Up to 60% of ovarian clear cell carcinomas (OCCC) have inactivating mutations in the ARID1A tumor suppressor gene. These mutations are known genetic drivers of this type of cancer, which typically does not respond to chemotherapy and carries the worst prognosis among all subtypes of ovarian cancer. ARID1A/BAF250 is part of a protein complex called SWI/SNF that modulates gene expression and chromatin remodeling. Beside the OCCC tumor, his gene has been commonly found mutated in gastric cancers and pancreatic cancer. In breast cancer distant metastases acquire inactivation mutations in ARID1A not seen in the primary tumor. This is thought to confer advantage to metastatic cells to become less sensitive to chemotherapy drugs. Scientists at The Wistar Institute, discovered that inactivating the ARID1A gene in ovarian cancer increase utilization of the glutamine amino acid making cancer cells dependent on glutamine metabolism. Researchers also showed that pharmacologic inhibition of glutamine metabolism may represent an effective therapeutic strategy for ARID1A-mutant ovarian cancer.
Since metabolism reprogramming is an hallmark of cancers, the authors investigated the transcriptional effect of ARID1A inactivation and found that GLS1, which encodes for the glutaminase enzyme, was the top upregulated gene among those controlling glutamine metabolism. Accordingly, GLS1 was expressed at significantly higher levels in tumor samples from patients with other cancer types that also carry mutations in the SWI/SNF complex. Mutations in this protein complex could be advantageous for cancer cells in another manner. ARID1A possesses at least two conserved pivotal domains for its function. First, it has an ARID domain, which is a DNA-binding domain that can specifically bind an AT-rich DNA sequences. Second, the C-terminus of the protein can stimulate glucocorticoid receptor-dependent transcriptional activation. Glucocorticoid dependent transcription is linked to the expression of genes involved in anti-inflammatory response and suppression of cell replication. This is something that tumor cells do not like. Both an inflammatory response and an higher proliferative rate are some of the classical feaature of a tumor.
Metastatization is linked to the expression of metalloproteases (MMPs), in order to degrade extracellular matrix main protein, i.e. collagen and propagate in the whole body. MMPs are classically repressed by glucocorticoids in the context of several inflammatory conditions like autoimmunities and osteoarthrosis. The fact that ovarian and breast cancer metastases loose ARID1A gene could be also for this reason, beyond to regulate a metabolic dependence on glutamine. The researchers at The Wistar Institute Cancer Center, are studying the effects of ARID1A inactivation to devise new mechanism-guided therapeutic strategies and combination approaches to enhance immunotherapy for ovarian cancer. The authors inactivated ARID1A in wild type ovarian cancer cells and observed increased glutamine consumption. Glutamine is normally required for cancer cells to grow, but ARID1A-mutant cells show a stronger dependence on this amino acid, which significantly enhanced the growth suppression induced by glutamine deprivation. Then scientists evaluated the therapeutic potential of inhibiting the glutamine metabolism by blocking the glutaminase enzyme with an inhibitor called Telanglenastat.
This molecule is under investigation in clinical trials and is well tolerated as a single agent and in combination with other anticancer therapies. When tested in vivo on OCCC mouse models, the drug significantly reduced tumor burden and prolonged survival. These studies were expanded to mice carrying patient-derived tumor transplants, confirming that telanglenastat impaired the growth of ARID1A-mutant but not ARID1A-wildtype tumors. Researchers also combined telanglenastat with anti-PDL1 treatment, revealing a synergy between glutaminase inhibitors and immune checkpoint blockade in suppressing the growth of ARID1A-mutant ovary tumors. Glutaminase inhibitors could become a new strategy to precisely target a specific vulnerability of OCCC cells associated with loss of ARID1A function. Other studies, are aiming with the same rationale to breast cancer. Scientists utilized human MDA-MB-231 and mouse 4T1 models that closely mimic human breast cancer metastasis. The MDA-MB-231 cells isolated after bone metastases showed reduced glucose uptake and glycolysis compared to parental cells, suggesting that these cells could shift their metabolic requirements for survival. Investigating glutamine, a common non-essential amino acid, in reduced glucose conditions both cell lines showed dependence on glutamine for cell survival. Glutamine withdrawal significantly increased the rate of programmed cell death (apoptosis). Glutamine was also critical for normal cell proliferation even in the presence of high glucose concentrations.
