CSF1R inhibition with PLX5622 affects multiple immune cell compartments and induces tissue-specific metabolic effects in lean mice.

AIMS/HYPOTHESIS: Colony stimulating factor 1 (CSF1) promotes the proliferation, differentiation and survival of macrophages, which have been implicated in both beneficial and detrimental effects on glucose metabolism. However, the physiological role of CSF1 signalling in glucose homeostasis and the potential therapeutic implications of modulating this pathway are not known. We aimed to study the composition of tissue macrophages (and other immune cells) following CSF1 receptor (CSF1R) inhibition and elucidate the metabolic consequences of CSF1R inhibition. METHODS: We assessed immune cell populations in various organs by flow cytometry, and tissue-specific metabolic effects by hyperinsulinaemic-euglycaemic clamps and insulin secretion assays in mice fed a chow diet containing PLX5622 (a CSF1R inhibitor) or a control diet. RESULTS: CSF1R inhibition depleted macrophages in multiple tissues while simultaneously increasing eosinophils and group 2 innate lymphoid cells. These immunological changes were consistent across different organs and were sex independent and reversible after cessation of the PLX5622. CSF1R inhibition improved hepatic insulin sensitivity but concomitantly impaired insulin secretion. In healthy islets, we found a high frequency of IL-1ß+ islet macrophages. Their depletion by CSF1R inhibition led to downregulation of macrophage-related pathways and mediators of cytokine activity, including Nlrp3, suggesting IL-1ß as a candidate insulin secretagogue. Partial restoration of physiological insulin secretion was achieved by injecting recombinant IL-1ß prior to glucose stimulation in mice lacking macrophages. CONCLUSIONS/INTERPRETATION: Macrophages and macrophage-derived factors, such as IL-1ß, play an important role in physiological insulin secretion. A better understanding of the tissue-specific effects of CSF1R inhibition on immune cells and glucose homeostasis is crucial for the development of targeted immune-modulatory treatments in metabolic disease. DATA AVAILABILITY: The RNA-Seq dataset is available in the Gene Expression Omnibus (GEO) under the accession number GSE189434 ( http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE189434 ).

The Presence of Colony-Stimulating Factor-1 and Its Receptor in Different Cells of the Testis; It Involved in the Development of Spermatogenesis In Vitro.

Spermatogenesis is a complex process, in which spermatogonial cells proliferate and differentiate in the seminiferous tubules of the testis to generate sperm. This process is under the regulation of endocrine and testicular paracrine/autocrine factors. In the present study, we demonstrated that colony stimulating factor-1 (CSF-1) is produced by mouse testicular macrophages, Leydig, Sertoli, peritubular cells and spermatogonial cells (such as CDH1-positively stained cells; a marker of spermatogonial cells). In addition, we demonstrated the presence of CSF-1 and its receptor (CSF-1R) in testicular macrophages, Leydig, Sertoli, peritubular cells and spermatogonial cells of human testis. We also show that the protein levels of CSF-1 were the highest in testis of 1-week-old mice and significantly decreased with age (2-12-week-old). However, the transcriptome levels of CSF-1 significantly increased in 2-3-week-old compared to 1-week-old, and thereafter significantly decreased with age. On the other hand, the transcriptome levels of CSF-1R was significantly higher in mouse testicular tissue of all examined ages (2-12-week-old) compared to 1-week-old. Our results demonstrate the involvement of CSF-1 in the induction the proliferation and differentiation of spermatogonial cells to meiotic and postmeiotic stages (BOULE- and ACROSIN-positive cells) under in vitro culture conditions, using methylcellulose culture system (MCS). Thus, it is possible to suggest that CSF-1 system, as a testicular paracrine/autocrine system, is involved in the development of different stages of spermatogenesis and may be used in the development of future therapeutic strategies for treatment of male infertility.

Interleukin-34, a Novel Paracrine/Autocrine Factor in Mouse Testis, and Its Possible Role in the Development of Spermatogonial Cells In Vitro.

Spermatogenesis is the process of spermatogonial stem cell (SSC) proliferation and differentiation to generate sperm. This process is regulated by cell-cell interactions between Sertoli cells and developing SSCs by autocrine/paracrine and endocrine factors. It is also affected by cells in the interstitial compartment, such as Leydig cells and peritubular cells. Here, we demonstrate, for the first time, the presence of interleukin-34 (IL-34) in Leydig, Sertoli, and peritubular cells and in the premeiotic, meiotic, and postmeiotic cells. Its receptor, colony-stimulating factor-1 (CSF-1), has already been demonstrated in Leydig, Sertoli, premeiotic, and meiotic cells. IL-34 was detected in testicular homogenates and Sertoli cell-conditioned media, and was affected by mouse age. We showed that the addition of IL-34 in vitro to isolated cells from the seminiferous tubules of 7-day-old mice, using the methylcellulose culture system (MCS), increased the percentages and expression of the premeiotic cells (VASA), the meiotic cells (BOULE), and the meiotic/postmeiotic cells (ACROSIN) after four weeks of culture, when examined by immunofluorescence staining (IF) and qPCR analysis. It is possible to suggest that IL-34 is a novel paracrine/autocrine factor involved in the development of spermatogenesis. This factor may be used in future therapeutic strategies for the treatment of male infertility.

