CSF-1 maintains pathogenic but not homeostatic myeloid cells in the central nervous system during autoimmune neuroinflammation.

The receptor for colony stimulating factor 1 (CSF-1R) is important for the survival and function of myeloid cells that mediate pathology during experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). CSF-1 and IL-34, the ligands of CSF-1R, have similar bioactivities but distinct tissue and context-dependent expression patterns, suggesting that they have different roles. This could be the case in EAE, given that CSF-1 expression is up-regulated in the CNS, while IL-34 remains constitutively expressed. We found that targeting CSF-1 with neutralizing antibody halted ongoing EAE, with efficacy superior to CSF-1R inhibitor BLZ945, whereas IL-34 neutralization had no effect, suggesting that pathogenic myeloid cells were maintained by CSF-1. Both anti­CSF-1 and BLZ945 treatment greatly reduced the number of monocyte-derived cells and microglia in the CNS. However, anti­CSF-1 selectively depleted inflammatory microglia and monocytes in inflamed CNS areas, whereas BLZ945 depleted virtually all myeloid cells, including quiescent microglia, throughout the CNS. Anti­CSF-1 treatment reduced the size of demyelinated lesions and microglial activation in the gray matter. Lastly, we found that bone marrow­derived immune cells were the major mediators of CSF-1R­dependent pathology, while microglia played a lesser role. Our findings suggest that targeting CSF-1 could be effective in ameliorating MS pathology, while preserving the homeostatic functions of myeloid cells, thereby minimizing risks associated with ablation of CSF-1R­dependent cells.

The Colony Stimulating Factor-1 Receptor (CSF-1R)-Mediated Regulation of Microglia/Macrophages as a Target for Neurological Disorders (Glioma, Stroke).

Immunomodulatory therapies have fueled interest in targeting microglial cells as part of the innate immune response after infection or injury. In this context, the colony-stimulating factor 1 (CSF-1) and its receptor (CSF-1R) have gained attention in various neurological conditions to deplete and reprogram the microglia/macrophages compartment. Published data in physiological conditions support the use of small-molecule inhibitors to study microglia/macrophages dynamics under inflammatory conditions and as a therapeutic strategy in pathologies where those cells support disease progression. However, preclinical and clinical data highlighted that the complexity of the spatiotemporal inflammatory response could limit their efficiency due to compensatory mechanisms, ultimately leading to therapy resistance. We review the current state-of-art in the field of CSF-1R inhibition in glioma and stroke and provide an overview of the fundamentals, ongoing research, potential developments of this promising therapeutic strategy and further application toward molecular imaging.

Discovery of (Z)-1-(3-((1H-Pyrrol-2-yl)methylene)-2-oxoindolin-6-yl)-3-(isoxazol-3-yl)urea Derivatives as Novel and Orally Highly Effective CSF-1R Inhibitors for Potential Colorectal Cancer Immunotherapy.

Inhibiting the polarization or survival of tumor-associated macrophages through blocking CSF-1/CSF-1R signal transduction has become a promising strategy for cancer immunotherapy. Herein, a series of (Z)-1-(3-((1H-pyrrol-2-yl)methylene)-2-oxoindolin-6-yl)-3-(isoxazol-3-yl)urea derivatives were designed, synthesized, and evaluated as novel and orally highly effective CSF-1R inhibitors for colorectal cancer immunotherapy. Among these derivatives, compound 21 was found to possess excellent CSF-1R inhibitory activity (IC50 = 2.1 nM) and potent antiproliferative activity against colorectal cancer cells. Compound 21 inhibited the progression of colorectal cancer by suppressing the migration of macrophages, reprograming M2-like macrophages to the M1 phenotype, and enhancing the antitumor immunity. More importantly, compound 21, as a single agent, showed significantly superior in vivo anticolorectal cancer efficacy over PLX3397, highlighting a promising candidate for the immunotherapy of colorectal cancer.

