MOMIPP, 3-(5-methoxy, 2-methyl-1H-indol-3-yl)-1-(4-pyridinyl)-2-propen-1-one, is a novel chalcone-related compound that induces non-apoptotic cell death in various cancer cell lines, including temozolomide-resistant glioblastoma (GBM) cells. The unique mechanism of cell death induced by MOMIPP has been termed “methuosis”. Morphological hallmarks of methuosis include early accumulation of large cytoplasmic vacuoles derived from macropinosomes, followed by detachment of cells from the substratum and necrosis-like rupture of the plasma membrane. Nuclear changes typical of apoptosis are absent. The targets of MOMIPP have not yet been identified and the mechanistic link between MOMIPP-induced vacuolization and cell death is poorly understood. Previous studies have shown that the non-clathrin coated macropinosome-derived vacuoles induced by MOMIPP fail to merge with lysosomes. In the present study we test the hypothesis that the cytotoxic activity of MOMIPP may entail perturbations of additional trafficking pathways that interface with lysosomes. We report that the post-translation proteolytic processing of pro-cathepsin D, which occurs in conjunction with trafficking of the pro-enzyme from late endosomes to lysosomes, is impaired in MOMIPP-treated GBM cells. In parallel, ligand-dependent turnover of the epidermal growth factor receptor is also attenuated. These findings are consistent with a global block in protein trafficking between late endosomes and lysosomes. Examining the lysosome-dependent process of macroautophagy, we found that MOMIPP caused an accumulation of the autophagosome marker, LC3-II, and decline in degradation of the autophagosome cargo, p62, consistent with a block in autophagosome-lysosome flux. Potentially related to the defects in protein degradation, we detected a robust activation of ER stress, as measured by increased expression of CHOP and phosphorylated-PERK in MOMIPP treated cells. In conjunction with the altered trafficking events, we observed swelling of acridine orange-positive acidic vesicles, in addition to the previously reported vacuolization of non-acidic macropinosomes. More precise identification of these compartments is in progress. Taken together, these results suggest that the induction of non-apoptotic cell death by MOMIPP may be related, at least in part, to dysfunctional trafficking at the nexus where macropinosomes, late endosomes and autophagosomes converge on lysosomes. Supported by NIH grant R01 CA115495 and the Harold and Helen McMaster Endowment

Citation Format: Nneka E. Mbah, Andrew D. Trunk, Bryan A. Dewitt, Jean H. Overmeyer, William A. Maltese. Non-apoptotic death induced in glioma cells by the indole-based chalcone, MOMIPP, involves disruption of endolysosomal trafficking and ER stress. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1343. doi:10.1158/1538-7445.AM2014-1343