FGFR1 (IC50 = 10 nM); cFMS (IC50 = 20 nM); FLT3 (IC50 = 160 nM); KDR (IC50 = 350 nM); LCK (IC50 = 860 nM); FLT1 (IC50 = 880 nM); NTRK3 (IC50 = 890 nM)

Pexidartinib (PLX-3397) is an ATP-competitive, potent, and selective inhibitor of CSF1R (cFMS) and c-Kit that exhibits selectivity for c-Kit and CSF1R over other related kinases, FLT3, KDR (VEGFR2), LCK, FLT1 (VEGFR1), and NTRK3 (TRKC), with IC50 values of 160, 350, 860, 880, and 890 nM, respectively.

Pexidartinib (PLX3397; 0.25, 1 mg/kg, twice daily for 8 days) prevents the growth of BrdU-positive cells and microglia in neonatal mice[2].
Pexidartinib (1 mg/kg, twice daily for 8 day) does not appear to have any noticeable effects on mice's cleaved caspase-3-positive cells[2].

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Pexidartinib (50 mg/kg; p.o.; every second day for 3 weeks) lowers tissue macrophage counts in mice without changing the homeostasis of glucose[4].
PLX3397 treatment substantially reduced macrophage numbers in adipose tissue of both chow and high-fat diet fed mice without affecting total myeloid cell levels. Despite this, PLX3397 did not greatly alter glucose homeostasis, did not affect high-fat diet-induced increases in visceral fat cytokine expression (Il-6 and Tnfa) and had limited effect on the phosphorylation of the stress kinases JNK and ERK and macrophage polarization.[4]

Biochemical selectivity and potency of Pexidartinib (PLX3397): [1]
Pexidartinib (PLX3397) selectively inhibits the c-Fms and the c-Kit receptor tyrosine kinases, with biochemical IC50 values of 0.02 µM and 0.01 µM respectively (Figure S6A). Pexidartinib (PLX3397) was identified as a potent CSF-1R and c-KIT kinase inhibitor by using a Scaffold- and X-ray structure-based discovery approach. In a comprehensive screen of 226 different kinases, including representatives of all protein kinase subfamilies and several lipid kinases, Pexidartinib (PLX3397) at 0.03 µM and 1.0 µM only inhibited five other kinases significantly. Pexidartinib (PLX3397) was selected based on inhibition of the CSF1-dependent proliferation of the murine myelogenous leukemia cell line M-NFS-60, with an IC50 of 0.44 µM the murine macrophage cell line Bac1.2F5, with an IC50 of 0.22 µM. The human acute megakaryoblastic leukemia cell line M-07e, which depends on the addition of SCF for growth, was inhibited by Pexidartinib (PLX3397) with an IC50 of 0.1 µM. These sub-micromolar potencies confirm that Pexidartinib (PLX3397) can enter cells and inhibit Fms-driven cell growth.[1]

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Pexidartinib (PLX-3397) is an ATP-competitive, potent, and selective inhibitor of CSF1R (cFMS) and c-Kit that exhibits selectivity for c-Kit and CSF1R over other related kinases, FLT3, KDR (VEGFR2), LCK, FLT1 (VEGFR1), and NTRK3 (TRKC), with IC50 values of 160, 350, 860, 880, and 890 nM, respectively.

CSF1R activity promote the growth of T-cell lymphomas in-vitro[5]
Having established the expression and activation of CSF1R in TCL, we adopted a loss-of-function strategy to address its potential oncogenic role in these TCL using complementary molecular and pharmacologic approaches. We first used a clinically available and rationally designed tyrosine kinase inhibitor that is selective for CSF1R (Pexidartinib, PLX3397). In order to confirm CSF1R inhibition upon pexidartinib treatment, TCL cells with autocrine-activation of CSF1R were treated with pexidartinib. A marked decrease in CSF1R phosphorylation was observed upon treatment with pexidartinib (Figure 2A, supplementary figure 4A). Importantly, pexidartinib did not show any effect on the phosphorylation levels of the oncogenic kinase NPM-ALK which is expressed in a portion of the TCL cells evaluated (supplementary figure 4B). In addition, a dose-dependent decrease in proliferation was observed with exposure to pexidartinib (Figure 2B and supplementary figure 4D–E), however these effects were not observed in TCL cells that do not express CSF1R, supporting the relative selectivity of this FDA-approved agent (supplementary figure 4C). Consistent with these findings, treatment with pexidartinib was associated with increased apoptosis of TCL cells, as demonstrated by phosphatidylserine exposure (Figure 2C–E), PARP cleavage and Caspase 3 cleavage[5].