Discovery of BPR1R024, an Orally Active and Selective CSF1R Inhibitor that Exhibits Antitumor and Immunomodulatory Activity in a Murine Colon Tumor Model.

Colony-stimulating factor-1 receptor (CSF1R) is implicated in tumor-associated macrophage (TAM) repolarization and has emerged as a promising target for cancer immunotherapy. Herein, we describe the discovery of orally active and selective CSF1R inhibitors by property-driven optimization of BPR1K871 (9), our clinical multitargeting kinase inhibitor. Molecular docking revealed an additional nonclassical hydrogen-bonding (NCHB) interaction between the unique 7-aminoquinazoline scaffold and the CSF1R hinge region, contributing to CSF1R potency enhancement. Structural studies of CSF1R and Aurora kinase B (AURB) demonstrated the differences in their back pockets, which inspired the use of a chain extension strategy to diminish the AURA/B activities. A lead compound BPR1R024 (12) exhibited potent CSF1R activity (IC50 = 0.53 nM) and specifically inhibited protumor M2-like macrophage survival with a minimal effect on antitumor M1-like macrophage growth. In vivo, oral administration of 12 mesylate delayed the MC38 murine colon tumor growth and reversed the immunosuppressive tumor microenvironment with the increased M1/M2 ratio.

Effect of CSF1R inhibitor on glial cells population and remyelination in the cuprizone model.

Multiple sclerosis is a kind of autoimmune and demyelinating disease with pathological symptoms such as inflammation, myelin loss, astrocytosis, and microgliosis. The colony stimulating factor 1 receptor (CSF1R) is an essential factor for the microglial function, and PLX3397 (PLX) is its specific inhibitor. In this wstudy, we assessed the effect of different doses of PLX for microglial ablation on glial cell population and remyelination process. Sixty male C57BL/6 mice (8 weeks old) were divided into 6 groups. The animals were fed with 0.2% cuprizone diet for 12 weeks. For microglial ablation, PLX (290 mg/kg) was added to the animal food for 3, 7, 14 and 21 days. Glial cell population was measured using immunohistochemistry. The rate of remyelination was evaluated using electron microscopy and Luxol Fast Blue staining. The expression levels of all genes were assessed by qRT-PCR method. Data were analysed using GraphPad Prism and SPSS software. The results showed that the administration of different doses of PLX significantly reduced microglial cells (p ≤ .001). PLX administration also significantly increased oligodendrocytes population (p ≤ .001) and remyelination compared to the cuprizone mice, which was aligned with the results of LFB and TEM. Gene results showed that PLX treatment reduced CSF1R expression. According to the results, the administration of PLX for 21 days enhanced remyelination by increasing oligodendrocytes in the chronic demyelination model. These positive effects could be related to the reduction of microglia.

The receptor of the colony-stimulating factor-1 (CSF-1R) is a novel prognostic factor and therapeutic target in follicular lymphoma.

Microenvironment contributes to follicular lymphoma (FL) pathogenesis and impacts survival with macrophages playing a controversial role. In the present study, using FL primary samples and HK follicular dendritic cells (FDC) to mimic the germinal center, together with mouse models, we have analyzed the three-way crosstalk of FL-FDC-macrophages and derived therapeutic opportunities. Ex vivo primary FL-FDC co-cultures (n = 19) and in vivo mouse co-xenografts demonstrated that FL-FDC crosstalk favors tumor growth and, via the secretion of CCL2 and CSF-1, promotes monocyte recruitment, differentiation, and polarization towards an M2-like protumoral phenotype. Moreover, FL-M2 co-cultures displayed enhanced angiogenesis, dissemination, and immunosuppression. Analysis of the CSF-1/CSF-1R pathway uncovered that CSF-1 was significantly higher in serum from grade 3A FL patients, and that high CSF-1R expression in FL biopsies correlated with grade 3A, reduced overall survival and risk of transformation. Furthermore, CSF-1R inhibition with pexidartinib (PLX3397) preferentially affected M2-macrophage viability and polarization program disrupting FL-M2 positive crosstalk. In vivo CSF1-R inhibition caused M2 reduction and repolarization towards M1 macrophages and antitumor effect cooperating with anti-CD20 rituximab. In summary, these results support the role of macrophages in FL pathogenesis and indicate that CSF-1R may be a relevant prognostic factor and a novel therapeutic target cooperating with anti-CD20 immunotherapy.

