Angiogenesis, a critical driver of tumor development, is controlled by interconnected signaling pathways. Vascular endothelial growth factor receptor (VEGFR) 2 and tyrosine kinase with immunoglobulin and epidermal growth factor homology domain 2 play crucial roles in the biology of normal and tumor vasculature. Regorafenib (BAY 73-4506), a novel oral multikinase inhibitor, potently inhibits these endothelial cell kinases in biochemical and cellular kinase phosphorylation assays. Furthermore, regorafenib inhibits additional angiogenic kinases (VEGFR1/3, platelet-derived growth factor receptor-b and fibroblast growth factor receptor 1) and the mutant oncogenic kinases KIT, RET and B-RAF. The antiangiogenic effect of regorafenib was demonstrated in vivo by dynamic contrast-enhanced magnetic resonance imaging. Regorafenib administered once orally at 10 mg/kg significantly decreased the extravasation of Gadomer in the vasculature of rat GS9L glioblastoma tumor xenografts. In a daily (qd)34 dosing study, the pharmacodynamic effects persisted for 48 hr after the last dosing and correlated with tumor growth inhibition (TGI). A significant reduction in tumor microvessel area was observed in a human colorectal xenograft after qd35 dosing at 10 and 30 mg/kg. Regorafenib exhibited potent dose-dependent TGI in various preclinical human xenograft models in mice, with tumor shrinkages observed in breast MDA-MB-231 and renal 786-O carcinoma models. Pharmacodynamic analyses of the breast model revealed strong reduction in staining of proliferation marker Ki-67 and phosphorylated extracellular regulated kinases 1/2. These data demonstrate that regorafenib is a well-tolerated, orally active multikinase inhibitor with a distinct target profile that may have therapeutic benefit in human malignancies.Activation of multiple signaling pathways in the tumor microenvironment, including the receptor tyrosine kinases (RTKs) vascular endothelial growth factor receptor (VEGFR), fibroblast growth factor receptor (FGFR) and platelet-derived growth factor receptor (PDGFR), controls the initiation of tumor neoangiogenesis. 1 Of these, VEGF was the first vascular-

Recent studies have demonstrated increased levels of IL-6 in the peritoneal cavity during CAPD peritonitis. The current investigation was initiated (i) to examine the human peritoneal mesothelial cell (HPMC) as a possible source of this secreted IL-6 and (ii) to characterize the released product and examine its regulation by other cytokines. Unstimulated HPMC under growth arrested conditions released IL-6 in a time dependent manner. After 24-hour HPMC IL-6 release (mean +/- SEM, N = 13) (expressed as pg/micrograms cell protein) was 1.67 +/- 0.33. Stimulation of HPMC with IL-1 beta or TNF alpha resulted in a time (increasing up to 48 hr) and dose dependent IL-6 generation. After 24 hours the levels induced by IL-1 beta and TNF alpha (both at 1000 pg/ml) were (mean +/- SEM, N = 13) 19.08 +/- 2.98 and 6.62 +/- 1.72, respectively. Stimulation with combinations of IL-1 beta and TNF alpha resulted in additive increases in IL-6 release. This release could be inhibited by co-incubation with anti-IL-1 beta and/or anti-TNF alpha antibodies. The level of released HPMC IL-6 measured by immunometric assay (ELISA) correlated directly with that detected in the 7TD1 IL-6 bioassay (r = 0.63; P < 0.001). Western blot analysis of concentrated HPMC supernatants using specific anti-IL-6 antibody demonstrated immunoreactive bands at 23 and 28 Kd following IL-1 beta or TNF alpha treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The activation of the transcription factor hypoxia-inducible factor-1 (HIF-1) plays an essential role in tumor development, tumor progression, and resistance to chemo- and radiotherapy. In order to identify compounds targeting the HIF pathway, a small molecule library was screened using a luciferase-driven HIF-1 reporter cell line under hypoxia. The high-throughput screening led to the identification of a class of aminoalkyl-substituted compounds that inhibited hypoxia-induced HIF-1 target gene expression in human lung cancer cell lines at low nanomolar concentrations. Lead structure BAY 87-2243 was found to inhibit HIF-1α and HIF-2α protein accumulation under hypoxic conditions in non-small cell lung cancer (NSCLC) cell line H460 but had no effect on HIF-1α protein levels induced by the hypoxia mimetics desferrioxamine or cobalt chloride. BAY 87-2243 had no effect on HIF target gene expression levels in RCC4 cells lacking Von Hippel–Lindau (VHL) activity nor did the compound affect the activity of HIF prolyl hydroxylase-2. Antitumor activity of BAY 87-2243, suppression of HIF-1α protein levels, and reduction of HIF-1 target gene expression in vivo were demonstrated in a H460 xenograft model. BAY 87-2243 did not inhibit cell proliferation under standard conditions. However under glucose depletion, a condition favoring mitochondrial ATP generation as energy source, BAY 87-2243 inhibited cell proliferation in the nanomolar range. Further experiments revealed that BAY 87-2243 inhibits mitochondrial complex I activity but has no effect on complex III activity. Interference with mitochondrial function to reduce hypoxia-induced HIF-1 activity in tumors might be an interesting therapeutic approach to overcome chemo- and radiotherapy-resistance of hypoxic tumors.

