JAK3-IN-1 is a selective and orally active JAK3 inhibitor (IC50: 4.8 nM). JAK3-IN-1 displays over 180-fold more selective for JAK3 than JAK1 (IC50: 896 nM) and JAK2 (IC50: 1050 nM).

JAK3-IN-1 most potently inhibits JAK3 and identified fms-related tyrosine kinase 3 (FLT3) and several tyrosine protein kinase (TEC)-family kinases as being potential off-targets. JAK3-IN-1 selectively inhibits the proliferation of JAK3-dependent Ba/F3 cells (IC50 = 69 nM) relative to other JAK-dependent Ba/F3 cells, for which there was no antiproliferative effect at concentrations below 3.0 μM. JAK3-IN-1 displays very low inhibition scores for other JAKs and wild-type (WT) EGFR, which is consistent with the over 180-fold higher IC50s against EGFRWT and TYK2 (IC50s =409 nM, > 10000 respectively). JAK3-IN-1 possesses over 165-fold higher IC50s for BTK or ITK (IC50s = 794 and 1070 nM respectively). JAK3-IN-1( 0-5 μM; 3 hours; BMDMs cells) treatment fullly inhibits IL-4 induced p-STAT6 at a concentration of 500 nM and only partially inhibits IFNβ-induced p-STAT1 at a concentration of 5.0 μM. Enzymatic assays using the Z'-lyte or LanthaScreen formats confirmed enzymatic inhibition of FLT3 (IC50 = 13 nM), TTK protein kinase (TTK, IC50 = 49 nM), BLK proto-oncogene (BLK, IC50 = 157 nM) and tyrosine protein kinase TXK (TXK, IC50 = 36 nM) [1].

The numbers of B or T lymphocytes in the tumor-bearing lungs and spleens of treated mice is not affected, after oral administration with JAK3-IN-1(Compound 9) (75 mpk, QD) for 8 days, however, the number of NK cells is reduced. JAK3-IN-1 displays reasonable pharmacokinetic properties, with moderate T1/2 of 1.4 h, area under the curve (AUC) value of 795 ng*hr/mL following a 10 mg/Kg oral dose and good oral bioavailability of 66% [1].