Pulmonary administration of a CSF-1R inhibitor alters the balance of tumor-associated macrophages and supports first-line chemotherapy in a lung cancer model.

Lung cancers remain the leading cause of cancer-related death in both men and women. Infiltrating immune cells in the tumor microenvironment (TME) play a critical role in the formation, progression, and the response of solid tumors to therapy, including in lung cancers. Clinical studies have established that tumor-associated macrophages (TAMs) and their phenotypical composition are critical immune infiltrates in the lung TME, with the abundance of the M2-like phenotype negatively correlating with patient survival. Colony-Stimulating Factor 1 (CSF-1) receptor (CSF-1R) is a type III protein tyrosine kinase receptor that plays an important role in the recruitment and differentiation of monocytes into tumor-promoting M2-like TAMs and their survival. In this work we evaluated the therapeutic potential of PLX 3397 (PLX), a small molecule CSF-1R inhibitor (CSF-1Ri), upon local lung administration in an immune-competent mouse model of lung cancer. The efficacy of local lung delivered PLX as single therapy was investigated first. As assessed by immunofluorescence of sections of lung tumor nodules, a statistically significant reduction in M2-like TAMs and an increase in M1-like TAMs was observed, thus leading to a shift in the (M1/M2) balance. Those changes in abundance of immune infiltrates correlated with a significant decrease in tumor burden when compared to control. When combined with systemically administered cisplatin (CIS) PLX treatment provided further benefits, leading to a significant decrease in tumor burden when compared to either PLX or CIS treatments alone, as measured by bioluminescence intensity (BLI) in vivo (thoracic area) and ex vivo (lung tissue). This combination therapy led to the most pronounced increase in M1/M2 ratio, followed by a significant decrease in M2-like TAMs with the CIS therapy. This work is clinically relevant as it demonstrates the potential of local lung administration of PLX to support standard of care chemotherapy for lung cancer management. This is important as the pulmonary route of administration is a plausible strategy for reducing the total dose of CSF-1Ris as the tissue of interest (lungs) can be locally targeted. Because the major off-target effect of CSF-1Ris is liver toxicity, reducing systemic concentration will support translation of those therapies, especially in combination with standard of care chemotherapy that has significant off-target toxicity and patient attrition itself. This work is scientifically relevant as we demonstrate for the first time that local administration of a CSF-1Ri to the lungs leads to a shift in the balance of TAMs in the TME of a model of lung tumor, adding to the sparse literature of CSF-1Ris related to lung cancers.

Prospects of Treating Tenosynovial Giant Cell Tumor through Pexidartinib: A Review.

BACKGROUND: Tenosynovial giant cell tumor refers to a group of rarely occurring tumors that are formed in the joints, which are characterized by pain, swelling, and limitation of movement of the joint. Surgery is the main treatment strategy, but the tumor is likely to recur, especially in pigmented villonodular synovitis, which is the diffuse-type giant cell tumor. Pexidartinib was approved in August 2019 by the Food and Drug Administration (FDA) with a brand name TURALIO as the first systemic approved therapy for patients having Tenosynovial Giant Cell Tumors (TGCT). OBJECTIVE: In this review, different aspects pertaining to pexidartinib have been summarized, including the pathophysiology of TGCT, chemistry, pharmacokinetics and pharmacodynamics of pexidartinib. Special attention is given to various reported clinical trials of pexidartinib. METHODS: A comprehensive literature search was conducted in the relevant databases to identify studies published in this field during recent years. CONCLUSION: Pexidartinib acts by inhibiting the Colony-Stimulating Factor (CSF1)/CSF1 receptor pathway, which leads to the inhibition of the cell lines proliferation and promotes the autophosphorylation process of the ligand-induced CSF1 receptor. Pexidartinib emerged as a potential drug candidate for the treatment of TGCT.

