XL019

XL019 is a potent and selective inhibitor of JAK2 with IC50 value of 2.2 nM.
JAK kinases were first identified in 1989 and characterized by the presence of two tyrosine kinase domains. There are four members in the JAK family, which are JAK1, JAK2, JAK3 and TYK2. JAK2 played an important role in the pathways that control erythroid, myeloid and megakaryocytic development. JAK2 mediates signaling through erythropoietin receptor, thrombopoietin receptor and cytokine receptor that harbor the common β-chain (e.g. IL3 receptor) and IFN-γ receptors [38]. JAK2 inhibitors are a novel class of agents with promising results for treating patients with polycythemia vera (PV), essential thrombocythemia (ET) and myelofibrosis (MF) [1]. XL019 was selected as a clinical candidate and advanced into human clinical trials where it was evaluated in patients with PMF, post-PV, or post-ET MF [2].
XL019 shows good biochemical and cellular potency against JAK2 with good selectivity, against a panel of over 100 serine/threonine and tyrosine kinases, including other members of the JAK family [2]. Analogue XL019 was evaluated against a select panel of 118 kinases. Targets for which XL019 exhibited IC50 <1000 nM are displayed. XL019 is a highly selective JAK2 inhibitor displaying >50-fold selectivity against all kinases tested including JAK1 and TYK2. XL019 was a desirable CYP, hERG (16 μM), and P-glycoprotein inhibition (>20 μM).
XL019 had a superior pharmacodynamic profile and thus was evaluated in an efficacy experiment measuring growth inhibition of HEL.92.1.7 xenograft tumors in mice. Derivative XL019 demonstrated 60% and 70% inhibition when dosed orally at 200 mg/kg and 300 mg/kg respectively twice a day for 14 days. Thirty patients received XL019 for a median of 91 days. All of them have discontinued XL019 therapy. Toxicity: N/A Clinical trial: A Safety Study of XL-019 in Adults With Myelofibrosis [2].
References:
[1]. Fabio P.S. Santos, Srdan Verstovsek. JAK2 inhibitors: What's the true therapeutic potential?. Blood Reviews, 2011, 25: 53-63.
[2]. Srdan Verstovsek, Constantine S. Tam, Martha Wadleigh, et al. Phase I evaluation of XL019, an oral, potent, and selective JAK2 inhibitor. Leukemia Research, 2014, 38: 316-322.

Phase I evaluation of XL019, an oral, potent, and selective JAK2 inhibitor.[Pubmed:24374145]

Leuk Res. 2014 Mar;38(3):316-22.

This phase I study evaluated selective JAK2 inhibitor XL019 in 30 patients with myelofibrosis. The initial dose cohorts were 100, 200, and 300 mg orally on days 1-21 of a 28-day cycle. Central and/or peripheral neurotoxicity developed in all patients. Subsequently, patients were treated on lower doses; neurotoxicity was again observed, leading to study termination. Peripheral neuropathy resolved in 50%, and central neurotoxicity in all patients within months after therapy cessation. Myelosuppression was minimal. The terminal half-life of XL019 was approximately 21 h, with steady state reached by Day 8. International Working Group defined responses were seen in three (10%) patients.

XL019 is a potent，orally active, and selective JAK2 inhibitor, with IC50s of 2.2, 134.3, and 214.2 nM for JAK2, JAK1 and JAK3, respectively. XL019 shows 50-fold or greater selectivity for JAK2, versus a panel of over 100 serine/threonine and tyrosine kinases, including other members of the JAK family. XL019 potently inhibits STAT3 and STAT5 phosphorylation in cells harboring either JAK2V617F or wild-type JAK2.

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