A chalcone-related small molecule that induces methuosis, a novel form of non-apoptotic cell death, in glioblastoma cells

Abstract

BackgroundMethuosis is a unique form of non-apoptotic cell death triggered by alterations in the trafficking of clathrin-independent endosomes, ultimately leading to extreme vacuolization and rupture of the cell.ResultsHere we describe a novel chalcone-like molecule, 3-(2-methyl-1H- indol-3-yl)-1-(4-pyridinyl)-2-propen-1-one (MIPP) that induces cell death with the hallmarks of methuosis. MIPP causes rapid accumulation of vacuoles derived from macropinosomes, based on time-lapse microscopy and labeling with extracellular fluid phase tracers. Vacuolization can be blocked by the cholesterol-interacting compound, filipin, consistent with the origin of the vacuoles from non-clathrin endocytic compartments. Although the vacuoles rapidly acquire some characteristics of late endosomes (Rab7, LAMP1), they remain distinct from lysosomal and autophagosomal compartments, suggestive of a block at the late endosome/lysosome boundary. MIPP appears to target steps in the endosomal trafficking pathway involving Rab5 and Rab7, as evidenced by changes in the activation states of these GTPases. These effects are specific, as other GTPases (Rac1, Arf6) are unaffected by the compound. Cells treated with MIPP lose viability within 2-3 days, but their nuclei show no evidence of apoptotic changes. Inhibition of caspase activity does not protect the cells, consistent with a non-apoptotic death mechanism. U251 glioblastoma cells selected for temozolomide resistance showed sensitivity to MIPP-induced methuosis that was comparable to the parental cell line.ConclusionsMIPP might serve as a prototype for new drugs that could be used to induce non-apoptotic death in cancers that have become refractory to agents that work through DNA damage and apoptotic mechanisms.

Uses and abuses of macropinocytosis

“…Its physiological role might be in homeostatic responses to nutrient deprivation. A recent study has shown that TORC1 inhibits the utilisation of extracellular protein that has been ingested through macropinocytosis, suggesting that this growthregulatory complex is intimately connected with the control of macropinocytosis in the context of nutrient acquisition (Palm et al, 2015). Further investigations into the normal developmental and homeostatic roles of CendR-mediated macropinocytosis in vertebrate cells, and its effects on vascular permeability (Pang et al, 2015), could thus not only lead to its use as a therapeutic tool but could also help to improve our understanding of its evolutionary relationships with other uptake mechanisms.…”

“…Screens have identified small molecules that can induce this form of death in malignant cells, offering hope for new treatments of glioblastoma (Overmeyer et al, 2011;Kitambi et al, 2014). The precise cause of cell death is not clear in some instances of methuosis (Maltese and Overmeyer, 2014), but in acute druginduced vacuolisation, the cytoplasmic swelling causes the plasma membrane to rupture (Overmeyer et al, 2011;Kitambi et al, 2014).…”

“…The polypeptides taken up from extracellular fluid, which is normally rich in protein, are digested in the endocytic pathway, and allow the growth and survival of cells that are otherwise limited by the availability of essential and non-essential amino acids (Commisso et al, 2013;Palm et al, 2015). TORC1 plays a complex role in regulating these responses -extracellular amino acids promote growth through TORC1-mediated signals, whereas amino acids that have been derived from extracellular protein and have been digested in lysosomes suppress the proliferation of K-Ras-mutant cells in which TORC1 is active (Palm et al, 2015) (Fig. 3).…”

Unravelling the Mechanism of TrkA-Induced Cell Death by Macropinocytosis in Medulloblastoma Daoy Cells

“…In addition to our observations in MEDs, hyperstimulation of macropinocytosis has also been found to result in cell death in some human GB cell lines as well as in other cancer cell lines (19)(20)(21)(22). Interestingly, overexpression of oncogenic Harvey-Ras Cell culture and transfections.…”

Heterocyclic scaffolds as promising anticancer agents against tumours of the central nervous system: Exploring the scope of indole and carbazole derivatives

“…[65] In 2011 the same group reported an indole named MIPP (Figure 14(a)) which induced methuosis in a glioblastoma cell line. [66] In 2012 they reported on a small library of MIPP analogues, and attempted to elucidate structure-activity relationships when tested against the glioblastoma cell line U251. [67] group, implying that this structural change is responsible for the improvment in activity.…”