Background/Purpose: Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by loss of tolerance to nuclear components; this results in production of autoantibodies, immune complex formation, and tissue damages. Because SLE is a multifactorial disease with an underlying pathogenic mechanism that is poorly understood, few effective treatments are available. Human and mouse studies indicate a role for Th17 in progression of SLE. Renal damage, which occurs in about half of patients with SLE, is the leading cause of morbidity and mortality. We recently showed that serum concentrations of s-CD95L (also known as FasL) in SLE patients are higher than those in healthy subjects and are associated with disease severity via promotion of Th17 trafficking to inflamed kidneys (Immunity, 2016). CD95L is a transmembrane ligand that is cleaved by metalloproteases to release a soluble ligand (s-CD95L). Both s-CD95L and its transmembrane counterpart (m-CD95L) bind CD95. In the presence of m-CD95L, the death domain (DD) of CD95 recruits FADD, which in turn aggregates caspase-8 to trigger apoptosis. By contrast, interaction between s-CD95L and CD95 fails to recruit caspase-8 and FADD but instead induces a Ca²⁺ response via docking of PLCg1 to a novel domain within CD95, called the calcium-inducing domain (CID). In patients with SLE, this pathway induces accumulation of inflammatory Th17 cells in damaged organs, thereby aggravating disease pathology.

Methods: Here, we developed a protein-fragment complementation assay (PCA) and performed a high-throughput screening (HTS) to identify drugs that disrupted the CD95/PLCg1 interaction without affecting CD95/FADD binding. In parallel, a structure-activity relationship approach was performed to synthesize CID peptidomimetics that abrogated both the CD95-driven Ca²⁺ response and transmigration of CD4⁺ Th17 cells. Finally, we established the in vivo therapeutic effects of both the peptidomimetic and the best lead identified from the HTS assay in lupus-prone mice (MRL^lpr/+).

Results: HTS identified the HIV protease inhibitor ritonavir as a potent disruptor of the CD95/PLCg1 interaction. Lymphocytes from HIV patients treated with ritonavir or its structural derivatives failed to respond to the inflammatory cytokine s-CD95L. The second structure-activity approach revealed that ritonavir is a peptidomimetic that shares structural characteristics with both human and mouse CID with respect to docking to the SH3 domain of PLCg1. Administration of lupus mice with either ritonavir or a peptidomimetic designated DB550 led to: 1/ a significant reduction in the mesangial proliferation and in the adhesion of the Bowman’s capsule; 2/ a significant reduction of inflammatory infiltrates (especially of Th17 cells) and the normalization of kidney architecture; 3/ a reduced C3 deposition and dsDNA antibody levels, as well as an improvement of blood filtration of creatinine.

Conclusion: Overall, this study establishes that HIV protease inhibitors and the peptidomimetic DB550 represent novel and attractive drugs that can be used in the treatment of human lupus.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/hiv-protease-inhibitors-cure-lupus-prone-mice-and-prevent-t-helper-17-cell-driven-inflammation-by-inhibiting-cd95-non-apoptotic-signaling-pathway/