Inhibition of de novo purine synthesis in human prostate cells results in ATP depletion, AMPK activation and induces senescence

A Drug Repositioning Approach Identifies a Combination of Compounds as a Potential Regimen for Chronic Lymphocytic Leukemia Treatment

Drug repositioning is a promising and powerful innovative strategy in the field of drug discovery. In this study, we screened a compound-library containing 800 Food and Drug Administration approved drugs for their anti-leukemic effect. All screening activities made use of human peripheral blood mononuclear cells (PBMCs), isolated from healthy or leukemic donors. Compounds with confirmed cytotoxicity were selected and classified in three groups: i) anti-neoplastic compounds which are drugs used in leukemia treatment, ii) compounds known to have an anti-cancer effect and iii) compounds demonstrating an anti-leukemic potential for the first time. The latter group was the most interesting from a drug repositioning perspective and yielded a single compound, namely Isoprenaline which is a non-selective β-adrenergic agonist. Analysis of the cytotoxic effect of this drug indicated that it induces sustainable intracellular ATP depletion leading, over time, to necrotic cell death. We exploited the Isoprenaline-induced intracellular ATP depletion to sensitize primary leukemic cells to fludarabine (purine analogue) and Ibrutinib (Bruton's tyrosine kinase inhibitor) treatment. In-vitro treatment of primary leukemic cells with a combination of Isoprenaline/fludarabine or Isoprenaline/Ibrutinib showed a very high synergistic effect. These combinations could constitute a new efficient regimen for CLL treatment following successful evaluation in animal models and clinical trials.

Bifunctional enzyme ATIC promotes propagation of hepatocellular carcinoma by regulating AMPK-mTOR-S6 K1 signaling

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the cancer types with poor prognosis. To effectively treat HCC, new molecular targets and therapeutic approaches must be identified. 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/inosine monophosphate (IMP) cyclohydrolase (ATIC), a bifunctional protein enzyme, catalyzes the last two steps of the de novo purine biosynthetic pathway. Whether ATIC contributes to cancer development remains unclear.

METHODS

ATIC mRNA levels in different types of human HCC samples or normal tissues were determined from Gene Expression across Normal and Tumor tissue (GENT) database. The expression level of ATIC in human HCC samples or cell lines were examined by RT-PCR and western blot. Overall survival and disease-free survival of HCC patients in the ATIC low and ATIC high groups were determined by Kaplan-Meier analysis. Effects of ATIC knockdown by lentivirus infection were evaluated on cell-proliferation, cell-apoptosis, colony formation and migration. The mechanisms involved in HCC cells growth, apoptosis and migration were analyzed by western blot and Compound C (C-C) rescue assays.

RESULTS

Here, we first demonstrated that expression of ATIC is aberrantly up-regulated in HCC tissues and high level of ATIC is correlated with poor survival in HCC patients. Knockdown of ATIC expression resulted in a dramatic decrease in proliferation, colony formation and migration of HCC cells. We also identified ATIC as a novel regulator of adenosine monophosphate-activated protein kinase (AMPK) and its downstream signaling mammalian target of rapamycin (mTOR). ATIC suppresses AMPK activation, thus activates mTOR-S6 K1-S6 signaling and supports growth and motility activity of HCC cells.

CONCLUSION

Taken together, our results indicate that ATIC acts as an oncogenic gene that promotes survival, proliferation and migration by targeting AMPK-mTOR-S6 K1 signaling.

Endocrine-related cancers and the role of AMPK

AMP-activated protein kinase (AMPK) is a master regulator of energy homeostasis involved in the regulation of a number of physiological processes including β-oxidation of fatty acids, lipogenesis, protein and cholesterol synthesis, as well as cell cycle inhibition and apoptosis. Important changes to these processes are known to occur in cancer due to changes in AMPK activity within cancer cells and in the periphery. This review aims to present findings relating to the role and regulation of AMPK in endocrine-related cancers. Obesity is a known risk factor for many types of cancers and a number of endocrine factors, including adipokines and steroid hormones, are regulated by and regulate AMPK. A clear role for AMPK in breast cancer is evident from the already impressive body of work published to date. However, information pertaining to its role in prostate cancer is still contentious, and future work should unravel the intricacies behind its role to inhibit, in some cases, and stimulate cancer growth in others. This review also presents data relating to the role of AMPK in cancers of the endometrium, ovary and colon, and discusses the possible use of AMPK-activating drugs including metformin for the treatment of all endocrine-related cancers.

