Altered methionine metabolism, DNA methylation and oncogene expression in carcinogenesis. A review and synthesis

Targeting Methionine Addiction of Cancer Cells with Methioninase

All types of cancer cells are addicted to methionine, which is known as the Hoffman effect. Restricting methionine inhibits the growth and proliferation of all tested types of cancer cells, leaving normal cells unaffected. Targeting methionine addiction with methioninase (METase), either alone or in combination with common cancer chemotherapy drugs, has been shown as an effective and safe therapy in various types of cancer cells and animal cancer models. About six years ago, recombinant METase (rMETase) was found to be able to be taken orally as a supplement, resulting in anecdotal positive results in patients with advanced cancer. Currently, there are 8 published clinical studies on METase, including two from the 1990s and six more recent ones. This review focuses on the results of clinical studies on METase-mediated methionine restriction, in particular, on the dosage of oral rMETase taken alone as a supplement or in combination with common chemotherapeutic agents in patients with advanced cancer.

Serum metabolomic analysis of the dose-response effect of dietary choline in overweight male cats fed at maintenance energy requirements

Choline participates in methyl group metabolism and has been recognized for its roles in lipid metabolism, hepatic health and muscle function in various species. Data regarding the impacts of choline on feline metabolic pathways are scarce. The present study investigated how choline intake affects the metabolomic profile of overweight cats fed at maintenance energy. Overweight (n = 14; body condition score:6-8/9) male adult cats were supplemented with five doses of choline in a 5x5 Latin Square design. Cats received a daily dose of choline on extruded food (3620 mg choline/kg diet) for three weeks at maintenance energy requirements (130 kcal/kgBW0.4). Doses were based on body weight (BW) and the daily recommended allowance (RA) for choline for adult cats (63 mg/kg BW0.67). Treatment groups included: Control (no additional choline, 1.2 x NRC RA, 77 mg/kg BW0.67), 2 x NRC RA (126 mg/kg BW0.67), 4 x NRC RA (252 mg/kg BW0.67), 6 x RA (378 mg/kg BW0.67), and 8 x NRC RA (504 mg/kg BW0.67). Serum was collected after an overnight fast at the end of each treatment period and analyzed for metabolomic parameters through nuclear magnetic resonance (NMR) spectroscopy and direct infusion mass spectrometry (DI-MS). Data were analyzed using GLIMMIX, with group and period as random effects, and dose as the fixed effect. Choline up to 8 x NRC RA was well-tolerated. Choline at 6 and 8 x NRC RA resulted in greater concentrations of amino acids and one-carbon metabolites (P < 0.05) betaine, dimethylglycine and methionine. Choline at 6 x NRC RA also resulted in greater phosphatidylcholine and sphingomyelin concentrations (P < 0.05). Supplemental dietary choline may be beneficial for maintaining hepatic health in overweight cats, as it may increase hepatic fat mobilization and methyl donor status. Choline may also improve lean muscle mass in cats. More research is needed to quantify how choline impacts body composition.

Screening, characterization and anti-cancer application of purified intracellular MGL

L-methionine-γ-lyase (MGL) producing bacterial isolates were screened from soil samples that further characterized as 'Klebsiella oxytoca BLM-1' by biochemical and 16S rDNA sequencing. Intracellular MGL obtained from K. oxytoca BLM-1 by sonication was purified by Octyl-Sepharose and Sephadex G-200 column chromatography. MALDI-TOF-MS analysis of protein band (Mr ~ 63 kDa) confirmed the PLP-dependence and structural similarity with MGL enzyme. Purified MGL (1.1 μg) exhibited the maximum activity in potassium phosphate buffer (80 mM; with L-met 20 mM pH 7.0) at 37 °C. That further enhanced in the presence of NaCl (2 mM), Tween-80 (1.0 %; v/v) and EDTA (5 mM). K_m and V_max for purified MGL by using L-met as substrate was found to be 5.32 mM and 0.386 U/mL/min. The purified MGL showed PLP dependence and the half-life was 365.59 min. The MGL was effective against breast cancer (MCF7), gastric adenocarcinoma and human glioblastoma (U87MG) cancer cell lines with IC₅₀ values of purified MGL 0.041 U/mL, 0.008 U/mL and 0.009 U/mL, respectively. The U87MG, greatly affected by MGL treatment, when cultured in DMEM medium (10 mL) with PLP, homocysteine and 10 % FCS as compared to control/untransformed mouse spleen cells.

The Impact of Natural Dietary Compounds and Food-Borne Mycotoxins on DNA Methylation and Cancer

Cancer initiation and progression is an accumulation of genetic and epigenetic modifications. DNA methylation is a common epigenetic modification that regulates gene expression, and aberrant DNA methylation patterns are considered a hallmark of cancer. The human diet is a source of micronutrients, bioactive molecules, and mycotoxins that have the ability to alter DNA methylation patterns and are thus a contributing factor for both the prevention and onset of cancer. Micronutrients such as betaine, choline, folate, and methionine serve as cofactors or methyl donors for one-carbon metabolism and other DNA methylation reactions. Dietary bioactive compounds such as curcumin, epigallocatechin-3-gallate, genistein, quercetin, resveratrol, and sulforaphane reactivate essential tumor suppressor genes by reversing aberrant DNA methylation patterns, and therefore, they have shown potential against various cancers. In contrast, fungi-contaminated agricultural foods are a source of potent mycotoxins that induce carcinogenesis. In this review, we summarize the existing literature on dietary micronutrients, bioactive compounds, and food-borne mycotoxins that affect DNA methylation patterns and identify their potential in the onset and treatment of cancer.

