Design considerations of an IL13Rα2 antibody-drug conjugate for diffuse intrinsic pontine glioma

Abstract

Diffuse intrinsic pontine glioma (DIPG), a rare pediatric brain tumor, afflicts approximately 350 new patients each year in the United States. DIPG is noted for its lethality, as fewer than 1% of patients survive to five years. Multiple clinical trials involving chemotherapy, radiotherapy, and/or targeted therapy have all failed to improve clinical outcomes. Recently, high-throughput sequencing of a cohort of DIPG samples identified potential therapeutic targets, including interleukin 13 receptor subunit alpha 2 (IL13Rα2) which was expressed in multiple tumor samples and comparably absent in normal brain tissue, identifying IL13Rα2 as a potential therapeutic target in DIPG. In this work, we investigated the role of IL13Rα2 signaling in progression and invasion of DIPG and viability of IL13Rα2 as a therapeutic target through the use of immunoconjugate agents. We discovered that IL13Rα2 stimulation via canonical ligands demonstrates minimal impact on both the cellular proliferation and cellular invasion of DIPG cells, suggesting IL13Rα2 signaling is non-essential for DIPG progression in vitro. However, exposure to an anti-IL13Rα2 antibody-drug conjugate demonstrated potent pharmacological response in DIPG cell models both in vitro and ex ovo in a manner strongly associated with IL13Rα2 expression, supporting the potential use of targeting IL13Rα2 as a DIPG therapy. However, the tested ADC was effective in most but not all cell models, thus selection of the optimal payload will be essential for clinical translation of an anti-IL13Rα2 ADC for DIPG.

Keywords: Antibody–drug conjugates; Diffuse intrinsic pontine glioma; IL13Rα2; Immunotherapy; Pediatric cancer.

Fig. 1

Gene expression in DIPG. High-throughput RNA sequencing of 33 DIPG tumor samples vs. 20 normal brain samples across two cohorts. a IL13Rα2 tumor expression versus normal expression (p < 0.01). b Tumor-normal expression ratios of IL13Rα2 and IL13Rα1 across patient-matched DIPG samples (p < 0.01). c IL13Rα2 tumor expression versus normal expression (p < 0.0001). d Expression of IL13Rα2 in DIPG and GBM cell models (HEK293 as positive control) determined by immunoblotting. SF-8628, CHLA-200, DIPG-6, and DIPG-17 are IL13Rα2-high models, while DIPG-24 is IL13Rα2-low

Fig. 2

IL13Rα2 ligand stimulation growth and invasion assay results. Cell models were stimulated with IL13Rα2 ligands to determine effect of IL13Rα2-mediated signaling on cell proliferation and invasion. In a-d, cells were stimulated with recombinant IL-4 and IL-13 at concentrations between 0.5 and 100 ng/mL. In e–g, cells were stimulated with recombinant IL-13 at concentrations at 20 ng/mL, 50 ng/mL, and 100 ng/mL. a SF-8628 stimulated with recombinant human IL-4. b SF-8628 with recombinant human IL-13. c DIPG-24 stimulated with recombinant human IL-4. d DIPG-24 stimulated with recombinant human IL-13. e SF-8628 cellular invasion following IL-13 stimulation. f DIPG-24 cellular invasion following IL-13 stimulation. g CHLA-200 cellular invasion following IL-13 stimulation

Fig. 3

Results from anti-IL13Rα2::PBD ADC cell viability assays in DIPG/GBM cell models. a Cell viability following incubation with anti-IL13Rα2::PBD ADC for four DIPG cell models (DIPG-17, SF-8628, DIPG-6, DIPG-24) and one GBM cell model (CHLA-200). Values in parentheses are IC₅₀ values. b Cell viability of SF-8628 ex ovo xenograft following anti-IL13Rα2::PBD ADC treatment. The value in parentheses is the IC₅₀ value. Dose response points represent minimum n = 7 quail per concentration