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PLX3397 is found to be a strong inhibitor of both CSF-1R and c-KIT kinase through the application of scaffold- and X-ray structure-based discovery methodology. The SelectScreen^TM profiling service provided the IC50 data.

MMTV-PyMT mice
40 mg/kg/day
p.o.

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Two murine models of mammary tumor development were used to analyze response to chemotherapy (Supplementary Fig. S3). The first model used MMTV-PyMT mice (Supplementary Fig. S3A). The 80-day-old MMTV-PyMT female littermates were randomized by initial tumor volume and fed either PLX3397 (20, 61, 62) formulated in mouse chow or control chow (provided by Plexxikon Inc). PLX3397 was formulated in mouse chow so that the average dose per animal per day was 40 mg/kg. When PLX3397-treated MMTV-PyMT mice reached 85 days of age, they were then administered PTX (Hospira) every 5 days by i.v. injection into the retroorbital plexus. PTX was given at 10 mg/kg of the animal per injection, diluted in PBS. Tumor burden was evaluated by caliper measurement every 5 days following the start of PLX3397 treatment. Prior to tissue collection, mice were cardiac-perfused with PBS to clear peripheral blood. Mammary tumor tissue from PBS-perfused MMTV-PyMT mice was analyzed by flow cytometry and qRT-PCR 2 days after the second dose of PTX, when metastatic burden and tumor grade were determined. Primary tumor burden was determined by caliper measurements on live sedated mice. Metastatic burden was assessed by serial sectioning of formalin-fixed paraffin-embedded lung tissue whereby the entire lung was sectioned and the number of metastatic foci (>5 cells) was determined on 6 sections taken every 100 µm following H&E staining. Lungs from >10 mice/group were analyzed[1].

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A Ten-week-old mice were fed a chow or high-fat diet for 10 weeks and then treated with PLX3397 via oral gavage (50 mg/kg) every second day for 3 weeks, with subsequent monitoring of glucose tolerance, insulin sensitivity and assessment of adipose tissue immune cells.PLX3397 treatment substantially reduced macrophage numbers in adipose tissue of both chow and high-fat diet fed mice without affecting total myeloid cell levels. Despite this, PLX3397 did not greatly alter glucose homeostasis, did not affect high-fat diet-induced increases in visceral fat cytokine expression (Il-6 and Tnfa) and had limited effect on the phosphorylation of the stress kinases JNK and ERK and macrophage polarization.[4]

Absorption, Distribution and Excretion
Following administration of single doses in healthy subjects and multiple doses in patients, the mean Cmax was 8625 ng/mL and the mean AUC was 77465 ngxh/mL. The median Tmax was 2.5 hours and the time to reach the steady state was approximately 7 days. Administration of pexidartinib with a high fat meal resulted in an increased drug Cmax and AUC by 100%, with a delay in Tmax by 2.5 hours.
Pexidartinib is predominantly excreted via feces, where fecal excretion accounts for 65% of total pexidartinib elimination. Via this route of elimination, about 44% of the compound found in feces is recovered as unchanged parent drug. The renal elimination accounts for 27% of pexidartinib elimination, where more than 10% of the compound is found as the N-glucuronide metabolite.
The apparent volume of distribution of pexidartinib is about 187 L. In rats, pexidartinib was shown to penetrate into the central nervous system.
The apparent clearance is about 5.1 L/h.

