O6.01 TARGETING THE IMMUNE CHECKPOINT NETWORK WITH MIR-138 EXERTS THERAPEUTIC EFFICACY IN MURINE MODELS OF GLIOMA

• Published in: Neuro-oncology (Charlottesville, Va.) Vol. 16; no. suppl 2; p. ii12
• Main Authors: Heimberger, A., Wei, J., Nduom, E., Kong, L., Ivan, C., Fuller, G. N., Gilbert, M. R., Conrad, C. A., Calin, G. A.
• Format: Journal Article
• Language: English
• Published: 01-09-2014
• ISSN: 1522-8517; 1523-5866
• DOI: 10.1093/neuonc/nou174.42

Antibody therapeutic targeting of the immune checkpoints CTLA-4 and PD-1 has demonstrated marked tumor regression in clinical trials; however, this requires multimodality treatment and has known toxicity. Furthermore, the targeting of one checkpoint often results in the up-regulation of another. MicroRNAs (miRNAs) can modulate gene transcripts, including those of tumor-mediated immune suppressive pathways and networks. Additionally, miRNAs can be delivered to the systemic immune compartment, which can initiate anti-tumor immune response, including within the central nervous system, thereby overcoming the confounding issue of miRNA delivery to the tumor. To identify potential immune modulatory miRNA therapeutics, we exploited human glioblastoma miRNA expression assays followed by a screening process of predicted binding sites in the 3' UTR of immune suppressive pathways and immune checkpoints. MiR-138 emerged as a leading candidate with three predicted binding sites in the 3' UTR of CTLA-4 and one within PD-1, which was functionally confirmed with luciferase expression assays. The miR-138 targeting of CTLA-4 and PD-1 was further validated by expression analysis of transfected human CD4+ T cells. Using human glioma tumor microarrays and in situ hybridization, heterogeneous expression of miR-138 was found amongst all glioma grades and pathological subtypes. The PD-1 ligand, PD-L1, was frequently expressed in glioblastomas based on immunohistochemistry and ex vivo flow cytometry from fresh human glioblastoma. Analysis of TCGA database revealed that co-expression of PD-1 and PD-L1 impacts glioblastoma survival. Given the previously documented role of CTLA-4 as an operational mechanism of glioblastoma-mediated immune suppression, this cumulative data suggests that dual targeting of CTLA-4 and PD-1 with miR-138 in glioblastoma patients may have anti-tumor activity. In vivo treatment with miR-138 in immune-competent mice with GL261 gliomas demonstrated marked tumor regression, a 43% increase in median survival (P = 0.011), and an associated decrease in intratumoral FoxP3+ Tregs, CTLA-4, and PD-1 expression. Conversely, in an immune-incompetent animal background, miR-138 failed to exert any therapeutic effect, indicating that miR-138 mediates in vivo activity via the immune system. Cumulatively, our data indicate that miR-138 may be an active and novel immunotherapeutic agent for human glioblastoma patients.