Genetic variants in RUNX3, AMD1 and MSRA in the methionine metabolic pathway and survival in nonsmall cell lung cancer patients

Abnormal methionine dependence in cancer cells has led to methionine restriction as a potential therapeutic strategy. We hypothesized that genetic variants involved in methionine-metabolic genes are associated with survival in nonsmall cell lung cancer (NSCLC) patients. Therefore, we investigated associations of 16,378 common single-nucleotide polymorphisms (SNPs) in 97 methionine-metabolic pathway genes with overall survival (OS) in NSCLC patients using genotyping data from two published genome-wide association study (GWAS) datasets. In the single-locus analysis, 1,005 SNPs were significantly associated with NSCLC OS (p < 0.05 and false-positive report probability < 0.2) in the discovery dataset. Three SNPs (RUNX3 rs7553295 G > T, AMD1 rs1279590 G > A and MSRA rs73534533 C > A) were replicated in the validation dataset, and their meta-analysis showed an adjusted hazards ratio [HR] of 0.82 [95% confidence interval (CI) =0.75-0.89] and pmeta  = 2.86 × 10-6 , 0.81 (0.73-0.91) and pmeta  = 4.63 × 10-4 , and 0.77 (0.68-0.89) and pmeta  = 2.07 × 10-4 , respectively). A genetic score of protective genotypes of these three SNPs revealed an increased OS in a dose-response manner (ptrend  < 0.0001). Further expression quantitative trait loci (eQTL) analysis showed significant associations between these genotypes and mRNA expression levels. Moreover, differential expression analysis further supported a tumor-suppressive effect of MSRA, with lower mRNA levels in both lung squamous carcinoma and adenocarcinoma (p < 0.0001 and < 0.0001, respectively) than in adjacent normal tissues. Additionally, low mutation rates of these three genes indicated the critical roles of these functional SNPs in cancer progression. Taken together, these genetic variants of methionine-metabolic pathway genes may be promising predictors of survival in NSCLC patients.

Methioninase Cell-Cycle Trap Cancer Chemotherapy

Cancer cells are methionine (MET) dependent compared to normal cells as they have an elevated requirement for MET in order to proliferate. MET restriction selectively traps cancer cells in the S/G₂ phase of the cell cycle. The cell cycle phase can be visualized by color coding with the fluorescence ubiquitination-based cell cycle indicator (FUCCI). Recombinant methioninase (rMETase) is an enzyme that effectively degrades MET. rMETase induces S/G₂-phase blockage of cancer cells which is identified by the cancer cells' green fluorescence with FUCCI imaging. Cancer cells in G₁/G₀ are the majority of the cells in solid tumors and are resistant to the chemotherapy. Treatment of cancer cells with standard chemotherapy drugs only led to the majority of the cancer cell population being arrested in G₀/G₁ phase, identified by the cancer cells' red fluorescence in the FUCCI system. The G₀/G₁-phase cancer cells are chemo-resistant. Tumor targeting Salmonella typhimurium A1-R (S. typhimurium A1-R) was used to decoy quiescent G₀/G₁ stomach cancer cells growing in nude mice to cycle, with subsequent rMETase treatment to selectively trap the decoyed cancer cells in S/G₂ phase, which made them highly sensitive to chemotherapy. Subsequent cisplatinum (CDDP) or paclitaxel (PTX) chemotherapy was then administered to kill the decoyed and trapped cancer cells, which completely prevented or regressed tumor growth. In a subsequent experiment, a patient-derived orthotopic xenograft (PDOX) model of recurrent CDDP-resistant metastatic osteosarcoma was eradicated by the combination of Salmonella typhimurium A1-R decoy, rMETase S/G₂-phase cell cycle trap, and CDDP cell kill. Salmonella typhimurium A1-R and rMETase pre-treatment thereby overcame CDDP resistance. These results demonstrate the effectiveness of the new chemotherapy paradigm of "decoy, trap, and kill" chemotherapy.

Targeting DNA Hypomethylation in Malignancy by Epigenetic Therapies

DNA methylation is a chemically reversible epigenetic modification that regulates the chromatin structure and gene expression, and thereby takes part in various cellular processes like embryogenesis, genomic imprinting, X-chromosome inactivation, and genome stability. Alterations in the normal methylation levels of DNA may contribute to the development of pathological conditions like cancer. Even though both hypo- and hypermethylation-mediated abnormalities are prevalent in the cancer genome, the field of cancer epigenetics has been more focused on targeting hypermethylation. As a result, DNA hypomethylation-mediated abnormalities remained relatively less explored, and currently, there are no approved drugs that can be clinically used to target hypomethylation. Understanding the precise role of DNA hypomethylation is not only crucial from a mechanistic point of view but also for the development of pharmacological agents that can reverse the hypomethylated state of the DNA. This chapter focuses on the causes and impact of DNA hypomethylation in the development of cancer and describes the possible ways to pharmacologically target it, especially by using a naturally occurring physiologic agent S-adenosylmethionine (SAM).

