Abstract A24: Targeting of ERKs with magnolin inhibits EGF-induced anchorage-independent cell transformation

Abstract

Abstract An activated Ras mutation (RasG12V; constitutively active Ras) has exhibited in many human solid cancers with high occurrences including colon cancer (45%), pancreatic cancer (90%), non-small-cell lung cancer (35%) and melanomas (15%). Our previous results demonstrated that the ERKs signaling pathways including the ERKs/RSK2/histone H3 and ERKs/RSK2/cAMP-dependent transcription factor 1 (ATF1) signaling axes plays an important role in cell proliferation and transformation induced by growth factor stimulation such as epidermal growth factor (EGF). However, although ERKs are an important target molecule of anti-cancer drugs or chemopreventive agents, the identification or development of small molecules as ERKs inhibitors has been barely studied. Recently, several ERK specific inhibitors have been found by high-throughput phosphorylation assays with an in-house chemical library. For example, small molecule FR180204 is an inhibitor of ERK1 and ERK2 with IC50 values of 0.51 nM and 0.33 nM, respectively. More recently, FR148083 was identified as an ERK2 inhibitor and it suppressed ERK2 activity with an IC50 value of 80 nM on an enzyme assay screening. However, these compounds also showed inhibition of other enzymes such as TGF-β-induced AP-1-dependent luciferase expression with an IC50 value of 50 nM. The Magnolia species has been traditionally used as an oriental medicine to treat nasal congestion associated with headache, sinusitis, anti-inflammation, and allergic rhinitis. Magnolin is an ingredient found in the Magnolia species, and it has been widely used in oriental medicine to treat human diseases including empyema, nasal congestion, sinusitis and inflammation, and has been shown to inhibit the production of tumor necrosis factor-α (TNF-α). Recent studies have shown that magnolin influences nitric oxide (NO) and prostaglandin E2 (PGE2) production by inhibiting extracellular signal-regulated kinase (ERK). In this study, we found that magnolin directly targeted and inhibited ERK1 and ERK2 kinase activities with IC50 values of 87 nM and 16.5 nM by competing with ATP in an active pocket, respectively. Notably, EGF-induced p90RSKs phosphorylation at Thr359/Ser363 was inhibited by magnolin treatment, resulted in inhibition of cell proliferation by suppression of the G1/S cell cycle transition. Importantly, inhibition of ERKs/RSK2 signaling axis by magnolin suppresses the EGF-induced anchorage-independent cell transformation by the abrogation of ATF1 and AP-1 transactivation activities. Taken together, these results demonstrated that magnolin might be a naturally occurring chemoprevention and therapeutic agent capable of inhibiting cell proliferation and transformation by targeting ERK1 and ERK2. Citation Format: Cheol-Jung Lee, Hye Suk Lee, Hyung Won Ryu, Mee-Hyun Lee, Ji-Young Lee, Hyoung-Kyu Lee, Sei-Ryang Oh, Yong-Yeon Cho. Targeting of ERKs with magnolin inhibits EGF-induced anchorage-independent cell transformation. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr A24.