IL-13 receptors as possible therapeutic targets in diffuse intrinsic pontine glioma

Abstract

Diffuse intrinsic pontine glioma (DIPG) is a universally fatal childhood cancer of the brain. Despite the introduction of conventional chemotherapy and radiotherapy, improvements in survival have been marginal and long-term survivorship is uncommon. Thus, new targets for therapeutics are critically needed. Early phase clinical trials exploring molecularly-targeted therapies against the epidermal growth factor receptor (EGFR) and novel immunotherapies targeting interleukin receptor-13α2 (IL-13Rα2) have demonstrated activity in this disease. To identify additional therapeutic markers for cell surface receptors, we performed exome sequencing (16 new samples, 22 previously published samples, total 38 with 26 matched normal DNA samples), RNA deep sequencing (17 new samples, 11 previously published samples, total 28 with 18 matched normal RNA samples), and immunohistochemistry (17 DIPG tissue samples) to examine the expression of the interleukin-4 (IL-4) signaling axis components (IL-4, interleukin 13 (IL-13), and their respective receptors IL-4Rα, IL-13Rα1, and IL-13Rα2). In addition, we correlated cytokine and receptor expression with expression of the oncogenes EGFR and c-MET. In DIPG tissues, transcript-level analysis found significant expression of IL-4, IL-13, and IL-13Rα1/2, with strong differential expression of IL-13Rα1/2 in tumor versus normal brain. At the protein level, immunohistochemical studies revealed high content of IL-4 and IL-13Rα1/2 but notably low expression of IL-13. Additionally, a strong positive correlation was observed between c-Met and IL-4Rα. The genomic and transcriptional landscape across all samples was also summarized. These data create a foundation for the design of potential new immunotherapies targeting IL-13 cell surface receptors in DIPG.

Fig 1. Landscape of exome mutations and differential gene expression of frequently-mutated DIPG genes and IL-4 pathway targets in DIPG samples.

(A) Mutational landscape of frequently-mutated DIPG genes and IL-family genes. Exome sequencing was performed on 38 DIPG samples to identify somatic mutations and copy number variations. When possible, tumor samples were compared against matched normal samples. (B) Gene expression of frequently-mutated DIPG genes and IL-family genes. The set of genes is identical to those in Fig A. RNA sequencing was performed on 28 DIPG samples: 18 tumor samples with matched normal samples, 10 unmatched tumor samples. Average fold change and tumor vs. normal p-values were calculated across the set of expressed genes. Note that IL-13Rα1 and IL-13Rα2 are significantly overexpressed in tumor compared to normal, but are mutationally silent.

Fig 2. Immunohistochemical studies of the IL-4R signaling axis, EGFR and c-Met protein expression.

Representative immunohistochemical staining of DIPG archival cases for (A) IL-4 (B) IL-4Rα (C) IL-13 (D) IL-13Rα1 (E) IL-13Rα2 (F) EGFR (G) c-Met.