Small-molecule CSF1R kinase inhibitors; review of patents 2015-present.

INTRODUCTION: Colony stimulating factor 1 receptor (CSF-1R, also known as c-FMS kinase) is in the class III receptor tyrosine kinase family, along with c-Kit, Flt3 and PDGFRα. CSF-1/CSF-1R signaling promotes the differentiation and survival of myeloid progenitors into populations of monocytes, macrophages, dendritic cells and osteoclasts, as well as microglial cells and also recruits host macrophages to develop into tumor-associated macrophages (TAMs), which promote tumor progression and metastasis. AREAS COVERED: In the last 5 years, and recently stimulated by the approval of pexidartinib (Turalio™, Daiichi Sankyo) in 2019 for the treatment of tenosynovial giant cell tumors, there has been a large increase in activity (both journal articles and patent applications) around small molecule inhibitors of CSF1R. Features of this work have been the surprising diversity of chemical classes shown to be potent and selective inhibitors, and the breadth of disease states (cancer, arthritis, and 'cytokine storm' syndromes) covered by CSF1R inhibitors. All these aspects are covered in the following sections. EXPERT OPINION: The field has developed rapidly from 2014 to the present, with many different chemotypes proving to be potent inhibitors. The range of potential utilities of CSF1R inhibitors has also expanded to include dementia, ulcerative colitis/Crohn's disease, rheumatoid arthritis inflammation, and fibrosis.

Therapeutic Targeting of Retinal Immune Microenvironment With CSF-1 Receptor Antibody Promotes Visual Function Recovery After Ischemic Optic Neuropathy.

Retinal ischemia/reperfusion injury (RI) is a common cause of irreversible visual impairment and blindness in elderly and critical unmet medical need. While no effective treatment is available for RI, microglial activation and local immune responses in the retina are thought to play important roles in the pathophysiology of neurodegeneration. While survival and activation of microglia depend critically on colony-stimulating factor receptor (CSF-1R) signaling, it remains unclear if targeting the retinal immune microenvironments by CSF-1RAb after RI is sufficient to rescue vision and present a potentially effective therapy. Here we used rodent models of RI and showed that retinal ischemia induced by acute elevation of intraocular pressure triggered an early activation of microglia and macrophages in the retina within 12 h. This was followed by lymphocyte infiltration and increased production of pro-inflammatory cytokines. Intravitreal injection of CSF-1R neutralizing antibody (CSF-1RAb) after RI significantly blocked microglial activation and the subsequent T cell recruitment. This also led to improved retinal ganglion cell survival and function measured by cell quantification and electroretinogram positive scotopic threshold responses, as well as increased visual acuity and contrast sensitivity as assessed by optomotor reflex-based assays, when compared to the isotype-treated control group. Moreover, the administration of CSF-1RAb efficiently attenuated inflammatory responses and activation of human microglia in culture, suggesting a therapeutic target with human relevance. These results, together with the existing clinical safety profiles, support that CSF-1RAb may present a promising therapeutic avenue for RI, a currently untreatable condition, by targeting microglia and the immune microenvironment in the retina to facilitate neural survival and visual function recovery.

Phase Ib study of anti-CSF-1R antibody emactuzumab in combination with CD40 agonist selicrelumab in advanced solid tumor patients.

