Interleukin-1β (IL-1β) binds to the
IL-1 receptor (IL-1R) and is a key
cytokine mediator of
inflammasome activation. IL-1β signaling leads to parturition in
preterm birth (PTB) and contributes to the
retinal vaso-obliteration characteristic of
oxygen-induced retinopathy (OIR) of premature infants.
Therapeutics targeting IL-1β and IL-1R are approved to treat
rheumatoid arthritis; however, all are large
proteins with clinical limitations including immunosuppression, due in part to inhibition of NF-κB signaling, which is required for immuno-vigilance and cytoprotection. The all-D-
amino acid peptide 1 (101.10, H-d-Arg-d-Tyr-d-Thr-d-Val-d-Glu-d-Leu-d-Ala-NH2) is an allosteric IL-1R modulator, which exhibits functional selectivity and conserves NF-κB signaling while inhibiting other IL-1-activated pathways.
Peptide 1 has proven effective in experimental models of PTB and OIR. Seeking understanding of the structural requirements for the activity and biased signaling of 1, a panel of twelve derivatives was synthesized employing the various stereochemical isomers of α-amino-γ-
lactam (Agl) and α-amino-β-hydroxy-γ-
lactam (Hgl) residues to constrain the D-Thr-D-Val
dipeptide residue. Using circular dichroism spectroscopy, the
peptide conformation in
solution was observed to be contingent on Agl, Hgl, and Val stereochemistry. Moreover, the
lactam mimic structure and configuration influenced biased
IL-1 signaling in an in vitro panel of cellular assays as well as in vivo activity in murine models of PTB and OIR. Remarkably, all Agl and Hgl analogs of
peptide 1 did not inhibit NF-κB signaling but blocked other pathways, such as JNK and ROCK2 phosphorylation contingent on structure and configuration. Efficacy in preventing
preterm labor correlated with a capacity to block IL-1β-induced IL-1β synthesis. Furthermore, the importance of inhibition of JNK and ROCK2 phosphorylation for enhanced activity was highlighted for prevention of vaso-obliteration in the OIR model. Taken together,
lactam mimic structure and stereochemistry strongly influenced conformation and biased signaling. Selective modulation of
IL-1 signaling was proven to be particularly beneficial for curbing
inflammation in models of
preterm labor and
retinopathy of prematurity (ROP). A class of biased
ligands has been created with potential to serve as selective probes for studying
IL-1 signaling in disease. Moreover, the small
peptide mimic prototypes are promising leads for developing
immunomodulatory therapies with easier administration and maintenance of beneficial effects of NF-κB signaling.