ephrins and the angiopoetin-Tie-2s receptors. The nonreceptor tyrosine kinases c-Abl, Src, Janus, and STATs have also been shown to participate in SSc-associated tissue fibrosis. Currently, there are no effective disease-modifying therapies for SSc-associated tissue fibrosis. Therefore, extensive investigation has been conducted to examine whether tyrosine kinase inhibitors (TKIs) may exert antifibrotic effects. Here, we review the role of receptor and nonreceptor tyrosine kinases in the pathogenesis of the frequently progressive cutaneous and systemic fibrotic alterations in SSc, and the potential of TKIs as SSc disease-modifying antifibrotic therapeutic agents.

Complex roles of discoidin domain receptor tyrosine kinases in cancer

Discoidin domain receptors, DDR1 and DDR2 are members of the receptor tyrosine kinase (RTK) family that serves as a non-integrin collagen receptor and were initially identified as critical regulators of embryonic development and cellular homeostasis. In recent years, numerous studies have focused on the role of these receptors in disease development, in particular, cancer where they have been reported to augment ECM remodeling, invasion, drug resistance to facilitate tumor progression and metastasis. Interestingly, accumulating evidence also suggests that DDRs promote apoptosis and suppress tumor progression in various human cancers due to which their functions in cancer remain ill-defined and presents a case of an interesting therapeutic target. The present review has discussed the role of DDRs in tumorigenesis and the metastasis.

Discoidin domain receptors orchestrate cancer progression: A focus on cancer therapies

Discoidin domain receptors (DDR), including DDR1 and DDR2, are special types of the transmembrane receptor tyrosine kinase superfamily. DDR are activated by binding to the triple-helical collagen and, in turn, DDR can activate signal transduction pathways that regulate cell-collagen interactions involved in multiple physiological and pathological processes such as cell proliferation, migration, apoptosis, and cytokine secretion. Recently, DDR have been found to contribute to various diseases, including cancer. In addition, aberrant expressions of DDR have been reported in various human cancers, which indicates that DDR1 and DDR2 could be new targets for cancer treatment. Considerable effort has been made to design DDR inhibitors and several molecules have shown therapeutic effects in pre-clinical models. In this article, we review the recent literature on the role of DDR in cancer progression, the development status of DDR inhibitors, and the clinical potential of targeting DDR in cancer therapies.

Protein Tyrosine Kinases: Their Roles and Their Targeting in Leukemia

Simple Summary

Protein phosphorylation is a key regulatory mechanism that controls a wide variety of cellular responses. This process is catalysed by the members of the protein kinase superfamily that are classified into two main families based on their ability to phosphorylate either tyrosine or serine and threonine residues in their substrates. Massive research efforts have been invested in dissecting the functions of tyrosine kinases, revealing their importance in the initiation and progression of human malignancies. Based on these investigations, numerous tyrosine kinase inhibitors have been included in clinical protocols and proved to be effective in targeted therapies for various haematological malignancies. In this review, we provide insights into the role of tyrosine kinases in leukaemia and discuss their targeting for therapeutic purposes with the currently available inhibitory compounds.