Regorafenib, a novel multikinase inhibitor, has recently demonstrated overall survival benefits in metastatic colorectal cancer (CRC) patients. Our study aimed to gain further insight into the molecular mechanisms of regorafenib and to assess its potential in combination therapy. Regorafenib was tested alone and in combination with irinotecan in patient-derived (PD) CRC models and a murine CRC liver metastasis model. Mechanism of action was investigated using in vitro functional assays, immunohistochemistry and correlation with CRC-related oncogenes. Regorafenib demonstrated significant inhibition of growth-factor-mediated vascular endothelial growth factor receptor (VEGFR) 2 and VEGFR3 autophosphorylation, and intracellular VEGFR3 signaling in human umbilical vascular endothelial cells (HuVECs) and lymphatic endothelial cells (LECs), and also blocked migration of LECs. Furthermore, regorafenib inhibited proliferation in 19 of 25 human CRC cell lines and markedly slowed tumor growth in five of seven PD xenograft models. Combination of regorafenib with irinotecan significantly delayed tumor growth after extended treatment in four xenograft models. Reduced CD31 staining indicates that the antiangiogenic effects of regorafenib contribute to its antitumor activity. Finally, regorafenib significantly delayed disease progression in a murine CRC liver metastasis model by inhibiting the growth of established liver metastases and preventing the formation of new metastases in other organs. In addition, our results suggest that regorafenib displays antimetastatic activity, which may contribute to its efficacy in patients with metastatic CRC. Combination of regorafenib and irinotecan demonstrated an increased antitumor effect and could provide a future treatment option for CRC patients.What's new?Regorafenib is a multikinase inhibitor with antiangiogenic activity recently approved in the US and in Europe for the treatment of metastatic colorectal cancer in patients who failed previous therapies. Here, a research team led by Bayer Pharma AG, the discoverer of the drug, confirms inhibition of key mediators of angiogenesis and lymphangiogenesis (VEGFR2 and VEGFR3) as the potential antiangiogenic mechanism of action of the drug. Regorafenib further inhibited growth of established and prevented formation of new liver metastases, and in combination with the chemotherapeutic drug irinotecan led to significant tumor growth delay in four patient-derived colorectal cancer xenograft models. The authors speculate that combination treatments including regorafenib may provide novel therapeutic opportunities for patients with therapy-resistant colorectal cancer.

Angiogenesis is a complex process that can be regarded as a series of sequential events comprising a variety of tissue cells. The major problem when studying angiogenesis in vitro is the lack of a model system mimicking the various aspects of the process in vivo. In this study we have used two in vitro models, each representing different and distinct aspects of angiogenesis. Differentially expressed genes in the two culture forms were identified using the suppression subtractive hybridization technique to prepare subtracted cDNA libraries. This was followed by a differential hybridization screen to pick up overexpressed clones. Using comparative multiplex RT-PCR we confirmed the differential expression and showed differences up to 14-fold. We identified a broad range of genes already known to play an important role during angiogenesis like Flt1 or TIE2. Furthermore several known genes are put into the context of endothelial cell differentiation, which up to now have not been described as being relevant to angiogenesis, like NrCAM, Claudin14, BMP-6, PEA-15 and PINCH. With ADAMTS4 and hADAMTS1/METH-1 we further extended the set of matrix metalloproteases expressed and regulated by endothelial cells.Keywords: differential gene expression; MVEC; angiogenesis; suppression subtractive hybridization.Angiogenesis, the formation of new capillaries from preexisting blood vessels, plays a crucial role in a wide range of normal and pathological processes, and is necessary for the continous growth of solid tumors [1,2]. Angiogenesis takes not place in a single step, but is a complex sequential process that relies on a controled cross-talk between endothelial cells and the surrounding avascular environment [2,3]. Upon activation by growth factors or cytokines, endothelial cells start to degrade the surrounding extracellular matrix and invade the avascular tissue. The tight endothelial cell-cell adhesion is disrupted, the cells start to proliferate and migrate into the avascular environment. Finally they stop proliferating and differentiate to tubular structures (reviewed in [3]). Most recent studies have focused on the effect of specific growth factors and cytokines secreted by non endothelial cells on angiogenesis, but little is known about the sequential events taking place in the activated endothelial cells during the formation of new blood vessels.In this work we chose a model system where human microvascular endothelial cells (MVEC) are cultured on a gel composed of extracted basement membrane derived from mouse Engelbreth±Holm±Swarm sarcoma (matrigel) [4]. When seeded at a certain density the cells stop proliferating and virtually all cells are induced rapidly to form capillary-like, lumen containing structures [4,5]. These cells were compared against nondifferentiating, proliferating MVEC again representing an important step during the formation of new blood vessels [2,3]. The advantage of these culture systems is that they can be performed with one and the same cell type resulting in two different homogenous populatio...