We have studied non-steroidal ligands of the human androgen receptor (hAR) and have shown elsewhere that when photoactivated by visible light they collide with O₂ to yield singlet oxygens (¹O₂) in vitro. Here we report cell killing following brief light activation (405 nm) of 1,2,3,4-tetrahydro-2,2-dimethyl-6-(trifluoromethyl)-8-pyridono[5,6-g]quinoline (TDPQ) in human prostate tumor cells. TDPQ/AR complexes were required for the death response since AR-positive LNCaP cells were killed, whereas AR-negative PC-3 cells were resistant. Excess dihydrotestosterone (DHT) blocked the TDPQ effect when the two were added together; irradiation of cells containing DHT alone had no effect. When LNCaP AR expression was suppressed using small interfering oligonucleotides targeting AR, photocytotoxicity was diminished. Conversely, stable transfection of hAR into PC-3 cells made the cells photosensitive to TDPQ. Similar results were obtained using a structural isomer of TDPQ, and also the synthetic steroidal AR ligand R1881. Cell death occurred via apoptosis as demonstrated by annexin V immunostaining, nuclear condensation and caspase inhibition. Death involved oxidative stress, since it was prevented by addition of the antioxidant ascorbic acid during photoactivation. Detection of elevated levels of 8-hydroxy-2'-deoxyguanosine in nuclei of irradiated cells indicated oxidative DNA damage. Apoptosis spread into adjacent non-irradiated cells by direct cell-cell contacts, indicative of a bystander effect. Other photoactivatable ligands are described, implying a general method for ablation of cells bearing specific nuclear hormone receptors.