Abstract

Protein kinases constitute a large group of enzymes catalysing protein phosphorylation and controlling multiple signalling events. The human protein kinase superfamily consists of 518 members and represents a complicated system with intricate internal and external interactions. Protein kinases are classified into two main families based on the ability to phosphorylate either tyrosine or serine and threonine residues. Among the 90 tyrosine kinase genes, 58 are receptor types classified into 20 groups and 32 are of the nonreceptor types distributed into 10 groups. Tyrosine kinases execute their biological functions by controlling a variety of cellular responses, such as cell division, metabolism, migration, cell–cell and cell matrix adhesion, cell survival and apoptosis. Over the last 30 years, a major focus of research has been directed towards cancer-associated tyrosine kinases owing to their critical contributions to the development and aggressiveness of human malignancies through the pathological effects on cell behaviour. Leukaemia represents a heterogeneous group of haematological malignancies, characterised by an uncontrolled proliferation of undifferentiated hematopoietic cells or leukaemia blasts, mostly derived from bone marrow. They are usually classified as chronic or acute, depending on the rates of their progression, as well as myeloid or lymphoblastic, according to the type of blood cells involved. Overall, these malignancies are relatively common amongst both children and adults. In malignant haematopoiesis, multiple tyrosine kinases of both receptor and nonreceptor types, including AXL receptor tyrosine kinase (AXL), Discoidin domain receptor 1 (DDR1), Vascular endothelial growth factor receptor (VEGFR), Fibroblast growth factor receptor (FGFR), Mesenchymal–epithelial transition factor (MET), proto-oncogene c-Src (SRC), Spleen tyrosine kinase (SYK) and pro-oncogenic Abelson tyrosine-protein kinase 1 (ABL1) mutants, are implicated in the pathogenesis and drug resistance of practically all types of leukaemia. The role of ABL1 kinase mutants and their therapeutic inhibitors have been extensively analysed in scientific literature, and therefore, in this review, we provide insights into the impact and mechanism of action of other tyrosine kinases involved in the development and progression of human leukaemia and discuss the currently available and emerging treatment options based on targeting these molecules.

Biological information and functional analysis reveal the role of discoidin domain receptor 1 in oral squamous cell carcinoma

OBJECTIVES

This study aimed to establish a framework for the role of discoidin domain receptor 1 (DDR1) in oral squamous cell carcinoma (OSCC) through biological data and functional analysis.

STUDY DESIGN

The GSE31056 series of the Gene Expression Omnibus database and UALCAN website were used to assess DDR1 expression in head and neck squamous cell carcinoma (HNSCC) and OSCC. DDR1 RNA sequencing data for 260 HNSCC samples from The Cancer Genome Atlas were overlaid to evaluate its association with tumor progression and prognosis. To identify the function of DDR1 in OSCC, 38 patients with OSCC were followed for 8 years and immunohistochemical analysis, western blotting, Cell Counting Kit-8, and colony formation assays were conducted on OSCC cell lines to reveal DDR1 expression and function.

RESULTS

DDR1 was overexpressed in HNSCC and OSCC tumor specimens and its expression correlated with overall survival and T-stage classification (P = .049, P = .0316). Furthermore, DDR1 was related to OSCC tumor growth because its expression increased with the T-stage level (P = .0071) but not N-stage level, histologic stage, or recurrence (P > .05). DDR1 was highly expressed in OSCC cell lines and promoted cell proliferation, which was repressed by nilotinib (P < .05).

CONCLUSIONS

DDR1 has an oncogenic role in OSCC and might be a novel target for anti-OSCC therapy.

Protective effect of exogenous hydrogen sulfide on diaphragm muscle fibrosis in streptozotocin-induced diabetic rats

IMPACT STATEMENT

Diabetes mellitus is a group of chronic metabolic disorders, which causes serious damage to a variety of organs, such as the retina, heart, and skeletal muscle. The diaphragm is an important skeletal muscle involved in respiration in mammals. Fibrosis of the diaphragm muscle affects its contractility, which in turn impairs respiratory function. Accumulating evidence suggests that exogenous hydrogen sulfide (H₂S) exhibits anti-fibrotic activity in diabetes mellitus, but whether and how H₂S exerts this anti-fibrotic effect in the diabetic diaphragm remains unclear. The current work for the first time reveals that exogenous H₂S attenuates hyperglycemia-induced fibrosis of the diaphragm muscle and strengthens diaphragmatic biomechanical properties in diabetes mellitus, and the mechanism may involve the alleviation of collagen deposition by suppression of the nucleotide-binding oligomerization domain-like receptor protein (NLRP) 3 inflammasome-mediated inflammatory reaction. Therefore, H₂S supplementation could be used as an efficient targeted therapy against the NLRP3 inflammasome in the diabetic diaphragm.

