Synthesis and biological evaluation of a fluorine-18 derivative of dasatinib.

Tyrosine kinases often play pivotal roles in the pathogenesis of cancer and are good candidates for therapeutic intervention and targeted molecular imaging. The precursor synthesis, radiosynthesis, and biological characterization of a fluorine-18 analog of dasatinib, a multitargeted kinase inhibitor, are reported. Compound 5 potently inhibits Abl, Src, and Kit kinases and inhibits K562 and M07e/p210bcr-abl human leukemic cell growth. Using positron emission tomography, we visualized K562 tumor xenografts in mice with [18F]-5.

Characterization of potent inhibitors of the Bcr-Abl and the c-kit receptor tyrosine kinases.

The early stage of chronic myelogenous leukemia (CML) is caused by the tyrosine kinase Bcr-Abl. Imatinib mesylate (also known as STI-571 and Gleevec), a tyrosine kinase inhibitor, has shown encouraging results in CML clinical trials and has become a paradigm for targeted cancer therapeutics. Recent reports of resistance to imatinib argue for further development of therapies for CML. During studies of signal transduction, we observed that the pyrido[2,3-d]pyrimidine src tyrosine kinase inhibitor PD173955 inhibited Bcr-Abl-dependent cell growth. Subsequently, a related compound, PD180970, was reported as a potent inhibitor of Bcr-Abl. We have compared the potency of these two compounds and four other analogues with imatinib on Bcr-Abl-dependent cell growth, cytokine-dependent cell growth, and tyrosine kinase inhibition. PD173955 inhibited Bcr-Abl-dependent cell growth with an IC(50) of 2-35 nM in different cell lines. Fluorescence-activated cell-sorting analyses of cells treated with PD173955 showed cell cycle arrest in G(1). PD173955 has an IC(50) of 1-2 nM in kinase inhibition assays of Bcr-Abl, and in cellular growth assays it inhibits Bcr-Abl-dependent substrate tyrosine phosphorylation. Of the six pyrido[2,3-d]pyrimidine analogues studied, PD166326 was the most potent inhibitor of Bcr-Abl-dependent cell growth. PD173955 inhibited kit ligand-dependent c-kit autophosphorylation (IC(50) = approximately 25 nM) and kit ligand-dependent proliferation of M07e cells (IC(50) = 40 nM) but had a lesser effect on interleukin 3-dependent (IC(50) = 250 nM) or granulocyte macrophage colony-stimulating factor (IC(50) = 1 microM)-dependent cell growth. These compounds are potent inhibitors of both the Bcr-Abl and c-kit receptor tyrosine kinases and deserve further study as potential treatments for both CML and for diseases in which c-kit has a role.

Direct evidence that Bcr-Abl tyrosine kinase activity disrupts normal synergistic interactions between Kit ligand and cytokines in primary primitive progenitor cells.

We previously reported that chronic myelogenous leukemia (CML) primitive granulocyte-monocyte (GM) progenitors have a greatly reduced requirement for kit ligand (KL) to achieve optimal growth with granulocyte colony-stimulating factor (G-CSF) + granulocyte-monocyte colony-stimulating factor (GM-CSF). Conversely, others have demonstrated that unlike normal, CML CD34+ progenitors can proliferate in response to KL as a sole stimulus. To address these seemingly paradoxical findings, we examined the growth responses of CML CD34+ GM progenitors to various cytokines with and without a potent inhibitor of Bcr-Abl tyrosine kinase activity, PD173955. The heightened growth responses of CML GM progenitors to KL alone and to G-CSF + GM-CSF were abrogated by 10 nM PD173955 while having no effect on normal GM progenitors. While normal GM progenitors exhibited the expected synergistic response when KL was added to G-CSF + GM-CSF, CML GM progenitors had a minimal response; however, some synergism was restored by 10 nM PD173955. Normal erythroid progenitors require the synergistic interaction between KL and a saturating amount of erythropoietin (EPO, 1 unit) for optimal growth. In contrast, CML erythroid progenitors had up to 50% of optimal growth in KL alone, and, only a subthreshold amount of EPO (0.1 unit) was needed with KL to achieve 85% of the optimal response; these heightened growth responses were largely abrogated by 10 nM PD173955. Thus, direct evidence is provided that constitutively activated Bcr-Abl kinase pathways in primitive CML progenitors cooperate with single growth factors producing a heightened growth response, and, in so doing, disrupt the normally required synergistic interactions between KL and other cytokines to achieve activation and optimal growth of primitive progenitors. Coupled with our previous findings that a larger than normal proportion of CML primitive progenitors are at a later stage of maturation, we propose that this disruption of normal synergistic responses leads to increased progenitor recruitment into a committed pool by a process of accelerated maturation.