Lysosome Membrane Permeabilization and Disruption of the Molecular Target of Rapamycin (mTOR)-Lysosome Interaction Are Associated with the Inhibition of Lung Cancer Cell Proliferation by a Chloroquinoline Analog

Abstract

Lysosomes degrade cellular proteins and organelles and regulate cell signaling by providing a surface for the formation of critical protein complexes, notably molecular target of rapamycin (mTOR) complex 1 (mTORC1). Striking differences in the lysosomes of cancer versus normal cells suggest that they could be targets for drug development. Although the lysomotropic drugs chloroquine (CQ) and hydroxychloroquine (HCQ) have been widely investigated, studies have focused on their ability to inhibit autophagy. We synthesized a novel compound, called EAD1, which is structurally related to CQ but is a 14-fold more potent inhibitor of cell proliferation. Here we find that EAD1 causes rapid relocation, membrane permeabilization (LMP), and deacidification of lysosomes, and it induces apoptosis and irreversibly blocks proliferation of human lung cancer H460, H520, H1299, HCC827, and H1703 cells. EAD1 causes dissociation of mTOR from lysosomes and increases mTOR’s perinuclear versus cytoplasmic localization, changes previously shown to inactivate mTORC1. The effect on mTOR was not seen with HCQ, even at >10-fold greater concentrations. Phosphorylation of a downstream target of mTORC1, ribosomal protein S6, was inhibited by EAD1. Although EAD1 also inhibited autophagy, it retained full antiproliferative activity in autophagy-deficient H1650 lung cancer cells, which have a biallelic deletion of Atg7, and in H460 Atg7-knockout cells. As Atg7 is critical for the canonical autophagy pathway, it is likely that inhibition of autophagy is not how EAD1 inhibits cell proliferation. Further studies are needed to determine the relationship of LMP to mTORC1 disruption and their relative contributions to drug-induced cell death. These studies support the lysosome as an underexplored target for new drug development.