Synthesis, cytotoxicity, and insight into the mode of action of Re(CO)3 thymidine complexes

Nucleoside analogues are extensively used in the treatment of cancer and viral diseases. The antiproliferative properties of organorhenium(I) complexes, however, have been scarcely explored to date. Herein we present the syntheses, characterization, and in vitro evaluation of Re(I)(CO)(3) core complexes of thymidine and uridine. For the binding of the Re(I)(CO)(3) core, a tridentate dipicolylamine metal chelate was introduced at positions C5', C2', N3, and C5 with spacers of various lengths. The corresponding organometallic thymidine complexes were fully characterized by IR and NMR spectroscopy and mass spectrometry. Their cytotoxicity was assessed against the A549 lung carcinoma cell line. Toxicity is dependent on the site and mode of conjugation as well as on the nature and the length of the tether. Moderate toxicity was observed for conjugates carrying the rhenium moiety at position C5' or N3 (IC(50)=124-160 microM). No toxicity was observed for complexes modified at C2' or C5. Complex 53, with a dodecylene spacer at C5', exhibits remarkable toxicity and is more potent than cisplatin, with an IC(50) value of 6.0 microM. To the best of our knowledge, this is the first report of the antiproliferative properties of [M(CO)(3)](+1)-nucleoside conjugates. In competitive inhibition experiments with A549 cell lysates and purified recombinant human thymidine kinase 1 (hTK-1), enzyme inhibition was observed for complexes modified at either N3 or C5', but our results suggest that the toxicity cannot be attributed solely to interaction with hTK-1.