Studies on the mechanisms and consequences of drug-induced perturbations of lysosomal structure and function

Abstract

From a clinical perspective, a drug's pharmacokinetic properties (e.g., the volume of distribution, clearance, and half-life) are vitally important as these parameters are used to establish the proper dosing regimen necessary to achieve a desired drug exposure. Failure to properly account for changes to a drug's expected pharmacokinetic properties, whether perpetrated by pharmacological insult (drug-drug interaction) or a disease state, can result in an improper dosing regimen that either fails to achieve therapeutic drug levels or, conversely, can result in drug levels that reach toxic concentrations. Identifying conditions that can alter the expected pharmacokinetic properties of drugs is therefore immensely important. Previous work in our lab has shown that lysosomotropic drugs, i.e., drugs that preferentially accumulate within lysosomes due to an ion trapping-type mechanism, cause a marked expansion in the volume of lysosomes which can result in a drug-drug interaction involving lysosomes. Although this novel drug-drug interaction was well characterized the mechanistic basis explaining how it developed was not established. Within this work we have explored the cellular mechanisms underlying the development of the drug-induced expansion in lysosomal volume and the ensuing drug-drug interaction. Our data shows that the drug-induced expansion in lysosomal volume is achieved through a combination of reduced vesicle-mediated trafficking out of the lysosomes, the induction of autophagy, and the activation of lysosome biogenesis. We have additionally explored a structure activity relationship which implicates a drug's amphiphilicity and lysosomotropic properties as important features that correlate with their propensity to induce an expansion in lysosomal volume. Overall, the data presented in this work can be used to help explain the sources of variability seen in the pharmacokinetic properties of lysosomotropic drugs. In parallel to these studies we have also explored potential treatment strategies that can reduce the bloated lysosomal volume seen in cells with dysfunctional lysosomes. Using two cell models that exhibit dysfunctional lysosomes (lysosomotropic drug-treated cells or lysosomal storage diseased cells), we have examined how vitamin E helps to recover lysosomal volume. Our data indicates that vitamin E reduces both ion trapping-dependent (aqueous volume of lysosomes) and ion trapping-independent (lipid binding) drug accumulation mechanisms within cells. To our knowledge, this is the first report detailing that vitamin E reduces the aqueous volume of lysosomes. This finding is important as it helps to more fully explain how vitamin E is eliciting its positive effects within cells. Additionally, we have also examined a structure activity relationship of vitamin E and its ability to reduce lysosomal volume. Our data indicates that the physical structure of vitamin E, rather than its antioxidant properties, is the primary feature of vitamin E that correlates with its ability to reduce the bloated lysosomal volume seen in cells with dysfunctional lysosomes. Overall, this data can be used as a foundation to stage additional studies that could ultimately lead to the development of more potent and better drug-like molecules that could be used to treat lysosomal storage diseases and the toxic effects of lysosomotropic drug-treatments.