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Metabolism / Metabolites
Pexidartinib primarily undergoes oxidation mediated by hepatic CYP3A4 and glucuronidation by UGT1A4. Following UGT1A4-mediated glucuronidation, a major inactive N-glucuronide metabolite is formed with approximately 10% higher exposure than the parent drug after a single dose administration of pexidartinib. Based on the findings of _in vitro_ studies, CYP1A2 and CYP2C9 may also play a minor role in drug metabolism.

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Biological Half-Life
The elimination half-life is about 26.6 hours.

Hepatotoxicity
Elevations in serum aminotransferase levels are common during pexidartinib therapy, occurring in 50% to 90% of patients and rising above 5 times the upper limit of the normal range in 12% to 20%. In addition, elevations in alkaline phosphatase levels occur in up to 20% of treated persons. In registration trials, clinically apparent liver injury with jaundice developed in 5% of patients. The time to onset of liver injury was typically between 2 and 6 weeks, and the pattern of liver enzyme elevations was mixed or cholestatic. Autoimmune and immune-allergic features were not prominent. Liver biopsy demonstrated bile duct injury and loss, and at least 3 patients in studies for conditions other than TGCT developed bile duct paucity and features of vanishing bile duct syndrome that ultimately led to liver transplantation in one subject. Pexidartinib has had limited clinical use and the frequency and spectrum of acute liver injury with its use is not yet well defined.
Likelihood score: B (likely cause of clinically apparent liver injury).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
No information is available on the clinical use of pexidartinib during breastfeeding. Because pexidartinib is over 99% bound to plasma proteins, the amount in milk is likely to be low. However, the manufacturer recommends that breastfeeding be discontinued during pexidartinib therapy and for 1 week after the last dose.
◉ Effects in Breastfed Infants
Relevant published information was not found as of the revision date.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

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Protein Binding
Based on the findings of _in vitro_ plasma protein binding study, pexidartinib is about 99% bound to serum proteins, where it is extensively bound to human serum albumin by 99.9% and alpha-1-acid glycoprotein by 89.9%.

[1]. Leukocyte complexity predicts breast cancer survival and functionally regulates response to chemotherapy. Cancer Discov. 2011 Jun;1(1):54-67.

[2]. Microglia increases the proliferation of retinal precursor cells during postnatal development. Mol Vis. 2018 Jul 30;24:536-545.

[3]. A phase I study of pexidartinib, a colony-stimulating factor 1 receptor inhibitor, in Asian patients with advanced solid tumors. Invest New Drugs. 2020 Feb;38(1):99-110.

[4]. The CSF1 receptor inhibitor pexidartinib (PLX3397) reduces tissue macrophage levels without affecting glucose homeostasis in mice. Int J Obes (Lond). 2020;44(1):245-253.

[5]. Colony-stimulating Factor 1 Receptor (CSF1R) Activates AKT/mTOR Signaling and Promotes T-cell Lymphoma Viability. Clin Cancer Res. 2020 Feb 1; 26(3): 690–703.

