Polb 001, an Oral p38 MAPK Inhibitor, Reduces Cytokine Release Syndrome (CRS) in a Mouse Model of Immunotherapy-Induced CRS

Background

Cancer immunotherapies such as chimeric antigen receptor (CAR) T cell therapies and bispecific antibodies are highly effective treatments for patients with haematological malignancies. However, these immunotherapies are frequently associated with systemic toxicities such as cytokine release syndrome (CRS). In addition to its impact on patient survival and performance status, CRS complicates the administration of the immunotherapies and restricts availability to specialist tertiary centres with access to high-dependency units. CRS is thought to arise from on-target effects of immunotherapy involving undue amplification of specific inflammatory responses. Treatment of CRS includes anti-pyretic or anti-cytokine therapies such as tocilizumab (anti-IL-6R), anakinra (anti-IL-1RA), and corticosteroids. No prophylactic treatments are currently approved. POLB 001 is an oral p38 MAPK inhibitor in development for the prevention of immunotherapy-induced CRS. Inhibition of p38 MAPK is expected to selectively target key inflammatory pathways without causing broad immunosuppressive properties. Adalimumab, an anti-TNF antibody, is a potent inhibitor of CRS in humanized mouse models. The current study was designed to evaluate the effect of POLB 001 on cytokine release compared to adalimumab in a well-characterized animal model of CRS.

Methods

The Jackson Laboratory provided optimized mouse models, in which CRS was reliably induced in peripheral blood mononuclear cells (PBMC) humanised CD19+ Raji-luc cancer bearing mice. Briefly, to model immunotherapy-induced CRS, female NSG-MHC I/II DKO mice were irradiated at 100 cGy and injected with PBMCs intravenously (15 x 10⁶ cells) which were left to grow for 4 days. On day 4 until study terminus, mice were treated twice daily via subcutaneous injection with either vehicle or POLB 001 at low (2 mg/kg), medium (10 mg/kg), or high (25 mg/kg) doses for 5 days. On day 5, mice were injected intravenously with Raji-luc cells (2 x 10⁶ cells). On day 6, mice were intravenously injected with anti-CD28. The positive control group was immediately dosed intraperitoneally with adalimumab (5 mg/kg). Whole blood was collected from mice by retro-orbital bleeding, samples were used for flow cytometry analysis or processed to serum to measure human cytokines. Mice were euthanised by CO₂ asphyxiation for necropsy once they reached the humane endpoint or on the scheduled study terminus. Where mice reached study terminus, whole blood was collected via cardiocentesis for sample analysis. The study objective was to examine the effect of POLB 001 on inflammatory responses following anti-CD28 stimulation, including cytokine analysis and T cell expansion in addition to clinical observations of CRS. A One-Way ANOVA was fitted to the data and comparisons of interest were made using a Bonferroni test to adjust for multiple testing.

Results

All doses of POLB 001 significantly reduced clinically observed CRS scores (2 mg/kg p<0.05, 10 mg/kg and 25 mg/kg p<0.001). POLB 001 treatment showed statistically significant reductions in IL-6 (at high-dose), IL-4 (low- and high-dose), IL-8 (all doses) and MIP-1α (all doses) and a trend of reduced cytokine production in all other cytokines tested (IFN-γ, TNF, IL-10, IL-2). Adalimumab and POLB 001 (10 mg/kg and 25 mg/kg) effectively prevented CRS symptoms, however POLB 001 produced superior cytokine inhibition (ns). While adalimumab also significantly reduced IFN-γ, TNF, IL-6, and MIP-1α, some cytokines were elevated, including IL-10, IL-4, and IL-2 and there was no significant effect on IL-8. These results indicate that POLB 001 may be effective in preventing CRS. Both test articles were well tolerated.

Conclusion

In a model of anti-CD28 induced CRS, POLB 001 was shown to dose dependently reduce clinical CRS scores. POLB 001 significantly reduced peak serum levels of IL-4, IL-6, IL-8 and MIP1-α; all other cytokines tested, including IFN-γ, TNF, IL-10 and IL-2, showed trends of reduced peak serum levels. In combination with a previous successful trial in healthy human volunteers, the results of this animal study further support development of POLB 001 in a Phase 2 clinical study as a prophylactic for the prevention of immunotherapy-induced CRS.