Metabolomic fingerprint reveals that metformin impairs one-carbon metabolism in a manner similar to the antifolate class of chemotherapy drugs

Metabolomic fingerprint of breast cancer cells treated with the antidiabetic drug metformin revealed a significant accumulation of 5-formimino-tetrahydrofolate, one of the tetrahydrofolate forms carrying activated one-carbon units that are essential for the de novo synthesis of purines and pyrimidines. De novo synthesis of glutathione, a folate-dependent pathway interconnected with one-carbon metabolism was concomitantly depleted in response to metformin. End-product reversal studies demonstrated that thymidine alone leads to a significant but incomplete protection from metformin's cytostatic effects. The addition of the substrate hypoxanthine for the purine salvage pathway produces major rightward shifts in metformin's growth inhibition curves. Metformin treatment failed to activate the DNA repair protein ATM kinase and the metabolic tumor suppressor AMPK when thymidine and hypoxanthine were present in the extracellular milieu. Our current findings suggest for the first time that metformin can function as an antifolate chemotherapeutic agent that induces the ATM/AMPK tumor suppressor axis secondarily following the alteration of the carbon flow through the folate-related one-carbon metabolic pathways.

Activation of p21-Dependent G1/G2 Arrest in the Absence of DNA Damage as an Antiapoptotic Response to Metabolic Stress

The folate enzyme, FDH (10-formyltetrahydrofolate dehydrogenase, ALDH1L1), a metabolic regulator of proliferation, activates p53-dependent G1 arrest and apoptosis in A549 cells. In the present study, we have demonstrated that FDH-induced apoptosis is abrogated upon siRNA knockdown of the p53 downstream target PUMA. Conversely, siRNA knockdown of p21 eliminated FDH-dependent G1 arrest and resulted in an early apoptosis onset. The acceleration of FDH-dependent apoptosis was even more profound in another cell line, HCT116, in which the p21 gene was silenced through homologous recombination (p21(-/-) cells). In contrast to A549 cells, FDH caused G2 instead of G1 arrest in HCT116 p21(+/+) cells; such an arrest was not seen in p21-deficient (HCT116 p21(-/-)) cells. In agreement with the cell cycle regulatory function of p21, its strong accumulation in nuclei was seen upon FDH expression. Interestingly, our study did not reveal DNA damage upon FDH elevation in either cell line, as judged by comet assay and the evaluation of histone H2AX phosphorylation. In both A549 and HCT116 cell lines, FDH induced a strong decrease in the intracellular ATP pool (2-fold and 30-fold, respectively), an indication of a decrease in de novo purine biosynthesis as we previously reported. The underlying mechanism for the drop in ATP was the strong decrease in intracellular 10-formyltetrahydrofolate, a substrate in two reactions of the de novo purine pathway. Overall, we have demonstrated that p21 can activate G1 or G2 arrest in the absence of DNA damage as a response to metabolite deprivation. In the case of FDH-related metabolic alterations, this response delays apoptosis but is not sufficient to prevent cell death.

Oxidation in the nucleotide pool, the DNA damage response and cellular senescence: Defective bricks build a defective house

Activation of persistent DNA damage response (DDR) signaling is associated with the induction of a permanent proliferative arrest known as cellular senescence, a phenomenon intrinsically linked to both tissue aging as well as tumor suppression. The DNA damage observed in senescent cells has been attributed to elevated levels of reactive oxygen species (ROS), failing DNA damage repair processes, and/or oncogenic activation. It is not clear how labile molecules such as ROS are able to damage chromatin-bound DNA to a sufficient extent to invoke persistent DNA damage and DDR signaling. Recent evidence suggests that the nucleotide pool is a significant target for oxidants and that oxidized nucleotides, once incorporated into genomic DNA, can lead to the induction of a DNA strand break-associated DDR that triggers senescence in normal cells and in cells sustaining oncogene activation. Evasion of this DDR and resulting senescence is a key step in tumor progression. This review will explore the role of oxidation in the nucleotide pool as a major effector of oxidative stress-induced genotoxic damage and DDR in the context of cellular senescence and tumorigenic transformation.

Inference of combinatorial Boolean rules of synergistic gene sets from cancer microarray datasets

MOTIVATION

Gene set analysis has become an important tool for the functional interpretation of high-throughput gene expression datasets. Moreover, pattern analyses based on inferred gene set activities of individual samples have shown the ability to identify more robust disease signatures than individual gene-based pattern analyses. Although a number of approaches have been proposed for gene set-based pattern analysis, the combinatorial influence of deregulated gene sets on disease phenotype classification has not been studied sufficiently.

RESULTS

We propose a new approach for inferring combinatorial Boolean rules of gene sets for a better understanding of cancer transcriptome and cancer classification. To reduce the search space of the possible Boolean rules, we identify small groups of gene sets that synergistically contribute to the classification of samples into their corresponding phenotypic groups (such as normal and cancer). We then measure the significance of the candidate Boolean rules derived from each group of gene sets; the level of significance is based on the class entropy of the samples selected in accordance with the rules. By applying the present approach to publicly available prostate cancer datasets, we identified 72 significant Boolean rules. Finally, we discuss several identified Boolean rules, such as the rule of glutathione metabolism (down) and prostaglandin synthesis regulation (down), which are consistent with known prostate cancer biology.

AVAILABILITY

Scripts written in Python and R are available at http://biosoft.kaist.ac.kr/~ihpark/. The refined gene sets and the full list of the identified Boolean rules are provided in the Supplementary Material.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.