DNA Binding Ellipticine Analogues: Synthesis, Biological Evaluation, and Structure–Activity Relationships

Novel angular and branched ellipticine‐correlated anticancer agents were developed. In particular, compound 24 , with two basic side chains on opposite sides of the molecule, exhibits cytotoxicity in the nanomolar range, acting as a DNA intercalator and topoisomerase II inhibitor. SAR studies with pyridocarbazole derivatives in comparison with corresponding smaller pyrroloquinolines are discussed. magnified image In connection with our interest in the synthesis and study of the biological properties of ellipticine analogues as anticancer agents, some 7 H ‐pyrido[2,3‐ c ]carbazoles (7 H ‐PyC) and their corresponding tetrahydro derivatives (7 H ‐THPyC) were synthesized. A common multistep pathway characterized by conventional reactions involving carbazole Fischer and Conrad–Limpach quinoline syntheses yielded the tetracyclic compounds. With the aim to improve the cytotoxic activity of the new 7 H ‐PyC derivatives, we provided them with one or two diethylaminoethyl side chains. The new THPyCs, PyCs, and smaller pyrroloquinoline (PQ) derivatives were tested for their in vitro cytotoxic properties against several human tumor cell lines. Most of the compounds tested showed considerable cytotoxic activity, particularly compound 24 , which, with two basic alkylamino chains, has IC 50 values in the sub‐micromolar range, about one order of magnitude lower than those of the reference compound, ellipticine. Chemosensitivity tests on cisplatin‐, mitoxantrone‐, and multidrug‐resistant (MDR) phenotypes indicated that compound 24 shows no cross‐resistance; this suggests that, besides not being a potential MDR substrate, it might act as a mixed inhibitor of topoisomerases I and II. Flow cytometric and caspase‐3 activation analyses revealed that 24 induces a caspase‐3‐dependent apoptotic cell‐death mechanism. Linear dichroism and unwinding experiments suggested that the most active compounds act as DNA intercalators. For compound 24 , an inhibitory concentration‐dependent effect on topoisomerases II and I was demonstrated. Herein we discuss interesting structure–activity relationships with respect to molecular size and planarity, as well as the substitution and position of one side chain on the PyC nucleus, in comparison with corresponding smaller PQs.