In vitro and in vivo activity of cabozantinib (XL184), an inhibitor of RET, MET, and VEGFR2, in a model of medullary thyroid cancer.

BACKGROUND: A limited number of approved therapeutic options are available to metastatic medullary thyroid cancer (MTC) patients, and the response to conventional chemotherapy and/or radiotherapy strategies is inadequate. Sporadic and inherited mutations in the tyrosine kinase RET result in oncogenic activation that is associated with the pathogenesis of MTC. Cabozantinib is a potent inhibitor of MET, RET, and vascular endothelial factor receptor 2 (VEGFR2), as well as other tyrosine kinases that have been implicated in tumor development and progression. The object of this study was to determine the in vitro biochemical and cellular inhibitory profile of cabozantinib against RET, and in vivo antitumor efficacy using a xenograft model of MTC. METHODS: Cabozantinib was evaluated in biochemical and cell-based assays that determined the potency of the compound against wild type and activating mutant forms of RET. Additionally, the pharmacodynamic modulation of RET and MET and in vivo antitumor activity of cabozantinib was examined in a MTC tumor model following subchronic oral administration. RESULTS: In biochemical assays, cabozantinib inhibited multiple forms of oncogenic RET kinase activity, including M918T and Y791F mutants. Additionally, it inhibited proliferation of TT tumor cells that harbor a C634W activating mutation of RET that is most often associated with MEN2A and familial MTC. In these same cells grown as xenograft tumors in nude mice, oral administration of cabozantinib resulted in dose-dependent tumor growth inhibition that correlated with a reduction in circulating plasma calcitonin levels. Moreover, immunohistochemical analyses of tumors revealed that cabozantinib reduced levels of phosphorylated MET and RET, and decreased tumor cellularity, proliferation, and vascularization. CONCLUSIONS: Cabozantinib is a potent inhibitor of RET and prevalent mutationally activated forms of RET known to be associated with MTC, and effectively inhibits the growth of a MTC tumor cell model in vitro and in vivo.

Cabozantinib (XL184), a novel MET and VEGFR2 inhibitor, simultaneously suppresses metastasis, angiogenesis, and tumor growth.

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.

Inhibition of tumor cell growth, invasion, and metastasis by EXEL-2880 (XL880, GSK1363089), a novel inhibitor of HGF and VEGF receptor tyrosine kinases.

The Met receptor tyrosine kinase and its ligand, hepatocyte growth factor (HGF), are overexpressed and/or activated in a wide variety of human malignancies. Vascular endothelial growth factor (VEGF) receptors are expressed on the surface of vascular endothelial cells and cooperate with Met to induce tumor invasion and vascularization. EXEL-2880 (XL880, GSK1363089) is a small-molecule kinase inhibitor that targets members of the HGF and VEGF receptor tyrosine kinase families, with additional inhibitory activity toward KIT, Flt-3, platelet-derived growth factor receptor beta, and Tie-2. Binding of EXEL-2880 to Met and VEGF receptor 2 (KDR) is characterized by a very slow off-rate, consistent with X-ray crystallographic data showing that the inhibitor is deeply bound in the Met kinase active site cleft. EXEL-2880 inhibits cellular HGF-induced Met phosphorylation and VEGF-induced extracellular signal-regulated kinase phosphorylation and prevents both HGF-induced responses of tumor cells and HGF/VEGF-induced responses of endothelial cells. In addition, EXEL-2880 prevents anchorage-independent proliferation of tumor cells under both normoxic and hypoxic conditions. In vivo, these effects produce significant dose-dependent inhibition of tumor burden in an experimental model of lung metastasis. Collectively, these data indicate that EXEL-2880 may prevent tumor growth through a direct effect on tumor cell proliferation and by inhibition of invasion and angiogenesis mediated by HGF and VEGF receptors.

Inhibition of the T790M gatekeeper mutant of the epidermal growth factor receptor by EXEL-7647.

