Targeting pyrimidine synthesis accentuates molecular therapy response in glioblastoma stem cells

Inhibition of HDAC1/2 Along with TRAP1 Causes Synthetic Lethality in Glioblastoma Model Systems

The heterogeneity of glioblastomas, the most common primary malignant brain tumor, remains a significant challenge for the treatment of these devastating tumors. Therefore, novel combination treatments are warranted. Here, we showed that the combined inhibition of TRAP1 by gamitrinib and histone deacetylases (HDAC1/HDAC2) through romidepsin or panobinostat caused synergistic growth reduction of established and patient-derived xenograft (PDX) glioblastoma cells. This was accompanied by enhanced cell death with features of apoptosis and activation of caspases. The combination treatment modulated the levels of pro- and anti-apoptotic Bcl-2 family members, including BIM and Noxa, Mcl-1, Bcl-2 and Bcl-xL. Silencing of Noxa, BAK and BAX attenuated the effects of the combination treatment. At the metabolic level, the combination treatment led to an enhanced reduction of oxygen consumption rate and elicited an unfolded stress response. Finally, we tested whether the combination treatment of gamitrinib and panobinostat exerted therapeutic efficacy in PDX models of glioblastoma (GBM) in mice. While single treatments led to mild to moderate reduction in tumor growth, the combination treatment suppressed tumor growth significantly stronger than single treatments without induction of toxicity. Taken together, we have provided evidence that simultaneous targeting of TRAP1 and HDAC1/2 is efficacious to reduce tumor growth in model systems of glioblastoma.

High expression levels of pyrimidine metabolic rate-limiting enzymes are adverse prognostic factors in lung adenocarcinoma: a study based on The Cancer Genome Atlas and Gene Expression Omnibus datasets

Reprogramming of metabolism is described in many types of cancer and is associated with the clinical outcomes. However, the prognostic significance of pyrimidine metabolism signaling pathway in lung adenocarcinoma (LUAD) is unclear. Using the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) datasets, we found that the pyrimidine metabolism signaling pathway was significantly enriched in LUAD. Compared with normal lung tissues, the pyrimidine metabolic rate–limiting enzymes were highly expressed in lung tumor tissues. The high expression levels of pyrimidine metabolic–rate limiting enzymes were associated with unfavorable prognosis. However, purinergic receptors P2RX1, P2RX7, P2RY12, P2RY13, and P2RY14 were relatively downregulated in lung cancer tissues and were associated with favorable prognosis. Moreover, we found that hypo-DNA methylation, DNA amplification, and TP53 mutation were contributing to the high expression levels of pyrimidine metabolic rate–limiting enzymes in lung cancer cells. Furthermore, combined pyrimidine metabolic rate–limiting enzymes had significant prognostic effects in LUAD. Comprehensively, the pyrimidine metabolic rate–limiting enzymes were highly expressed in bladder cancer, breast cancer, colon cancer, liver cancer, and stomach cancer. And the high expression levels of pyrimidine metabolic rate–limiting enzymes were associated with unfavorable prognosis in liver cancer. Overall, our results suggested the mRNA levels of pyrimidine metabolic rate–limiting enzymes CAD, DTYMK, RRM1, RRM2, TK1, TYMS, UCK2, NR5C2, and TK2 were predictive of lung cancer as well as other cancers.

CRISPR/Cas9 knockout of human arylamine N-acetyltransferase 1 in MDA-MB-231 breast cancer cells suggests a role in cellular metabolism

Human arylamine N-acetyltransferase 1 (NAT1), present in all tissues, is classically described as a phase-II xenobiotic metabolizing enzyme but can also catalyze the hydrolysis of acetyl-Coenzyme A (acetyl-CoA) in the absence of an arylamine substrate using folate as a cofactor. NAT1 activity varies inter-individually and has been shown to be overexpressed in estrogen receptor-positive (ER+) breast cancers. NAT1 has also been implicated in breast cancer progression however the exact role of NAT1 remains unknown. The objective of this study was to evaluate the effect of varying levels of NAT1 N-acetylation activity in MDA-MB-231 breast cancer cells on global cellular metabolism and to probe for unknown endogenous NAT1 substrates. Global, untargeted metabolomics was conducted via ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) on MDA-MB-231 breast cancer cell lines constructed with siRNA and CRISPR/Cas9 technologies to vary only in NAT1 N-acetylation activity. Many metabolites were differentially abundant in NAT1-modified cell lines compared to the Scrambled parental cell line. N-acetylasparagine and N-acetylputrescine abundances were strongly positively correlated (r = 0.986 and r = 0.944, respectively) with NAT1 N-acetylation activity whereas saccharopine abundance was strongly inversely correlated (r = −0.876). Two of the most striking observations were a reduction in de novo pyrimidine biosynthesis and defective β-oxidation of fatty acids in the absence of NAT1. We have shown that NAT1 expression differentially affects cellular metabolism dependent on the level of expression. Our results support the hypothesis that NAT1 is not just a xenobiotic metabolizing enzyme and may have a role in endogenous cellular metabolism.

