Kinase inhibitors have found applications in multiple oncology settings due to their ability to target key signaling pathways in many different cancers. In general, the broad-spectrum kinase inhibitors have yielded better clinical outcomes than more selective ones because they block more than one pathway critical for tumor growth. We describe herein the pharmacological profile of TG02, a multi-kinase inhibitor being developed by Tragara Pharmaceuticals, which combines cell cycle regulatory and transcriptional CDK inhibition with activity against kinase targets important in the etiology of various leukemias.

In vitro potency against the kinases was evaluated using recombinant enzymes with synthetic substrates. Potency on intracellular signaling pathways was assessed by Western blot analyses of the phosphorylated substrates in cell lysates. Functional potency was assessed using proliferation assays performed on human tumor cell lines as well as hematopoietic progenitors expanded from patients' blood. Evaluation of pharmacokinetics, pharmacodynamic biomarkers and anti-tumor efficacy was performed in nude mouse xenograft models of leukemia.

TG02 was shown to be a potent inhibitor of several key CDKs (IC50 = 19, 11, 37 & 10nM vs. CDK1, 2, 7 & 9) as well as two other kinases implicated in hematological malignancies, FLT3 and JAK2, with similar potency. The CDK spectrum includes both cell cycle regulatory and transcriptional CDKs. TG02 potently inhibits proliferation across a broad panel of human liquid tumor cell lines (IC50 from 68 to 230 nM). Comparison with reference inhibitors that block only one of the kinase targets of interest demonstrated the significant added benefit of combined CDK and JAK2 targeting. Inhibition of signaling by the CDK and FLT3-JAK2 pathways in leukemia cell lines was detected at the same range (0.10 to 0.35 μM). TG02 was generally cleared from the blood within 8 hours of oral administration but was retained in tumor masses at supratherapeutic levels for 24-48 hours, depending on dose. Accordingly, pathway-related biomarkers were markedly suppressed for 24-72 hours after dosing. In a murine model of FLT3-mutated leukemia (MV4-11), TG02 induced tumor regression after oral daily dosing (40 mg/kg for 21 days). Furthermore, in an orthotopic model of AML with WT FLT3 and JAK2 (HL60), TG02 significantly prolonged median survival time (59 days vs. 40 days) after treatment at 100 mg/kg p.o. 2d on/5d off. Proliferation assays using hematopoietic progenitors expanded from patients with JAK2 mutations or FLT3 wild-type or mutant acute myeloid leukemia revealed higher efficacy of TG02 compared to reference inhibitors targeting only one of the kinases of interest, again demonstrating the benefits of co-targeting CDKs and additional kinases.

TG02 is a multi-kinase inhibitor with a previously unreported spectrum of targets that shows promising preclinical activity for the treatment of hematological malignancies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2542.