Novel polyamine transport inhibitors have been synthesized and demonstrated to block the uptake of native polyamines into human cancer cells. A combination therapy of the transport inhibitor and DFMO (a drug which blocks polyamine biosynthesis) provided synergistic activity against a metastatic human colon cancer cell line. The strategy uses polyamine depletion and polyamine metabolism to generate reactive oxygen species within cells as a novel way to treat cancers. This approach may be implemented for widespread use in the treatment of diseases which rely upon polyamine transport activity for proliferation.