A macrocyclic zinc(II) fluorophore as a detector of apoptosis

Our originally designed dansylamidoethylcyclen 4 as a biomimetic Zn(2+)-selective fluorophore has been demonstrated to be a good detector of the apoptosis (induced by an anticancer agent, etoposide, and H(2)O(2)) in cancer cells such as HeLa and HL60 cells. The macrocyclic Zn(2+) ligand 4 (mostly as a deprotonated form) is cell-permeable to show weak fluorescence (emission at 550 nm), which forms a strong fluorescent 1:1 Zn(2+) complex 5 (emission at 530 nm) when Zn(2+) is incorporated into the cells by a zinc(II) ionophore pyrithione. Thus formed, Zn(2+) complex 5 is cell-impermeable and remains intact over a few hours. When apoptosis in HeLa or HL60 cells is artificially induced, 4 selectively and strongly stains apoptotic cells only at early stages, which was verified by using the conventional apoptosis detection probe annexin V-Cy3. Detection of the apoptotic cells by 4 was perhaps due to significantly increased free Zn(2+) flux at early stages of apoptosis. Apoptotic detection by 4 has been compared with a presently available Zn(2+) fluorophore, Zinquin 1. We present that 4 has advantages in detection of apoptosis over annexin V-Cy3 and Zinquin 1.