The signaling pathway of the receptor tyrosine kinase MET and its ligand hepatocyte growth factor (HGF) is important for cell growth, survival, and motility and is functionally linked to the signaling pathway of VEGF, which is widely recognized as a key effector in angiogenesis and cancer progression. Dysregulation of the MET/VEGF axis is found in a number of human malignancies and has been associated with tumorigenesis. Cabozantinib (XL184) is a small-molecule kinase inhibitor with potent activity toward MET and VEGF receptor 2 (VEGFR2), as well as a number of other receptor tyrosine kinases that have also been implicated in tumor pathobiology, including RET, KIT, AXL, and FLT3. Treatment with cabozantinib inhibited MET and VEGFR2 phosphorylation in vitro and in tumor models in vivo and led to significant reductions in cell invasion in vitro. In mouse models, cabozantinib dramatically altered tumor pathology, resulting in decreased tumor and endothelial cell proliferation coupled with increased apoptosis and dose-dependent inhibition of tumor growth in breast, lung, and glioma tumor models. Importantly, treatment with cabozantinib did not increase lung tumor burden in an experimental model of metastasis, which has been observed with inhibitors of VEGF signaling that do not target MET. Collectively, these data suggest that cabozantinib is a promising agent for inhibiting tumor angiogenesis and metastasis in cancers with dysregulated MET and VEGFR signaling.
The Met receptor tyrosine kinase and its ligand,
Proliferating cell nuclear antigen (PCNA) is an essential protein in both DNA replication and DNA damage repair. A novel 15 kD protein, p15 PAF , was identi®ed as a PCNA-associated factor in a yeast two-hybrid screen using PCNA as the bait. p15 PAF is localized primarily in the nucleus. p15 PAF shares the conserved PCNA binding motif with several other PCNA binding proteins including CDK inhibitor p21. Overexpression of p15 PAF competes with p21-PCNA binding. Mutation of this motif in p15 PAF abolished its PCNA-binding activity. Notably, p15 PAF expression in several types of tumor tissues was signi®cantly increased, especially in esophageal tumors. Like PCNA, p15 PAF may possess prognostic signi®cance in a broad array of human cancers. Oncogene (2001) 20, 484 ± 489.
The ERK/MAP kinase cascade is a key mechanism subject to dysregulation in cancer and is constitutively activated or highly upregulated in many tumor types. Mutations associated with upstream pathway components RAS and Raf occur frequently and contribute to the oncogenic phenotype through activation of MEK and then ERK. Inhibitors of MEK have been shown to effectively block upregulated ERK/MAPK signaling in a range of cancer cell lines and have further demonstrated early evidence of efficacy in the clinic for the treatment of cancer. Guided by structural insight, a strategy aimed at the identification of an optimal diphenylamine-based MEK inhibitor with an improved metabolism and safety profile versus PD-0325901 led to the discovery of development candidate 1-({3,4-difluoro-2-[(2-fluoro-4-iodophenyl)amino]phenyl}carbonyl)-3-[(2S)-piperidin-2-yl]azetidin-3-ol (XL518, GDC-0973) (1). XL518 exhibits robust in vitro and in vivo potency and efficacy in preclinical models with sustained duration of action and is currently in early stage clinical trials. KEYWORDS: MAPK pathway, MEK, cancer, kinase inhibitor, XL518, GDC-0973 T he MAPK cascade, or mitogen-activated protein kinase signal transduction pathway, is a mechanism commonly subject to dysregulation in cancer, and constitutive or highly upregulated signaling is a frequent hallmark of oncogenic transformation and progression. Controlled by activation of RAS at the cell surface interior, the subsequent stimulation of Raf and then MEK and ERK serves to regulate a range of key intracellular effectors associated with cell proliferation, 1 invasion, 2 angiogenesis, 3 and apoptotic resistance. 4 Mutated RAS is associated with almost one-third of human cancers, and a majority of malignant melanomas and papillary thyroid cancers harbor B-Raf mutations. 5,6 Inhibitors of MEK have demonstrated efficacy against malignant tumors characterized by mutations in either RAS or Raf in preclinical models, and early development candidates including GSK1120212, In some tumors, activation of both the RAS driven ERK/ MAPK cascade and the PI3K-Akt pathway is observed, resulting in degenerate and convergent oncogenic signals, and upregulation or constitutive PI3K pathway activation is associated with resistance to MEK inhibitor single agent treatment.10 Several combination approaches using inhibitors of mTor, PI3K, Akt, and Raf have more recently been validated in preclinical models and are being pursued clinically. Herein, the discovery of XL518 (GDC-0973) (1), a potent and selective MEK inhibitor, is described. XL518 is currently in early stage clinical testing as both a single agent and in combination with the class I PI3K inhibitor GDC-0941. 11Our goal at the outset was the identification of a potent and selective MEK inhibitor with sustained duration of efficacy suitable for qd dosing and an optimized safety profile relative to clinical precursors. The diphenylamine series disclosed by the Pfizer/Warner Lambert groups served as a starting point for our effort. A key aspect tha...
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