Sunitinib and SU11652 Inhibit Acid Sphingomyelinase, Destabilize Lysosomes, and Inhibit Multidrug Resistance

Abstract

Defective apoptosis signaling and multidrug resistance are major barriers for successful cancer treatment. To identify drugs capable of targeting treatment-resistant cancer cells, we screened small-molecule kinase inhibitor libraries for compounds that decrease the viability of apoptosis-resistant human MCF7-Bcl-2 breast cancer cells. SU11652, a multitargeting receptor tyrosine kinase inhibitor, emerged as the most potent compound in the screen. In addition to MCF7-Bcl-2 cells, it effectively killed HeLa cervix carcinoma, U-2-OS osteosarcoma, Du145 prostate carcinoma, and WEHI-S fibrosarcoma cells at low micromolar concentration. SU11652 accumulated rapidly in lysosomes and disturbed their pH regulation and ultrastructure, eventually leading to the leakage of lysosomal proteases into the cytosol. Lysosomal destabilization was preceded by an early inhibition of acid sphingomyelinase, a lysosomal lipase that promotes lysosomal membrane stability. Accordingly, Hsp70, which supports cancer cell survival by increasing lysosomal acid sphingomyelinase activity, conferred partial protection against SU11652-induced cytotoxicity. Remarkably, SU11652 killed multidrug-resistant Du145 prostate cancer cells as effectively as the drug-sensitive parental cells, and subtoxic concentrations of SU11652 effectively inhibited multidrug-resistant phenotype in Du145 prostate cancer cells.

Lysosomal Sequestration Determines Intracellular Imatinib Levels

“…Autophagy is inhibited by the addition of strong lysosomotropic agents such as chloroquine or NH 4 Cl, causing increased cell death. There are indications that high intracellular levels of imatinib, or other tyrosine kinase inhibitors, entrapped in lysosomes for prolonged periods of time may lead to lysosomal dysfunction, including lysosomal membrane permeabilization, impaired autophagy, and eventually lysosomal-mediated cell death (Ellegaard et al, 2013;Groth-Pedersen and Jaattela, 2013). It is conceivable that the biologic activity and anticancer efficacy of imatinib are in part mediated through the lysosomal compartment.…”

S100 and annexin proteins identify cell membrane damage as the Achilles heel of metastatic cancer cells

“…56 This fragility has been harnessed for the development of novel therapeutics. 58,59 Similar to lysosomal membrane, PM of cancer cells are more unstable and have reduced stiffness, which is caused by an increase in saturated phospholipids. 60 The PM stiffness is inversely correlated with the ability of the cancer cell to migrate and invade 3-dimensional matrix.…”

An adapted protocol to overcome endosomal damage caused by polyethylenimine (PEI) mediated transfections.

“…Several studies suggest that permeabilization occurs at the lysosome [11] [12] [10], while our data indicate PEI-mediated transfection affects endosomes. Permeabilization of the lysosomal membrane can lead to release of lysosomal enzymes from the lysosomal lumen to the cytoplasm, which ultimately can cause cell death [23] [24]. To study lysosomal integrity after PEI-mediated transfection, we used a galectin3 based assay that detects lysosomal membrane permeabilization [25].…”