Pexidartinib is a pyrrolopyridine that is 5-chloro-1H-pyrrolo[2,3-b]pyridine which is substituted by a [6-({[6-(trifluoromethyl)pyridin-3-yl]methyl}amino)pyridin-3-yl]methyl group at position 3. It is a potent multi-targeted receptor tyrosine kinase inhibitor of CSF-1R, KIT, and FLT3 (IC50 of 20 nM, 10 nM and 160 nM, respectively). Approved by the FDA for the treatment of adult patients with symptomatic tenosynovial giant cell tumor (TGCT). It has a role as an EC 2.7.10.1 (receptor protein-tyrosine kinase) inhibitor and an antineoplastic agent. It is a pyrrolopyridine, an organochlorine compound, an aminopyridine, an organofluorine compound and a secondary amino compound.
Pexidartinib is a selective tyrosine kinase inhibitor that works by inhibiting the colony-stimulating factor (CSF1)/CSF1 receptor pathway. Pexidartinib was originally developed by Daiichi Sankyo, Inc. and it was approved by the FDA in August 2019 as the first systemic therapy for adult patients with symptomatic tenosynovial giant cell tumor. Tenosynovial giant cell tumor is a rare form of non-malignant tumor that causes the synovium and tendon sheaths to thicken and overgrow, leading to damage in surrounding joint tissue. Debilitating symptoms often follow with tenosynovial giant cell tumors, along with a risk of significant functional limitations and a reduced quality of life in patients. While surgical resection is a current standard of care for tenosynovial giant cell tumor, there are tumor types where surgeries are deemed clinically ineffective with a high risk of lifetime recurrence. Pexidartinib works by blocking the immune responses that are activated in tenosynovial giant cell tumors. In clinical trials, pexidartinib was shown to promote improvements in patient symptoms and functional outcomes in TGCT. Pexidartinib is available in oral formulations and it is commonly marketed as Turalio.
Pexidartinib is a Kinase Inhibitor. The mechanism of action of pexidartinib is as a Kinase Inhibitor, and Tyrosine Kinase Inhibitor, and Colony Stimulating Factor Receptor Type 1 (CSF-1R) Inhibitor, and Cytochrome P450 3A Inducer, and Cytochrome P450 2B6 Inhibitor, and UGT1A1 Inhibitor.
Pexidartinib is an orally available small molecule multi-kinase inhibitor that is used as an antineoplastic agent in the treatment of tenosynovial giant cell tumors. Pexidartinib is associated with a high rates of serum aminotransferase and alkaline phosphatase elevations during therapy and has been implicated in several cases of clinically apparent liver injury marked by progressive intrahepatic bile duct injury, some of which resulted in liver transplantation or were fatal.
Pexidartinib is a small-molecule receptor tyrosine kinase (RTK) inhibitor of proto-oncogene receptor tyrosine kinase (KIT), colony-stimulating factor-1 receptor (CSF1R) and FMS-like tyrosine kinase 3 (FLT3), with antineoplastic activity. Upon oral administration, pexidartinib targets, binds to and inhibits phosphorylation of KIT, CSF1R and FLT3 harboring an internal tandem duplication (ITD) mutation. This results in the inhibition of tumor cell proliferation. FLT3, CSF1R and FLT3 are overexpressed or mutated in many cancer cell types and play major roles in tumor cell proliferation and metastasis.
See also: Pexidartinib Hydrochloride (has salt form).

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Drug Indication
Pexidartinib is indicated for the treatment of adult patients with symptomatic tenosynovial giant cell tumor (TGCT) associated with severe morbidity or functional limitations and not amenable to improvement with surgery.
Treatment of tenosynovial giant cell tumour.
Treatment of benign soft tissue neoplasms

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Mechanism of Action
Tenosynovial giant cell tumor is a rare, non-malignant neoplasm that causes abnormal growth and damage to the synovium, bursae, or tendon sheaths. Recruitment of immune cells, specifically macrophages, is closely associated with the tumor mass formation in tenosynovial giant cell tumors. Macrophages drive tumor-promoting inflammation and play a central role in every stage of tumor progression. As the most abundant immune cells in the tumor microenvironment of solid tumors, macrophages promote processes that enhance tumor survival, such as angiogenesis, tumor cell invasion, and intravasation at the primary site. They also modulate the immune response to tumors to inhibit tumor clearance and directly engage with tumor cells to activate pro-survival signaling pathways. The recruitment, proliferation, and irreversible differentiation of macrophages are regulated by colony-stimulating factor-1 (CSF-1), which is a cytokine that is often translocated and highly expressed in tenosynovial giant cell tumors. Elevated expression of CSF-1 and CSF-1 receptor (CSF1R) has also been implicated in various models of malignant cancers and tumors. Pexidartinib targets the CSF1/CSF1R pathway as a selective CSF1R inhibitor. It stimulates the autoinhibited state of the CSF1R by interacting with the juxtamembrane region of CSF1R, which is responsible for folding and inactivation of the kinase domain, and preventing the binding of CSF1 and ATP to the region. Without the binding of CSF1 to the receptor, CSF1R cannot undergo ligand-induced autophosphorylation. By inhibiting the CSF1R signaling pathway, pexidartinib works to inhibit tumor cell proliferation and downmodulate cells involved in the disease, such as macrophages. It was also shown to inhibit the CD117 or proto-oncogene receptor tyrosine kinase (cKIT), mutant fms-like tyrosine kinase 3 (FLT3), and platelet-derived growth factor receptor (PDGFR)-β, which are all receptor tyrosine kinases that regulate critical cellular processes such as cell proliferation and survival.