BACKGROUND: This phase Ib study evaluated the safety, clinical activity, pharmacokinetics, and pharmacodynamics (PD) of emactuzumab (anti-colony stimulating factor 1 receptor monoclonal antibody (mAb)) in combination with selicrelumab (agonistic cluster of differentiation 40 mAb) in patients with advanced solid tumors. METHODS: Both emactuzumab and selicrelumab were administered intravenously every 3 weeks and doses were concomitantly escalated (emactuzumab: 500 to 1000 mg flat; selicrelumab: 2 to 16 mg flat). Dose escalation was conducted using the product of independent beta probabilities dose-escalation design. PD analyzes were performed on peripheral blood samples and tumor/skin biopsies at baseline and on treatment. Clinical activity was evaluated using investigator-based and Response Evaluation Criteria In Solid Tumors V.1.1-based tumor assessments. RESULTS: Three dose-limiting toxicities (all infusion-related reactions (IRRs)) were observed at 8, 12 and 16 mg of selicrelumab together with 1000 mg of emactuzumab. The maximum tolerated dose was not reached at the predefined top doses of emactuzumab (1000 mg) and selicrelumab (16 mg). The most common adverse events were IRRs (75.7%), fatigue (54.1%), facial edema (37.8%), and increase in aspartate aminotransferase and creatinine phosphokinase (35.1% both). PD analyzes demonstrated an increase of Ki67+-activated CD8+ T cells accompanied by a decrease of B cells and the reduction of CD14Dim CD16bright monocytes in peripheral blood. The best objective clinical response was stable disease in 40.5% of patients. CONCLUSION: Emactuzumab in combination with selicrelumab demonstrated a manageable safety profile and evidence of PD activity but did not translate into objective clinical responses. TRIALREGISTRATION NUMBER: NCT02760797.

Targeting colony stimulating factor-1 receptor signalling to treat ectopic pregnancy.

1-2% of pregnancies are ectopic, the majority implanting in the Fallopian tube. A single, systemic dose of methotrexate, a DNA-synthesis (S phase) inhibitor, has been used since 1991 for outpatient treatment of women with stable EP. However, methotrexate has limited clinical and cost effectiveness, restricting its use to 25-30% of these women. There is an unmet need for better medical treatment for EP. Colony stimulating factor-1 (CSF-1) promotes placentation and creates a pro-inflammatory environment that is fundamental for the maintenance of a normal pregnancy. We hypothesised that CSF-1 is also involved in the placentation and maintenance of an EP. Herein, we demonstrate the immunolocalisation of the CSF-1 receptor (CSF-1R) as well as its ligand (CSF-1) in immortalised first trimester trophoblast cells. We show that a specific CSF-1R kinase inhibitor, GW2580, abolishes CSF-1 induced trophoblast cell proliferation and migration and can be cytotoxic. We then demonstrate the expression of CSF-1R and CSF-1 in the cytotrophoblast and syncytiotrophoblast within ectopic implantation sites from women with EP. Our data suggests that CSF-1 is involved in the survival and proliferation of trophoblast cells in EP. This suggests that pharmacological disruption of CSF-1/CSF-1R signaling axis could be the basis of a new therapeutic for EP.

Immunomodulatory Activity of a Colony-stimulating Factor-1 Receptor Inhibitor in Patients with Advanced Refractory Breast or Prostate Cancer: A Phase I Study.

