Serum Glutamate Levels Correlate with Gleason Score and Glutamate Blockade Decreases Proliferation, Migration, and Invasion and Induces Apoptosis in Prostate Cancer Cells

Abstract

Purpose During glutaminolysis, glutamine is catabolized to glutamate and incorporated into citric acid cycle and lipogenesis. Serum glutamate levels were measured in patients with primary prostate cancer (PCa) or metastatic castrate-resistant PCa (mCRPCa) to establish clinical relevance. The effect of glutamate-deprivation or blockade by metabotropic glutamate receptor 1 (GRM1)-antagonists was investigated on PCa cells’ growth, migration, and invasion to establish biological relevance. Experimental Design Serum glutamate levels were measured in normal men (n = 60) and patients with primary PCa (n = 197) or mCRPCa (n = 109). GRM1 expression in prostatic tissues was examined using immunohistochemistry (IHC). Cell growth, migration, and invasion were determined using cell cytotoxicity and modified Boyden chamber assays, respectively. Apoptosis was detected using immunoblotting against cleaved caspases, PARP and γ-H2AX. Results Univariate and multivariate analyses demonstrated significantly higher serum glutamate levels in Gleason score ≥ 8 than in the Gleason sscore ≤ 7 and in African Americans than in the Caucasian Americans. African Americans with mCRPCa significantly higher serum glutamate levels than those with primary PCa or benign prostate. However, in Caucasian Americans, serum glutamate levels were similar in normal research subjects and patients with mCRPC. IHC demonstrated weak or no expression of GRM1 in luminal acinar epithelial cells of normal or hyperplastic glands, but high expression in primary or metastatic PCa tissues. Glutamate deprivation or blockade decreased PCa cells’ proliferation, migration, and invasion and led to apoptotic cell death. Conclusions Glutamate expression is mechanistically associated with and may provide a biomarker of PCa aggressiveness.

18F-fluorodeoxyglucose PET/CT for detection of disease in patients with prostate-specific antigen relapse following radical treatment of a local-stage prostate cancer

“…In the future, an increased and altered glutamate metabolism is being considered as a biological marker for patients with a Gleason score >8, i.e., for those with aggressive PCa. In aggressive PCa, increased glutamate metabolism increases the rate of positive subjects and also affects sensitivity due to increased FDG-PET activity (36). A strong correlation exists between the Warburg effect and the mitochondrial metabolism of the tumor cells, even in the patients with normal PSA values, suggesting that 18 F-FDG PET/CT may be used in such patients (37).…”

Glutamate, a metabolic biomarker of aggressiveness and a potential therapeutic target for prostate cancer

“…One important characteristic of glutamate is that its level in the systemic circulation is kept within a stable range 3,4 and its abnormal circulatory level reflects pathological conditions or disturbances in metabolic homeostasis as has been shown in our study. 5 To examine clinical significance of glutamate in PCa, serum glutamate levels were examined in healthy adult males (n560) and patients with primary PCa (n5197) or metastatic castrate-resistant PCa (n5109). Statistical analyses showed a significant positive correlation between serum glutamate and Gleason score (f7 vs. o8) both in African Americans and Caucasian Americans.…”

“…Glutamate levels for both the African Americans and Caucasian Americans followed the same general trend within aggressiveness subgroups of primary PCa, but diverged greatly when going from the high aggressiveness subgroup (Gleason sum o8, or prostate-specific antigen .20 ng ml 21 , or Gleason sum57, and stage cT3-cT4) to the metastatic castrateresistant PCa. 5 The biological relevance of glutamate in PCa cells was established by testing the effect of glutamate deprivation or pharmacological antagonists in PCa cells. Glutamate deprivation or blockade with metabotropic glutamate receptor 1 (GRM1)-antagonists (i.e., Riluzole, BAY 36-7620) decreased PCa cell growth, migration and invasion, and led to apoptotic-cell death as demonstrated by dose-dependent increases in cleaved caspases-3, -7 and -9, poly (ADP-ribose) polymerase (PARP) and phospho-H2AXSer 139 levels.…”

“…Glutamate deprivation or blockade with metabotropic glutamate receptor 1 (GRM1)-antagonists (i.e., Riluzole, BAY 36-7620) decreased PCa cell growth, migration and invasion, and led to apoptotic-cell death as demonstrated by dose-dependent increases in cleaved caspases-3, -7 and -9, poly (ADP-ribose) polymerase (PARP) and phospho-H2AXSer 139 levels. 5 Glutamate can enter mammalian cells by glutamate transporters (GT), ionotropic glutamate receptors (iGluRs) or metabotropic glutamate receptors (mGluRs). The expression of various members of glutamate uptake/ receptors system in PCa is not known.…”

“…In addition, GRM1 expression in androgen-stimulated LNCaP or primary African American (i.e., E006AA) PCa cell lines was less than androgen-independent PC-3, DU145 and androgen-independent bone metastatic PCa cell lines including VCaP and MDA-PCa 2b (of African American origin). 5 Large-scale immunohistochemical studies are required to cover a range of clinical conditions (e.g., BPH, normal glands, primary or metastatic PCa from untreated patients, castrate-resistant primary or metastatic tumors, etc.) and racial groups (Caucasian Americans and African Americans).…”