Methionine restriction induces apoptosis of prostate cancer cells via the c-Jun N-terminal kinase-mediated signaling pathway

Rescue of Methionine Dependence by Cobalamin in a Human Colorectal Cancer Cell Line

Methionine dependence is a characteristic of most cancer cells where they are unable to proliferate when the essential amino acid methionine is replaced with its precursor homocysteine in the growing media. Normal cells, on the other hand, thrive under these conditions and are referred to as methionine-independent. The reaction that adds a methyl group from 5-methyltetrahydrofolate to homocysteine to regenerate methionine is catalyzed by the enzyme methionine synthase with the cofactor cobalamin (vitamin B12). However, decades of research have shown that methionine dependence in cancer is not due to a defect in the activity of methionine synthase. Cobalamin metabolism has been tied to the dependent phenotype in rare cell lines. We have identified a human colorectal cancer cell line in which the cells regain the ability to proliferation in methionine-free, L-homocystine-supplemented media when cyanocobalamin is supplemented at a level of 1 µg/mL. In human SW48 cells, methionine replacement with L-homocystine does not induce any measurable increase in apoptosis or reactive oxygen species production in this cell line. Rather, proliferation is halted, then restored in the presence of cyanocobalamin. Our data show that supplementation with cyanocobalamin prevents the activation of the integrated stress response (ISR) in methionine-deprived media in this cell line. The ISR-associated cell cycle arrest, characteristic of methionine-dependence in cancer, is also prevented, leading to the continuation of proliferation in methionine-deprived SW48 cells with cobalamin. Our results highlight differences between cancer cell lines in the response to cobalamin supplementation in the context of methionine dependence.

Differences in cell death in methionine versus cysteine depletion

Restriction of the sulfur amino acids methionine and cysteine has recently been proposed as potential adjuvant therapy in cancer. While cysteine depletion has been associated with ferroptotic cell death, methionine depletion has not. We hypothesized that comparing the response of melanoma cell lines to depletion of the amino acids methionine and cysteine would give us insight into the critical role in cancer of these two closely related amino acids. We analyzed the response to three conditions: methionine depletion, methionine replacement with homocysteine, and cysteine depletion. In cancer cells, the transcription factor ATF4 was induced by all three tested conditions. The replacement of methionine with homocysteine produced a strong ferroptotic gene signature. We also detected an activation of the NRF2 antioxidant pathway by both methionine and cysteine depletion. Total glutathione levels were decreased by 42% in melanoma cells grown without methionine, and by 95% in cells grown without cysteine. Lipid peroxidation was increased in cells grown without cysteine, but not in cells grown without methionine. Despite the large degree of overlap in gene expression between methionine and cysteine depletion, methionine depletion and replacement of methionine with homocysteine was associated with apoptosis while cysteine depletion was associated with ferroptosis. Glutamine depletion produced comparable gene expression patterns and was associated with a 28% decrease in glutathione. Apoptosis was detected in these cells. In this experiment, a strong ATF4-driven ferroptotic gene signature was insufficient to induce ferroptosis without a concomitant profound decrease in glutathione levels.

Methionine Restriction and Cancer Biology

The essential amino acid, methionine, is important for cancer cell growth and metabolism. A growing body of evidence indicates that methionine restriction inhibits cancer cell growth and may enhance the efficacy of chemotherapeutic agents. This review summarizes the efficacy and mechanism of action of methionine restriction on hallmarks of cancer in vitro and in vivo. The review highlights the role of glutathione formation, polyamine synthesis, and methyl group donation as mediators of the effects of methionine restriction on cancer biology. The translational potential of the use of methionine restriction as a personalized nutritional approach for the treatment of patients with cancer is also discussed.

Prostate cancer-specific hallmarks of amino acids metabolism: Towards a paradigm of precision medicine

So far multiple differences in prostate cancer-specific amino acids metabolism have been discovered. Moreover, attempts to utilize these alterations for prostate cancer diagnosis and treatment have been made. The prostate cancer metabolism and biosynthesis of amino acids are particularly focused on anaplerosis more than on energy production. Other crucial requirements on amino acids pool come from the serine, one‑carbon cycle, glycine synthesis pathway and folate metabolism forming major sources of interproducts for synthesis of nucleobases necessary for rapidly proliferating cells. Considering the lack of some amino acids biosynthetic pathways and/or their extraordinary importance for prostate cancer cells, there is a widespread potential for targeted therapeutic applications with no effect on non-malignant cells. This review summarizes the up-to-date knowledge of the importance of amino acids for prostate cancer pathogenesis with a special emphasis on potential applications of metabolic variabilities in the new oncologic paradigm of precision medicine.

