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.

Purpose: Foretinib is an oral multikinase inhibitor targeting Met, RON, Axl, and vascular endothelial growth factor receptor. We conducted a phase I, first-time-in-human, clinical trial using escalating doses of oral foretinib. The primary objectives are to identify a maximum tolerated dose and determine the safety profile of foretinib. Secondary objectives included evaluation of plasma pharmacokinetics, longterm safety after repeated administration, preliminary antitumor activity, and pharmacodynamic activity.Experimental Design: Patients had histologically confirmed metastatic or unresectable solid tumors for which no standard measures exist. All patients received foretinib orally for 5 consecutive days every 14 days. Dose escalation followed a conventional "3+3" design.Results: Forty patients were treated in eight dose cohorts. The maximum tolerated dose was defined as 3.6 mg/kg, with a maximum administered dose of 4.5 mg/kg. Dose-limiting toxicities included grade 3 elevations in aspartate aminotransferase and lipase. Additional non-dose-limiting adverse events included hypertension, fatigue, diarrhea, vomiting, proteinuria, and hematuria. Responses were observed in two patients with papillary renal cell cancer and one patient with medullary thyroid cancer. Stable disease was identified in 22 patients. Foretinib pharmacokinetics increased linearly with dose. Pharmacodynamic evaluation indicated inhibition of MET phosphorylation and decreased proliferation in select tumor biopsies at submaximal doses.Conclusions: The recommended dose of foretinib was determined to be 240 mg, given on the first 5 days of a 14-day cycle. This dose and schedule were identified as having acceptable safety and pharmacokinetics, and will be the dose used in subsequent phase II trials.