Amine-containing molecules and the induction of an expanded lysosomal volume phenotype: a structure-activity relationship study.

Many weakly basic amine-containing compounds have a strong propensity to become highly concentrated in lysosomes by virtue of an ion-trapping-type mechanism; the substrates for this are referred to as lysosomotropic. We have previously shown that many lysosomotropic drugs can produce a significant expansion in the apparent volume of lysosomes, which can ultimately result in an intracellular distribution-based drug-drug interaction. In this study, we have systematically evaluated the physicochemical and structural features of weakly basic molecules that correlate with their ability to induce an expanded lysosomal volume phenotype (ELVP) in cultured human fibroblasts. By quantitatively evaluating the cellular accumulation of Lysotracker Red, a fluorescent lysosomotropic probe, the volume of the lysosomal compartment was determined. We specifically explored the influence that lysosomotropism, molecular size, and amphiphilicity had on a molecule's ability to induce an ELVP. The capacity of these molecules to intercalation into biological membranes was also evaluated using a red blood cell hemolysis assay. The present results suggest that a molecule's potency in eliciting an ELVP is influenced by lysosomotropism, amphiphilicity, and its ability to intercalate into biological membranes. Despite being highly lysosomotropic, low-molecular-weight, nonaromatic amines failed to cause an ELVP at all concentrations evaluated.