Effect of the CSF1R inhibitor PLX3397 on remyelination of corpus callosum in a cuprizone-induced demyelination mouse model.

Multiple sclerosis (MS) is a chronic inflammatory disease affecting the central nervous system (CNS). Despite introducing multiple immunomodulatory approaches for MS, there are still major concerns about possible ways for improving remyelination in this disease. Microglia exert essential roles in regulation of myelination processes, and interaction between colony-stimulating factor 1 (CSF1) with its receptor CSF1R is considered as a key regulator of microglial differentiation and survival. The aim of this study was to investigate possible roles for a CSF1R inhibitor PLX3397 in recovery of central myelination processes. Chronic demyelination was induced in mice by addition of 0.2% cuprizone to the chow for 12 weeks. Next, animals were undergoing a diet containing 290 mg/kg PLX3397 to induce microglial ablation. The PLX3397 treatment caused a significant decrease in the rate of expression for the CSF1/CSF1R axis, and a reduction in the protein expressions for the microglial marker Iba-1 and for the oligodendrocyte marker Olig-2. Findings from Luxol fast blue (LFB) staining and transmission electron microscopy (TEM) showed an increase in the rate of myelination for the mice receiving PLX3397. The rate of destruction in the nerve fibers and the extent of the gaps formed between layers of myelin sheaths was also reduced after the treatment with PLX3397. In addition, animals experienced an improvement in recovery of motor deficit after receiving PLX3397 (for all P < 0.05). It could be concluded that PLX3397 could retain myelination in the MS model possibly through regulation of the myelin environment.

Expression of A New Endogenous Retrovirus-Associated Transcript in Hodgkin Lymphoma Cells.

During characterization of a cDNA library from the Hodgkin lymphoma (HL) cell line L-1236, we discovered a new transcript derived from chromosome 1 at the long intergenic non-protein coding RNA 1768 (LINC01768)/colony stimulating factor 1 (CSF1) region. The first exon of this transcript from Hodgkin lymphoma cells (THOLE) starts in the predicted exon 4 of LINC01768 and is part of an endogenous retrovirus (ERV) from the HUERS-P1/LTR8 family. High expression of THOLE was only detectable in HL cell line L-1236. The expression of THOLE in L-1236 cell is another example for ERV/LTR-associated gene expression in HL cells. At the genome level, the HUERS-P1/LTR8 region including THOLE is only present in Hominoidea. The influence of ERV/LTRs on gene expression might explain the characteristic phenotype of human HL.

c-Abl-dependent molecular circuitry involving Smad5 and phosphatidylinositol 3-kinase regulates bone morphogenetic protein-2-induced osteogenesis.

Skeletal remodeling consists of timely formation and resorption of bone by osteoblasts and osteoclasts in a quantitative manner. Patients with chronic myeloid leukemia receiving inhibitors of c-Abl tyrosine kinase often show reduced bone remodeling due to impaired osteoblast and osteoclast function. BMP-2 plays a significant role in bone generation and resorption by contributing to the formation of mature osteoblasts and osteoclasts. The effects of c-Abl on BMP-2-induced bone remodeling and the underlying mechanisms are not well studied. Using a pharmacological inhibitor and expression of a dominant negative mutant of c-Abl, we show an essential role of this tyrosine kinase in the development of bone nodules containing mature osteoblasts and formation of multinucleated osteoclasts in response to BMP-2. Calvarial osteoblasts prepared from c-Abl null mice showed the absolute requirement of this tyrosine kinase in maturation of osteoblasts and osteoclasts. Activation of phosphatidylinositol 3-kinase (PI 3-kinase)/Akt signaling by BMP-2 leads to osteoblast differentiation. Remarkably, inhibition of c-Abl significantly suppressed BMP-2-stimulated PI 3-kinase activity and its downstream Akt phosphorylation. Interestingly, c-Abl regulated BMP-2-induced osteoclastogenic CSF-1 expression. More importantly, we identified the requirements of c-Abl in BMP-2 autoregulation and the expressions of alkaline phosphatase and osterix that are necessary for osteoblast differentiation. c-Abl contributed to BMP receptor-specific Smad-dependent transcription of CSF-1, osterix, and BMP-2. Finally, c-Abl associates with BMP receptor IA and regulates phosphorylation of Smad in response to BMP-2. We propose that activation of c-Abl is an important step, which induces into two signaling pathways involving noncanonical PI 3-kinase and canonical Smads to integrate BMP-2-induced osteogenesis.

Optical controlled and nuclear targeted CECR2 competitor to downregulate CSF-1 for metastatic breast cancer immunotherapy.

