Asperuloside exhibits a novel anti-leukemic activity by triggering ER stress-regulated apoptosis via targeting GRP78

Acute myeloid leukemia (AML) is a complicated disease of hematopoietic stem cell disorders. However, its pathogenesis mechanisms and therapeutic treatments still remain vague. Asperuloside (ASP) is an iridoid glycoside found in Herba Paederiae, and is a component from traditional Chinese herbal medicine. ASP has been suggested to have various pharmacological activities, such as anti-tumor and anti-inflammation. In this study, we explored the effects of ASP on apoptosis and endoplasmic reticulum (ER) stress in human leukemia cells and in human primary leukemia blasts. ASP treatments selectively reduced the cell viability of human leukemia cells and primary leukemia blasts in a dose-dependent manner. We also found that ASP induced cell death via promoting the cleavage of Caspase-9, -3 and poly (ADP-ribose) polymerase (PARP), which was along with the loss of mitochondrial membrane potential and Cyto-c release from the mitochondria. In addition, we found that ASP significantly induced ER stress in leukemia cells by improving the protein expression levels of glucose-regulated protein of 78 kDa (GRP78), phosphorylated protein kinase RNA-like ER kinase (PERK), phosphorylated eukaryotic translation initiation factor 2 alpha (eIF2α), C/EBP homologous protein (CHOP), phosphorylated inositol-requiring enzyme 1 (p-IRE1), X-box binding protein 1 (XBP1), activating transcription factor-6 (ATF6) and cleaved Caspase-12. Moreover, ER stress suppression markedly abrogated ASP-induced apoptosis. In addition, GRP78 knockdown significantly diminished ER stress and apoptosis triggered by ASP. Importantly, co-immunoprecipitation (IP) analysis further indicated that ASP regulated the interaction between GRP78 and PERK, subsequently meditating the apoptotic cell death. In vivo leukemia xenografts finally validated ER stress and apoptosis were related to the tumor growth reduction induced by ASP. The overall survival of mice was also improved by ASP treatments, accompanied with the significantly reduced number of white blood cells and elevated red blood cells. Together, our present results showed that ASP exerted anti-leukemic effects at least partially via inducing apoptosis regulated by ER stress, and suggested that ASP might be a novel and effective therapeutic strategy for treating human leukemia.