PURPOSE: Tumor-associated macrophages correlate with increased invasiveness, growth, and immunosuppression. Activation of the colony-stimulating factor-1 receptor (CSF-1R) results in proliferation, differentiation, and migration of monocytes/macrophages. This phase I study evaluated the immunologic and clinical activity, and safety profile of CSF-1R inhibition with the mAb LY3022855. PATIENTS AND METHODS: Patients with advanced refractory metastatic breast cancer (MBC) or metastatic castration-resistant prostate cancer (mCRPC) were treated with LY3022855 intravenously in 6-week cycles in cohorts: (A) 1.25 mg/kg every 2 weeks (Q2W); (B) 1.0 mg/kg on weeks 1, 2, 4, and 5; (C) 100 mg once weekly; (D)100 mg Q2W. mCRPC patients were enrolled in cohorts A and B; patients with MBC were enrolled in all cohorts. Efficacy was assessed by RECIST and Prostate Cancer Clinical Trials Working Group 2 criteria. RESULTS: Thirty-four patients (22 MBC; 12 mCRPC) received ≥1 dose of LY3022855. At day 8, circulating CSF-1 levels increased and proinflammatory monocytes CD14DIMCD16BRIGHT decreased. Best RECIST response was stable disease in five patients with MBC (23%; duration, 82-302 days) and three patients with mCRPC (25%; duration, 50-124 days). Two patients with MBC (cohort A) had durable stable disease >9 months and a third patient with MBC had palpable reduction in a nontarget neck mass. Immune-related gene activation in tumor biopsies posttreatment was observed. Common any grade treatment-related adverse events were fatigue, decreased appetite, nausea, asymptomatic increased lipase, and creatine phosphokinase. CONCLUSIONS: LY3022855 was well tolerated and showed evidence of immune modulation. Clinically meaningful stable disease >9 months was observed in two patients with MBC.

CSF-1R inhibition attenuates ischemia-induced renal injury and fibrosis by reducing Ly6C+ M2-like macrophage infiltration.

Acute kidney injury (AKI) to chronic kidney disease (CKD) progression has become a life-threatening disease. However, an effective therapeuticstrategyis still needed. The pathophysiology of AKI-to-CKD progression involves chronic inflammation and renal fibrosis driven by macrophage activation, which is physiologically dependent on colony-stimulating factor-1 receptor (CSF-1R) signaling. In this study, we modulated macrophage infiltration through oral administration of the CSF-1R inhibitor GW2580 in an ischemia-reperfusion (I/R)-induced AKI model to evaluate its therapeutic effects on preventing the progression of AKI to CKD. We found that GW2580 induced a significant reduction in the number of macrophages in I/R-injured kidneys and attenuated I/R-induced renal injury and subsequent interstitial fibrosis. By flow cytometry, we observed that the reduced macrophages were primarily Ly6C+ inflammatory macrophages in the GW2580-treated kidneys, while there was no significant difference in the number and percentage of Ly6C-CX3CR1+ macrophages. We further found that these reduced macrophages also demonstrated some characteristics of M2-like macrophages, which have been generally regarded as profibrotic subtypes in chronic inflammation. These results indicate the existence of phenotypic and functional crossover between Ly6C+ and M2-like macrophages in I/R kidneys, which induces AKI worsening to CKD. In conclusion, therapeutic GW2580 treatment alleviates acute renal injury and subsequent fibrosis by reducing Ly6C+ M2-like macrophage infiltration in ischemia-induced AKI.

The M-CSF receptor in osteoclasts and beyond.

Colony-stimulating factor 1 receptor (CSF1R, also known as c-FMS) is a receptor tyrosine kinase. Macrophage colony-stimulating factor (M-CSF) and IL-34 are ligands of CSF1R. CSF1R-mediated signaling is crucial for the survival, function, proliferation, and differentiation of myeloid lineage cells, including osteoclasts, monocytes/macrophages, microglia, Langerhans cells in the skin, and Paneth cells in the intestine. CSF1R also plays an important role in oocytes and trophoblastic cells in the female reproductive tract and in the maintenance and maturation of neural progenitor cells. Given that CSF1R is expressed in a wide range of myeloid cells, altered CSF1R signaling is implicated in inflammatory, neoplastic, and neurodegenerative diseases. Inhibiting CSF1R signaling through an inhibitory anti-CSF1R antibody or small molecule inhibitors that target the kinase activity of CSF1R has thus been a promising therapeutic strategy for those diseases. In this review, we cover the recent progress in our understanding of the various roles of CSF1R in osteoclasts and other myeloid cells, highlighting the therapeutic applications of CSF1R inhibitors in disease conditions.

Anti-c-fms Antibody Prevents Osteoclast Formation and Bone Resorption in Co-Culture of Osteoblasts and Osteoclast Precursors In Vitro and in Ovariectomized Mice.