Preclinical Breast Cancer Models to Investigate Metabolic Priming by Methionine Restriction

We have developed a novel therapeutic paradigm ("metabolic priming") for cancer whereby restriction of the essential amino acid methionine activates a number of cell-stress-response pathways that can be selectively targeted to enhance the therapeutic impact of methionine restriction. One example of metabolic priming is the combination of methionine restriction with proapoptotic TRAIL receptor-2 (TRAIL-R2) agonists. Methionine restriction enhances the cell surface expression of TRAIL-R2 selectively in transformed breast epithelial cells and renders them more susceptible to cell death induction by TRAIL-R2 agonists in cellular and murine models of breast cancer. This methods review focuses on preclinical models of breast cancer to investigate metabolic priming by methionine restriction. Multiple cell-based methods are detailed to measure cell viability, cell survival, caspase activity, apoptosis, and matrix detachment-induced cell death (anoikis). In addition, we describe an orthotopic model of metastatic breast cancer that utilizes mCherry-fluorescently-labeled human breast cancer cells. This model captures the entire metastatic cascade from the mammary gland to the lung and mimics key features of the human disease. These breast-cancer models can be readily adapted to other tumor types. Overall, we provide a stepwise, translationally-relevant approach to study metabolic priming in the context of cancer.

Amino Acid Profiling of Zinc Resistant Prostate Cancer Cell Lines: Associations With Cancer Progression

BACKGROUND

Failure in intracellular zinc accumulation is a key process in prostate carcinogenesis. Nevertheless, epidemiological studies of zinc administration have provided contradicting results. In order to examine the impact of the artificial intracellular increase of zinc(II) ions on prostate cancer metabolism, PNT1A, 22Rv1, and PC-3 prostatic cell lines-depicting different stages of cancer progression-and their zinc-resistant counterparts were used. To determine "benign" and "malignant" metabolic profiles, amino acid patterns, gene expression, and antioxidant capacity of these cell lines were assessed.

METHODS

Amino acid profiles were examined using an ion-exchange liquid chromatography. Intracellular zinc content was measured by atomic absorption spectrometry. Metallothionein was quantified using differential pulse voltammetry. The content of reduced glutathione was determined using high performance liquid chromatography coupled with an electrochemical detector. Cellular antioxidant capacity was determined by the ABTS test and gene expression analysis was performed by qRT-PCR.

RESULTS AND CONCLUSIONS

Long-term zinc treatment was shown to reroute cell metabolism from benign to more malignant type. Long-term application of high concentration of zinc(II) significantly enhanced cisplatin resistance, invasiveness, cellular antioxidant capacity, synthesis of glutathione, and expression of treatment resistance- and stemness-associated genes (SOX2, POU5F1, BIRC5). Tumorous cell lines universally displayed high accumulation of aspartate and sarcosine and depletion of essential amino acids. Increased aspartate/threonine, aspartate/methionine, and sarcosine/serine ratios were associated with cancer phenotype with high levels of sensitivity and specificity. Prostate 77: 604-616, 2017. © 2017 Wiley Periodicals, Inc.

Pleiotropic responses to methionine restriction

Methionine restriction (MR) extends lifespan across different species. The main responses of rodent models to MR are well-documented in adipose tissue (AT) and liver, which have reduced mass and improved insulin sensitivity, respectively. Recently, molecular mechanisms that improve healthspan have been identified in both organs during MR. In fat, MR induced a futile lipid cycle concomitant with beige AT accumulation, producing elevated energy expenditure. In liver, MR upregulated fibroblast growth factor 21 and improved glucose metabolism in aged mice and in response to a high-fat diet. Furthermore, MR also reduces mitochondrial oxidative stress in various organs such as liver, heart, kidneys, and brain. Other effects of MR have also been reported in such areas as cardiac function in response to hyperhomocysteinemia (HHcy), identification of molecular mechanisms in bone development, and enhanced epithelial tight junction. In addition, rodent models of cancer responded positively to MR, as has been reported in colon, prostate, and breast cancer studies. The beneficial effects of MR have also been documented in a number of invertebrate model organisms, including yeast, nematodes, and fruit flies. MR not only promotes extended longevity in these organisms, but in the case of yeast has also been shown to improve stress tolerance. In addition, expression analyses of yeast and Drosophila undergoing MR have identified multiple candidate mediators of the beneficial effects of MR in these models. In this review, we emphasize other in vivo effects of MR such as in cardiovascular function, bone development, epithelial tight junction, and cancer. We also discuss the effects of MR in invertebrates.

