Titanium(IV) compounds are excellent anticancer drug candidates with a broad spectrum of effect. Formulation issues due to the solution instability of these compounds and the generation of inert Ti(IV) oxide species have hindered their transition to the drug market. Several biomolecules, namely the serum protein transferrin (Tf), circumvent this problem by providing stable coordination sites that enable Ti(IV) to be transported in the body. The proposal herein seeks to exploit the Tf metal binding site and its intracellular metal transport in the development of a biomimetic drug design strategy for Ti(IV)-based anticancer compounds. Novel ligands will be synthesized specific to facilitating the anticancer properties of Ti(IV) by containing two important structural components. One component is a bioactive peptide to enable selective and receptor-mediated transport into cancer cells. The bioactive peptides substance P (SP) and transferrin receptor 1 binding peptides are excellent candidates for the peptide component of the Ti(IV) ligands because their primary receptors are overexpressed in many cancer cells relative to normal cells. These receptors are not overexpressed in the same cancer cell lines and thus this study will show how bioactive peptides can be used to fine-tune targeting of select cancers. The peptide component will be conjugated to a Tf mimicking metal binding moiety with a metal coordination preference that can be manipulated for Ti(IV) release in cancer cells. The N,N'-di(o-hydroxybenzyl) ethylenediamine-N,N'-diacetic acid (HBED) and deferasirox metal binding ligands are suitable for this purpose. HBED binds Ti(IV) with a high affinity but binds Fe(III) with an even stronger affinity and the same is expected of deferasirox. The ligands have the potential to stably transport Ti(IV) into cells and then release Ti(IV) in exchange for Fe(III). By depleting cancer cells of Fe(III), which have a higher requirement for the metal ion, the ligands can work in synergism with Ti(IV) to trigger cell death. A series of cytotoxicity mechanistic studies of the Ti(IV) peptide-conjugate compounds will be performed to examine the contributions of the peptide, the metal binding moiety, and the Ti(IV) ion. The kinetics of Ti(IV) displacement by Fe(III) will be investigated to determine its physiological feasibility. Structure activity relatioship studies will be performed to elucidate the structural properties of both the peptide and metal binding moiety components that maximize the cytotoxicity of Ti(IV). In addition, insight into intracellular Ti(IV) target sites and metabolic pathways inhibited by Ti(IV) will be garnered through a combination of metallomics and metabolomics mass spectrometry studies. These mechanistic studies will afford optimization of the rationally designed Ti(IV) compounds.
Drawing inspiration from biomolecular binding and transport of the anticancer agent Ti(IV), a novel family of ligands specific to Ti(IV) are designed to both selectively target cancer cells and activate cytotoxicity. Applying a biomimetic drug design strategy, the ligands are a conjugate of a peptide to facilitate receptor- mediated transport into cancer cells and a metal binding moiety with the coordination property to release Ti(IV) in cells in exchange for Fe(III). The overall goal of this proposal is to understand the mechanism of action of the Ti(IV) peptide-conjugate compounds and the contributions of each of their components for design optimization.
