Marine compounds with pyridoacridine skeletons are known to exhibit interesting antitumor activities. Among these compounds, meridine has already been reported as having significant antitumor activities in vitro. We synthesized 24 analogues of meridine substituted on ring A with the aim of obtaining compounds that display significantly higher in vitro antitumor activities than meridine. The 24 compounds and meridine used as a control compound were tested at 6 different concentrations on 12 different human cancer cell lines including various histopathological types (glioblastomas and breast, colon, lung, prostate, and bladder cancers). The IC(50) value (i.e., the drug concentration inhibiting the mean growth value of the 12 cell lines by 50%) of these 25 compounds ranged over 5 log concentrations, i.e., between 10 and 0.0001 microM, with four of the compounds exhibiting a significantly higher in vitro antitumor activity than meridine. These compounds will now be subjected to further pharmacological investigation including in vivo testing on both conventional murine tumors and human tumors grafted onto nude mice.