The relevance of considering metal–ligand speciation in aquaporin modulation by cu, Zn, and V complexes with 1,10-phenanthroline ligands

Aquaporins (AQPs) are transmembrane proteins that facilitate the bidirectional transport of water, glycerol, and small solutes across cell membranes. AQPs are potential targets for drug development, namely for cancer treatment. In this work, we address the effect of several Cu-, Zn- and V-phen complexes on AQP1, which is selective for water transport, and AQP3, mainly involved in the transport of water and glycerol. A group of M(Xphen)₂²⁺ compounds (M = Cu²⁺, Zn²⁺, V^IVO²⁺; Xphen = 1,10-phenanthroline, 5-amino-1,10-phenanthroline (Amphen), 4,7-dimethyl-1,10-phenanthroline), known to be cytotoxic agents against several human cancer-cell lines, were evaluated for their inhibitory effect of AQP1 and AQP3 by testing membrane water and glycerol permeability of human erythrocytes. In most cases, the inhibitory effects of the metal-complexes and those of the free Xphen compounds on the AQP1 and AQP3 permeability were not significantly different, suggesting that the effects are mostly due to the free Xphen compounds. The only exception is V^IVO(Amphen)₂(SO₄), with an IC₅₀ value of (9.11 ± 0.03 μM) in AQP1-mediated water permeation; this represents a promising compound for inhibition of AQP1, since until now there are no known potent and selective AQP1 inhibitors. At 100 μM, CuSO₄ slightly inhibited glycerol permeability, whereas ZnCl₂, NaV^VO₃, and NH₄V^VO₃ showed negligible effects. Speciation modelling indicates that hydrolysis and the formation of multiple metal-containing species occur under experimental conditions, except for Cu(Xphen)₂²⁺ complexes. These results highlight the importance of considering metal complex speciation in biological environments and suggest that encapsulation strategies may be required to preserve the integrity of labile metal complexes.