Cyclo(Phe-Pro)

Anticancer Res. 2005 Nov-Dec;25(6B):4197-202.

Caspase-3 activation and induction of PARP cleavage by cyclic dipeptide cyclo(Phe-Pro) in HT-29 cells.[Pubmed: 16309216]

Cyclo(Phe-Pro) has been shown to inhibit cancer cell growth and induce apoptosis in HT-29 colon cancer cells.
METHODS AND RESULTS:
The molecular mechanisms mediating Cyclo(Phe-Pro)-induced apoptosis in HT-29 cells were investigated. Cells were treated with 5 mM or 10 mM Cyclo(Phe-Pro) for varying times. Immunoblot analysis was used to detect poly(ADP-ribose)polymerase (PARP) cleavage. A fluorescence-based enzymatic assay was used to measure caspase-3 activity.Cyclo(Phe-Pro) (10 mM) induced time-dependent cleavage of PARP, detected as early as 8 hours post treatment. PARP cleavage was blocked by co-administration with the broad-range caspase inhibitor Z-VAD-FMK Cyclo(Phe-Pro) also induced a time-dependent increase (p < 0.01) in caspase-3 activity. This increase in activity was blocked in the presence of the caspase-3 inhibitor Ac-DEVD-CHO.
CONCLUSIONS:
These results provide evidence that Cyclo(Phe-Pro)-induced apoptosis in HT-29 cells is mediated by a caspase cascade. These findings warrant further investigation into the potential antitumour activity of Cyclo(Phe-Pro) and its related cyclic dipeptide derivatives.

Infect Immun. 2015 Mar;83(3):1150-61.

Cyclo(Phe-Pro) produced by the human pathogen Vibrio vulnificus inhibits host innate immune responses through the NF-κB pathway.[Pubmed: 25561711]

Cyclo(Phe-Pro) (cFP) is a secondary metabolite produced by certain bacteria and fungi. Although recent studies highlight the role of Cyclo(Phe-Pro) in cell-to-cell communication by bacteria, its role in the context of the host immune response is poorly understood. In this study, we investigated the role of Cyclo(Phe-Pro) produced by the human pathogen Vibrio vulnificus in the modulation of innate immune responses toward the pathogen.
METHODS AND RESULTS:
Cyclo(Phe-Pro) suppressed the production of proinflammatory cytokines, nitric oxide, and reactive oxygen species in a lipopolysaccharide (LPS)-stimulated monocyte/macrophage cell line and in bone marrow-derived macrophages. Specifically, Cyclo(Phe-Pro) inhibited inhibitory κB (IκB) kinase (IKK) phosphorylation, IκBα degradation, and nuclear factor κB (NF-κB) translocation to the cell nucleus, indicating that Cyclo(Phe-Pro) affects the NF-κB pathway. We searched for genes that are responsible for Cyclo(Phe-Pro) production in V. vulnificus and identified VVMO6_03017 as a causative gene. A deletion of VVMO6_03017 diminished Cyclo(Phe-Pro) production and decreased virulence in subcutaneously inoculated mice.
CONCLUSIONS:
In summary, Cyclo(Phe-Pro) produced by V. vulnificus actively suppresses the innate immune responses of the host, thereby facilitating its survival and propagation in the host environment.

MBio. 2013 Aug 27;4(5):e00366-13.

Vibrio cholerae ToxR downregulates virulence factor production in response to cyclo(Phe-Pro).[Pubmed: 23982069]

Vibrio cholerae is an aquatic organism that causes the severe acute diarrheal disease cholera. The ability of V. cholerae to cause disease is dependent upon the production of two critical virulence determinants, cholera toxin (CT) and the toxin-coregulated pilus (TCP). The expression of the genes that encode for CT and TCP production is under the control of a hierarchical regulatory system called the ToxR regulon, which functions to activate virulence gene expression in response to in vivo stimuli. Cyclic dipeptides have been found to be produced by numerous bacteria, yet their biological function remains unknown. V. cholerae has been shown to produce Cyclo(Phe-Pro). Previous studies in our laboratory demonstrated that Cyclo(Phe-Pro) inhibited V. cholerae virulence factor production.
METHODS AND RESULTS:
For this study, we report on the mechanism by which Cyclo(Phe-Pro) inhibited virulence factor production. We have demonstrated that exogenous Cyclo(Phe-Pro) activated the expression of leuO, a LysR-family regulator that had not been previously associated with V. cholerae virulence. Increased leuO expression repressed aphA transcription, which resulted in downregulation of the ToxR regulon and attenuated CT and TCP production. The Cyclo(Phe-Pro)-dependent induction of leuO expression was found to be dependent upon the virulence regulator ToxR. Cyclo(Phe-Pro) did not affect toxR transcription or ToxR protein levels but appeared to enhance the ToxR-dependent transcription of leuO. These results have identified leuO as a new component of the ToxR regulon and demonstrate for the first time that ToxR is capable of downregulating virulence gene expression in response to an environmental cue. IMPORTANCE: The ToxR regulon has been a focus of cholera research for more than three decades. During this time, a model has emerged wherein ToxR functions to activate the expression of Vibrio cholerae virulence factors upon host entry. V. cholerae and other enteric bacteria produce Cyclo(Phe-Pro), a cyclic dipeptide that we identified as an inhibitor of V. cholerae virulence factor production. This finding suggested that Cyclo(Phe-Pro) was a negative effector of virulence factor production and represented a molecule that could potentially be exploited for therapeutic development. In this work, we investigated the mechanism by which Cyclo(Phe-Pro) inhibited virulence factor production. We found that Cyclo(Phe-Pro) signaled through ToxR to activate the expression of leuO, a new virulence regulator that functioned to repress virulence factor production.
CONCLUSIONS:
Our results have identified a new arm of the ToxR regulon and suggest that ToxR may play a broader role in pathogenesis than previously known.

J Bacteriol. 2010 Jul;192(14):3829-32.

The cyclic dipeptide cyclo(Phe-Pro) inhibits cholera toxin and toxin-coregulated pilus production in O1 El Tor Vibrio cholerae.[Pubmed: 20453095]

Cyclo(Phe-Pro) is a cyclic dipeptide produced by multiple Vibrio species.
METHODS AND RESULTS:
In this work, we present evidence that Cyclo(Phe-Pro) inhibits the production of the virulence factors cholera toxin (CT) and toxin-coregulated pilus (TCP) in O1 El Tor Vibrio cholerae strain N16961 during growth under virulence gene-inducing conditions.
CONCLUSIONS:
The Cyclo(Phe-Pro) inhibition of CT and TCP production correlated with reduced transcription of the virulence regulator tcpPH and was alleviated by overexpression of tcpPH.