Osteoporosis morphology is characterized by bone resorption and decreases in micro-architecture parameters. Anti-osteoporosis therapy targets osteoclasts because bone resorption is a unique function of osteoclasts. Anti-c-fms antibodies against the receptor for macrophage colony-stimulating factor (M-CSF) inhibit osteoclast formation and bone resorption in vitro and in vivo. However, the effect of anti-c-fms antibodies on bone resorption in ovariectomized (OVX) mice is unknown. In this study, we evaluated the effect of anti-c-fms antibodies on osteoclast formation and bone resorption in osteoblast-osteoclast precursor co-culture in vitro and in OVX mice. Osteoblast and osteoclast precursor co-cultures treated with anti-c-fms antibodies showed significantly inhibited osteoclast formation, while cultures without anti-c-fms antibody treatment showed osteoclast formation. However, anti-c-fms antibodies did not change the receptor activator of nuclear factor kappa-B ligand (RANKL) or osteoprotegrin (OPG) expression during osteoblast and osteoclast differentiation in vitro. These results indicate that anti-c-fms antibodies directly affected osteoclast formation from osteoclast precursors in co-culture. OVX mice were treated with intraperitoneal injections of anti-c-fms antibody. The trabecular bone structure of the femur was assessed by micro-computer tomography. The anti-c-fms antibody inhibited osteoclast formation and bone loss compared with PBS-treated OVX mice. These results indicate potential for the therapeutic application of anti-c-fms antibodies for postmenopausal osteoporosis.

Cerebrospinal fluid penetration of the colony-stimulating factor-1 receptor (CSF-1R) inhibitor, pexidartinib.

PURPOSE: Pexidartinib (PLX3397) is a colony-stimulating factor-1 receptor (CSF-1R) inhibitor under clinical evaluation for potential CNS tumor treatment. This study aims to evaluate plasma pharmacokinetic parameters and estimate CNS penetrance of pexidartinib in a non-human primate (NHP) cerebrospinal fluid (CSF) reservoir model. METHODS: Five male rhesus macaques, each with a previously implanted subcutaneous CSF ventricular reservoir and central venous lines, were used. NHPs received a single dose of 40 mg/kg pexidartinib (human equivalent dose of 800 mg/m2), administered orally as 200 mg tablets. Serial paired samples of blood and CSF were collected at 0-8, 24, 48, and 72 h. Pexidartinib concentrations were assayed by Integrated Analytical Solutions, Inc. (Berkeley, CA, USA) using HPLC/MS/MS. Pharmacokinetic (PK) analysis was performed using noncompartmental methods. RESULTS: Samples from four NHPs were evaluable. Average (± SD) plasma PK parameters were as follows: Cmax = 16.50 (± 6.67) µg/mL; Tmax = 5.00 (± 2.58) h; AUClast = 250.25 (± 103.76) h*µg/mL; CL = 0.18 (± 0.10) L/h/kg. In CSF, pexidartinib was either quantifiable (n = 2), with Cmax values of 16.1 and 10.1 ng/mL achieved 2-4 h after plasma Tmax, or undetected at all time points (n = 2, LLOQCSF = 5 ng/mL). CONCLUSION: Pexidartinib was well-tolerated in NHPs, with no Grade 3 or Grade 4 toxicities. The CSF penetration of pexidartinib after single-dose oral administration to NHPs was limited.

Blockade of the colony-stimulating factor-1 receptor reverses bone loss in osteoporosis mouse models.

