This invention relates to anti-cancer compounds and to methods for treating or preventing cancer. In one aspect the invention concerns mitochondrially delivered pro-oxidant anti-cancer compounds that generate reactive oxygen species and induce apoptosis of cancerous cells. The delivery moiety can be a lipophilic cation and the pro-oxidant vitamin E analogue, such as α-tocopheryl succinate, α-tocopheryl maleate, α-tocopheryl maleyl amide, or 2,5,7,8-tetramethyl-2R-(4R,8R,12-trimethyltridecyl)-chroman-6-yloxyacetic acid (α-tocopheryloxyacetic acid).