BioProject

Malignant gliomas are common and aggressive primary brain tumors which are incurable by conventional therapies. Immunotherapy with the immune checkpoint inhibitors is not effective due to the highly immunosuppressive tumor microenvironment (TME). Clinical and experimental data show upregulation of Arginase1 (ARG1) expression in rodent and human malignant gliomas. The elevated ARG1 activity leads to depletion of L-arginine required for proliferation of T lymphocytes and natural killer cells. Inhibition of ARG1 in TME may unblock T cell proliferation and activate effective antitumor responses. To explore an antitumor potential of ARG1 inhibition, first we analyzed bulk and single cell RNA sequencing (scRNA-seq) data from human and murine gliomas, and found upregulation of ARG1 expression in malignant gliomas, both in tumor cells and in tumor infiltrating microglia, monocytes/macrophages. We employed the novel, selective arginase inhibitor - OAT-1746 to interfere with microglia-induced glioma invasion in microglia-glioma co-cultures. We determined its antitumor efficacy as a monotherapy and in combination with immunotherapy. In a Matrigel invasion assay OAT-1746 blocked microglia-dependent invasion of U87-MG and LN18 glioma cells better than reference compounds, without affecting cell viability. OAT-1746 effectively crossed the BBB and increased arginine levels in brains of GL261 glioma bearing mice. The compound reduced glioma growth and increased antitumor effects of the anti-PD-1 antibody. Treatment with OAT-1746 modified TME as demonstrated by profound transcriptomic changes visualized by RNA sequencing. Our findings provide the evidence that inhibition of ARG1 in tumor cells and myeloid cells in TME abolishes the immunosuppressive reprograming of myeloid cells and improves the efficacy of immunotherapy. Overall design: RNA libraries for sequencing were prepared using a KAPA Stranded mRNA-Seq Kit (Kapa Biosystems, MA, USA) Poly-A mRNAs were purified from 100ng of total RNA using poly-T-oligo-magnetic beads. First-strand cDNA was synthesized using reverse transcriptase and random hexamers. Second cDNA synthesis was performed by removing RNA templates and synthesizing replacement strands, incorporating dUTP in place of dTTP to generate double-stranded (ds) cDNA. Libraries were loaded at a concentration of 8,5 pM onto a rapid run flow cell and were paired-end sequenced on an Illumina HiSeq 1500. Illumina-specific adapters, short reads and low quality 5' and 3' bases were filtered out in the FASTQ format files using Trimmomatic tool. Resulting RNA sequencing reads were aligned to a reference mouse genome sequence. differential expression analysis was performed to identify transcriptomic differences across groups. Gene Ontology Biological Processes (GO: BP) was employed to better understand the mechanistic insights of enriched gene lists. The variance stabilizing transformation (vst function) was used for visualization purposes. A pathway enrichment analysis was performing by selecting statistically significantly genes (adjusted p-values < 0.05) and type I errors in multiple testing was corrected using the Bonferroni-Hochberg (BH) method.