PLX5622

• CAT Number: I018176
• CAS Number: 1303420-67-8
• Molecular Formula: C21H19F2N5O
• Molecular Weight: 395.41
• Purity: ≥95%
• Synonyms: 6-fluoro-N-[(5-fluoro-2-methoxypyridin-3-yl)methyl]-5-[(5-methyl-1H-pyrrolo[2,3-b]pyridin-3-yl)methyl]pyridin-2-amine
• InChI: InChI=1S/C21H19F2N5O/c1-12-5-17-14(9-26-20(17)25-8-12)6-13-3-4-18(28-19(13)23)24-10-15-7-16(22)11-27-21(15)29-2/h3-5,7-9,11H,6,10H2,1-2H3,(H,24,28)(H,25,26)
• InChIKey: NSMOZFXKTHCPTQ-UHFFFAOYSA-N
• SMILES: CC1=CC2=C(NC=C2CC3=C(N=C(C=C3)NCC4=C(N=CC(=C4)F)OC)F)N=C1

PLX5622 is a highly selective brain penetrant and orally active CSF1R inhibitor (IC50=0.016 µM; Ki=5.9 nM). PLX5622 allows for extended and specific microglial cells elimination, preceding and during pathology development. PLX5622 demonstrates desirable PK properties in varies animals. PLX5622 is mostly used in the way of feed free diet (HY-114153C)[1][2].
PLX5622 (1-20 μM; 3 days) effectively depletes microglia without affecting oligodendrocytes or astrocytes in cerebellar slices. PLX5622 (4 μM; 3 days) 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 in preclinical studies
PLX5622 (1200 ppm; chow; for 3 weeks or 3 days; adult C57/Bl6 wild type mice) 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) 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) leads to reduction in microglia throughout the CNS in 14-month-old 5xfAD mice[6].

Pharmacokinetics of PLX5622 in preclinical species[1]

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[1]
PLX5622 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]