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Immune-regulated pathways influence multiple aspects of cancer development. In this article we demonstrate that both macrophage abundance and T-cell abundance in breast cancer represent prognostic indicators for recurrence-free and overall survival. We provide evidence that response to chemotherapy is in part regulated by these leukocytes; cytotoxic therapies induce mammary epithelial cells to produce monocyte/macrophage recruitment factors, including colony stimulating factor 1 (CSF1) and interleukin-34, which together enhance CSF1 receptor (CSF1R)-dependent macrophage infiltration. Blockade of macrophage recruitment with CSF1R-signaling antagonists, in combination with paclitaxel, improved survival of mammary tumor-bearing mice by slowing primary tumor development and reducing pulmonary metastasis. These improved aspects of mammary carcinogenesis were accompanied by decreased vessel density and appearance of antitumor immune programs fostering tumor suppression in a CD8+ T-cell-dependent manner. These data provide a rationale for targeting macrophage recruitment/response pathways, notably CSF1R, in combination with cytotoxic therapy, and identification of a breast cancer population likely to benefit from this novel therapeutic approach.[1]

C20H15CLF3N5

417.81

417.096

C, 57.49; H, 3.62; Cl, 8.49; F, 13.64; N, 16.76

1029044-16-3

Pexidartinib hydrochloride;2040295-03-0

25151352

Yellow solid powder

1.5±0.1 g/cm3

580.0±50.0 °C at 760 mmHg

304.6±30.1 °C

0.0±1.6 mmHg at 25°C

1.662

4.77

2

7

5

29

537

0

ClC1C([H])=NC2=C(C=1[H])C(=C([H])N2[H])C([H])([H])C1=C([H])N=C(C([H])=C1[H])N([H])C([H])([H])C1=C([H])N=C(C(F)(F)F)C([H])=C1[H]

JGWRKYUXBBNENE-UHFFFAOYSA-N

InChI=1S/C20H15ClF3N5/c21-15-6-16-14(10-28-19(16)29-11-15)5-12-2-4-18(26-7-12)27-9-13-1-3-17(25-8-13)20(22,23)24/h1-4,6-8,10-11H,5,9H2,(H,26,27)(H,28,29)

5-[(5-chloro-1H-pyrrolo[2,3-b]pyridin-3-yl)methyl]-N-[[6-(trifluoromethyl)pyridin-3-yl]methyl]pyridin-2-amine

Pexidartinib; CML-261; FP-113; PLX3397; PLX 3397; CML 261; CML261; PLX-3397;FP 113; FP113; Pexidartinib (PLX3397); CML-261; Pexidartinib [INN]; trade name: Turalio

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 5 mg/mL (11.97 mM) in 5% DMSO + 40% PEG300 + 5% Tween80 + 50% Saline (add these co-solvents sequentially from left to right, and one by one), suspension solution; with sonication.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (4.98 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.08 mg/mL (4.98 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 4: ≥ 2.08 mg/mL (4.98 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL corn oil and mix evenly.

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Solubility in Formulation 5: 10% DMSO+40% PEG 300+ddH2O: 15 mg/mL

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 (Please use freshly prepared in vivo formulations for optimal results.)