Methionine restriction alters bone morphology and affects osteoblast differentiation

Methionine restriction (MR) extends the lifespan of a wide variety of species, including rodents, drosophila, nematodes, and yeasts. MR has also been demonstrated to affect the overall growth of mice and rats. The objective of this study was to evaluate the effect of MR on bone structure in young and aged male and female C57BL/6J mice. This study indicated that MR affected the growth rates of males and young females, but not aged females. MR reduced volumetric bone mass density (vBMD) and bone mineral content (BMC), while bone microarchitecture parameters were decreased in males and young females, but not in aged females compared to control-fed (CF) mice. However, when adjusted for bodyweight, the effect of MR in reducing vBMD, BMC and microarchitecture measurements was either attenuated or reversed suggesting that the smaller bones in MR mice is appropriate for its body size. In addition, CF and MR mice had similar intrinsic strength properties as measured by nanoindentation. Plasma biomarkers suggested that the low bone mass in MR mice could be due to increased collagen degradation, which may be influenced by leptin, IGF-1, adiponectin and FGF21 hormone levels. Mouse preosteoblast cell line cultured under low sulfur amino acid growth media attenuated gene expression levels of Col1al, Runx2, Bglap, Alpl and Spp1 suggesting delayed collagen formation and bone differentiation. Collectively, our studies revealed that MR altered bone morphology which could be mediated by delays in osteoblast differentiation.

•

MR affected the growth rates of males and young females, but not aged females.

•

CF and MR mice had similar intrinsic strength properties.

•

Low methionine media attenuated bone differentiation genes in MC3T3-E1 preosteoblast cells.

•

The lower bone mass in MR mice is appropriate for its smaller body size.

Molecular Imaging of Prostate Cancer

Prostate cancer is the most common noncutaneous malignancy among men in the Western world. The natural history and clinical course of prostate cancer are markedly diverse, ranging from small indolent intraprostatic lesions to highly aggressive disseminated disease. An understanding of this biologic heterogeneity is considered a necessary requisite in the quest for the adoption of precise and personalized management strategies. Molecular imaging offers the potential for noninvasive assessment of the biologic interactions underpinning prostate carcinogenesis. Currently, numerous molecular imaging probes are in clinical use or undergoing preclinical or clinical evaluation. These probes can be divided into those that image increased cell metabolism, those that target prostate cancer-specific membrane proteins and receptor molecules, and those that bind to the bone matrix adjacent to metastases to bone. The increased metabolism and vascular changes in prostate cancer cells can be evaluated with radiolabeled analogs of choline, acetate, glucose, amino acids, and nucleotides. The androgen receptor, prostate-specific membrane antigen, and gastrin-releasing peptide receptor (ie, bombesin) are overexpressed in prostate cancer and can be targeted by specific radiolabeled imaging probes. Because metastatic prostate cancer cells induce osteoblastic signaling pathways of adjacent bone tissue, bone-seeking radiotracers are sensitive tools for the detection of metastases to bone. Knowledge about the underlying biologic processes responsible for the phenotypes associated with the different stages of prostate cancer allows an appropriate choice of methods and helps avoid pitfalls.

Methionine protects against hyperthermia-induced cell injury in cultured bovine mammary epithelial cells

The aim of this study was to investigate the effects of methionine on cell proliferation, antioxidant activity, apoptosis, the expression levels of related genes (HSF-1, HSP70, Bax and Bcl-2) and the expression levels of protein (HSP70) in mammary epithelial cells, after heat treatment. Methionine (60 mg/L) increased the viability and attenuated morphological damage in hyperthermia-treated bovine mammary epithelial cells (BMECs). Additionally, methionine significantly reduced lactate dehydrogenase leakage, malondialdehyde formation, nitric oxide, and nitric oxide synthase activity. Superoxide dismutase, catalase, and glutathione peroxidase enzymatic activity was increased significantly in the presence of methionine. Bovine mammary epithelial cells also exhibited a certain amount of HSP70 reserve after methionine pretreatment for 24 h, and the expression level of the HSP70 gene and protein further increased with incubation at 42 °C for 30 min. Compared to the control, the expression of HSF-1 mRNA increased, and there was a significantly reduced expression of Bax/Bcl-2 mRNA and a reduced activity of caspase-3 against heat stress. Methionine also increased survival and decreased early apoptosis of hyperthermia-treated BMECs. Thus, methionine has cytoprotective effects on hyperthermia-induced damage in BMECs.

Applying proteomic methodologies to analyze the effect of methionine restriction on proliferation of human gastric cancer SGC7901 cells

BACKGROUND

Methionine dependence is a feature unique to cancer cells, exhibited as inability to grow in a methionine-depleted environment supplemented with homocysteine, the immediate metabolic precursor of methionine. However, the molecular mechanisms by which methionine restriction inhibits cancer cells growth have not been elucidated. The effect of methionine restriction on the protein expression in gastric cancer cells was studied.

