Acute graft-versus-host disease prophylactic mitigation via novel ST2 inhibition

Hematopoietic stem cell transplantation (HSCT) represents a potentially curative treatment option for many patients with hematological malignancies. Despite its success, HSCT can result in graft-versus-host-disease (GvHD) in up to 50% of patients, whereby donor T cells attack the host, causing extensive tissue and organ damage.¹ Immunosuppressants such as tacrolimus and sirolimus are used in current GvHD prophylaxis to prevent the activation of proinflammatory T cells and reduce the severity of GvHD progression.

The Janus kinase/signal transducers and activator of transcription pathway and interleukin (IL)-1 receptor family have been shown to play a key role in the proinflammatory response during GvHD development.¹ Previous research has identified the GvHD prognostic biomarker, soluble ST2 (sST2), encoded by the IL-1 receptor-like 1 (IL1RL1) gene of the IL-1 receptor family, as a potential therapeutic target for GvHD. The ST2 receptor plays a critical role in GvHD pathophysiology and has an association with treatment resistance.² HSCT conditioning regimens can cause damage to the gastrointestinal epithelium. Fibroblastic reticular cells in turn produce IL-33, which binds to ST2 receptors on donor T helper 1 cells. This can induce T helper 1 cell differentiation and expansion, promoting GvHD. In addition, serum concentrations of soluble ST2 have been shown to predict GvHD severity and subsequent mortality.²

In murine models of GvHD, administration of an ST2 antibody or a small-molecule ST2 inhibitor decreased sST2, reduced GvHD scores, improved survival, and supported the graft versus leukemia effect in allogeneic-HSCT.¹

Recently, Yuan et al.¹ published an article in ACS Pharmacology & Translational Science detailing XY52, the lead ST2 inhibitor from their optimization campaign, which we are pleased to summarize below.

Results¹

Compound optimization and structure−activity relationship

A systematic compound optimization regimen utilizing AlphaLISA and HEK-Blue assays and mouse microsomal studies for a previously identified STL2 inhibitor led to the development of compound XY52. Comparing XY52 to previous compounds, it exhibited improved metabolic stability, and inhibitory activity, and a lack of cell toxicity.

Effects on T-cell proliferation

XY52 was functionally validated via an in vitro mixed lymphocyte reaction experiment, alongside three other compounds of interest with both positive and negative controls. All four new ST2 inhibitors induced dose-dependent reductions in cluster of differentiation (CD)4⁺ and CD8⁺ T-cell proliferation, promoted CD4⁺ Foxp3⁺ regulatory T cell expansion, and had no significant toxicity to human peripheral blood mononuclear cells.

Pharmacokinetics and in vivo metabolic stability

The in vivo pharmacokinetic profile of XY52 indicated persistent metabolic stability of t_1/2 >7h, and a modest bioavailability at 36.5%. XY52 also showed a relatively high tissue distribution among GvHD-targeted organs.

In vivo GvHD model study

In an established preclinical minor-mismatched GvHD mouse model, the new ST2 inhibitors, including XY52, demonstrated significant in vivo efficacy. Administered using a 21-day prophylactic treatment schedule, XY52 effectively mitigated GvHD severity, resulting in reduced GvHD scores and improved survival when compared with the control group, with all treated mice surviving up to Day 78. Additionally, up to Day 28 post-HSCT, no induced adverse toxicity was observed in mice treated with XY52, as no significant weight changes were found between the treatment and control groups.

Histopathological analysis of liver and intestinal tissues supported the GvHD scores and survival data, revealing reduced tissue damage in mice treated with XY52, marked by decreased lymphocyte infiltration and apoptosis. Furthermore, XY52 reduced the concentration of plasma biomarkers such as sST2 and interferon-γ and influenced T cell populations, decreasing proinflammatory CD4⁺ and CD8⁺ T cells while increasing immune-tolerant regulatory T cells.

Conclusion

The development of drugs that target protein-protein interactions remains a challenging task, but the compound XY52 represents a promising small-molecule inhibitor that can effectively disrupt the binding between ST2 and IL-33 in cytokine receptors. The compound has demonstrated improved biochemical and cell-based activities, along with enhanced in vivo and ex vivo stability, in comparison to its predecessors.

The findings indicate that ST2 inhibitors may represent an effective biomarker-based treatment strategy for mitigating inflammatory T cell responses associated with GvHD in HSCT. The evaluation of post-HSCT treatment efficacy and the potential synergistic effects of combining ST2 inhibitors with other therapeutic agents will provide avenues for future investigation.