The crosstalk between breast cancer cells and tumor associated macrophages (TAMs) greatly contributes to tumor progression and immunosuppression. In this work, cat eye syndrome chromosome region candidate 2 (CECR2) is identified to overexpress in breast cancer patients, which can recognize v-rel avian reticuloendotheliosis viral oncogene homolog A (RelA) and activate nuclear factor κB (NF-κB) to release colony stimulating factor-1 (CSF-1). Pharmacological inhibition of CECR2 by the bromodomain competitor (Bromosporine, Bro) can downregulate CSF-1 to inhibit M2 type TAMs. To amplify the immunotherapeutic effect, a chimeric peptide-based and optical controlled CECR2 competitor (designated as N-PB) is constructed to enhance the nuclear targeted delivery of Bro and initiate an immunogenic cell death (ICD). In vivo results indicate a favorable breast cancer targeting ability and primary tumor suppression effect of N-PB under optical irradiation. Importantly, N-PB downregulates CSF-1 by competitive inhibition of CECR2 and NF-κB(RelA) interactions, thus inhibiting immunosuppressive M2-like TAMs while improving the antitumorigenic M1-like phenotype. Ultimately, the systemic anti-tumor immunity is activated to suppress the metastatic breast cancer in an optical controlled manner. This study provides a promising therapeutic target and reliable strategy for metastatic breast cancer treatment by interrupting immunosuppressive crosstalk between tumor cells and macrophages.

Liver enzyme delayed clearance in rat treated by CSF1 receptor specific antagonist Sotuletinib.

Sotuletinib (BLZ945), a CSF1-R specific kinase inhibitor developed for the treatment of Amyotrophic Lateral Sclerosis, induced liver enzyme elevation in absence of hepatocellular lesions in preclinical rat and monkey studies. The monocytic cell family, including Kupffer cells, e.g., the liver-resident macrophages, are dependent upon CSF1 pathway activation for their survival, proliferation, and differentiation. Kupffer cells act as the main body compartment responsible for elimination of some blood-borne proteins, like ALT, AST, and few others. The depletion of Kupffer cells through CSF1 pathway inhibition has already been hypothesized as responsible for apparent liver enzyme elevation without detectable corresponding liver damage. However, a release of these biomarkers from unseen hepatic lesions or from other organs cannot be excluded. In order to eliminate a potential contribution of ALT elevation from an internal organ source, we injected recombinant his-Tagged ALT1 into rats pretreated with Sotuletinib. The elimination rate of the exogenous ALT1 was significantly lower in treated animals, demonstrating a delayed clearance independently of any potential organ lesions.

The evolving landscape of 'next-generation' immune checkpoint inhibitors: A review.

'First-generation' immune checkpoint inhibitors targeting Cytotoxic T-Lymphocyte Antigen 4 (CTLA4) and Programmed death-ligand 1 (PD(L)1) have undoubtedly revolutionised the treatment of multiple cancers in the advanced setting. Targeting signalling pathways other than core inhibitory modules may strongly impact the outcome of the antitumour immune response. Drugs targeting these pathways ('next-generation' immune modulators, NGIMs) constitute a major frontier in translational research and have generated unprecedented scientific and financial investment. Here, we systematically reviewed published literature, abstracts from major cancer conferences and pharma pipelines to identify NGIMs that have reached clinical development. We identified 107 molecules targeting 16 pathways, which we classified into 6 groups according to function (inhibitory vs stimulatory) and cell of predominant expression (lymphoid, non-lymphoid and natural killer). We identified all registered past and ongoing clinical trials (n = 428). We summarise the preclinical rationale for these targets, extracting translationally relevant information, and review published and preliminary clinical results. Some targets like indoleamine-2,3-dioxygenase 1, lymphocyte activation gene-3 and IL15 have experienced exceptional growth of interest, measured in terms of activated studies and expected patient enrolment over time. We conclude that in this vast and rapidly changing drug development landscape, novel trial designs and better biomarker identification are necessary to optimise resource allocation.

Increased Microglial CSF1R Expression in the SIV/Macaque Model of HIV CNS Disease.

Chronic microglial activation and associated neuroinflammation are key factors in neurodegenerative diseases including HIV-associated neurocognitive disorders. Colony stimulating factor 1 receptor (CSF1R)-mediated signaling is constitutive in cells of the myeloid lineage, including microglia, promoting cell survival, proliferation, and differentiation. In amyotrophic lateral sclerosis and Alzheimers disease, CSF1R is upregulated. Inhibiting CSF1R signaling in animal models of these diseases improved disease outcomes. In our studies, CNS expression of the CSF1R ligand, colony-stimulating factor 1 (CSF1) was significantly increased in a SIV/macaque model of HIV CNS disease. Using a Nanostring nCounter immune panel, we found CSF1 overexpression was strongly correlated with upregulation of microglial genes involved in antiviral and oxidative stress responses. Using in situ hybridization, we found that CSF1R mRNA was only present in Iba-1 positive microglia. By ELISA and immunostaining with digital image analysis, SIV-infected macaques had significantly higher CSF1R levels in frontal cortex than uninfected macaques (p = 0.018 and p = 0.02, respectively). SIV-infected macaques treated with suppressive ART also had persistently elevated CSF1R similar to untreated SIV-infected macaques. Coordinate upregulation of CSF1 and CSF1R expression implicates this signaling pathway in progressive HIV CNS disease.