Small Molecule Therapeutics Characterization of LY2228820 Dimesylate, a Potent and Selective Inhibitor of p38 MAPK with Antitumor Activity

p38a mitogen-activated protein kinase (MAPK) is activated in cancer cells in response to environmental factors, oncogenic stress, radiation, and chemotherapy. p38a MAPK phosphorylates a number of substrates, including MAPKAP-K2 (MK2), and regulates the production of cytokines in the tumor microenvironment, such as TNF-a, interleukin-1b (IL-1b), IL-6, and CXCL8 (IL-8). p38a MAPK is highly expressed in human cancers andmay play a role in tumor growth, invasion,metastasis, and drug resistance. LY2228820 dimesylate (hereafter LY2228820), a trisubstituted imidazole derivative, is a potent and selective, ATP-competitive inhibitor of the aand b-isoforms of p38 MAPK in vitro (IC50 1⁄4 5.3 and 3.2 nmol/L, respectively). In cellbased assays, LY2228820 potently and selectively inhibited phosphorylation of MK2 (Thr334) in anisomycinstimulated HeLa cells (at 9.8 nmol/L by Western blot analysis) and anisomycin-induced mouse RAW264.7 macrophages (IC50 1⁄4 35.3 nmol/L) with no changes in phosphorylation of p38aMAPK, JNK, ERK1/2, c-Jun, ATF2, or c-Myc 10 mmol/L. LY2228820 also reduced TNF-a secretion by lipopolysaccharide/IFNg–stimulated macrophages (IC50 1⁄4 6.3 nmol/L). In mice transplanted with B16-F10 melanoma, tumor phospho-MK2 (p-MK2) was inhibited by LY2228820 in a dose-dependent manner [threshold effective dose (TED)701⁄4 11.2mg/kg]. Significant target inhibition (>40% reduction inp-MK2)wasmaintained for 4 to 8 hours following a single 10mg/kg oral dose. LY2228820 produced significant tumor growth delay inmultiple in vivo cancer models (melanoma, non–small cell lung cancer, ovarian, glioma, myeloma, breast). In summary, LY2228820 is a p38 MAPK inhibitor, which has been optimized for potency, selectivity, drug-like properties (such as oral bioavailability), and efficacy in animal models of human cancer. Mol Cancer Ther; 13(2); 1–11.