Extensive research is currently being conducted into metal complexes that can selectively deliver cytotoxins to hypoxic regions in tumours. The development of pharmacologically suitable agents requires an understanding of appropriate ligand–metal systems for chaperoning cytotoxins. In this study, cobalt complexes with tripodal tren (tris-(2-aminoethyl)amine) and tpa (tris-(2-pyridylmethyl)amine) ligands were prepared with ancillary hydroxamic acid, β-diketone and catechol ligands and several parameters, including: pKa, reduction potential and cytotoxicity were investigated. Fluorescence studies demonstrated that only tpa complexes with β-diketones showed any reduction by ascorbate in situ and similarly, cellular cytotoxicity results demonstrated that ligation to cobalt masked the cytotoxicity of the ancillary groups in all complexes except the tpa diketone derivative [Co(naac)tpa](ClO4)2 (naac = 1-methyl-3-(2-naphthyl)propane-1,3-dione). Additionally, it was shown that the hydroxamic acid complexes could be isolated in both the hydroxamate and hydroximate form and the pKa values (5.3–8.5) reveal that the reversible protonation/deprotonation of the complexes occurs at physiologically relevant pHs. These results have clear implications for the future design of prodrugs using cobalt moieties as chaperones, providing a basis for the design of cobalt complexes that are both more readily reduced and more readily taken up by cells in hypoxic and acidic environments.
目前正在对能够选择性地将细胞毒素输送到肿瘤缺氧区域的
金属复合物进行广泛的研究。要开发出药理上合适的药物,就必须了解合适的
配体-
金属系统,以引导细胞毒素。本研究制备了具有三重tren(
三(2-氨基乙基)胺)和tpa(
三(2-吡啶基甲基)胺)
配体的
钴配合物,并辅以羟
肟酸、
β-二酮和
儿茶酚配体,研究了包括pKa、还原电位和细胞毒性在内的多个参数。荧光研究表明,只有与
β-二酮配体的 tpa 复合物才会被
抗坏血酸原位还原。同样,细胞毒性结果表明,除了 tpa 二酮衍
生物 [Co(naac)tpa](
ClO4)2 (naac = 1-甲基-3-(2-
萘基)
丙烷-1,3-二酮)外,与
钴的配位掩盖了所有复合物中辅助基团的细胞毒性。此外,研究还表明,羟
肟酸复合物可以以羟
肟酸酯和羟
肟酸酯两种形式分离出来,其 pKa 值(5.3-8.5)显示,复合物的可逆质子化/去质子化发生在生理相关的 pH 值条件下。这些结果对今后设计使用
钴分子作为伴侣的原药有明显的影响,为设计在缺氧和酸性环境中更容易被还原和更容易被细胞吸收的
钴复合物提供了基础。