2-indolyl imidazo[4,5-d]phenanthroline compounds of Formula I that are capable of intracellular chelation of transition metals and of exerting antiproliferative effects in cancer cells, that are cytostatic and/or cytotoxic, are provided. Compounds of Formula I can also induce apoptosis in cancer cells and are thus capable of exerting a cytotoxic effect on cancer cells. The compounds of Formula I are also capable of selectively inhibiting the proliferation of one or more of prostate cancer cells, colon cancer cells, non-small lung cancer cells and leukemia cells. The compounds of Formula I are also capable of increasing the expression of the zinc-regulated tumour suppressor, KLF4 and thus are useful in inhibiting the proliferation of cancer cells in which KLF4 functions as a tumour-suppressor, including, but not limited to, bladder cancer, cancers of the gastrointestinal tract and various leukemias.