Association of glutaminase expression with immune-suppressive tumor microenvironment, clinicopathologic features, and clinical outcomes in endometrial cancer.

OBJECTIVE

Increased glutamine metabolism by cancer cells via upregulation of the drug-targetable enzyme glutaminase may contribute to an immune-suppressive tumor microenvironment. Inhibiting glutamine metabolism can not only suppress tumor growth, but also enhance tumor-specific immunity. We investigated the relationship between glutaminase expression, the immune tumor microenvironment, and clinicopathologic features in endometrial cancer.

METHODS

Tissue microarrays constructed from 87 primary endometrial cancer specimens were stained by immunohistochemistry for glutaminase, c-Myc, mutL homolog 1 (MLH1), mutS homolog 2 (MSH2), mutS homolog 6 (MSH6), postmeiotic segregation increased 2 (PMS2), estrogen receptor (ER), progresterone receptor (PR), CD8, FoxP3, CD68, programmed cell death protein 1 (PD-1), and programmed cell death ligand 1 (PD-L1). We compared the immune tumor microenvironment and clinicopathologic features between glutaminase-high (H-score≥median) versus glutaminase-low (H-score<median) endometrial cancers. We also evaluated data from The Cancer Genome Atlas (TCGA) for 527 endometrial cancer patients in whom RNA-Seq for glutaminase expression was performed and compared long-term clinical outcomes between glutaminase-high (RNA-Seq Z-score≥median) versus glutaminase-low (RNA-Seq score<median) patients.

RESULTS

In the tissue microarray analysis, glutaminase expression was positively correlated with c-Myc expression (r=0.4226, p<0.0001). Glutaminase-high endometrial cancers were associated with non-endometrioid histology (p=0.0001), high histologic grade (p=0.0004), myometrial invasion (p=0.017), advanced stage (p=0.012), increased FoxP3+ regulatory T cells (p=0.008), increased CD68+ tumor-associated macrophages (p=0.010), and higher PD-L1 combined positive scores (p=0.043). In the TCGA analysis, glutaminase-high (RNA-Seq Z-score≥median) patients showed worse overall (p=0.004) and progression-free (p=0.032) survival than glutaminase-low (RNA-Seq score<median) patients.

CONCLUSIONS

Our findings indicate that increased glutaminase expression is associated with an immune-suppressive tumor microenvironment, poor clinicopathologic features, and worse long-term outcomes in patients with endometrial cancer.