Cytotoxic activities of 4 natural products – carnosic acid, xanthohumol, caffeic acid phenethyl ester and (-) eburnamonine - Nga, DT; Juan, QH; Kyung, KE; Batmunkh, T; Yeon, SJ; Hoon, KY; Sup, KM; Sun, LG; Burm-Jong, L; Ah, KK (Planta Medica, 2007)