Catechol (pyrocathechol, 1,2-dihydroxybenzene) is a chemical that is used by industry in the manufacture of certain products. Many natural compounds contain catechol as a functional group found in various fruits and vegetables such as apple, apricot, grape, bananas, soybean, peanut, pear, plum, mango, avocado, and mushroom. Extracellular signal-regulated kinase 2 (ERK2), a protein kinase that belongs to MAPK family, modulates many important functions such as cell growth, apoptosis and transcriptional regulation in cancer. The expression levels of ERK2 mRNA and protein are reportedly very high in many human cancers, including leukemia, colon, breast, lung and skin cancer. Previously, we reported that norathyriol and caffeic acid, which possess the catechol moiety, and catechol itself directly bind and inhibit ERK2 kinase activity. Those findings led us to test catechol moiety-containing natural compounds, luteolin, quercetin, fisetin, 7,3’,4’-trihydroxyisoflavone, and cyanidin, against ERK2 kinase activity. We found that all of these compounds directly bind to ERK2 and inhibit its activity. We further confirmed the results by resolving a co-crystal structure of ERK2 bound with luteolin in the ATP binding site. To apply this finding to cancer, the effect of the compounds was tested on the K562 human myelogenous leukemia cell line where ERK2 is highly expressed and knock-down of the protein reduced anchorage-independent growth. Five newly-found ERK2 inhibitors (luteolin, quercetin, fisetin, 7,3’,4’-trihydroxyisoflavone and cyanidin) and three known ERK2 inhibitors (norathyriol, caffeic acid and catechol) decreased cell viability of K562 at 40 ìM. When the eight compounds were used at the same dose in combination (5 ìM each and 40 ìM total), the mixture inhibited ERK2 and reduced cell viability of K562 cells. In summary, using in vitro kinase assays and co-crystallography, we identified new ERK2 inhibitors that contain the catechol functional group, and showed anti-cancer effects of the compounds by cell viability assay and soft agar assay. This work impacts the cancer prevention community by showing that many natural compounds can work together targeting ERK2, an important target in cancer.

Citation Format: Seung Ho Shin, Margarita Malakhova, Igor Kurinov, Do Young Lim, Ann M. Bode, Zigang Dong. Discovery of catechol moiety-containing natural compounds as direct ERK2 inhibitors by in vitro kinase assay and co-crystallography. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 821.