A patent review of discoidin domain receptor 1 (DDR1) modulators (2014-present)

Introduction: Discoidin domain receptor 1 (DDR1) is a collagen-activated receptor tyrosine kinase. Upon collagen binding, DDR1 undergoes tyrosine autophosphorylation, which consequently triggers downstream genetic and cellular pathways and plays critical roles in the regulation of cellular morphogenesis, differentiation, proliferation, adhesion, migration, and invasion. Increasing evidence suggests the potential roles of DDR1 in various human diseases including cancer, fibrosis, atherosclerosis, and other inflammatory disorders. Modulating the activity of DDR1 may be considered as a new therapeutic strategy for human cancer and inflammation-related diseases.Areas covered: This article summarizes current progress on the development of selective DDR1 inhibitors and their potential therapeutic application during the period from 2014 to 2019.Expert opinion: DDR1 is closely linked to a variety of human diseases, including fibrotic disorders, atherosclerosis, and cancer, etc. Thus, DDR1 has been considered as a new potential target for drug discovery. A number of DDR1 inhibitors has been identified in the past 5 years, but most of them display relatively broad inhibition across the kinome. New generation DDR1 inhibitors targeting the allosteric sites outside of the canonical ATP-binding pocket or extracellular domain (allosteric inhibitors) may offer a new opportunity for selective DDR1 inhibition therapy development.

Discovery of VU6015929: A Selective Discoidin Domain Receptor 1/2 (DDR1/2) Inhibitor to Explore the Role of DDR1 in Antifibrotic Therapy

Herein, we report the discovery of a potent and selective dual DDR1/2 inhibitor, 7e (VU6015929), displaying low cytotoxicity, good kinome selectivity, and possessing an acceptable in vitro DMPK profile with good rodent in vivo pharmacokinetics. VU6015929 potently blocks collagen-induced DDR1 activation and collagen-IV production, suggesting DDR1 inhibition as an exciting target for antifibrotic therapy.

Loss of Discoidin Domain Receptor 1 Predisposes Mice to Periodontal Breakdown

The discoidin domain receptors, DDR1 and DDR2, are nonintegrin collagen receptors and tyrosine kinases. DDRs regulate cell functions, and their extracellular domains affect collagen fibrillogenesis and mineralization. Based on the collagenous nature of dentoalveolar tissues, we hypothesized that DDR1 plays an important role in dentoalveolar development and function. Radiography, micro-computed tomography (micro-CT), histology, histomorphometry, in situ hybridization (ISH), immunohistochemistry (IHC), and transmission electron microscopy (TEM) were used to analyze Ddr1 knockout (Ddr1^-/-) mice and wild-type (WT) controls at 1, 2, and 9 mo, and ISH and quantitative polymerase chain reaction (qPCR) were employed to assess Ddr1/DDR1 messenger RNA expression in mouse and human tissues. Radiographic images showed normal molars but abnormal mandibular condyles, as well as alveolar bone loss in Ddr1^-/- mice versus WT controls at 9 mo. Histological, histomorphometric, micro-CT, and TEM analyses indicated no differences in enamel or dentin Ddr1^-/- versus WT molars. Total volumes (TVs) and bone volumes (BVs) of subchondral and ramus bone of Ddr1^-/- versus WT condyles were increased and bone volume fraction (BV/TV) was reduced at 1 and 9 mo. There were no differences in alveolar bone volume at 1 mo, but at 9 mo, severe periodontal defects and significant alveolar bone loss (14%; P < 0.0001) were evident in Ddr1^-/- versus WT mandibles. Histology, ISH, and IHC revealed disrupted junctional epithelium, connective tissue destruction, bacterial invasion, increased neutrophil infiltration, upregulation of cytokines including macrophage colony-stimulating factor, and 3-fold increased osteoclast numbers (P < 0.05) in Ddr1^-/- versus WT periodontia at 9 mo. In normal mouse tissues, ISH and qPCR revealed Ddr1 expression in basal cell layers of the oral epithelia and in immune cells. We confirmed a similar expression pattern in human oral epithelium by ISH and qPCR. We propose that DDR1 plays an important role in periodontal homeostasis and that absence of DDR1 predisposes mice to periodontal breakdown.