This means that these metastatic cells have undergo to a metabolic switch and researchers were able to pinpoint the hinge in the protein kinase C zeta (PKC-ζ). A seven-fold downregulation of protein PKC-ζ expression levels in bone-derived MDA-MB-231 (triple negative lineage; TNBC) cells was seen compared to the parental population. The PKC-ζ levels were also significantly reduced in metastatic 4T1 cells, compared to non-metastatic MT1A2 cells. It is known that PKC-ζ deficiency promotes glutamine utilization via serine biosynthesis. Indeed, levels of enzymes involved in serine biosynthesis, phosphoglycerate dehydrogenase (3-PGDH), phosphoserine phosphatase (PSPH) and phosphoserine aminotransferase (PSAT1) showed upregulation following glucose deprivation with PKC-ζ deficiency. A more complicated yet complementary picture involves the regulation of another enzyme of the glutamine metabolism, called glutaminase (GLS). The rate-limiting step in glutamine metabolism is the conversion of glutamine to glutamate, which is catalyzed by the enzyme glutaminase. Glutaminase exists in several tissue-specific variants, encoded by two genes in mammals, kidney-type glutaminase (GLS1), and liver-type glutaminase (GLS2). GLS1 plays a central role in tumorigenesis, whereas the role of GLS2 in cancer remains unclear.
GLS1 has been found to be higher expressed in TNBC compared to other subgroups of breast cancer and is essential for the survival of these cells with a deregulated glutamine breakdown. Telanglenastat is found to be specific to GLS1 and not to GLS2. And MDA-MB-231 cell lines display a higher sensitivity to this drug compared to estrogen-positive cell lines. Tumor cell-specific loss of glutaminase can improve anti-tumor T cell activation in both a spontaneous mouse TNBC model and tumor grafts. The glutamine transporter inhibitor V-9302 selectively blocked glutamine uptake by TNBC cells but not CD8+ T lymphocytes since they do not express ASCT2, a transporter for aminoacids like alanine, serine, cysteine but also glutamine. This way, lymphocytes may go undisturbed in synthesis of GSH, a major cellular antioxidant to improve their effector function. This might lay the foundation for a better immunotherapy protocols. For example, immune checkpoint inhibitors and adoptive tumor-infiltrating lymphocyte (TIL) therapies have profoundly improved the survival of melanoma patients. However, a majority of patients do not respond to these agents, and many responders experience disease relapse.
While numerous innovative treatments are being explored to offset the limitations of these agents, novel therapeutic combinations with immunotherapies have the potential to improve patient responses. In a very recently published study, scientists from The University of Texas MD Anderson Cancer Center investigated the anti-melanoma activity of immunotherapy combinations with Telaglenastat. In in vitro TIL-tumor co-culture studies, the drug treatment improved the cytotoxic activity of autologous TILs on patient-derived melanoma cells. The conversion of glutamine to alpha-ketoglutarate (αKGA) was more potently affected in tumor cells versus TILs in these co-cultures. These results suggest that telanglenastat may weaken cancer cells while sparing any toxicity against immune cells. When administered to grafted mice, the inhibitor activated melanoma antigen-specific T cells, and improved their tumor killing activity in an immune-competent mouse model of adoptive T cell therapy. Additionally, combination with anti-PD1 or anti-CTLA4 antibodies increased tumor infiltration by effector T cells and improved the anti-tumor activity of these checkpoint inhibitors in a high mutation burden mouse melanoma model.
It looks like that another avenue is already opened, to be taken advantage of. But it is an old acquaintance: glutamine antagonists have been tried in the past to cure carcinomas and sarcomas, though with poor outcomes. The main reason was the high toxicity of these drugs, namely azaserine and L-DON. However, with a more accurate undestanding of the glutamine network, the linkage of oncogenes with metabolic enzymes and the improvements of the modern medicinal chemistry, old glories could come back to the fore. Very recently, for example, Johns Hopkins scientists have obtained concrete results on the use of glutamine-driven cellular interference against chemoresistant ovary cancer.
After all, drug repurposing is now a convenient trend.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
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