Light-activated ruthenium (II)-bicalutamide prodrugs for prostate cancer

Targeted delivery of clinically approved anticancer drug to tumor sites is an effective way to achieve enhanced drug efficacy as well as reduced side effects and toxicity. Here bicalutamide is caged by the Ru(II) center through the nitrile group, and three photoactive Ru(II) complexes were designed and synthesized. Docking study showed that the ruthenium(II) fragments can effectively block the binding of complexes 1–3 with AR (androgen receptor) owing to the large steric structures , thus bicalutamide in complexes 1–3 could not interact with AR-LBD (ligand binding domain). Once irradiation with blue light (465   nm), complexes 1–3 can release bicalutamide and anticancer Ru(II) fragments, which possesses dual-action of AR binding and DNA interaction simultaneously. In vitro cytotoxicity study on these complexes further confirmed that complexes 1–3 exhibited considerable cytotoxicity upon irradiation with blue light. Significantly, complex 3 could be activated at 660   nm, which greatly increases the scope of complex 3 to treat deeper within tissue. Theoretical calculations showed that the lowest singlet excitation energy of complex 3 is lower than those of complexes 1–2 , which explains the experimental results well. Moreover, the 3 MC (metal centered) states of these complexes are more stable than their 3 MLCT (metal to ligand charge transfer) states, indicating that the photoactive processes of these complexes are likely to result in ligand dissociation.