BACKGROUND: Mice lacking either colony-stimulating factor-1 (CSF-1) or its receptor, CSF-1R, display osteopetrosis. Accordingly, genetic deletion or pharmacological blockade of CSF-1 prevents the bone loss associated with estrogen deficiency. However, the role of CSF-1R in osteoporosis models of type-1 diabetes (T1D) and ovariectomy (OVX) has not been examined. Thus, we evaluated whether CSF-1R blockade would relieve the bone loss in a model of primary osteoporosis (female mice with OVX) and a model of secondary osteoporosis (female with T1D) using micro-computed tomography. METHODS: Female ICR mice at 10 weeks underwent OVX or received five daily administrations of streptozotocin (ip, 50 mg/kg) to induce T1D. Four weeks after OVX and 14 weeks after first injection of streptozotocin, mice received an anti-CSF-1R (2G2) antibody (10 mg/kg, ip; once/week for 6 weeks) or vehicle. At the last day of antibody administration, mice were sacrificed and femur and tibia were harvested for micro-computed tomography analysis. RESULTS: Mice with OVX had a significant loss of trabecular bone at the distal femoral and proximal tibial metaphysis. Chronic treatment with anti-CSF-1R significantly reversed the trabecular bone loss at these anatomical sites. Streptozotocin-induced T1D resulted in significant loss of trabecular bone at the femoral neck and cortical bone at the femoral mid-diaphysis. Chronic treatment with anti-CSF-1R antibody significantly reversed the bone loss observed in mice with T1D. CONCLUSION: Our results demonstrate that blockade of CSF-1R signaling reverses bone loss in two different mouse models of osteoporosis.

Evaluation of the Neuroprotective Effect of Microglial Depletion by CSF-1R Inhibition in a Parkinson's Animal Model.

PURPOSE: Neuroinflammation in Parkinson's disease (PD) is known to play a pivotal role in progression to neuronal degeneration. It has been reported that colony-stimulation factor 1 receptor (CSF-1R) inhibition can effectively deplete microglia. However, its therapeutic efficacy in PD is unclear still now. PROCEDURES: To elucidate this issue, we examined the contribution of microglial depletion to PD by behavioral testing, positron emission tomography (PET) imaging, and immunoassays in sham, PD, and microglial depletion PD model (PLX3397 was administered to PD groups, with n = 6 in each group). RESULTS: The microglial depletion in PD model showed improved sensory motor function and depressive-like behavior. NeuroPET revealed that PLX3397 treatment resulted in partial recovery of striatal neuro-inflammatory functions (binding values of [18F]DPA-174 for PD, 1.47 ± 0.12, p < 0.01 vs. for PLX3397 in PD: 1.33 ± 0.26) and the dopaminergic (binding values of 18F-FP-CIT for PD, 1.32 ± 0.07 vs. for PLX3397 in PD: 1.54 ± 0.10, p < 0.01) and glutamatergic systems (binding values of [18F]FPEB for PD: 9.22 ± 0.54 vs. for PLX3397 Tx in PD: 9.83 ± 0.96, p > 0.05). Western blotting for microglia showed similar changes. CONCLUSION: Microglial depletion has inflammation-related therapeutic effects, which have beneficial effects on motor and nonmotor symptoms of PD.

Novel Class of Colony-Stimulating Factor 1 Receptor Kinase Inhibitors Based on an o-Aminopyridyl Alkynyl Scaffold as Potential Treatment for Inflammatory Disorders.

Colony-stimulating factor 1 receptor (CSF-1R) is involved in inflammatory disorders as well as in many types of cancer. Based on high-throughput screening and docking results, we performed a detailed structure-activity-relationship study, leading to the discovery of a new series of compounds with nanomolar IC50 values against CSF-1R without the inhibition of fibroblast growth factor receptors. One of the most promising hits, compound 29, potently inhibited CSF-1R kinase with an IC50 value of 0.7 nM, while it showed no inhibition to the same family member FMS-like tyrosine kinase 3. Compound 29 displayed excellent anti-inflammatory effects against RAW264.7 macrophages indicated by significant inhibition against the activation of the CSF-1R pathway with low cytotoxicity. In addition, compound 29 exhibited strong in vivo anti-inflammatory efficacy alongside favorable drug characteristics. This novel compound 29 may serve as a new drug candidate with promising applications in inflammatory disorders.