JANEX-1 is a cell-permeable, reversible, potent, ATP-competitive, and specific inhibitor of JAK3 (IC50 = 78 μM) and has no effect on JAK1, JAK2, or Zap/Syk or SRC tyrosine kinases.
The Janus kinase (JAK) signal transducer and activator of transcription (STAT) signaling pathway serves as an important downstream mediator for a variety of cytokines, hormones, and growth factors[3]. JANEX-1 (WHI-P131) shows potent JAK3-inhibitory activity (IC50 of 78 μM).JANEX-1 induces apoptosis in JAK3-expressing human leukemia cell lines NALM-6 and LC1;19 but not in melanoma (M24-MET) or squamous carcinoma (SQ20B) cells. WHI-P131 inhibits the clonogenic growth of JAK3-positive leukemia cell lines DAUDI, RAMOS, LC1;19, NALM-6, MOLT-3, and HL-60 in a concentration-dependent fashion. WHI-P131 inhibits clonogenic growth in a concentration-dependent fashion with EC50s of 24.4 μM for NALM-6 cells and 18.8 μM for DAUDI cells. At 100 μM, WHI-P131 inhibits the in vitro colony formation by these leukemia cell lines by >99%. In contrast, JANEX-1 does not inhibit the clonogenic growth of JAK3-negative M24-MET melanoma or SQ20B squamous carcinoma cell lines[4].JANEX-1 is administered at doses ranging from 5 to 100 mg/kg. Evaluation of CPK activity revealed a dose-response curve with an effective dose 50 (ED50) value of 7.44 mg/kg. Mice receiving JANEX-1 displayed significantly reduced CPK and LDH levels.In addition, the infarct size of JANEX-1-treated mice (30.16±2.79%) is significantly decreased when compared with I/R-operated mice (65.64±3.76%)[5]. JANEX-1 (WHI-P131) is absorbed rapidly, and the time to reach the maximum plasma JANEX-1 concentration (tmax) is 24.7±1.7 min. JANEX-1 is rapidly eliminated with an elimination half-life of 45.6±5.5 min. Although the predicted maximum plasma JANEX-1 concentration is 10.5 ± 0.8 μM, which is only half of the Cmax following i.v. administration of the same bolus dose, the i.p. bioavailability is 94.6% and the systemic exposure levels (i.e., AUC) are very similar to those observed after i.v. injection (17.1±2.2 μM•h versus 18.1±1.2 μM•h) [6].
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