Purpose of the study: To investigate the functional role of Akt and JNK signaling cascades in apigenin-induced apoptosis in human leukemia cells (in vitro) and anti-leukemic activity of apigenin in U937 xenografts (in vivo).

Experimental Design: Leukemia cells were treated with apigenin in dose and time dependent manners, after which apoptosis, caspases activation, Akt and JNK signaling pathways were evaluated by pharmacologic and genetic approaches. Parallel studies were also conducted in Jurkat, HL60 and normal peripheral blood mononuclear cells. In vivo anti-leukemic activity mediated by apigenin was evaluated using U937 xenograft mouse model.

Results: Exposure of apigenin caused pronounced increase in apoptosis in leukemia cells but not in normal peripheral blood mononuclear cells. Apigenin-induced apoptosis by inactivation of Akt with concomitant activation of JNK, cytochrome c release from mitochondria and caspases activation in dose and time dependent manners. Enforced activation of Akt by a constitutively active myristolated Akt prevented apigenin-induced JNK and caspases activation and apoptosis. Conversely, PI3K (phosphatidyl 3-kinase) inhibitor LY294002 and a dominant negative construct of Akt potentiated apigenin-induced apoptosis in leukemia cells. In addition, Akt kinase activity was diminished after exposure to apigenin in leukemia cells. Interruption of JNK pathway by pharmacologic (SP600125) and genetic (JNK1 siRNA) approaches showed marked reduction in apigenin-induced caspases activation and apoptosis in leukemia cells. Furthermore, in vivo administration of apigenin via intraperitoneal route resulted in attenuation of tumor growth in U937 xenografts accompanied by apoptosis.

Conclusions: Collectively, these findings suggested a hierarchical model of apigenin-induced apoptosis in human leukemia cells in which apigenin-induced Akt inactivation represents a primary event resulting in JNK activation and culminating in caspases activation and apoptosis. In addition, attenuation of tumor growth in U937 xenografts by apigenin raise the possibility that apigenin may have clinical implications for therapeutic intervention against leukemia.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4593. doi:10.1158/1538-7445.AM2011-4593

©2011 American Association for Cancer Research
2011