The Extracellular Matrix Receptor Discoidin Domain Receptor 1 Regulates Collagen Transcription by Translocating to the Nucleus

BACKGROUND

The discoidin domain receptor 1 (DDR1) is activated by collagens, upregulated in injured and fibrotic kidneys, and contributes to fibrosis by regulating extracellular matrix production, but how DDR1 controls fibrosis is poorly understood. DDR1 is a receptor tyrosine kinase (RTK). RTKs can translocate to the nucleus via a nuclear localization sequence (NLS) present on the receptor itself or a ligand it is bound to. In the nucleus, RTKs regulate gene expression by binding chromatin directly or by interacting with transcription factors.

METHODS

To determine whether DDR1 translocates to the nucleus and whether this event is mediated by collagen-induced DDR1 activation, we generated renal cells expressing wild-type or mutant forms of DDR1 no longer able to bind collagen. Then, we determined the location of the DDR1 upon collagen stimulation. Using both biochemical assays and immunofluorescence, we analyzed the steps involved in DDR1 nuclear translocation.

RESULTS

We show that although DDR1 and its natural ligand, collagen, lack an NLS, DDR1 is present in the nucleus of injured human and mouse kidney proximal tubules. We show that DDR1 nuclear translocation requires collagen-mediated receptor activation and interaction of DDR1 with SEC61B, a component of the Sec61 translocon, and nonmuscle myosin IIA and β-actin. Once in the nucleus, DDR1 binds to chromatin to increase the transcription of collagen IV, a major collagen upregulated in fibrosis.

CONCLUSIONS

These findings reveal a novel mechanism whereby activated DDR1 translates to the nucleus to regulate synthesis of profibrotic molecules.

Mechanical regulation of myofibroblast phenoconversion and collagen contraction

Activated fibroblasts promote physiological wound repair following tissue injury. However, dysregulation of fibroblast activation contributes to the development of fibrosis by enhanced production and contraction of collagen-rich extracellular matrix. At the peak of their activities, fibroblasts undergo phenotypic conversion into highly contractile myofibroblasts by developing muscle-like features, including formation of contractile actin-myosin bundles. The phenotype and function of fibroblasts and myofibroblasts are mechanically regulated by matrix stiffness using a feedback control system that is integrated with the progress of tissue remodelling. The actomyosin contraction machinery and cell-matrix adhesion receptors are critical elements that are needed for mechanosensing by fibroblasts and the translation of mechanical signals into biological responses. Here, we focus on mechanical and chemical regulation of collagen contraction by fibroblasts and the involvement of these factors in their phenotypic conversion to myofibroblasts.

Liver fibrosis: Direct antifibrotic agents and targeted therapies

Liver fibrosis and in particular cirrhosis are the major causes of morbidity and mortality of patients with chronic liver disease. Their prevention or reversal have become major endpoints in clinical trials with novel liver specific drugs. Remarkable progress has been made with therapies that efficiently address the cause of the underlying liver disease, as in chronic hepatitis B and C. Highly effective antiviral therapy can prevent progression or even induce reversal in the majority of patients, but such treatment remains elusive for the majority of liver patients with advanced alcoholic or nonalcoholic steatohepatitis, genetic or autoimmune liver diseases. Moreover, drugs that would speed up fibrosis reversal are needed for patients with cirrhosis, since even with effective causal therapy reversal is slow or the disease may further progress. Therefore, highly efficient and specific antifibrotic agents are needed that can address advanced fibrosis, i.e., the detrimental downstream result of all chronic liver diseases. This review discusses targeted antifibrotic therapies that address molecules and mechanisms that are central to fibrogenesis or fibrolysis, including strategies that allow targeting of activated hepatic stellate cells and myofibroblasts and other fibrogenic effector cells. Focus is on collagen synthesis, integrins and cells and mechanisms specific including specific downregulation of TGFbeta signaling, major extracellular matrix (ECM) components, ECM-crosslinking, and ECM-receptors such as integrins and discoidin domain receptors, ECM-crosslinking and methods for targeted delivery of small interfering RNA, antisense oligonucleotides and small molecules to increase potency and reduce side effects. With an increased understanding of the biology of the ECM and liver fibrosis and an improved preclinical validation, the translation of these approaches to the clinic is currently ongoing. Application to patients with liver fibrosis and a personalized treatment is tightly linked to the development of noninvasive biomarkers of fibrosis, fibrogenesis and fibrolysis.

