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-

Our results show the ability of sorafenib to potently inhibit the growth of both ectopically- and orthotopically-implanted Renca and 786-O tumors. The observed tumor growth inhibition and tumor stasis or stabilization correlated strongly with decreased tumor angiogenesis, which was due, at least in part, to inhibition of VEGF and PDGF-mediated endothelial cell and pericyte survival. Finally, sorafenib-mediated inhibition of tumor growth and angiogenesis occurred at concentrations equivalent to those achieved in patients in the clinic.

BAY 43-9006, a multikinase inhibitor that targets Raf, prevents tumor cell proliferation in vitro and inhibits diverse human tumor xenografts in vivo. The mechanism of action of BAY 43-9006 remains incompletely defined. In the present study, the effects of BAY 43-9006 on the antiapoptotic Bcl-2 family member Mcl-1 were examined. Treatment of A549 lung cancer cells with BAY 43-9006 diminished Mcl-1 levels in a time- and dose-dependent manner without affecting other Bcl-2 family members. Similar BAY 43-9006-induced Mcl-1 downregulation was observed in ACHN (renal cell), HT-29 (colon), MDA-MB-231 (breast), KMCH (cholangiocarcinoma), Jurkat (acute T-cell leukemia), K562 (chronic myelogenous leukemia) and MEC-2 (chronic lymphocytic leukemia) cells. Mcl-1 mRNA levels did not change in BAY 43-9006-treated cells. Instead, BAY 43-9006 enhanced proteasome-mediated Mcl-1 degradation. This Mcl-1 downregulation was followed by mitochondrial cytochrome c release and caspase activation as well as enhanced sensitivity to other proapoptotic agents. The caspase inhibitor Boc-D-fmk inhibited BAY 43-9006-induced caspase activation but not cytochrome c release. In contrast, Mcl-1 overexpression inhibited cytochrome c release and other features of BAY 43-9006-induced apoptosis. Conversely, Mcl-1 downregulation by short hairpin RNA enhanced BAY 43-9006-induced apoptosis. Collectively, these findings demonstrate that drug-induced Mcl-1 downregulation contributes to the proapoptotic effects of BAY 43-9006.

This study was undertaken to characterize preclinical cytotoxic interactions for human malignancies between the multikinase inhibitor sorafenib (BAY 43-9006) and proteasome inhibitors bortezomib or MG132. Multiple tumor cell lines of varying histiotypes, including A549 (lung adenocarcinoma), 786-O (renal cell carcinoma), HeLa (cervical carcinoma), MDA-MB-231 (breast), K562 (chronic myelogenous leukemia), Jurkat (acute T-cell leukemia), MEC-2 (B-chronic lymphocytic leukemia), and U251 and D37 (glioma), as well as cells derived from primary human glioma tumors that are likely a more clinically relevant model were treated with sorafenib or bortezomib alone or in combination. Sorafenib and bortezomib synergistically induced a marked increase in mitochondrial injury and apoptosis, reflected by cytochrome c release, caspase-3 cleavage, and poly(ADPribose) polymerase degradation in a broad range of solid tumor and leukemia cell lines. These findings were accompanied by several biochemical changes, including decreased phosphorylation of vascular endothelial growth factor receptor-2, platelet-derived growth factor receptor-B, and Akt and increased phosphorylation of stress-related c-Jun NH 2 -terminal kinase (JNK). Inhibition of Akt was required for synergism, as a constitutively active Akt protected cells against apoptosis induced by the combination. Alternatively, the JNK inhibitor SP600125 could also protect cells from apoptosis induced by the combination, indicating that both inhibition of Akt and activation of JNK were required for the synergism. These findings show that sorafenib interacts synergistically with bortezomib to induce apoptosis in a broad spectrum of neoplastic cell lines and show an important role for the Akt and JNK pathways in mediating synergism. Further clinical development of this combination seems warranted. [Mol Cancer Ther 2006;5(9):2378 -87]

The effects of the cyclooxygenase inhibitors indomethacin and carprofen on the enhancement of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis by dietary linoleate have been compared in female Sprague-Dawley rats. Indomethacin and carprofen, 0.004% and 0.02% (w/w) in the diet, respectively, were fed to rats receiving 20% fat diets containing 0.5, 4 or 12% linoleate starting 7 days after administration of 5 mg DMBA i.g. Indomethacin was shown to have a marked inhibitory effect on mammary tumorigenesis in rats fed the 4 and 12% linoleate diets, but did not alter tumorigenesis in rats fed the 0.5% linoleate diet. In contrast, carprofen was not inhibitory in any of these dietary groups, or in a separate experiment in which a 5% fat--3% linoleate diet was fed. The effect of each drug on prostaglandin E2 (PGE2) levels in normal mammary glands enriched in epithelial cells after a 3-week pretreatment with 17 beta-estradiol and progesterone was also investigated. Carprofen was shown to reduce PGE2 levels to a similar or greater extent than indomethacin at each level of linoleate in the diet. These data demonstrate that a reduction in PGE2 synthesis in the mammary epithelium does not correlate with inhibition of mammary tumorigenesis, and that other factors, including possible alterations in other products of the arachidonic acid cascade, are responsible for this inhibitory effect.