Zn2+ triazamacrocyclic chelators with methylpyridine pendant arms for B-cell apoptosis: a structure-activity study.

Three macrocyclic tacn (1,4,7-triazacyclononane) derivatives containing one, two and three 2-methylpyridine pendant arms (no1py, no2py and no3py), compared to the linear diamine analogue tpen (N,N,N',N'-tetrakis(2-methylpyridinyl)-ethylenediamine) known for its capacity to induce cell apoptosis by Zn2+ chelation and/or ROS production, have shown cytotoxic activity on the Daudi B-cell line and CLL (chronic lymphoid leukemia) primary B cell model. These properties have been evidenced using an Incucyte® Live-Cell Analysis System. Evaluation of caspase 3/7 activation by incubation with the four studied chelators has exhibited caspase-dependent apoptotic death. Investigation of the chelator action mechanism has shown no ROS (reactive oxygen species) production for the macrocyclic chelators no1py, no2py and no3py, unlike the linear counterpart tpen for which ROS production was revealed. A significant inhibition effect of macrocyclic chelator cytotoxicity has been established by extracellular addition of cationic salts (Zn2+ and Cu2+) and the Zinquin emission fluorescence method has evidenced intracellular labile zinc chelation for no2py and no3py, while no1py acts differently. The acid-base properties of the chelators and their Zn2+ complexation constants have been obtained, discussed and correlated with the demonstrated biological properties.