A family of PIKFYVE inhibitors with therapeutic potential against autophagy-dependent cancer cells disrupt multiple events in lysosome homeostasis.

ABSTRACT

High-throughput screening identified 5 chemical analogs (termed the WX8-family) that disrupted 3 events in lysosome homeostasis (1) lysosome fission via tubulation without preventing homotypic lysosome fusion; (2) trafficking of molecules into lysosomes without altering lysosomal acidity, and (3) heterotypic fusion between lysosomes and autophagosomes. Remarkably, these compounds did not prevent homotypic fusion between lysosomes, despite the fact that homotypic fusion required some of the same machinery essential for heterotypic fusion. These effects varied 400-fold among WX8-family members, were time and concentration dependent, reversible, and resulted primarily from their ability to bind specifically to the PIKFYVE phosphoinositide kinase. The ability of the WX8-family to prevent lysosomes from participating in macroautophagy/autophagy suggested they have therapeutic potential in treating autophagy-dependent diseases. In fact, the most potent family member (WX8) was 100-times more lethal to 'autophagy-addicted' melanoma A375 cells than the lysosomal inhibitors hydroxychloroquine and chloroquine. In contrast, cells that were insensitive to hydroxychloroquine and chloroquine were also insensitive to WX8. Therefore, the WX8-family of PIKFYVE inhibitors provides a basis for developing drugs that could selectively kill autophagy-dependent cancer cells, as well as increasing the effectiveness of established anti-cancer therapies through combinatorial treatments. Abbreviations ACTB actin beta; Baf bafilomycin A1; BECN1 beclin 1; BODIPY boron-dipyrromethene; BORC BLOC-1 related complex; BRAF B-Raf proto-oncogene, serine/threonine kinase; BSA bovine serum albumin; CTSD cathepsin D; CQ chloroquine; DNA deoxyribonucleic acid; EC50 half maximal effective concentration; GAPDH glyceraldehyde-3-phosphate dehydrogenase; GFP green fluorescent protein; HCQ hydroxychloroquine; HOPS complex homotypic fusion and protein sorting complex; Kd equilibrium binding constant; IC50 half maximal inhibitory concentration; KO knockout; LAMP1 lysosomal associated membrane protein 1; MAP1LC3A microtubule associated protein 1 light chain 3 alpha; MES 2-(N-morpholino)ethanesulphonic acid; MTOR mechanistic target of rapamycin kinase; µM micromolar; NDF 3-methylbenzaldehyde (2,6-dimorpholin-4-ylpyrimidin-4-yl)hydrazine;NEM N-ethylmaleimide; NSF N-ethylmaleimide sensitive factor; PBS phosphate-buffered saline; PIKFYVE phosphoinositide kinase, FYVE-type zinc finger containing; PIP4K2C phosphatidylinositol-5-phosphate 4-kinase type 2 gamma; PtdIns3P phosphatidylinositol 3-phosphate; PtdIns(3,5)P2 phosphatidylinositol 3,5-biphosphate; RFP red fluorescent protein; RPS6 ribosomal protein S6; RPS6KB1 ribosomal protein S6 kinase B1; SQSTM1 sequestosome 1; TWEEN 20 polysorbate 20; V-ATPase vacuolar-type H+-translocating ATPase; VPS39 VPS39 subunit of HOPS complex; VPS41 VPS41 subunit of HOPS complex; WWL benzaldehyde [2,6-di(4-morpholinyl)-4-pyrimidinyl]hydrazone; WX8 1H-indole-3-carbaldehyde [4-anilino-6-(4-morpholinyl)-1,3,5-triazin-2-yl]hydrazine; XBA N-(3-chloro-4-fluorophenyl)-4,6-dimorpholino-1,3,5-triazin-2-amine hydrochloride; XB6 N-(4-ethylphenyl)-4,6-dimorpholino-1,3,5-triazin-2-amine hydrochloride.