Methionine gamma lyase from Clostridium sporogenes increases the anticancer effect of doxorubicin in A549 cells and human cancer xenografts

The anti-cancer efficacy of methionine γ-lyase (MGL) from Clostridium sporogenes (C. sporogenes) is described. MGL was active against cancer models in vitro and in vivo. The calculated EC50 values for MGL were 4.4 U/ml for A549, 7.5 U/ml for SK-BR3, 2.4 U/ml for SKOV3, and 0.4 U/ml for MCF7 cells. The combination of doxorubicin (DOX) and MGL was more effective for A549 human lung cancer growth inhibition than either agent alone in vitro and in vivo. MGL reduced the EC50 of doxorubicin from 35.9 μg/mL to 0.01-0.265 μg/mL. The growth inhibitory effect of DOX + MGL on A549 xenografts in vivo was reflective of the results obtained in vitro. The inhibition rate of tumor growth in the combined arm was 57%, significantly higher than that in the doxorubicin (p = 0.033)-alone arm.

Targeting cancer's metabolic co-dependencies: A landscape shaped by genotype and tissue context

Tumors cells reprogram their metabolism to fuel rapid growth. The ability to trace nutrient fluxes in the context of specific alterations has provided new mechanistic insight into the process of oncogenic transformation. A broad array of complementary genetic, epigenetic, transcriptional and translational mechanisms has been identified, revealing a metabolic landscape of cancer. However, cancer metabolism is not a static or uniform process, including within a single tumor. Tumor cells adapt to changing environmental conditions, profoundly shaping the enzymatic dependencies of individual cells. The underlying molecular mechanisms of adaptation, and the specific interactions between tumor genotype, oncogenic signaling, and tissue/biochemical context, remain incompletely understood. In this review, we examine dynamic aspects of how metabolic dependencies develop in cancer, shaped both by genotype and biochemical environment, and review how these interlaced processes generate targetable metabolic vulnerabilities. This article is part of a Special Issue entitled: Cancer Metabolism edited by Dr. Chi Van Dang.

Recombinant methioninase combined with doxorubicin (DOX) regresses a DOX-resistant synovial sarcoma in a patient-derived orthotopic xenograft (PDOX) mouse model

Synovial sarcoma (SS) is a recalcitrant subgroup of soft tissue sarcoma (STS). A tumor from a patient with high grade SS from a lower extremity was grown orthotopically in the right biceps femoris muscle of nude mice to establish a patient-derived orthotopic xenograft (PDOX) mouse model. The PDOX mice were randomized into the following groups when tumor volume reached approximately 100 mm³: G1, control without treatment; G2, doxorubicin (DOX) (3 mg/kg, intraperitoneal [i.p.] injection, weekly, for 2 weeks; G3, rMETase (100 unit/mouse, i.p., daily, for 2 weeks); G4 DOX (3mg/kg), i.p. weekly, for 2 weeks) combined with rMETase (100 unit/mouse, i.p., daily, for 2 weeks). On day 14 after treatment initiation, all therapies significantly inhibited tumor growth compared to untreated control, except DOX: (DOX: p = 0.48; rMETase: p < 0.005; DOX combined with rMETase < 0.0001). DOX combined with rMETase was significantly more effective than both DOX alone (p < 0.001) and rMETase alone (p < 0.05). The relative body weight on day 14 compared with day 0 did not significantly differ between any treatment group or untreated control. The results indicate that r-METase can overcome DOX-resistance in this recalcitrant disease.

Tumor-targeting Salmonella typhimurium A1-R combined with recombinant methioninase and cisplatinum eradicates an osteosarcoma cisplatinum-resistant lung metastasis in a patient-derived orthotopic xenograft (PDOX) mouse model: decoy, trap and kill chemotherapy moves toward the clinic

In the present study, a patient-derived orthotopic xenograft (PDOX) model of recurrent cisplatinum (CDDP)-resistant metastatic osteosarcoma was treated with Salmonella typhimurium A1-R (S. typhimurium A1-R), which decoys chemoresistant quiescent cancer cells to cycle, and recombinant methioninase (rMETase), which selectively traps cancer cells in late S/G₂, and chemotherapy. The PDOX models were randomized into the following groups 14 days after implantation: G1, control without treatment; G2, CDDP (6 mg/kg, intraperitoneal (i.p.) injection, weekly, for 2 weeks); G3, rMETase (100 unit/mouse, i.p., daily, for 2 weeks). G4, S. typhimurium A1-R (5 × 10⁷ CFU/100 μl, i.v., weekly, for 2 weeks); G5, S. typhimurium A1-R (5 × 10⁷ CFU/100 μl, i.v., weekly, for 2 weeks) combined with rMETase (100 unit/mouse, i.p., daily, for 2 weeks); G6, S. typhimurium A1-R (5 × 10⁷ CFU/100 μl, i.v., weekly, for 2 weeks) combined with rMETase (100 unit/mouse, i.p., daily, for 2 weeks) and CDDP (6 mg/kg, i.p. injection, weekly, for 2 weeks). On day 14 after initiation, all treatments except CDDP alone, significantly inhibited tumor growth compared to untreated control: (CDDP: p = 0.586; rMETase: p = 0.002; S. typhimurium A1-R: p = 0.002; S. typhimurium A1-R combined with rMETase: p = 0.0004; rMETase combined with both S. typhimurium A1-R and CDDP: p = 0.0001). The decoy, trap and kill combination of S. typhimurium A1-R, rMETase and CDDP was the most effective of all therapies and was able to eradicate the metastatic osteosarcoma PDOX.

