Ning-Kui Niu,1–3 Zi-Li Wang,1 Shu-Ting Pan,2,4 Hui-Qiang Ding,1 Giang HT Au,2 Zhi-Xu He,5 Zhi-Wei Zhou,2,5 Guozhi Xiao,6 Yin-Xue Yang,7 Xueji Zhang,8 Tianxin Yang,9 Xiao-Wu Chen,10Jia-Xuan Qiu,4 Shu-Feng Zhou2 1Department of Spinal Surgery, General Hospital of Ningxia Medical University, Yinchuan, People’s Republic of China; 2Department of Pharmaceutical Sciences, College of Pharmacy, University of South Florida, Tampa, FL, USA; 3Department of Orthopedics, General Hospital of Tianjin Medical University, Tianjin, 4Department of Oral and Maxillofacial Surgery, The First Affiliated Hospital of Nanchang University, Nanchang, Jiangxi, 5Guizhou Provincial Key Laboratory for Regenerative Medicine, Stem Cell and Tissue Engineering Research Center and Sino-US Joint Laboratory for Medical Sciences, Guizhou Medical University, Guiyang, Guizhou, People’s Republic of China; 6Department of Biochemistry, Medical Center, Rush University, Chicago, IL, USA; 7Department of Colorectal Surgery, General Hospital of Ningxia Medical University, Yinchuan, 8Research Center for Bioengineering and Sensing Technology, University of Science and Technology Beijing, Beijing, People’s Republic of China; 9Department of Internal Medicine, University of Utah and Salt Lake Veterans Affairs Medical Center, Salt Lake City, UT, USA; 10Department of General Surgery, The First People’s Hospital of Shunde affiliated to Southern Medical University, Foshan, Guangdong, People’s Republic of China Abstract: Osteosarcoma (OS) is the most common malignant bone tumor occurring mostly in children and adolescents between 10 and 20 years of age with poor response to current therapeutics. Alisertib (ALS, MLN8237) is a selective Aurora kinase A inhibitor that displays anticancer effects on several types of cancer. However, the role of ALS in the treatment of OS remains unknown. This study aimed to investigate the effects of ALS on the cell growth, apoptosis, autophagy, and epithelial to mesenchymal transition (EMT) and the underlying mechanisms in two human OS cell lines U-2 OS and MG-63. The results showed that ALS had potent growth inhibitory, pro-apoptotic, pro-autophagic, and EMT inhibitory effects on U-2 OS and MG-63 cells. ALS remarkably induced G2/M arrest and down-regulated the expression levels of cyclin-dependent kinases 1 and 2 and cyclin B1 in both U-2 OS and MG-63 cells. ALS markedly induced mitochondria-mediated apoptosis with a significant increase in the expression of key pro-apoptotic proteins and a decrease in main anti-apoptotic proteins. Furthermore, ALS promoted autophagic cell death via the inhibition of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) and p38 mitogen-activated protein kinase (p38 MAPK) signaling pathways, and activation of 5'-AMP-dependent kinase (AMPK) signaling pathway. Inducers or inhibitors of apoptosis or autophagy simultaneously altered ALS-induced apoptotic and autophagic death in both U-2 OS and MG-63 cells, suggesting a crosstalk between these two primary modes of programmed cell death. Moreover, ALS suppressed EMT-like phenotypes with a marked increase in the expression of E-cadherin but a decrease in N-cadherin in U-2 OS and MG-63 cells. ALS treatment also induced reactive oxygen species (ROS) generation but inhibited the expression levels of sirtuin 1 and nuclear factor-erythroid-2-related factor 2 (Nrf2) in both cell lines. Taken together, these findings show that ALS promotes apoptosis and autophagy but inhibits EMT via PI3K/Akt/mTOR, p38 MAPK, and AMPK signaling pathways with involvement of ROS- and sirtuin 1-associated pathways in U-2 OS and MG-63 cells. ALS is a promising anticancer agent in OS treatment and further studies are needed to confirm its efficacy and safety in OS chemotherapy. Keywords: ALS, autophagy, apoptosis, osteosarcoma, PI3K/Akt/mTOR pathway, EMT