METHODS

SGC7901 cells were treated with M-H+ medium for 5 days, which was followed by analysis of total cellular protein from cells by a combination of 2-DE and MS. Then the differential expressional levels of partially identified proteins were determined by Western blot analysis.

RESULTS

The well-resolved, reproducible 2-DE patterns of SGC7901 cells cultured in M+H- or M-H+ medium were established. The 10 differential proteins between pairs of gastric cancer cells SGC7901 cultured either in M+H- medium or M-H+ medium, were identified by MALDI-TOF/TOF MS, and the differential expression levels of 2 identified proteins were confirmed.

CONCLUSION

These data will be valuable for further study of the molecular mechanisms by which methionine restriction induces cell cycle arrest and apoptosis in human gastric cancer.

Mitogen Activated Protein kinase signal transduction pathways in the prostate

The biochemistry of the mitogen activated protein kinases ERK, JNK, and p38 have been studied in prostate physiology in an attempt to elucidate novel mechanisms and pathways for the treatment of prostatic disease. We reviewed articles examining mitogen-activated protein kinases using prostate tissue or cell lines. As with other tissue types, these signaling modules are links/transmitters for important pathways in prostate cells that can result in cellular survival or apoptosis. While the activation of the ERK pathway appears to primarily result in survival, the roles of JNK and p38 are less clear. Manipulation of these pathways could have important implications for the treatment of prostate cancer and benign prostatic hypertrophy.

Reduction of c-Src activity by substituted 5,7-diphenyl-pyrrolo[2,3-d]-pyrimidines induces osteoclast apoptosis in vivo and in vitro. Involvement of ERK1/2 pathway

We employed potent and selective c-Src inhibitors to investigate the functional and molecular consequences of inhibited c-Src tyrosine kinase activity in osteoclasts. These pyrrolopyrimidine derivatives reduced osteoclast numbers and induced osteoclast disruption in vivo. In vitro, they inhibited resorption pit formation and osteoclastogenesis, impaired adhesion ability and actin ring organization, and induced programmed cell death in mature osteoclasts. The cell death receptor Fas and p53 were insensitive to c-Src modulation. The expression of the cyclin-dependent kinase (CDK)-inhibitor p21WAF1/CIP1 was markedly reduced, but neither Bcl-2 nor Bcl-xL or Bax were modulated by c-Src inhibition. Caspase-9, and to a lesser extent caspase-3, but not caspase-8, were transiently cleaved (activated) by treatment with the c-Src inhibitors. c-Src inhibition stabilized p38 mitogen-activated protein kinase (MAPK), whereas the c-Jun N-terminal kinase (JNK) pathway did not appear to be modulated by our compounds. Most interestingly, transient extracellular signal regulated kinase (ERK1/2) dephosphorylation followed by sustained remarkable rephosphorylation overwhelming control levels was observed in response to c-Src inhibition. Blockade of ERK1/2 rephosphorylation by PD98059 reduced osteoclast nuclear disruption, suggesting the involvement of this pathway in apoptosis. Collectively, these data demonstrate that small pyrrolopyrimidine derivatives impair osteoclast function and induce cell damage suggestive of apoptosis in vivo and in vitro, with mechanisms presumably involving selective sustained ERK1/2 phosphorylation.

The apoptotic action of the retinoid CD437/AHPN: diverse effects, common basis

Retinoids, such as all-TRANS-retinoic acid (RA), have found applications in several different types of (cancer) therapies. The synthetic retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437 or AHPN), an RA receptor (RAR)gamma agonist, not only induces RARgamma-dependent differentiation, but in contrast to RA, it also induces RARgamma-independent apoptosis in many tumor cells. This observation makes this and similar new retinoids very interesting from a clinical perspective. Several genes have been associated with CD437/AHPN-mediated apoptosis, but the multiple activities of this compound and the apparent cell-type-specific responses to treatment have made it difficult to discern a common biochemical basis for the mechanism of its apoptotic action. In this brief review, we present a model which links all CD437/AHPN-associated apoptotic effects. CD437/AHPN rapidly induces DNA adduct formation through an as-yet unknown reaction which is independent of cell type. This is followed by a cell-type-specific, largely p53-independent DNA damage response which can result in engagement of multiple cell death pathways and activation of caspases as a common endpoint. At the same time, the RARgamma-dependent pathway leads to regulation of differentiation-associated, cell-type-specific genes. CD437/AHPN, with its simultaneous differentiation and apoptosis-inducing activities, is a good prototype for new drugs which may be clinically more efficacious than those with a single activity.