Cationic Amphiphilic Drugs Cause a Marked Expansion of Apparent Lysosomal Volume: Implications for an Intracellular Distribution-Based Drug Interaction

Abstract

How a drug distributes within highly compartmentalized mammalian cells can affect both the activity and pharmacokinetic behavior. Many commercially available drugs are considered to be lysosomotropic, meaning they are extensively sequestered in lysosomes by an ion trapping-type mechanism. Lysosomotropic drugs typically have a very large apparent volume of distribution and a prolonged half-life in vivo, despite minimal association with adipose tissue. In this report we tested the prediction that the accumulation of one drug (perpetrator) in lysosomes could influence the accumulation of a secondarily administered one (victim), resulting in an intracellular distribution-based drug interaction. To test this hypothesis cells were exposed to nine different hydrophobic amine-containing drugs, which included imipramine, chlorpromazine and amiodarone, at a 10 µM concentration for 24 to 48 hours. After exposure to the perpetrators the cellular accumulation of LysoTracker Red (LTR), a model lysosomotropic probe, was evaluated both quantitatively and microscopically. We found that all of the tested perpetrators caused a significant increase in the cellular accumulation of LTR. Exposure of cells to imipramine caused an increase in the cellular accumulation of other lysosomotropic probes and drugs including LyosTracker Green, daunorubicin, propranolol and methylamine; however, imipramine did not alter the cellular accumulation of non-lysosomotropic amine-containing molecules including MitoTracker Red and sulforhodamine 101. In studies using ionophores to abolish intracellular pH gradients we were able to resolve ion trapping-based cellular accumulation from residual pH-gradient independent accumulation. Results from these evaluations in conjunction with lysosomal pH measurements enabled us to estimate the relative aqueous volume of lysosomes of cells before and after imipramine treatment. Our results suggest that imipramine exposure caused a 4-fold expansion in the lysosomal volume, which provides the basis for the observed drug interaction. The imipramine-induced lysosomal volume expansion was shown to be both time- and temperature-dependent and reversed by exposing cells to hydroxypropyl-β-cyclodextrin, which reduced lysosomal cholesterol burden. This suggests that the expansion of lysosomal volume occurs secondary to perpetrator-induced elevations in lysosomal cholesterol content. In support of this claim, the cellular accumulation of LTR was shown to be higher in cells isolated from patients with Niemann-Pick Type C disease, which are known to hyper-accumulate cholesterol in lysosomes.

Gleevec shifts APP processing from a β-cleavage to a nonamyloidogenic cleavage

“…The effect of these drugs on lysosomal volume are consistent with the effects of other amphipathic, cationic molecules containing aromatic rings, which cause an increase in lysosomal volume, purportedly through intercalation of lysosomotropic drugs within lipid bilayers, but with no change in lysosomal pH (43). Such compounds also have been shown to increase the trafficking of proteins from the plasma membrane or endoplasmic reticulum to lysosomes (44,45), and by doing so would be expected to reduce the quantity of APP exposed to amyloidogenic processing by BACE and γ-secretase.…”

Detecting ordered small molecule drug aggregates in live macrophages: a multi-parameter microscope image data acquisition and analysis strategy

“…Nevertheless, understanding the mechanisms responsible for the accumulation of drugs within intracellular compartments is important as it may explain why some drugs fail to reach proper therapeutic concentrations at a site of action or to explain unfavorable drug-drug interactions that may occur through bioaccumulation dependent pathways [35]. Drug trapping and accumulation can lead to alterations in the structure and function of organelles, affecting cell physiology [36].…”

Lysosomal Sequestration (Trapping) of Lipophilic Amine (Cationic Amphiphilic) Drugs in Immortalized Human Hepatocytes (Fa2N-4 Cells)

“…Competition for lysosomal trapping has been the subject of some speculation as a potential mechanism of drug-drug interactions (DDIs) (Daniel and Wojcikowski, 1999;Chadwick et al, 2005;Funk and Krise, 2012;Logan et al, 2012). Because many central nervous system and cardiovascular drugs are lysosomotropics (drugs that undergo lysosomal sequestration), there is the possibility that concomitant administration of lysosomotropics could lead to elevated drug exposure levels as competition for lysosomal sequestration increases or lysosomal pH is elevated by amine accumulation Vestal et al, 1980;Logan et al, 2012).…”