Elevated intracellular copper levels predispose cancerous cells to ionophoric-copper sensitivity and several classes of copper coordinating lipophilic compounds (hydroxyquinolines, dithiocarbamates and thiosemicarbazones) are being investigated as potential anticancer therapeutics(1-4). Despite reports dating back to the 1970s, which demonstrate that cancerous cells harbor elevated copper(1), there is still insufficient information on how cellular transformation drives copper accumulation, or on the mechanism(s) by which cells adapt to tolerate the ensuing oxidative pressure (not mutually exclusive). Nonetheless, ionophoric-copper therapy may be applicable to a range of cancer types including prostate, breast, ovarian, cervical, lung, stomach, and leukaemia, where copper levels are intrinsically augmented (reviewed in(1)). We assessed the therapeutic efficacy of two bis(thiosemicarbazoneato) copper complexes, glyoxalbis[N(4)-methylthiosemi-carbazonato]CuII [CuII(gtsm)] and diacetylbis[N4-methylthiosemicarbazonato]CuII [CuII(atsm)] for the treatment of prostate cancer. Distinctively, copper dissociates intracellularly from CuII(gtsm) but is retained by CuII(atsm). We further demonstrated that intracellular H2gtsm [reduced CuII(gtsm)] continues to redistribute intracellular copper into an exchangeable (bioavailable) pool. Both CuII(gtsm) and CuII(atsm) selectively kill transformed (hyperplastic and carcinoma) prostatic cell lines without affecting the viability of primary prostate epithelial cells. Increasing extracellular copper enhanced their therapeutic capacity and both H2gtsm and H2atsm ligands were only toxic towards cancerous prostate cells when combined with copper. Treatment of the TRAMP mouse model with CuII(gtsm) significantly reduced prostate cancer burden and severity (grade), while treatment with CuII(atsm) was ineffective at the given dose. Finally, we demonstrated that CuII(gtsm) inhibits proteasomal chymotrypsin-like activity, a feature further established as being common to copper-ionophores that increase intracellular bioavailable copper. We provide compelling evidence that increasing intracellular bioavailable copper can selectively kill cancerous prostate cells in vitro and in vivo and reveal the potential for bis(thiosemicarbazone) copper complexes to be developed as therapeutics for prostate cancer.