Celastrol targets proteostasis and acts synergistically with a heat-shock protein 90 inhibitor to kill human glioblastoma cells

Abstract

Glioblastoma multiforme is a devastating disease of the central nervous system and, at present, no effective therapeutic interventions have been identified. Celastrol, a natural occurring triterpene, exhibits potent anti-tumor activity against gliomas in xenograft mouse models. In this study, we describe the cell death mechanism employed by celastrol and identify secondary targets for effective combination therapy against glioblastoma cell survival. In contrast to the previously proposed reactive oxygen species (ROS)-dependent mechanism, cell death in human glioblastoma cells is shown here to be mediated by alternate signal transduction pathways involving, but not fully dependent on, poly(ADP-ribose) polymerase-1 and caspase-3. Our studies indicate that celastrol promotes proteotoxic stress, supported by two feedback mechanisms: (i) impairment of protein quality control as revealed by accumulation of polyubiquitinated aggregates and the canonical autophagy substrate, p62, and (ii) the induction of heat-shock proteins, HSP72 and HSP90. The Michael adduct of celastrol and N-acetylcysteine, 6-N-acetylcysteinyldihydrocelastrol, had no effect on p62, nor on HSP72 expression, confirming a thiol-dependent mechanism. Restriction of protein folding stress with cycloheximide was protective, while combination with autophagy inhibitors did not sensitize cells to celastrol-mediated cytotoxicity. Collectively, these findings imply that celastrol targets proteostasis by disrupting sulfyhydryl homeostasis, independently of ROS, in human glioblastoma cells. This study further emphasizes that targeting proteotoxic stress responses by inhibiting HSP90 with 17-N-Allylamino-17-demethoxygeldanamycin sensitizes human glioblastoma to celastrol treatment, thereby serving as a novel synergism to overcome drug resistance.

Natural Products Discovered in a High-Throughput Screen Identified as Inhibitors of RGS17 and as Cytostatic and Cytotoxic Agents for Lung and Prostate Cancer Cell Lines

“…47,48 Compound 2 (celastrol) has been reported to have activity against osteosarcoma, head and neck cancer, and glioblastoma. 49–51 Additionally, both compounds 1 and 2 have been reported to have activity against lung and prostate cancer cell lines through a variety of mechanisms. Compound 1 was reported to inhibit A549 and PC3 cell growth through glutathione depletion mechanisms, 52,53 while 2 inhibited A549 cells through activation of mitochondrial and Fas/FasL (Fas receptor/Fas ligand) apoptotic pathways and to have activity against DU145 prostate cancer cells via an hERG-dependent mechanism.…”

Autophagic degradation of epidermal growth factor receptor in gefitinib-resistant lung cancer by celastrol

“…Celastrol exhibits selective cytotoxic effect and mobilizes cytosolic calcium towards EGFR mutant NSCLCs. The natural triterpenoid compound celastrol is a promising cytotoxic agent in a great variety of cancer models (17)(18)(19)(20). It was previously reported that celastrol has the potency to combat gefitinib-resistant NSCLCs by inducing apoptosis through caspase-dependent pathways and Hsp90 client protein degradation.…”

Celastrol and its Potential Health Benefits

“…ise gliom hücrelerinde celastrol uyarımı ile meydana gelen paraptozisin apoptozdan bağımsız olarak meydana geldiğini göstermişlerdir. 32 Bu bağlamda celastrolün paraptozdan ziyade, hücresel şartlara ve hücre tiplerine bağlı olarak farklı hücre ölüm şekillerini uyarabileceği söylenebilmektedir.…”