Time-dependent effects of hydrophobic amine-containing drugs on lysosome structure and biogenesis in cultured human fibroblasts.

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.

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.

Evaluating the roles of autophagy and lysosomal trafficking defects in intracellular distribution-based drug-drug interactions involving lysosomes.

Many currently approved drugs possess weakly basic properties that make them substrates for extensive sequestration in acidic intracellular compartments such as lysosomes through an ion trapping-type mechanism. Lysosomotropic drugs often have unique pharmacokinetic properties that stem from the extensive entrapment in lysosomes, including an extremely large volume of distribution and a long half-life. Accordingly, pharmacokinetic drug-drug interactions can occur when one drug modifies lysosomal volume such that the degree of lysosomal sequestration of secondarily administered drugs is significantly altered. In this work, we have investigated potential mechanisms for drug-induced alterations in lysosomal volume that give rise to drug-drug interactions involving lysosomes. We show that eight hydrophobic amines, previously characterized as perpetrators in this type of drug-drug interaction, cause a significant expansion in lysosomal volume that was correlated with both the induction of autophagy and with decreases in the efficiency of lysosomal egress. We also show that well-known chemical inducers of autophagy caused an increase in apparent lysosomal volume and an increase in secondarily administered lysosomotropic drugs without negatively impacting vesicle-mediated lysosomal egress. These results could help rationalize how the induction of autophagy could cause variability in the pharmacokinetic properties of lysosomotropic drugs.

Drug-drug interactions involving lysosomes: mechanisms and potential clinical implications.

INTRODUCTION: Many commercially available, weakly basic drugs have been shown to be lysosomotropic, meaning they are subject to extensive sequestration in lysosomes through an ion trapping-type mechanism. The extent of lysosomal trapping of a drug is an important therapeutic consideration because it can influence both activity and pharmacokinetic disposition. The administration of certain drugs can alter lysosomes such that their accumulation capacity for co-administered and/or secondarily administered drugs is altered. AREAS COVERED: In this review the authors explore what is known regarding the mechanistic basis for drug-drug interactions involving lysosomes. Specifically, the authors address the influence of drugs on lysosomal pH, volume and lipid processing. EXPERT OPINION: Many drugs are known to extensively accumulate in lysosomes and significantly alter their structure and function; however, the therapeutic and toxicological implications of this remain controversial. The authors propose that drug-drug interactions involving lysosomes represent an important potential source of variability in drug activity and pharmacokinetics. Most evaluations of drug-drug interactions involving lysosomes have been performed in cultured cells and isolated tissues. More comprehensive in vivo evaluations are needed to fully explore the impact of this drug-drug interaction pathway on therapeutic outcomes.