Activation of inflammasome by attenuated Salmonella typhimurium in bacteria-mediated cancer therapy.
Escherichia coli and attenuated Salmonella both naturally accumulate in a tumor mass, yet have distinct therapeutic efficacy: the E. coli K-12 strain (MG1655) cannot induce as significant a tumor suppression as attenuated Salmonella typhimurium, despite similar levels of accumulation in the tumor. To elucidate the mechanism of the robust antitumor effect of S. typhimurium, the cytokine profiles elicited by bacterial colonization in tumors were analyzed. C57BL/6 mice bearing MC38 tumors were injected with Salmonella or MG1655 in the tail vein. Tumors were collected 3 days post-infection and homogenized. Inflammasome-related signals were measured by real-time PCR, ELISA and western blot analysis. Only attenuated Salmonella triggered significant levels of the inflammatory cytokine IL-1β in the tumor, whereas tumor growth was significantly suppressed. In addition, transcript levels of the core molecules of inflammasome signaling, IPAF, NLRP3 and P2X7, were significantly elevated only in Salmonella-treated tumors. Upon direct interaction between Salmonella and BMDM, BMDM expressed inflammasome-related proteins such as NLRP3, IPAF and caspase-1 p10, and secreted a significant amount of IL-1β in supernatants. Coincubation assays with BMDM and Salmonella-treated MC38 cells (damaged cancer cells) revealed secretion of IL-1β only when TLR4 and inflammasome were activated by both LPS and damaged cancer cells. ATP released from damaged cancer cells was also identified as a mechanism of NLRP3 activation. In conclusion, Salmonella activate the inflammasome pathway using damage signals released from cancer cells and through direct interaction with macrophages.
Laboratory of In Vivo Imaging, Department of Nuclear Medicine, Chonnam National University Medical School and Hwasun Hospital.
Thuy Xuan
TX
Phan
Laboratory of In Vivo Imaging, Department of Nuclear Medicine, Chonnam National University Medical School and Hwasun Hospital.
Vu Hong
VH
Nguyen
Laboratory of In Vivo Imaging, Department of Nuclear Medicine, Chonnam National University Medical School and Hwasun Hospital.
Mai Thi-Quynh
MT
Duong
Department of Microbiology, Chonnam National University Medical School, Gwangju, Korea.
Yeongjin
Y
Hong
Department of Microbiology, Chonnam National University Medical School, Gwangju, Korea.
Hyon E
HE
Choy
Laboratory of In Vivo Imaging, Department of Nuclear Medicine, Chonnam National University Medical School and Hwasun Hospital.|Department of Microbiology, Chonnam National University Medical School, Gwangju, Korea.
Jung-Joon
JJ
Min
D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage*; D004926:Escherichia coli / Q000502:physiology*; D006801:Humans; D058847:Inflammasomes / Q000502:physiology*; D008264:Macrophages / Q000276:immunology* / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009369:Neoplasms / Q000628:therapy*; D012486:Salmonella typhimurium / Q000276:immunology* / Q000502:physiology*
D000970:Antineoplastic Agents; D058847:Inflammasomes
IL-1β; Salmonella typhimurium; inflammasome