Dihydroorotate dehydrogenase in oxidative phosphorylation and cancer

Dihydroorotate dehydrogenase (DHODH) is an enzyme of the de novo pyrimidine synthesis pathway that provides nucleotides for RNA/DNA synthesis essential for proliferation. In mammalian cells, DHODH is localized in mitochondria, linked to the respiratory chain via the coenzyme Q pool. Here we discuss the role of DHODH in the oxidative phosphorylation system and in the initiation and progression of cancer. We summarize recent findings on DHODH biology, the progress made in the development of new, specific inhibitors of DHODH intended for cancer therapy, and the mechanistic insights into the consequences of DHODH inhibition.

A non-proliferative role of pyrimidine metabolism in cancer

Background

Nucleotide metabolism is a critical pathway that generates purine and pyrimidine molecules for DNA replication, RNA synthesis, and cellular bioenergetics. Increased nucleotide metabolism supports uncontrolled growth of tumors and is a hallmark of cancer. Agents inhibiting synthesis and incorporation of nucleotides in DNA are widely used as chemotherapeutics to reduce tumor growth, cause DNA damage, and induce cell death. Thus, the research on nucleotide metabolism in cancer is primarily focused on its role in cell proliferation. However, in addition to proliferation, the role of purine molecules is established as ligands for purinergic signals. However, so far, the role of the pyrimidines has not been discussed beyond cell growth.

Scope of the review

In this review we present the key evidence from recent pivotal studies supporting the notion of a non-proliferative role for pyrimidine metabolism (PyM) in cancer, with a special focus on its effect on differentiation in cancers from different origins.

Major conclusion

In leukemic cells, the pyrimidine catabolism induces terminal differentiation toward monocytic lineage to check the aberrant cell proliferation, whereas in some solid tumors (e.g., triple negative breast cancer and hepatocellular carcinoma), catalytic degradation of pyrimidines maintains the mesenchymal-like state driven by epithelial-to-mesenchymal transition (EMT). This review further broadens this concept to understand the effect of PyM on metastasis and, ultimately, delivers a rationale to investigate the involvement of the pyrimidine molecules as oncometabolites. Overall, understanding the non-proliferative role of PyM in cancer will lead to improvement of the existing antimetabolites and to development of new therapeutic options.

The multienzymatic protein CAD leading the de novo biosynthesis of pyrimidines localizes exclusively in the cytoplasm and does not translocate to the nucleus

CAD, the multienzymatic protein that initiates and controls the de novo biosynthesis of pyrimidines, plays a major role in nucleotide homeostasis, cell growth and proliferation. Despite its interest as a potential antitumoral target, there is a lack of understanding on CAD's structure and functioning mechanisms. Although mainly identified as a cytosolic complex, different studies support the translocation of CAD into the nucleus, where it could have a yet undefined function. Here, we track the subcellular localization of CAD by using fluorescent chimeras, cell fractionation and immunoblotting with specific antibodies. Contradicting previous studies, we demonstrate that CAD is exclusively localized at the cytosol and discard a possible translocation to the nucleus.

Targeting Glutamine Addiction in Gliomas

The most common malignant brain tumors are those of astrocytic origin, gliomas, with the most aggressive glioblastoma (WHO grade IV) among them. Despite efforts, medicine has not made progress in terms of the prognosis and life expectancy of glioma patients. Behind the malignant phenotype of gliomas lies multiple genetic mutations leading to reprogramming of their metabolism, which gives those highly proliferating cells an advantage over healthy ones. The so-called glutamine addiction is a metabolic adaptation that supplements oxidative glycolysis in order to secure neoplastic cells with nutrients and energy in unfavorable conditions of hypoxia. The present review aims at presenting the research and clinical attempts targeting the different metabolic pathways involved in glutamine metabolism in gliomas. A brief description of the biochemistry of glutamine transport, synthesis, and glutaminolysis, etc. will forego a detailed comparison of the therapeutic strategies undertaken to inhibit glutamine utilization by gliomas.

Cerpegin-derived furo[3,4-c]pyridine-3,4(1H,5H)-diones enhance cellular response to interferons by de novo pyrimidine biosynthesis inhibition

There is an increasing interest in the field of cancer therapy for small compounds targeting pyrimidine biosynthesis, and in particular dihydroorotate dehydrogenase (DHODH), the fourth enzyme of this metabolic pathway. Three available DHODH structures, featuring three different known inhibitors, were used as templates to screen in silico an original chemical library from Erevan University. This process led to the identification of P1788, a compound chemically related to the alkaloid cerpegin, as a new class of pyrimidine biosynthesis inhibitors. In line with previous reports, we investigated the effect of P1788 on the cellular innate immune response. Here we show that pyrimidine depletion by P1788 amplifies cellular response to both type-I and type II interferons, but also induces DNA damage as assessed by γH2AX staining. Moreover, the addition of inhibitors of the DNA damage response led to the suppression of the P1788 stimulatory effects on the interferon pathway. This demonstrates that components of the DNA damage response are bridging the inhibition of pyrimidine biosynthesis by P1788 to the interferon signaling pathway. Altogether, these results provide new insights on the mode of action of novel pyrimidine biosynthesis inhibitors and their development for cancer therapies.