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,

Angiogenesis, the process of development of a new microvasculature, is regulated by a balance of positive and negative factors. We show both in vivo and in vitro that the members of the human prolactin͞growth hormone family, i.e., human prolactin, human growth hormone, human placental lactogen, and human growth hormone variant are angiogenic whereas their respective 16-kDa N-terminal fragments are antiangiogenic. The opposite actions are regulated in part via activation or inhibition of mitogen-activated protein kinase signaling pathway. In addition, the N-terminal fragments stimulate expression of type 1 plasminogen activator inhibitor whereas the intact molecules have no effect, an observation consistent with the fragments acting via separate receptors. The concept that a single molecule encodes both angiogenic and antiangiogenic peptides represents an efficient model for regulating the balance of positive and negative factors controlling angiogenesis. This hypothesis has potential physiological importance for the control of the vascular connection between the fetal and maternal circulations in the placenta, where human prolactin, human placental lactogen, and human growth hormone variant are expressed.Prolactin (PRL), growth hormone (GH), and placental lactogen (PL) are homologous protein hormones believed to have arisen from a common ancestral gene (1). PRL participates in the regulation of reproduction, osmoregulation, and immunomodulation (2, 3) whereas GH is involved in regulating growth and morphogenesis (4). Human (h) GHs, unlike other mammalian GHs, bind to the PRL receptor and thus display PRL-like activity; however, hPRL does not bind to the hGH receptor (5). PRL and GH are produced mainly by the anterior pituitary in all vertebrates. PRL is expressed also in lymphocytes and in the decidua (6). The human placenta expresses two structural homologs of hGH, hPL and a variant of hGH (hGH-V) (7). hGH-V rather than pituitary hGH is believed to regulate maternal metabolism during the second half of pregnancy. hPL is somatotropic in fetal tissues and contributes to stimulating mammary cell proliferation (8). Rodent placentas express and secrete several proteins whose biological activities are more PRL-like than GH-like; these include proliferin (PLF) and a proliferin-related peptide (PRP) (9).Members of the PRL͞GH family and derived peptides have been reported to both stimulate and inhibit angiogenesis. PLF expressed during the first half of pregnancy in the mouse is angiogenic whereas PRP expressed later in gestation is antiangiogenic. These findings suggest that PLF and PRP might play a role in initiating and stopping placental neovascularization (9). Human GH was reported to be angiogenic in vitro (10) whereas both bovine and chicken GH were shown to be angiogenic in vivo (11). We have shown that the 16-kDa N-terminal fragments (16K) of rat PRL and hPRL are antiangiogenic both in vitro (12) and in vivo (13). Rat PRL is cleaved by cathepsin D (14) to yield a 16-kDa N-terminal fragment and a 7-kDa C...

Activated peritoneal macrophages are associated with endometriosis and may play a central role in its aetiology by releasing interleukin-1beta (IL-1beta) in response to refluxed endometrium. Pari passu with the establishment of endometriotic implants is the development of a vascular supply. In this study we investigated the angiogenic properties of two endometrial proteins, vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6), and assessed their production in response to IL-1beta stimulation in human stromal cells isolated from normal endometrium (NE) and endometriotic lesions (EI). Proliferation of bovine brain capillary endothelial cells (BBCE) with a [(3)H]-thymidine incorporation assay was observed when VEGF (2.1 +/- 0.2-fold; P < 0.05) or VEGF and IL-6 (1.8 +/- 0.1-fold; P < 0.05) were added in vitro, relative to saline-treated control cultures. Northern blot analysis showed induction of VEGF mRNA (2.6-fold; P < 0.05) and IL-6 mRNA (6.3-fold; P < 0.05) transcripts in EI cells, but not NE cells, exposed to IL-1beta. A similar induction was seen with VEGF and IL-6 protein secretion in the responsive EI cells. Reverse transcription-polymerase chain reaction (RT-PCR) for the IL-1 receptor type I (IL-1 RI) indicated that the differential effects of IL-1beta on NE and EI cells was associated with 2.4 +/- 0.1-fold more receptor mRNA in EI versus NE cells. We propose that the ability of IL-1beta to activate an angiogenic phenotype in EI stromal cells but not in NE cells, is mediated by the IL-1 RI.

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.

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Endometriotic lesions secrete chemokines that recruit immune cells into the peritoneal cavity. The accumulation of these immune cells, especially activated macrophages and T lymphocytes, is thought to mediate inflammatory symptoms associated with endometriosis. Previous studies have demonstrated that RANTES (regulated on activation, normal T cell expressed and secreted) is synthesized by endometriotic stromal cells and circulates in peritoneal fluid, commensurate with the stage of endometriosis. In the current studies, we used the human monocytic cell line, U937, to assay chemotactic activity in cell culture conditioned media and peritoneal fluid from patients with endometriosis and normal controls. We demonstrated expression of the human RANTES receptors CCR-1 and CCR-5 in U937 cells and peritoneal macrophages. Over a range of 0-1000 pg/ml recombinant human RANTES had a direct, linear effect on monocyte migration. Conditioned media and peritoneal fluid induced dose-dependent effects on monocyte migration that were correlated with concentrations of immunoreactive RANTES (as measured by enzyme-linked immunosorbent assay) and the severity of endometriosis. Heat denaturation of the RANTES protein or addition of anti-human RANTES antibodies neutralized the chemoattractant effects of conditioned media and peritoneal fluid. RANTES stimulation of monocyte recruitment may be an important pathogenetic target for the treatment of infertility and pain associated with endometriosis.

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 WTand 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 andT790M 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.