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[2].IC50 & Target:IC50: 0.016 μM (CSF1R); Ki: 5.9 nM (CSF1R)[2]In Vitro: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.In Vivo: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.
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).
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.

Pharmacokinetics of PLX5622 in preclinical species

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Preparation of gavage dosing suspensions for PLX5622
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.