Lysosomal accumulation of anticancer drugs triggers lysosomal exocytosis

Benny Zhitomirsky,Yehuda G Assaraf

doi:10.18632/oncotarget.15155

Abstract

We have recently shown that hydrophobic weak base anticancer drugs are highly sequestered in acidic lysosomes, inducing TFEB-mediated lysosomal biogenesis and markedly increased lysosome numbers per cell. This enhanced lysosomal sequestration of chemotherapeutics, away from their intracellular targets, provoked cancer multidrug resistance. However, little is known regarding the fate of lysosome-sequestered drugs. While we suggested that sequestered drugs might be expelled from cancer cells via lysosomal exocytosis, no actual drug-induced lysosomal exocytosis was demonstrated. By following the subcellular localization of lysosomes during exposure to lysosomotropic chemotherapeutics, we herein demonstrate that lysosomal drug accumulation results in translocation of lysosomes from the perinuclear zone towards the plasma membrane via movement on microtubule tracks. Furthermore, following translocation to the plasma membrane in drug-treated cells, lysosomes fused with the plasma membrane and released their cargo to the extracellular milieu, as also evidenced by increased levels of the lysosomal enzyme cathepsin D in the extracellular milieu. These findings suggest that lysosomal exocytosis of chemotherapeutic drug-loaded lysosomes is a crucial component of lysosome-mediated cancer multidrug resistance. We further argue that drug-induced lysosomal exocytosis bears important implications on tumor progression, as several lysosomal enzymes were found to play a key role in tumor cell invasion, angiogenesis and metastasis.

Highlights

Lysosomes are acidic intracellular organelles found in all eukaryotic cells, excluding erythrocytes
These LAMP1mCherry stably expressing HeLa cells were exposed to a single dose of the topoisomerase I inhibitor topotecan (10 μM) or the receptor tyrosine kinase (RTK) inhibitor sunitinib (10 μM), both of which are hydrophobic weak base anticancer drugs (Log P = 0.8, calculated pKa = 9.83 as well as log P = 5.2 and pKa = 8.95, respectively; derived from DrugBank [29]), and were previously shown to markedly accumulate in lysosomes [13, 14, 30]
We have demonstrated that exposure of cancer cells to hydrophobic weak base chemotherapeutics which highly accumulate in lysosomes via cation-trapping, results in a rapid onset of lysosomal exocytosis, which is initiated by microtubule-mediated translocation of lysosomes from the perinuclear zone (Figure 6A) towards the plasma membrane (Figure 6B)

Summary

INTRODUCTION

Lysosomes are acidic intracellular organelles found in all eukaryotic cells, excluding erythrocytes. Lysosomes contain an assortment of hydrolases with optimal catalytic activity at acidic pH; these enzymes breakdown various macromolecules and damaged organelles, arriving at the lysosome both from extracellular milieu, via endocytosis and phagocytosis, as well as from the intracellular compartment via autophagy [1] Apart from their role as the major recycling center of the cell, lysosomes are known to partake in a variety of cellular processes including nutrient sensing [1,2,3], plasma membrane repair [4] and apoptosis [5]. We further sought to study the impact of lysosomal accumulation of anticancer drugs on the secretion of lysosomal enzymes into the extracellular milieu via lysosomal exocytosis

RESULTS

DISCUSSION

MATERIALS AND METHODS