A series of newly asymmetric dimeric beta-carbolines with a spacer of 4-6 methylene units between the indole nitrogen and the harmine oxygen were synthesized. Structures of all the novel synthesized compounds were confirmed by their spectral and analytical studies. All of the synthesized compounds were screened for their in vitro cytotoxic activity against nine cancer cell lines. The results revealed that compounds 7c, 7o and 7s exhibited the highest cytotoxic activities with IC50 values of less than 20 AM against the tumor cell lines tested. Acute toxicities and antitumor efficacies of the selected compounds in mice were also evaluated, and compound 7o exhibited potent antitumor activities with the tumor inhibition rate of over 40%. The wound healing assay displayed a specific impairment in the motility of the HT-29 cells, which suggested the anti-metastatic potential of compound 7o. Moreover, compound 7o had obvious angiogenesis inhibitory effects in the chicken chorioallantoic membrane (CAM) assay. Preliminary structure-activity relationship (SAR) analysis indicated that: (1) 3-phenylpropyl substituent at the N-9-position of the indole ring was the most suitable group giving rise to potent cytotoxic agents: (2) the spacer length affected the antitumor potencies, and four methylene units were more favorable. (C) 2018 Elsevier Masson SAS. All rights reserved.