Antitumor Activity of the TLR-5 Ligand Flagellin in Mouse Models of Cancer

Abstract

Flagellin, the structural protein subunit of the bacterial flagellum, is specifically recognized by TLR-5 and has potent immunomodulatory effects. The antitumor effects of purified Salmonella typhimurium flagellin were evaluated in mice transplanted s.c. with a weakly immunogenic murine tumor or with its variant stably transfected to express the highly antigenic human HER-2 oncoprotein. Peritumoral administration of flagellin 8–10 days after tumor implantation did not affect the growth rate of the weakly immunogenic tumor but significantly inhibited growth of the antigenic variant tumor. In contrast, flagellin administered at the time of implantation of the antigenic tumor led to accelerated tumor growth. These contrasting effects of flagellin on tumor growth correlated with the type of immune response induced; i.e., late flagellin administration was associated with an increased IFN-γ:IL-4 ratio and the decreased frequency of CD4+CD25+ T regulatory cells, whereas flagellin treatment at the time of tumor implantation decreased the IFN-γ:IL-4 ratio and increased CD4+CD25+ T cell frequency. When the early flagellin treatment was combined with administration of CpG-containing oligodeoxynucleotides, tumor growth was completely suppressed, indicating synergy between flagellin and CpG-containing oligodeoxynucleotides. Together, these data provide evidence that flagellin can have contrasting effects on tumor growth.

Toll-like receptor-5 agonist, entolimod, suppresses metastasis and induces immunity by stimulating an NK-dendritic-CD8 + T-cell axis

“…In fact, activation of TLR5 by commensal bacteria was shown to drive malignant progression at extramucosal locations through the promotion of inflammation, which dampened antitumor immunity by expanding immunosuppressive networks (65). In contrast, we and others have shown that TLR5 activation has tumor growth suppressive effects and stimulates antitumor immunity (19)(20)(21)(22)(23)(24)(25)(26)53). Earlier studies in our laboratory showed that entolimod displayed a growth-inhibitory effect on a TLR5-expressing mouse xenograft model of human lung adenocarcinoma A549 (23), supporting a direct effect of TLR5 stimulation on tumor growth suppression.…”

“…Studies have shown that the only known natural TLR5 agonist, flagellin, flagellin-expressing Salmonella bacteria, and a pharmacologically optimized flagellin derivative named entolimod (CBLB502) have antitumor effects in several tumor models (19)(20)(21)(22)(23), including mouse models of liver metastases (24)(25)(26). Moreover, systemic administration of TLR5 agonists is uniquely safe because of the restricted pattern of expression of TLR5 (primarily in the gut, liver, and bladder) and the nature of the cytokines induced following TLR5 stimulation.…”

A TLR5 Agonist Enhances CD8+ T Cell-Mediated Graft-versus-Tumor Effect without Exacerbating Graft-versus-Host Disease

“…In contrast, flagellin was able to promote CD8 + T cell response when fused with OVA protein, SIINFEKL peptide, or viral Ags (21)(22)(23)(24)(25). In addition, flagellin has been reported to modulate antitumor immune responses (26). However, studies with tumor models have yielded conflicting results with regard to whether flagellin actually promotes or suppresses tumor growth (26)(27)(28).…”

Adenovirus-mediated gene transfer of pathogen-associated molecular patterns for cancer immunotherapy

“…Recently published data 42 show that purified flagellin administered peritumorally 8-10 days after tumor implantation did not affect the growth rate of a poorly immunogenic tumor, whereas it significantly inhibited the growth of an antigenic human ErB-2-transfected tumor variant. Low immunogenicity of B16F0-CAR cells might explain the lack of effect observed for Ad-flagellin.…”