IOA-244 is a Non-ATP-competitive, Highly Selective, Tolerable PI3K Delta Inhibitor That Targets Solid Tumors and Breaks Immune Tolerance

Abstract

PI3K delta (PI3Kδ) inhibitors are used to treat lymphomas but safety concerns and limited target selectivity curbed their clinical usefulness. PI3Kδ inhibition in solid tumors has recently emerged as a potential novel anticancer therapy through the modulation of T-cell responses and direct antitumor activity. Here we report the exploration of IOA-244/MSC2360844, a first-in-class non-ATP-competitive PI3Kδ inhibitor, for the treatment of solid tumors. We confirm IOA-244's selectivity as tested against a large set of kinases, enzymes, and receptors. IOA-244 inhibits the in vitro growth of lymphoma cells and its activity correlates with the expression levels of PIK3CD, suggesting cancer cell-intrinsic effects of IOA-244. Importantly, IOA-244 inhibits regulatory T cell proliferation while having limited antiproliferative effects on conventional CD4⁺ T cells and no effect on CD8⁺ T cells. Instead, treatment of CD8 T cells with IOA-244 during activation, favors the differentiation of memory-like, long-lived CD8, known to have increased antitumor capacity. These data highlight immune-modulatory properties that can be exploited in solid tumors. In CT26 colorectal and Lewis lung carcinoma lung cancer models, IOA-244 sensitized the tumors to anti-PD-1 (programmed cell death protein 1) treatment, with similar activity in the Pan-02 pancreatic and A20 lymphoma syngeneic mouse models. IOA-244 reshaped the balance of tumor-infiltrating cells, favoring infiltration of CD8 and natural killer cells, while decreasing suppressive immune cells. IOA-244 presented no detectable safety concerns in animal studies and is currently in clinical phase Ib/II investigation in solid and hematologic tumors.

Significance: IOA-244 is a first-in-class non-ATP-competitive, PI3Kδ inhibitor with direct antitumor in vitro activity correlated with PI3Kδ expression. The ability to modulate T cells, in vivo antitumor activity in various models with limited toxicity in animal studies provides the rationale for the ongoing trials in patients with solid tumors and hematologic cancers.

FIGURE 1

IOA-244 is a unique non–ATP-competitive, selective PI3Kδ inhibitor. A, Structural formula of IOA-244. B, Schematic Michaelis–Menten representation of an ATP-competitive versus a non–ATP-competitive inhibitor. Representative competition studies with idelalisib (C) and IOA-244 (D) on PI3Kδ varying in parallel compound and ATP concentrations. E, Heatmap presentation of the selectivity of selected PI3Kδ inhibitors and idelalisib main metabolite GS-563117 based on activity in Jurkat cell lysate as measured using the KiNativ method.

FIGURE 2

Tumor-intrinsic effect of IOA-244. A, Activity of IOA-244 in 67 human lymphoma cell lines. AUC was calculated after IOA-244 treatment at increasing concentration (13.7 nmol/L to 10 μmol/L; 1- to 3-fold dilution) of the drug for 72 hours with Prism software v8.0 (GraphPad). B, Correlation between AUC and PIK3CD transcript expression in 59 B and T-cell lymphoma cell lines. AUC was calculated after IOA-244 treatment at increasing concentration of the drug for 72 hours; PIK3CD RNA expression was extrapolated by RNA-seq of each cell line at baseline conditions. R², Spearman correlation.

FIGURE 3

Dose-dependent inhibition of T_reg proliferation by IOA-244. Proliferation of CD4⁺ Tconv cells (A), Tregs (B), and CD8⁺ T cells (C) proliferation was analyzed by flow cytometry 5 days after stimulation with αCD3/αCD28 or resting, alongside IL2 and compounds at a range of concentrations and IL2. Dilution of ef450 proliferation dye was used to determine the frequency of cells that had undergone cellular division. Three donors were used (n = 3) and the statistics shown are two-way ANOVAs relative to the 0 nmol/L control group (*, P < 0.05; **, P < 0.01; ***, P < 0.001). D, Experimental layout. E, Percentage of CD4 and CD8 T cells out of live cells (n = 3 human donors/group). F, Percentage of Tregs out of CD4 population (measured by CD25high-CD127Low). G, Percentage of CD8T effector memory (Tem), CD8T central memory (Tcm), and CD8T stem-cell memory (Tscm) as measured by gating with CD45RO and CD62L. H, Percentage of long-lived memory CD8⁺ T cells, measured by coexpression of CD127 and CD62L. Statistics shown are one-way or two-way ANOVAs (G) relative to the DMSO vehicle group.

FIGURE 4

IOA-244 remodels the immune microenvironment and allow ICB-driven antitumor immune response. Flow cytometry analysis from CT26 tumors showing quantification of CD45⁺ cells (A), CD8/CD45 (B), CD4/CD45 (C), mMDSC/CD45 (D), gMDSC/CD45 (E). F and G, Efficacy of IOA-244 alone or combined with anti-PD-L1 in the LLC (H and I), A20 (H–I) and Pan-02 (J and K) syngeneic mouse tumor models, measuring tumor volumes. Statistics shown are two-way ANOVAs (Tukey multiple comparison test).