Recombinant methioninase effectively targets a Ewing's sarcoma in a patient-derived orthotopic xenograft (PDOX) nude-mouse model

Methionine dependence is due to the overuse of methionine for aberrant transmethylation reactions in cancer. Methionine dependence may be the only general metabolic defect in cancer. In order to exploit methionine dependence for therapy, our laboratory previously cloned L-methionine α-deamino-γ-mercaptomethane lyase [EC 4.4.1.11]). The cloned methioninase, termed recombinant methioninase, or rMETase, has been tested in mouse models of human cancer cell lines. Ewing's sarcoma is recalcitrant disease even though development of multimodal therapy has improved patients'outcome. Here we report efficacy of rMETase against Ewing's sarcoma in a patient-derived orthotopic xenograft (PDOX) model. The Ewing's sarcoma was implanted in the right chest wall of nude mice to establish a PDOX model. Eight Ewing's sarcoma PDOX mice were randomized into untreated control group (n = 4) and rMETase treatment group (n = 4). rMETase (100 units) was injected intraperitoneally (i.p.) every 24 hours for 14 consecutive days. All mice were sacrificed on day-15, 24 hours after the last rMETase administration. rMETase effectively reduced tumor growth compared to untreated control. The methionine level both of plasma and supernatants derived from sonicated tumors was lower in the rMETase group. Body weight did not significantly differ at any time points between the 2 groups. The present study is the first demonstrating rMETase efficacy in a PDOX model, suggesting potential clinical development, especially in recalcitrant cancers such as Ewing's sarcoma.

Targeting methionine with oral recombinant methioninase (o-rMETase) arrests a patient-derived orthotopic xenograft (PDOX) model of BRAF-V600E mutant melanoma: implications for chronic clinical cancer therapy and prevention

The elevated methionine (MET) use by cancer cells is termed MET dependence and may be the only known general metabolic defect in cancer. Targeting MET by recombinant methioninase (rMETase) can arrest the growth of cancer cells in vitro and in vivo. We previously reported that rMETase, administrated by intra-peritoneal injection (ip-rMETase), could inhibit tumor growth in a patient-derived orthotopic xenograft (PDOX) model of a BRAF-V600E mutant melanoma. In the present study, we compared ip-rMETase and oral rMETase (o-rMETase) for efficacy on the melanoma PDOX. Melanoma PDOX nude mice were randomized into four groups of 5 mice each: untreated control; ip-rMETase (100 units, i.p., 14 consecutive days); o-rMETase (100 units, p.o., 14 consecutive days); o-rMETase+ip-rMETase (100 units, p.o.+100 units, i.p., 14 consecutive days). All treatments inhibited tumor growth on day 14 after treatment initiation, compared to untreated control (ip-rMETase, p<0.0001; o-rMETase, p<0.0001; o-rMETase+ip-rMETase, p<0.0001). o-rMETase was significantly more effective than ip-rMETase (p = 0.0086). o-rMETase+ip-rMETase was significantly more effective than either mono-therapy: ip-rMETase, p = 0.0005; or o-rMETase, p = 0.0367. The present study is the first demonstrating that o-rMETase is effective as an anticancer agent. The results of the present study indicate the potential of clinical development of o-rMETase as an agent for chronic cancer therapy and for cancer prevention and possibly for life extension since dietary MET reduction extends life span in many animal models.

Intra-tumor L-methionine level highly correlates with tumor size in both pancreatic cancer and melanoma patient-derived orthotopic xenograft (PDOX) nude-mouse models

An excessive requirement for methionine (MET) for growth, termed MET dependence, appears to be a general metabolic defect in cancer. We have previously shown that cancer-cell growth can be selectively arrested by MET restriction such as with recombinant methioninase (rMETase). In the present study, we utilized patient-derived orthotopic xenograft (PDOX) nude mouse models with pancreatic cancer or melanoma to determine the relationship between intra-tumor MET level and tumor size. After the tumors grew to 100 mm³, the PDOX nude mice were divided into two groups: untreated control and treated with rMETase (100 units, i.p., 14 consecutive days). On day 14 from initiation of treatment, intra-tumor MET levels were measured and found to highly correlate with tumor volume, both in the pancreatic cancer PDOX (p<0.0001, R²=0.89016) and melanoma PDOX (p<0.0001, R²=0.88114). Tumors with low concentration of MET were smaller. The present results demonstrates that patient tumors are highly dependent on MET for growth and that rMETase effectively lowers tumor MET.