Mechanical signaling through the discoidin domain receptor 1 plays a central role in tissue fibrosis

The preservation of tissue and organ architecture and function depends on tightly regulated interactions of cells with the extracellular matrix (ECM). These interactions are maintained in a dynamic equilibrium that balances intracellular, myosin-generated tension with extracellular resistance conferred by the mechanical properties of the extracellular matrix. Disturbances of this equilibrium can lead to the development of fibrotic lesions that are associated with a wide repertoire of high prevalence diseases including obstructive cardiovascular diseases, muscular dystrophy and cancer. Mechanotransduction is the process by which mechanical cues are converted into biochemical signals. At the core of mechanotransduction are sensory systems, which are frequently located at sites of cell-ECM and cell-cell contacts. As integrins (cell-ECM junctions) and cadherins (cell-cell contacts) have been extensively studied, we focus here on the properties of the discoidin domain receptor 1 (DDR1), a tyrosine kinase that mediates cell adhesion to collagen. DDR1 expression is positively associated with fibrotic lesions of heart, kidney, liver, lung and perivascular tissues. As the most common end-point of all fibrotic disorders is dysregulated collagen remodeling, we consider here the mechanical signaling functions of DDR1 in processing of fibrillar collagen that lead to tissue fibrosis.

DDR1: A major player in renal diseases

Discoidin Domain Receptor 1 (DDR1) belongs to a family of two non-integrin collagen receptors, DDR1 and DDR2, which display a tyrosine kinase activity. DDR1 has been widely studied in different kind of pathologies including chronic kidney diseases (CKD). The aims of this commentary are 1. to review the existing information about DDR1 expression in healthy and diseased kidney, 2. to comment the data highlighting DDR1 as a major actor in CKD, 3. to suggest areas of research which require further investigation to better characterize the signaling pathways regulating DDR1 role in CKD. The results recapitulated in this commentary emphasize the involvement of DDR1 in the pro-inflammatory and pro-fibrotic processes which drives the development of CKD. They also underline the beneficial effect of its blockade in pre-clinical models and thus, reinforce its status of interesting therapeutic target.

Tumor-extrinsic discoidin domain receptor 1 promotes mammary tumor growth by regulating adipose stromal interleukin 6 production in mice

Discoidin domain receptor 1 (DDR1) is a collagen receptor that mediates cell communication with the extracellular matrix (ECM). Aberrant expression and activity of DDR1 in tumor cells are known to promote tumor growth. Although elevated DDR1 levels in the stroma of breast tumors are associated with poor patient outcome, a causal role for tumor-extrinsic DDR1 in cancer promotion remains unclear. Here we report that murine mammary tumor cells transplanted to syngeneic recipient mice in which Ddr1 has been knocked out (KO) grow less robustly than in WT mice. We also found that the tumor-associated stroma in Ddr1-KO mice exhibits reduced collagen deposition compared with the WT controls, supporting a role for stromal DDR1 in ECM remodeling of the tumor microenvironment. Furthermore, the stromal-vascular fraction (SVF) of Ddr1 knockout adipose tissue, which contains committed adipose stem/progenitor cells and preadipocytes, was impaired in its ability to stimulate tumor cell migration and invasion. Cytokine array-based screening identified interleukin 6 (IL-6) as a cytokine secreted by the SVF in a DDR1-dependent manner. SVF-produced IL-6 is important for SVF-stimulated tumor cell invasion in vitro, and, using antibody-based neutralization, we show that tumor promotion by IL-6 in vivo requires DDR1. In conclusion, our work demonstrates a previously unrecognized function of DDR1 in promoting tumor growth.