PURPOSE: Agents inhibiting the epidermal growth factor receptor (EGFR) have shown clinical benefit in a subset of non-small cell lung cancer patients expressing amplified or mutationally activated EGFR. However, responsive patients can relapse as a result of selection for EGFR gene mutations that confer resistance to ATP competitive EGFR inhibitors, such as erlotinib and gefitinib. We describe here the activity of EXEL-7647 (XL647), a novel spectrum-selective kinase inhibitor with potent activity against the EGF and vascular endothelial growth factor receptor tyrosine kinase families, against both wild-type (WT) and mutant EGFR in vitro and in vivo. EXPERIMENTAL DESIGN: The activity of EGFR inhibitors against WT and mutant EGFRs and their effect on downstream signal transduction was examined in cellular assays and in vivo using A431 and MDA-MB-231 (WT EGFR) and H1975 (L858R and T790M mutant EGFR) xenograft tumors. RESULTS: EXEL-7647 shows potent and long-lived inhibition of the WT EGFR in vivo. In addition, EXEL-7647 inhibits cellular proliferation and EGFR pathway activation in the erlotinib-resistant H1975 cell line that harbors a double mutation (L858R and T790M) in the EGFR gene. In vivo efficacy studies show that EXEL-7647 substantially inhibited the growth of H1975 xenograft tumors and reduced both tumor EGFR signaling and tumor vessel density. Additionally, EXEL-7647, in contrast to erlotinib, substantially inhibited the growth and vascularization of MDA-MB-231 xenografts, a model which is more reliant on signaling through vascular endothelial growth factor receptors. CONCLUSIONS: These studies provide a preclinical basis for clinical trials of XL647 in solid tumors and in patients bearing tumors that are resistant to existing EGFR-targeted therapies.

Connective tissue growth factor/IGF-binding protein-related protein-2 is a mediator in the induction of fibronectin by advanced glycosylation end-products in human dermal fibroblasts.

Expansion of extracellular matrix with fibrosis occurs in many tissues, including skin, as part of the end-organ complications in diabetes. Advanced glycosylation end-products (AGEs) have been implicated as a pathogenic factor in diabetic tissue fibrosis. Connective tissue growth factor (CTGF), also known as IGF-binding protein-related protein-2, induces extracellular matrix. We have recently shown that CTGF mRNA and protein are up-regulated by AGE treatment of cultured human dermal fibroblasts. The aim of this study was to determine whether CTGF is an autocrine mediator in the induction of fibronectin (FN) by AGE. Primary cultures of nonfetal human dermal fibroblasts in confluent monolayer were treated with synthesized soluble AGE BSA, 0-200 microg/ml. Analysis of mRNA, by quantitative real-time RT-PCR and conditioned media from treated cultures, showed that FN mRNA was increased by approximately 4-fold at 48 h, and FN protein levels by Western immunoblot and FN ELISA were doubled, compared with control. In the same system, added recombinant human CTGF (0-500 ng/ml) induced FN mRNA and protein levels dose dependently and in a rapid time course. To test whether AGE BSA acts through cell-derived CTGF to induce FN, a CTGF neutralizing antibody was shown to significantly attenuate, but not fully inhibit, the AGE induction of FN mRNA. A pan-specific PKC inhibitor, GF109203X, at 0.2 microM, inhibited the induction of FN mRNA by AGE BSA. Although the same inhibitor did not significantly affect the induction of CTGF mRNA by AGE, it blocked the induction of FN mRNA by recombinant human CTGF. In summary, the induction of FN by AGE is partly mediated by the AGE-induced up-regulation of cell-derived CTGF and is dependent on PKC activity. These results have potential implications for the expansion of extracellular matrix in diabetes mellitus by advanced glycosylation end products.

Impaired angiogenesis in the remnant kidney model: I. Potential role of vascular endothelial growth factor and thrombospondin-1.

Few studies have examined the role of the microvasculature in progressive renal disease. It was hypothesized that impaired angiogenesis might occur in the diseased kidney and could contribute to renal scarring. Progressive renal disease was induced in rats by 5/6 renal ablation and those rats were compared with sham-operated control animals at multiple time points, for examination of changes in the microvasculature and the expression of angiogenic factors. An early angiogenic response was documented in remnant kidneys, with increases in the proliferation of peritubular (1 wk) and glomerular (2 wk) endothelial cells. Subsequently, however, there was a decrease in endothelial cell proliferation, which was reduced to levels below those of sham-treated animals, in conjunction with interstitial expression of the antiangiogenic factor thrombospondin-1 (TSP-1) and decreased tubular expression of the proangiogenic factor vascular endothelial growth factor (VEGF). Both the increase in TSP-1 expression and the loss of VEGF expression were correlated with capillary loss and the development of glomerulosclerosis and interstitial fibrosis. Progressive macrophage infiltration was correlated both spatially and quantitatively with the sites of absent or diminished VEGF expression. In addition, macrophage-associated cytokines (interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha) inhibited VEGF mRNA expression and protein secretion by cultured tubular epithelial cells of the medullary thick ascending limb, under both normoxic and hypoxic conditions. Impaired angiogenesis characterizes the remnant kidney model and is correlated with progression. The impaired angiogenesis may be mediated by alterations in the renal expression of TSP-1 and VEGF, with the latter being regulated by macrophage-associated cytokines.