Bullatacin triggers immunogenic cell death of colon cancer cells by activating endoplasmic reticulum chaperones

Abstract

Background It is well accepted that the immune system efficiently contributes to positive outcomes of chemotherapeutic cancer treatment by activating immunogenic cell death (ICD). However, only a limited number of ICD-inducing compounds are well characterized at present; therefore, identification of novel ICD inducers is urgently needed for cancer drug discovery, and the need is becoming increasingly urgent. Methods Herein, we assessed the antitumour activity of bullatacin by MTS assay and apoptosis assay. ICD biomarkers, such as calreticulin (CRT), high-mobility group protein B1 (HMGB-1), heat shock protein (HSP)70, HSP90 and ATP, were assessed by Western blotting, ELISA and flow cytometry. Western blot and qPCR assays were performed to explore the underlying mechanisms of bullatacin-induced ICD. Flow cytometry was used to detect macrophage phagocytosis. Results First, bullatacin induced apoptosis in both SW480 cells and HT-29 cells in a time-dependent manner at 10 nM, as assessed by flow cytometry. Moreover, Western blot and flow cytometry assays showed that CRT and HSP90 (biomarkers of early ICD) significantly accumulated on the cell membrane surface after approximately 6 h of treatment with bullatacin. In addition, ELISAs and Western blot assays showed that the second set of hallmarks required for ICD (HMGB1, HSP70 and HSP90) were released in the conditioned media of both SW480 and HT-29 cells after 36 h of treatment. Furthermore, qPCR and Western blot assays indicated that bullatacin triggered ICD via activation of the endoplasmic reticulum stress (ERS) signalling pathway. Finally, bullatacin promoted macrophage phagocytosis. Conclusion This study documents that bullatacin, a novel ICD inducer, triggers immunogenic tumour cell death by activating ERS even at a relatively low concentration in vitro.

Induction of immunogenic cell death effect of licoricidin in cervical cancer cells by enhancing endoplasmic reticulum stress‐mediated high mobility group box 1 expression

“…The components of the ER stress mechanism may constitute clinically relevant drug trigger ICD, which releases vital immune stimuli or danger signs that ultimately drive effective antitumor immunity 28,29 . Several recent studies also reported that DAMPs exposure or release, such ATP, HMGB1, and CRT from cancer cells is associated with occurrence of ICD 30 . To clarify whether LCD could induce ICD response in cervical cancer cells, we analyzed the expression of CRT and HMGB1 using western blotting.…”

“…28,29 Several recent studies also reported that DAMPs exposure or release, such ATP, HMGB1, and CRT from cancer cells is associated with occurrence of ICD. 30 To clarify whether LCD could induce ICD response in cervical cancer cells, we analyzed the expression of CRT and HMGB1 using western blotting. The results revealed the expression of CRT was increased in HeLa and C-33A cells after LCD treatment.…”

Immunogenic Cell Death: An Emerging Target in Gastrointestinal Cancers

“…Huang et al demonstrated that the latter could elicit surface exposure of CALR and enhance the efficacy of neoadjuvant chemoradiotherapy (CRT) in BALB/c mice inoculated with CT26 mouse colon carcinoma cells; in fact, the complete response rate in the lipotecan-based CRT group was higher than that of the 5-fluorouracil-based CRT group (33.3 vs. 16.7%, respectively). These findings suggest that lipotecan could become part of neoadjuvant CRT in CRC and improve clinical outcomes in a setting in which recurrence rates are still relevant (5-15% at 5 years) [35,36].…”

Immunogenic cell death in colorectal cancer: a review of mechanisms and clinical utility

“…There is a clear need for novel therapeutics in colorectal cancer and high-throughput screening and validation platforms with a focus on harnessing ICD are essential. Recently, multiple agents have been identified as potential ER stress targeted therapies including ceapins (pyrazole amide ATF6 activators), HHQ-4 and plumbagin (GPR78 inhibitors), GSK2606414 and GSK2656157 (ATP-competitive PERK kinase inhibitors), and bullatacin with promising pre-clinical data emerging [ 42 – 47 ].…”