PLX5622 (1-20 μM; 3 days) hemifumarate effectively depletes microglia while not affecting oligodendrocytes or astrocytes in cerebellar slices. PLX5622 (4 μM; 3 days) hemifumarate leads to a 30-40% reduction in NG2+ or PDGFRα+ cells, increasing 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 causes 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) reduces 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) AUC 0-∞ (ng hr/mL) CL (mL/min/kg) Vss (L/kg) t 1/2 (hr) Dose (mg/kg) AUC 0-∞ (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.