Oncogenic PI3K promotes methionine dependency in breast cancer cells through the cystine-glutamate antiporter xCT

The precursor homocysteine is metabolized either through the methionine cycle to produce methionine or through the transsulfuration pathway to synthesize cysteine. Alternatively, cysteine can be obtained through uptake of its oxidized form, cystine. Many cancer cells exhibit methionine dependency such that their proliferation is impaired in growth media in which methionine is replaced by homocysteine. We showed that oncogenic PIK3CA and decreased expression of SLC7A11, a gene that encodes a cystine transporter also known as xCT, correlated with increased methionine dependency in breast cancer cells. Oncogenic PIK3CA was sufficient to confer methionine dependency to mammary epithelial cells, partly by decreasing cystine uptake through the transcriptional and posttranslational inhibition of xCT. Manipulation of xCT activity altered the proliferation of breast cancer cells in methionine-deficient, homocysteine-containing media, suggesting that it functionally contributed to methionine dependency. We propose that concurrent with decreased cystine uptake through xCT, PIK3CA mutant cells use homocysteine through the transsulfuration pathway to synthesize cysteine. Consequently, less homocysteine is available to produce methionine, contributing to methionine dependency. These results indicate that oncogenic PIK3CA alters methionine and cysteine utilization, partly by inhibiting xCT to contribute to the methionine dependency phenotype in breast cancer cells.

Patient-Derived Orthotopic Xenograft (PDOX) Models of Melanoma

Metastatic melanoma is a recalcitrant tumor. Although “targeted” and immune therapies have been highly touted, only relatively few patients have had durable responses. To overcome this problem, our laboratory has established the melanoma patient-derived orthotopic xenograft (PDOX) model with the use of surgical orthotopic implantation (SOI). Promising results have been obtained with regard to identifying effective approved agents and experimental therapeutics, as well as combinations of the two using the melanoma PDOX model.

Combination treatment with recombinant methioninase enables temozolomide to arrest a BRAF V600E melanoma in a patient-derived orthotopic xenograft (PDOX) mouse model

An excessive requirement for methionine termed methionine dependence, appears to be a general metabolic defect in cancer. We have previously shown that cancer-cell growth can be selectively arrested by methionine deprivation such as with recombinant methioninase (rMETase). The present study used a previously-established patient-derived orthotopic xenograft (PDOX) nude mouse model of BRAF V600E-mutant melanoma to determine the efficacy of rMETase in combination with a first-line melanoma drug, temozolomide (TEM). In the present study 40 melanoma PDOX mouse models were randomized into four groups of 10 mice each: untreated control (n=10); TEM (25 mg/kg, oral 14 consecutive days, n=10); rMETase (100 units, intraperitoneal 14 consecutive days, n=10); combination TEM + rMETase (TEM: 25 mg/kg, oral rMETase: 100 units, intraperitoneal 14 consecutive days, n=10). All treatments inhibited tumor growth compared to untreated control (TEM: p=0.0081, rMETase: p=0.0037, TEM-rMETase: p=0.0024) on day 14 after initiation. However, the combination therapy of TEM and rMETase was significantly more efficacious than either mono-therapy (TEM: p=0.0051, rMETase: p=0.0051). The present study is the first demonstrating the efficacy of rMETase combination therapy in a PDOX model, suggesting potential clinical development, especially in recalcitrant cancers such as melanoma, where rMETase may enhance first-line therapy.

Is DNA methylation the new guardian of the genome?

BACKGROUND

It has been known for more than 100 years that aneuploidy is an essence of cancer. The question is what keeps the genome stable, thereby preventing aneuploidy. For the past 25 years, it has been proposed that p53 is the "guardian of the genome." However, it has been shown that inactivation of p53 does not cause aneuploidy. Another essence of cancer is global DNA hypomethylation, which causes destabilization of the genome and subsequent aneupoloidy. Yet, another essence of cancer is excessive use of methionine, resulting in methionine dependence. Methionine dependence is due to possible "metabolic reprogramming" due to carcinogens, including chemical agents and infectious organisms, such as Helicobacter pylori, that result in altered and excessive transmethylation in cancer cells. Cancer cells appear to have a "methyl-sink" whereby methyl groups are diverted from DNA.

CONCLUSION

DNA hypomethylation destabilizes the genome, leading to aneuploidy and subsequent selection and speciation into autonomous cancers, leading to the conclusion that DNA methylation is the "guardian of the genome."

The wayward methyl group and the cascade to cancer

We propose here a hypothesis of the cause of cancer that brings together fundamental changes in methyl-group metabolism resulting in methionine dependence and global DNA hypomethylation which destabilizes the genome leading to aneuploid karyotypes which evolve and stabilize into autonomous cancer. Experimental support for this hypothesis is that methioine dependence is a general metabolic defect in caner. Methionine dependence is due to excess use of methionene for aberrant transmethylation reactions that apparently divert methyl groups from DNA. The resulting global DNA hypomethylation is also a general phenomena in cancer. Global hypomethylation leads to an unstable genomes and aneuploid karyotypes, another general phenomena in cancer. The excessive and aberrant use of methionine in cancer is strongly observed in [¹¹C]methionine PET imaging, where high uptake of [¹¹C]methionine results in a very strong and selective tumor signal compared with normal tissue background. [¹¹C]methionine is superior to [¹⁸C] fluorodeoxyglucose (FDG)-PET for PET imaging, suggesting methionine dependence is more tumor-specific than glucose dependence.

