After creating a combinatorial library of approximately 1000 bis-aryl urea analogs, these compounds were screened against Raf1 to find an analog with an IC50 of only 1.1 μM. Sorafenib was discovered after several substitutions and modifications of functional groups. Not only could sorafenib inhibit Raf1, but it could also inhibit the wild-type BRaf, the oncogenic b-raf V600E kinases, VEGFR-1, -2 and -3, PDGFR-β, fibroblast growth factor receptor 1, c-Kit, Flt-3 and RET.[12, 13] SORAFENIB WORKS BY inhibiting several kinases in the MAPK pathway (Fig. 1a). The G-protein Ras

is a key member of the MAPK pathway, and it helps regulate the Raf/Mek/Erk cascade.[12] Downstream from Ras is a family of Raf serine/threonine kinases. These kinases start Roxadustat nmr a phosphorylation cascade

that eventually leads to the transcription of genes that promote cell proliferation.[14] The Raf family is made up of ARaf, BRaf and Raf1. Sorafenib targets Raf1[15, 16] and BRaf.[12] Liu et al. showed that 3–10 μm of sorafenib inhibited Mek and Erk phosphorylation in PLC/PRF/5 HCC cells, and only 1–3 μm was needed for this same effect in HepG2 HCC cells.[17] Erk phosphorylation PF-02341066 cell line is also inhibited by sorafenib in MDA-MB-231 human breast carcinoma cells, Mia PaCa 2 human pancreatic tumor cells, and HCT 116 and HT-29 human colon tumor cell lines, but not the NCI-H460 and A549 non-small cell lung cancer cells.[12] Erk activates Myc, a transcription factor for cyclin D1, which may help promote cell proliferation. Sorafenib at 10 μm medchemexpress decreases the cyclin D1 level by inhibiting Mek/Erk in both HepG2 and PLC/PRF/5 cell lines.[17] Reduced cyclin D1 levels lead to decreased transcription of genes that are involved in cell proliferation. Sorafenib induces apoptosis in multiple

cancer cell lines by downregulating and inhibiting the translation of Mcl-1, a Bcl-2 family member (Fig. 1a).[17] The pro-survivor factor Mcl-1 normally works to prevent apoptosis. It does this by inhibiting Bak, a protein that promotes apoptosis. Studies completed by Rahmani et al. demonstrated a linkage between the translational factor elF4E and Mcl-1.[18] When 1 and 10 μm of sorafenib were introduced to the HepG2 and PLC/PRF/5 cell lines, they each reduced the amount of phosphorylated elF4E.[17] At 10 μm and 16 h later, Mcl-1 protein levels were also reduced.[17] The levels of elF4E phosphorylation and Mcl-1 were both unaffected by the Mek inhibitor U0126 in HepG2 cells, showing that these downregulations are independent of the Mek/Erk signaling pathway.[17] Thus, the working model suggests that sorafenib prevents elF4E phosphorylation, blocking the initiation of Mcl-1 translation. Sorafenib also caused DNA fragmentation with a half maximal effective concentration (EC50) of 7.7 μm in PLC/PRF/5 cells and an EC50 of 2.4 μm in HepG2 cells.[17] Sorafenib can also inhibit cancer tumor growth by targeting PDGFR-β, VEGFR-2 and VEGFR-3, three tyrosine kinases that promote angiogenesis (Fig. 1b).