Since the molecular revolution of the 1980s, knowledge of the aetiology of cancer has increased considerably, which has led to the discovery and development of targeted therapies tailored to inhibit cancer-specific pathways. The introduction and refinement of rapid, high-throughput screening technologies over the past decade has greatly facilitated this targeted discovery and development process. Here, we describe the discovery and continuing development of sorafenib (previously known as BAY 43-9006), the first oral multikinase inhibitor that targets Raf and affects tumour signalling and the tumour vasculature. The discovery cycle of sorafenib (Nexavar; Bayer Pharmaceuticals) - from initial screening for a lead compound to FDA approval for the treatment of advanced renal cell carcinoma in December 2005 - was completed in just 11 years, with approval being received approximately 5 years after the initiation of the first Phase I trial.

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-

SummaryWe studied the cytological and biochemical properties of the FtsA protein of Streptococcus pneumoniae . FtsA is a widespread bacterial cell division protein that belongs to the actin superfamily. In Escherichia coli and Bacillus subtilis , FtsA localizes to the septal ring after FtsZ, but its exact role in septation is not known. In S. pneumoniae , we found that, during exponential growth, the protein localizes to the nascent septa, at the equatorial zones of the dividing cells, where an average of 2200 FtsA molecules per cell are present. Likewise, FtsZ was found to localize with the same pattern and to be present at an average of 3000 molecules per cell. Consistent with the colocalization, FtsA was found to interact with FtsZ and with itself. Purified FtsA is able to bind several nucleotides, the affinity being highest for adenosine triphosphate (ATP), and lower for other triphosphates and diphosphates. The protein polymerizes in vitro , in a nucleotide-dependent manner, forming long corkscrew-like helixes, composed of 2 + 2 paired protofilaments. No nucleotide hydrolytic activity was detected. Consistent with the absence of an ATPase activity, the polymers are highly stable and not dynamic. These results suggest that the FtsA protein could also polymerize in vivo and the polymers participate in septation.

Activating internal tandem duplication (ITD) insertions in the juxtamembrane domain of the FLT3 tyrosine kinase are found in about one fourth of patients with acute myeloid leukemia and have been shown to be an independent negative prognostic factor for survival. We show that sorafenib (BAY 43-9006, Nexavar) potently inhibits FLT3 enzymatic and signaling activities. In HEK293 cells stably transfected with FLT3-WT or FLT3-ITD, sorafenib blocked basal and ligand dependent FLT3-mediated tyrosine autophosphorylation as well as extracellular signal-regulated kinase1/2 and Stat5 phosphorylation. In leukemia cell lines MV4-11 and EOL-1, sorafenib treatment resulted in decreased cell proliferation and inhibition of FLT3 signaling. The growth of the FLT3-independent RS4-11 cell line was only weakly inhibited by sorafenib. Cell cycle arrest and induction of apoptosis were observed upon treatment with sorafenib in MV4-11 and EOL-1 cells. The antitumor efficacy of sorafenib was evaluated against the MV4-11 leukemia grown subcutaneously in NCr nu/nu mice. Doses of 3 and 10 mg/kg administered orally for 14 days resulted in six and nine out of 10 animals with complete responses, respectively. The demonstration that sorafenib exhibits potent target inhibition and efficacy in FLT3-driven models suggests that this compound may have a therapeutic benefit for patients with FLT3-driven leukemias.

Raf kinase, an enzyme which acts downstream in the Ras signaling pathway, is involved in cancerous cell proliferation. Thus, small molecule inhibitors of Raf kinase activity may be important agents for the treatment of cancer. A novel class of Raf-1 inhibitors was discovered, using a combination of medicinal and combinatorial chemistry approaches. This effort culminated in the identification of the clinical candidate BAY 43-9006, currently undergoing Phase I clinical trials. The present review summarizes the medicinal chemistry development of ureas as highly potent inhibitors of Raf-1 kinase.