Contributions
Abstract: EP693
Type: E-Poster Presentation
Session title: Enzymopathies, membranopathies and other anemias
Background
Autoimmune hemolytic anemia (AIHA) is a rare acquired disorder in which autoantibodies directed against red blood cell (RBC) membrane antigens lead to accelerated RBC destruction. The disease can be distinguished on the basis of the autoantibody class and thermal characteristics: warm AIHA (immunoglobulin [Ig]-G–mediated) and cold agglutinin disease (IgM-mediated). The mortality rate is approximately 11%, and there are currently no regulatory approved AIHA treatments. Phosphatidylinositol 3-kinases (PI3Ks) are divided into 3 classes (Class I, II, and III) according to their structure, regulation, and substrate specificity. The Class I PI3K delta isoform (PI3Kδ) has been implicated in autoimmune diseases associated with aberrant B-cell and antibody responses. Parsaclisib is an oral, small-molecule PI3Kδ selective inhibitor without known adverse off-target toxicities that is being clinically evaluated in AIHA and hematologic malignancies.
Aims
To evaluate the efficacious potential of small-molecule PI3Kδ inhibition in preclinical models of antibody-mediated immunity, including spontaneous AIHA.
Methods
The relevance of PI3Kδ inhibition on de novo antibody production was characterized in 2 preclinical mouse models. Intravenous 2,4,6-trinitrophenyl lipopolysaccharide (TNP-LPS) triggers a rapid antigen-specific, B-cell–mediated IgM response. In contrast, intraperitoneal injection of 2,4-dinitrophenyl-keyhole limpet hemocyanin (DNP-KLH) drives an antigen-specific, T-cell–dependent, B-cell–mediated IgG immunity. The interleukin-2 knockout (IL-2 KO) mice spontaneously develop a systemic autoimmune disease, dying from complications of AIHA mediated by autoantibodies. The pharmacologic effect of PI3Kδ inhibition was quantified using antigen-specific enzyme-linked immunosorbent assays, complete blood count, and flow cytometry.
Results
In vitro enzymatic selectivity screening revealed that parsaclisib potently inhibited the PI3Kδ kinase enzyme (50% inhibitory concentration [IC50] = 1.1 ± 0.5 nM) with ~20,000-fold selectivity over the other PI3K family member enzymes. Oral prophylactic PI3Kδ inhibitor treatment dose-dependently reduced antigen-specific IgM and IgG antibody titers. The modulation of antigen-specific IgM and IgG responses following parsaclisib treatment was fully consistent with previously published data using TNP-LPS and DNP-KLH stimuli in PI3Kδ knockout mice. Selective pharmacologic inhibition of the PI3Kδ isoform ameliorated AIHA symptoms in the IL-2 KO mouse model, with disease modulation associated with the reduced presence of Ig-bound RBC. Hemoglobin and RBC levels were unaffected by PI3Kδ inhibition in healthy age-matched wild-type mice.
Conclusion
In preclinical models, PI3Kδ inhibition dose-dependently inhibited de novo IgM and IgG humoral responses and was highly efficacious in a spontaneous AIHA mouse model. These experimental data support the scientific rationale for clinically evaluating parsaclisib in AIHA (NCT03538041).
Keyword(s): Autoantibody, Autoimmune hemolytic anemia (AIHA), PI3K
Abstract: EP693
Type: E-Poster Presentation
Session title: Enzymopathies, membranopathies and other anemias
Background
Autoimmune hemolytic anemia (AIHA) is a rare acquired disorder in which autoantibodies directed against red blood cell (RBC) membrane antigens lead to accelerated RBC destruction. The disease can be distinguished on the basis of the autoantibody class and thermal characteristics: warm AIHA (immunoglobulin [Ig]-G–mediated) and cold agglutinin disease (IgM-mediated). The mortality rate is approximately 11%, and there are currently no regulatory approved AIHA treatments. Phosphatidylinositol 3-kinases (PI3Ks) are divided into 3 classes (Class I, II, and III) according to their structure, regulation, and substrate specificity. The Class I PI3K delta isoform (PI3Kδ) has been implicated in autoimmune diseases associated with aberrant B-cell and antibody responses. Parsaclisib is an oral, small-molecule PI3Kδ selective inhibitor without known adverse off-target toxicities that is being clinically evaluated in AIHA and hematologic malignancies.
Aims
To evaluate the efficacious potential of small-molecule PI3Kδ inhibition in preclinical models of antibody-mediated immunity, including spontaneous AIHA.
Methods
The relevance of PI3Kδ inhibition on de novo antibody production was characterized in 2 preclinical mouse models. Intravenous 2,4,6-trinitrophenyl lipopolysaccharide (TNP-LPS) triggers a rapid antigen-specific, B-cell–mediated IgM response. In contrast, intraperitoneal injection of 2,4-dinitrophenyl-keyhole limpet hemocyanin (DNP-KLH) drives an antigen-specific, T-cell–dependent, B-cell–mediated IgG immunity. The interleukin-2 knockout (IL-2 KO) mice spontaneously develop a systemic autoimmune disease, dying from complications of AIHA mediated by autoantibodies. The pharmacologic effect of PI3Kδ inhibition was quantified using antigen-specific enzyme-linked immunosorbent assays, complete blood count, and flow cytometry.
Results
In vitro enzymatic selectivity screening revealed that parsaclisib potently inhibited the PI3Kδ kinase enzyme (50% inhibitory concentration [IC50] = 1.1 ± 0.5 nM) with ~20,000-fold selectivity over the other PI3K family member enzymes. Oral prophylactic PI3Kδ inhibitor treatment dose-dependently reduced antigen-specific IgM and IgG antibody titers. The modulation of antigen-specific IgM and IgG responses following parsaclisib treatment was fully consistent with previously published data using TNP-LPS and DNP-KLH stimuli in PI3Kδ knockout mice. Selective pharmacologic inhibition of the PI3Kδ isoform ameliorated AIHA symptoms in the IL-2 KO mouse model, with disease modulation associated with the reduced presence of Ig-bound RBC. Hemoglobin and RBC levels were unaffected by PI3Kδ inhibition in healthy age-matched wild-type mice.
Conclusion
In preclinical models, PI3Kδ inhibition dose-dependently inhibited de novo IgM and IgG humoral responses and was highly efficacious in a spontaneous AIHA mouse model. These experimental data support the scientific rationale for clinically evaluating parsaclisib in AIHA (NCT03538041).
Keyword(s): Autoantibody, Autoimmune hemolytic anemia (AIHA), PI3K