Albumin Conjugates of Thiosemicarbazone and Imidazole-2-thione Prochelators: Iron Coordination and Antiproliferative Activity

The central role of iron in tumor progression and metastasis motivates the development of iron-binding approaches in cancer chemotherapy. Disulfide-based prochelators are reductively activated upon cellular uptake to liberate thiol chelators responsible for iron sequestration. Herein, a trimethyl thiosemicarbazone moiety and the imidazole-2-thione heterocycle are incorporated in this prochelator design. Iron binding of the corresponding tridentate chelators leads to the stabilization of a low-spin ferric center in 2 : 1 ligand-to-metal complexes. Native mass spectrometry experiments show that the prochelators form stable disulfide conjugates with bovine serum albumin, thus affording novel bioconjugate prochelator systems. Antiproliferative activities at sub-micromolar levels are recorded in a panel of breast, ovarian and colorectal cancer cells, along with significantly lower activity in normal fibroblasts.