Novel versatile europium and terbium complexes as bioprobes and anticancer agents

Abstract

Focusing on the pertinent research on dual activity (as probes and cancer inhibitors), two novel Eu and Tb lanthanide complexes were prepared in this work alongside their binuclear counterparts holding Cu as the secondary metal. Complexes that did not contain copper were found to be less effective in promoting cancer cell death, in contrast to their bimetallic counterparts, which could function as inhibiting molecules while sequestering Cu from the tumoral environment. The ANOVA test results showed that, for A549 cells, the Eu complexes didn’t present relevant differences, whereas the results for their Tb counterparts were confirmed as being different. All complexes were structurally characterized by using high-resolution mass spectrometry, vibrational, electronic and fluorescence spectroscopy. TD-DFT calculations were carried out to assess the nature of the electronic transitions and ANOVA test to evaluate whether each pair of complexes was similar concerning their activity on the cell lines (null hypothesis). Data showed that the mononuclear Eu and Tb complexes had, as expected, fluorescent properties while their binuclear counterparts (holding Cu) did not. The mononuclear complexes were titrated with Cu²⁺ confirming their ability to sequester the latter in a tumor microenvironment. All synthesized compounds were pH responsive, although they maintained their structures in the physiological pH range and were investigated in cell viability tests with HeLa (breast) and A549 (lung adenocarcinoma) cancer cell lines towards assessing how they induce cell death. Overall, this work showed that these complexes could play an important role as bioprobes as well as anticancer agents.