Induction of Apoptosis in Human Pancreatic Cancer Stem Cells by the Endoplasmic Reticulum-Targeted Alkylphospholipid Analog Edelfosine and Potentiation by Autophagy Inhibition

Abstract

Pancreatic cancer is one of the most lethal malignancies with a poor and gloomy prognosis and the highest mortality-to-incidence ratio. Pancreatic cancer remains an incurable malignancy, and current therapies are ineffective. We isolated cancer stem cells (CSCs) from the human PANC-1 pancreatic cancer cell line as CD44+CD24+EpCAM+ cells. These CSCs form pancreatic cancer spheres or spheroids and develop tumors in SCID mice after subcutaneous injection of as few as 100 cells per mouse. Here, we found that the alkylphospholipid analog edelfosine inhibited CSC pancreatic cancer spheroid formation and induced cell death, as assessed by an increase in the percentage of cells in the sub-G0/G1 region by means of flow cytometry, indicative of DNA breakdown and apoptosis. This correlated with an increase in caspase-3 activity and PARP breakdown, as a major substrate of caspase-3, following PANC-1 CSC treatment with edelfosine. The antitumor ether lipid edelfosine colocalized with the endoplasmic reticulum in both PANC-1 cells as well as PANC-1 CSCs by using a fluorescent edelfosine analog, and induced an endoplasmic reticulum stress response in both PANC-1 cells and PANC-1 CSCs, with a potent CHOP/GADD153 upregulation. Edelfosine elicited a strong autophagy response in both PANC-1 cells and PANC-1 CSCs, and preincubation of CSCs with autophagy inhibitors, chloroquine or bafilomycin A1, enhanced edelfosine-induced apoptosis. Primary cultures from pancreatic cancer patients were sensitive to edelfosine, as well as their respective isolated CSCs. Nontumorigenic pancreatic human cell line HPNE and normal human fibroblasts were largely spared. These data suggest that pancreatic CSCs isolated from established cell lines and pancreatic cancer patients are sensitive to edelfosine through its accumulation in the endoplasmic reticulum and induction of endoplasmic reticulum stress.

HCA (2-Hydroxy-Docosahexaenoic Acid) Induces Apoptosis and Endoplasmic Reticulum Stress in Pancreatic Cancer Cells

“…Several publications have described how inhibiting autophagy flux, as OT does when combined with HCA, enhances the apoptosis death induction via CHOP [ 52 ]. For instance, the compound Edelfosine induces apoptosis and ER stress and has been shown to potentiate apoptosis induction using autophagy inhibitors in pancreatic cancer stem cells [ 56 ]. The additive antiproliferative effect of HCA and OT could be also justified by the OT antitumor effect per se [ 34 ], in part due to the inhibition of transketolase, a key enzyme in the pentose-phosphate pathway [ 57 , 58 ], despite reducing C21:5n-3 levels.…”

Clusters of apoptotic signaling molecule-enriched rafts, CASMERs: membrane platforms for protein assembly in Fas/CD95 signaling and targets in cancer therapy

“…The antitumor agent edelfosine, which accumulates in lipid rafts as stated above, has also been located in the endoplasmic reticulum [118][119][120][121][122] and mitochondria [50,123,124] in different cancer cells. This could suggest a raft-mediated link between plasma membrane rafts and internal subcellular organelles during the apoptotic response.…”

The lipid rafts in cancer stem cell: a target to eradicate cancer

“…Moreover, emodin, celastrol, ginsenosides, and gambogic acid are all extracted from the herb phospholipids analogs, alkyl phospholipids (ALPs), and modified APL derivatives include edelfosine, miltefosine, perifosine, and erufosine interrupt lipid raft integrity by incorporating into lipid raft, thereby inducing cancer cell growth arrest and apoptosis [4,[185][186][187][188][189][190][191][192]. Miltefosine preferentially induces colorectal CSCs death by disrupting lipid raft [13], and the lipid raft-targeted edelfosine has been recently reported to induce apoptosis in pancreatic CSCs by autophagy inhibition [193]. In addition, the major active component of the rhizome of Rheum palmatum L, emodin, has been found to inhibit the lipid raft clustering by reducing cholesterol and sphingolipids, inhibiting cancer cell adhesion [127].…”