Hemolysin BL from novel Bacillus toyonensis BV-17 induces antitumor activity both in vitro and in vivo

Abstract

The gut microbiota plays an important role in cancer development and immunotherapy. Bacterial toxins have enormous antitumor potential due to their cytotoxicity and ability to activate the immune system. Using 16S rRNA gene sequencing, we compared the gut microbiota composition of fecal samples from healthy individuals and patients with colorectal cancer (CRC) and observed that the genus Bacillus was common in the healthy donors but was absent in the CRC patients. Further, we isolated a novel Bacillus toyonensis BV-17 from the fecal samples of the healthy individuals. Our results showed that the supernatant of the Bacillus toyonensis BV-17 cultures could quickly kill various tumor cell lines within minutes in vitro, by causing cell membrane disruption, blebbing, and leakage of cytoplasmic content. Fast protein liquid chromatography (FPLC) and mass spectrometry analysis identified hemolysin BL (HBL) as the effector molecule, which exhibits a different cytotoxicity mechanism compared to previous studies. Intra-tumor injection of low dose HBL inhibited the growth of both treated and untreated tumors in mice. The outcomes of this pioneer study suggest that HBL exhibits antitumor activity and is a potential chemotherapeutic agent that could be engineered to target only tumor cells in future.

Microbial metabolites: cause or consequence in gastrointestinal disease?

“…For instance, SCFAs produced by the healthy human bacterium E. coli KUB-36 strain exhibited anticancer and anti-inflammatory activities by affecting the inflammatory reactions in lipopolysaccharide-induced THP-1 macrophage cells and by suppressing the proinflammatory cytokines IL-1β, IL-6, IL-8, and TNF-α whil promoting the expression of anti-inflammatory cytokine IL-10 ( 123 ). Some proteins (e.g., hemolysin BL reported from Bacillus toyonensis ) and polysaccharides (e.g., polysaccharide A from Bacteroides fragilis ) directly synthesized by specific members of the microbiome exhibited beneficial effects against cancers by modulating the immune response ( 125 , 126 ).…”

“…The active molecule, a polysaccharide derivative, induced the expression of proinflammatory agents such as TNFα produced by dendritic cells and provided one possible mechanism for the association between R. gnavus and inflammatory disease ( 147 ). Another example based on bioactivity-guided fractionation is the identification of the antitumor molecule hemolysin BL from a fraction obtained from the supernatant of B. toyonensis BV-17, a member of the healthy human gut microbiome ( 125 ). In this study, the genus Bacillus was associated with healthy subjects and was absent in patients with colorectal cancer as revealed by 16S rRNA comparative metagenomics of the microbiome in both groups.…”

“…In this study, the genus Bacillus was associated with healthy subjects and was absent in patients with colorectal cancer as revealed by 16S rRNA comparative metagenomics of the microbiome in both groups. Hemolysin BL inhibited tumor growth in mice, providing a possible molecular explanation for the susceptibility to colorectal cancer and a potential therapeutic lead that can be further developed ( 125 ). Recently, 1-ethoxycarbonyl-β-carboline produced by Lactobacillus species was identified by bioactivity-guided fractionation as a bioactive compound against the opportunistic pathogen C. albicans ( 148 ).…”

Photodynamic Therapy of Novel Photosensitizer Ameliorates TNBS-Induced Ulcerative Colitis via Inhibition of AOC1

“…Abnormal immune responses to bacteria out of balance may disrupt this homeostasis and are related to human IBD ( Le Chatelier et al, 2013 ). Several studies have shown that intestinal flora affects intestinal mucosal immune function, intestinal cell metabolism and renewal and other processes, which can cause obesity, diabetes, malignant tumors, toxemia and IBD ( Chen et al, 2020 ; Ma et al, 2020 ; Wang et al, 2020 ). Therefore, exploring the role of the intestinal flora in the occurrence and development of UC, and restoring the balance of disordered flora is of great significance for the treatment of UC.…”

“…Significant differences were determined using one-way analysis of variance (ANOVA). Statistical differences in 16S rRNA high-throughput sequencing were assessed using Tukey’s HSD ( Li H. et al, 2020 ) , Chen et al, 2020 ). p < 0.05 was considered statistically significant.…”