Enhanced GSH synthesis by Bisphenol A exposure promoted DNA methylation process in the testes of adult rare minnow Gobiocypris rarus

DNA methylation is a commonly studied epigenetic modification. The mechanism of BPA on DNA methylation is poorly understood. The present study aims to explore whether GSH synthesis affects DNA methylation in the testes of adult male rare minnow Gobiocypris rarus in response to Bisphenol A (BPA). Male G. rarus was exposed to 1, 15 and 225μgL(-1) BPA for 7 days. The levels of global DNA methylation, hydrogen peroxide (H2O2) and glutathione (GSH) in the testes were analyzed. Meanwhile, the levels of enzymes involved in DNA methylation and de novo GSH synthesis, and the substrate contents for GSH production were measured. Furthermore, gene expression profiles of the corresponding genes of all studied enzymes were analyzed. Results indicated that BPA at 15 and 225μgL(-1) caused hypermethylation of global DNA in the testes. The 15μgL(-1) BPA resulted in significant decrease of ten-eleven translocation proteins (TETs) while 225μgL(-1) BPA caused significant increase of DNA methyltransferase proteins (DNMTs). Moreover, 225μgL(-1) BPA caused significant increase of H2O2 and GSH levels, and the de novo GSH synthesis was enhanced. These results indicated that the significant decrease of the level of TETs may be sufficient to cause the DNA hypermethylation by 15μgL(-1) BPA. However, the significantly increased of DNMTs contributed to the significant increase of DNA methylation levels by 225μgL(-1) BPA. Moreover, the elevated de novo GSH synthesis may promote the DNA methylation process.

Tumor-specific cell-cycle decoy by Salmonella typhimurium A1-R combined with tumor-selective cell-cycle trap by methioninase overcome tumor intrinsic chemoresistance as visualized by FUCCI imaging

We previously reported real-time monitoring of cell cycle dynamics of cancer cells throughout a live tumor intravitally using a fluorescence ubiquitination cell cycle indicator (FUCCI). Approximately 90% of cancer cells in the center and 80% of total cells of an established tumor are in G0/G1 phase. Longitudinal real-time FUCCI imaging demonstrated that cytotoxic agents killed only proliferating cancer cells at the surface and, in contrast, and had little effect on the quiescent cancer cells. Resistant quiescent cancer cells restarted cycling after the cessation of chemotherapy. Thus cytotoxic chemotherapy which targets cells in S/G2/M, is mostly ineffective on solid tumors, but causes toxic side effects on tissues with high fractions of cycling cells, such as hair follicles, bone marrow and the intestinal lining. We have termed this phenomenon tumor intrinsic chemoresistance (TIC). We previously demonstrated that tumor-targeting Salmonella typhimurium A1-R (S. typhimurium A1-R) decoyed quiescent cancer cells in tumors to cycle from G0/G1 to S/G2/M demonstrated by FUCCI imaging. We have also previously shown that when cancer cells were treated with recombinant methioninase (rMETase), the cancer cells were selectively trapped in S/G2, shown by cell sorting as well as by FUCCI. In the present study, we show that sequential treatment of FUCCI-expressing stomach cancer MKN45 in vivo with S. typhimurium A1-R to decoy quiescent cancer cells to cycle, with subsequent rMETase to selectively trap the decoyed cancer cells in S/G2 phase, followed by cisplatinum (CDDP) or paclitaxel (PTX) chemotherapy to kill the decoyed and trapped cancer cells completely prevented or regressed tumor growth. These results demonstrate the effectiveness of the praradigm of "decoy, trap and shoot" chemotherapy.

Recombinant Engineering of L-Methioninase Using Two Different Promoter and Expression Systems and in vitro Analysis of Its Anticancer Efficacy on Different Human Cancer Cell Lines

Recombinant methioninase (rMETase) is an enzyme that has antitumor activity. In this work, METase gene from Pseudomonas putida ATTCC 8209 was cloned to pT7-7 plasmid (yielded, PT7-METase-R7 clone) and expressed in E. coli strain BL21 (DE3). A protein band with a molecular massof 42 kDa was visualized by SDS-PAGE. The applied protocol yielded a total protein of 3.13 g with a recovery of 66.89% and a specific activity of 18.59 U mg-1 which considered as a low yield. However, when the METase gene was cloned to the vector (pTrc99A, clone: pTrc99A-MET-3) cells of E. coli JM109 yielded a total protein of 32.63 g with a recovery of 41.62% and a specific activity of 54.86 U mg-1 which revealed that the enhancement of METase gene expression by trc promoter was more than the T7 RNA polymerase promoter. The t1/2 of the rMETase was 2 h asanalyzed in mice by IV injection. Antitumor efficacy of rMETase was studied in five human cancer cell lines. At 1 U mL-1 the growth rate of treated colon cancer cell lines, Colo205 and SW620, with rMETase was 46 and 32% relative to control, respectively. With the ovarian cancer cell line (A2780) rMETase produced an inhibition effect of 54% at 1.5 U mL-1. In addition, the growth rate was reduced to 45 and 53% with the skin cancer cell line (A375) and the breast cancer cell line (MCF-7), respectively. These results indicate the feasibility of rMETase for use as a potent antitumor agent.

l-Methioninase from some Streptomyces isolates I: Isolation, identification of best producers and some properties of the crude enzyme produced

