PLX5622 hemifumarate

• CAT Number: I046047
• Molecular Formula: C23H21F2N5O3
• Molecular Weight: 453.45
• Purity: ≥95%

PLX5622 hemifumarate is a highly selective brain penetrant and orally active CSF1R inhibitor (IC50=0.016 µM; Ki=5.9 nM). PLX5622 hemifumarate allows for extended and specific microglial elimination, preceding and during pathology development. PLX5622 hemifumarate demonstrates desirable PK properties in varies animals[1][2].
PLX5622 (1-20 μM; 3 days) hemifumarate effectively depletes microglia without affecting oligodendrocytes or astrocytes in cerebellar slices. PLX5622 (4 μM; 3 days) hemifumarate causes a 30-40% reduction in NG2+ or PDGFRα+ cells, and this increased to 90-95% at 20 μM. No reduction of NG2+ or PDGFRα+ OPCs is observed in slices exposed to 1 μM or 2 μM PLX5622 despite robust (~95%) depletion of the microglial cells[3].
Pharmacodynamics of PLX5622 hemifumarate in preclinical studies
PLX5622 (1200 ppm; chow; for 3 weeks or 3 days; adult C57/Bl6 wild type mice) hemifumarate leads to around 80% of microglia lost after 3 days of treatment and a 99% microglia loss after 3 weeks of treatment. PLX5622 (adult C57/Bl6 wild type mice aged 3 months; diet for 3 weeks) decreases microglia in cortex, striatum, cerebellum and hippocampus[4].
PLX5622 (50 mg/kg; intraperitoneal injection; once (neonatal rat) or twice (adult rat) a day; for a total of 14 days) hemifumarate depletes microglia by 80-90% within 3 days of treatment, which increases to > 90% by 7 days. After 14 days of PLX5622 treatment, microglia is depleted by > 96% in both neonates and adults while preserving baseline astrocyte quantity. (A single daily injection of 0.65% PLX5622 suspended in 5% dimethyl sulfoxide and 20% Kolliphor RH40 in 0.01 M PBS is sufficient for neonatal microglia depletion, adult depletion requires injections twice daily)[5].
PLX5622 (formulated in AIN-76A standard chow at 1200 mg/kg; for 28 days) hemifumarate leads to reduction in microglia throughout the CNS in 14-month-old 5xfAD mice[6].

Pharmacokinetics of PLX5622 hemifumarate in preclinical species[4]

Species
IV
PO (gavage)

Dose(mg/kg)
AUC0-∞(ng•hr/mL)
CL(mL/min/kg)
Vss(L/kg)
t1/2(hr)
Dose(mg/kg)
AUC0-∞(ng•hr/mL)
Cmax(ng/mL)
F

Mouse
1.92
15,500
2.1
0.34
2.6
45
215,000
26,300
59%

Rat (male)
1.13
2,630
7.7
1.2
2.3
45
99,600
12,000
95%

Rat (female)
1.13
5,110
3.7
1.0
3.9
45
181,000
15,600
89%

Dog
1.00
6,230
3.0
2.3
15
45
96,500
3,630
34%

Monkey
1.35
2,100
11
1.6
2.2
ND
ND
ND
ND

Preparation of gavage dosing suspensions for PLX5622 hemifumarate[4]
PLX5622 hemifumarate is dissolved in DMSO at a concentration that is 20x the final dosing solution. The compound stock is protected from light. A fresh stock is made each week.
The components of the diluent generally are prepared a day or more in advance because they take time to dissolve completely: a) 2% hydroxypropyl methyl cellulose (HPMC): 2.0 g powder was brought to 100 mL deionized water; b) 25% Polysorbate 80 (PS80): 25 g was brought to 100 mL deionized water. To make 100 mL diluent, add 25 mL of 2% HPMC stock (0.5% final) and 4 mL of 25% PS80 stock (1% final) to 71 mL deionized water to have final 100 mL. Final composition after mixing with compound: 0.5% HPMC, 1% PS80, 5% DMSO.
On each dosing day, the compound stock is diluted 20-fold as follows: 19 volumes of diluent are measured into the tube, and 1 volume of the 20x compound/DMSO stock is added. The cap is closed and the content of the tube is mixed by inversion and placed in a sonicating water bath to make a uniform suspension.

Reference

[1]. Spangenberg E, et al. Sustained microglial depletion with CSF1R inhibitor impairs parenchymal plaque development in an Alzheimer’s disease model. Nat Commun. 2019 Aug 21;10(1):3758.
 [Content Brief]

[2]. Lee S, et al. Targeting macrophage and microglia activation with colony stimulating factor 1 receptor inhibitor is an effective strategy to treat injury-triggered neuropathic pain. Mol Pain. 2018 Jan-Dec;14:1744806918764979.
 [Content Brief]

[3]. Liu Y, et al. Concentration-dependent effects of CSF1R inhibitors on oligodendrocyte progenitor cells ex vivo and in vivo. Exp Neurol. 2019;318:32-41.
 [Content Brief]

[4]. Badimon A, et al. Negative feedback control of neuronal activity by microglia. Nature. 2020;586(7829):417-423.
 [Content Brief]

[5]. Andrew J. Riquier, et al. Astrocytic response to neural injury is larger during development than in adulthood and is not predicated upon the presence of microglia, Brain, Behavior, & Immunity-Health, Volume 1, 2020, 100010, ISSN 2666-3546.

[6]. Spangenberg EE, et al. Eliminating microglia in Alzheimer’s mice prevents neuronal loss without modulating amyloid-β pathology. Brain. 2016;139(Pt 4):1265-1281.
 [Content Brief]