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Many weakly basic amine-containing drugs are known to be extensively sequestered in acidic lysosomes by an ion trapping-type mechanism. The entrapment of drugs in lysosomes has been shown to influence drug activity, cancer cell selectivity, and pharmacokinetics and can cause the hyperaccumulation of various lipids associated with lysosomes. In this work, we have investigated the prolonged time-dependent effects of drugs on lysosomal properties. We have evaluated two amine-containing drugs with intermediate (propranolol) and high (halofantrine) relative degrees of lipophilicity. Interestingly, the cellular accumulation kinetics of these drugs exhibited a biphasic characteristic at therapeutically relevant exposure levels with an initial apparent steady-state occurring at 2 days followed by a second stage of enhanced accumulation. We provide evidence that this secondary drug accumulation coincides with the nuclear localization of transcription factor EB, a master regulator of lysosome biogenesis, and the appearance of an increased number of smaller and lipid-laden lysosomes. Collectively, these results show that hydrophobic lysosomotropic drugs can induce their own cellular accumulation in a time-dependent fashion and that this is associated with an expanded lysosomal volume. These results have important therapeutic implications and may help to explain sources of variability in drug pharmacokinetic distribution and elimination properties observed in vivo., (© 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.)

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., (© 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.)