Among 60 isolates of Streptomyces tested; only 40 isolates were capable to utilize l-methionine as the only source of nitrogen in medium. In addition, 24 of these isolates could grow in medium amended with l-methionine as a source of nitrogen and carbon. Qualitative rapid plate assay test shows the ability of 18 of these isolates to grow with a pink color surrounding their colonial growth, while 6 of these isolates could grow and utilize l-methionine without any pink color around their colonial growth. Quantitative assay test shows the rate of l-methioninase production by all isolates tested. Permeabilization treatment including chemical and physical methods proved that l-methioninase was found to be extracellularly produced. The results also indicate that l-methioninase production was not correlated with growth rate or l-methionine consumption in medium. On the other hand, quantitative assay test shows that these six isolates were l-methioninase negative and failed to produce any amount of l-methioninase. In addition, results also show that isolates No. 4 and No. 60 were the most suitable for l-methioninase production, these two isolates were characterized and identified as Streptomyces sp. DMMMH 4 and Streptomyces sp. MDMMH 60 using 16S rRNA with accession No. in gene bank. Furthermore, optimal conditions for enzyme activity produced by the two isolates were established in relation to temperature, pH, reaction time and type of buffer used and its molarities.

Purification, Characterization of L-Methioninase from Candida tropicalis, and Its Application as an Anticancer

The aim of the present study is to purify L-methioninase from Candida tropicalis 34.19-fold with 27.98% recovery after ion exchange chromatography followed by gel filtration. The purified enzyme revealed a single band on SDS-PAGE gel with a molecular weight of 46 KDa. Its optimum temperature was 45 to 55 and thermal stability was 55°C for 15 min. The enzyme had optimum pH at 6.5 and stability at a pH range of 5.5 to 7.0 for 24 hr. The maximum activity was observed with substrate concentration of 30 µM and Km was 0.5 mM. The enzyme was strongly inhibited by Cd(+2) and Cu(+2) while it was enhanced by Na(+), Ni(+2), and Mg(+2) at 10 mM while Ca(+2) had slight activation at 20 mM. In addition, the potential application of the L-methioninase as an anticancer agent against various types of tumor cell lines is discussed.

Selective methioninase-induced trap of cancer cells in S/G2 phase visualized by FUCCI imaging confers chemosensitivity

A major impediment to the response of tumors to chemotherapy is that the large majority of cancer cells within a tumor are quiescent in G₀/G₁, where cancer cells are resistant to chemotherapy. To attempt to solve this problem of quiescent cells in a tumor, cancer cells were treated with recombinant methioninase (rMETase), which selectively traps cancer cells in S/G₂. The cell cycle phase of the cancer cells was visualized with the fluorescence ubiquitination cell cycle indicator (FUCCI). At the time of rMETase-induced S/G₂-phase blockage, identified by the cancer cells' green fluorescence by FUCCI imaging, the cancer cells were administered S/G₂-dependent chemotherapy drugs, which interact with DNA or block DNA synthesis such as doxorubicin, cisplatin, or 5-fluorouracil. Treatment of cancer cells with drugs only, without rMETase-induced S/G₂ phase blockage, led to the majority of the cancer-cell population being blocked in G₀/G₁ phase, identified by the cancer cells becoming red fluorescent in the FUCCI system. The G₀/G₁ blocked cells were resistant to the chemotherapy. In contrast, trapping of cancer cells in S/G₂ phase by rMETase treatment followed by FUCCI-imaging-guided chemotherapy was highly effective in killing the cancer cells.

Development of recombinant methioninase to target the general cancer-specific metabolic defect of methionine dependence: a 40-year odyssey

INTRODUCTION

All tested cancer cell types are methionine dependent in that the cells arrest and eventually die when deprived of methionine, a condition that is generally nontoxic to normal cells. Methionine dependence is the only known general metabolic defect in cancer. Methionine-deprived cancer cells arrest at the S/G2 phase, an unusual position for cell cycle arrest. In order to exploit the cancer-specific metabolic defect of methionine dependence, methioninases were developed.

AREAS COVERED

The present Expert Opinion describes the phenomena of methionine dependence and a methioninase cloned from Pseudomonas putida (chemical name: l-methionine α-deamino-γ-mercaptomethane lyase [EC 4.4.1.11]). The cloned methioninase, termed recombinant methioninase, or rMETase, has been tested in mouse models of human cancer as well as in macaque monkeys and a pilot Phase I trial of human cancer patients. Efficacy of rMETase has been demonstrated against various cancer types in mouse models.

EXPERT OPINION

The most promising application of rMETase therapy is in sequential combination therapy, whereby the cancer cells within a tumor are trapped in S/G2 by methioninase treatment and then treated with chemotherapeutic agents active against cells in S/G2.

L-methionase: a therapeutic enzyme to treat malignancies

Cancer is an increasing cause of mortality and morbidity throughout the world. L-methionase has potential application against many types of cancers. L-Methionase is an intracellular enzyme in bacterial species, an extracellular enzyme in fungi, and absent in mammals. L-Methionase producing bacterial strain(s) can be isolated by 5,5′-dithio-bis-(2-nitrobenzoic acid) as a screening dye. L-Methionine plays an important role in tumour cells. These cells become methionine dependent and eventually follow apoptosis due to methionine limitation in cancer cells. L-Methionine also plays an indispensable role in gene activation and inactivation due to hypermethylation and/or hypomethylation. Membrane transporters such as GLUT1 and ion channels like Na²⁺, Ca²⁺, K⁺, and Cl⁻ become overexpressed. Further, the α-subunit of ATP synthase plays a role in cancer cells growth and development by providing them enhanced nutritional requirements. Currently, selenomethionine is also used as a prodrug in cancer therapy along with enzyme methionase that converts prodrug into active toxic chemical(s) that causes death of cancerous cells/tissue. More recently, fusion protein (FP) consisting of L-methionase linked to annexin-V has been used in cancer therapy. The fusion proteins have advantage that they have specificity only for cancer cells and do not harm the normal cells.

