Rhein analogues that exhibit anti-proliferative activity, particular against cancer cells, are described herein. In some embodiments, the compounds contain a flat or planar ring system. Such rings system by facilitate non-covalent binding of the compounds to the DNA complex, such as by intercalation. In some embodiment, the compounds contain a flat or planar ring system as described above and one or more substituents which are alkylating moieties, electrophilic groups or Michael acceptors or groups which contain one or more alkylating moieties, electrophilic groups and/or Michael acceptors. The compounds described herein can also contain one more functional groups to improve the solubility of the compounds.