Recurrent epimutations activate gene body promoters in primary glioblastoma

Aberrant DNA hypomethylation may play an important role in the growth rate of glioblastoma (GBM), but the functional impact on transcription remains poorly understood. We assayed the GBM methylome with MeDIP-seq and MRE-seq, adjusting for copy number differences, in a small set of non-glioma CpG island methylator phenotype (non-G-CIMP) primary tumors. Recurrent hypomethylated loci were enriched within a region of chromosome 5p15 that is specified as a cancer amplicon and also encompasses TERT, encoding telomerase reverse transcriptase, which plays a critical role in tumorigenesis. Overall, 76 gene body promoters were recurrently hypomethylated, including TERT and the oncogenes GLI3 and TP73. Recurring hypomethylation also affected previously unannotated alternative promoters, and luciferase reporter assays for three of four of these promoters confirmed strong promoter activity in GBM cells. Histone H3 lysine 4 trimethylation (H3K4me3) ChIP-seq on tissue from the GBMs uncovered peaks that coincide precisely with tumor-specific decrease of DNA methylation at 200 loci, 133 of which are in gene bodies. Detailed investigation of TP73 and TERT gene body hypomethylation demonstrated increased expression of corresponding alternate transcripts, which in TP73 encodes a truncated p73 protein with oncogenic function and in TERT encodes a putative reverse transcriptase-null protein. Our findings suggest that recurring gene body promoter hypomethylation events, along with histone H3K4 trimethylation, alter the transcriptional landscape of GBM through the activation of a limited number of normally silenced promoters within gene bodies, in at least one case leading to expression of an oncogenic protein.

Large-scale reconstruction of 3D structures of human chromosomes from chromosomal contact data

Chromosomes are not positioned randomly within a nucleus, but instead, they adopt preferred spatial conformations to facilitate necessary long-range gene–gene interactions and regulations. Thus, obtaining the 3D shape of chromosomes of a genome is critical for understanding how the genome folds, functions and how its genes interact and are regulated. Here, we describe a method to reconstruct preferred 3D structures of individual chromosomes of the human genome from chromosomal contact data generated by the Hi-C chromosome conformation capturing technique. A novel parameterized objective function was designed for modeling chromosome structures, which was optimized by a gradient descent method to generate chromosomal structural models that could satisfy as many intra-chromosomal contacts as possible. We applied the objective function and the corresponding optimization method to two Hi-C chromosomal data sets of both a healthy and a cancerous human B-cell to construct 3D models of individual chromosomes at resolutions of 1 MB and 200 KB, respectively. The parameters used with the method were calibrated according to an independent fluorescence in situ hybridization experimental data. The structural models generated by our method could satisfy a high percentage of contacts (pairs of loci in interaction) and non-contacts (pairs of loci not in interaction) and were compatible with the known two-compartment organization of human chromatin structures. Furthermore, structural models generated at different resolutions and from randomly permuted data sets were consistent.

Dietary methionine intake and risk of incident colorectal cancer: a meta-analysis of 8 prospective studies involving 431,029 participants

Background

Methionine is one of the key components of one carbon metabolism. Experimental studies indicate that methionine may reduce inflammation-induced colon cancer. However, epidemiologic findings as to whether dietary methionine intake influences colorectal cancer incidence in humans are inconsistent.

Objective

To investigate the relationship between dietary methionine intake and risk of colorectal cancer by performing a meta-analysis of prospective studies.

Methods

Eligible studies were identified by searching PubMed and Embase and by reviewing the bibliographies of the retrieved publications. The summary risk estimates were computed using both a random- effects and a fixed-effects model.

Results

Eight eligible prospective cohort studies involving 431,029 participants and 6,331 colorectal cancer cases were identified. According to the random-effects model, the summary relative risks (RRs) for the highest compared with the lowest intake of methionine were 0.89 (95% confidence interval [CI] = 0.77-1.03) for colorectal cancer, 0.77 (95% CI = 0.64 - 0.92) for colon cancer, and 0.88 (95% CI = 0.55-1.42) for rectal cancer. In the stratified analysis, a significant inverse association between dietary methionine intake and risk of colorectal cancer was observed in studies with longer follow-up time (RR=0.81, 95% CI= 0.70- 0.95), in Western studies (RR= 0.83, 95% CI = 0.73 - 0.95) and in men (RR = 0.75, 95% CI= 0.57-0.99). We found no indication of publication bias.

Conclusion

This meta-analysis indicates that dietary methionine intake may be associated with decreased risk of colorectal cancer, especially colon cancer. More prospective studies with long follow-up time are needed to confirm these findings.

Accuracy of methionine-PET in predicting the efficacy of heavy-particle therapy on primary adenoid cystic carcinomas of the head and neck

BACKGROUND

We evaluated whether or not PET or PET/CT using L-methyl-[11C]-methionine (MET) can allow for the early prediction of local recurrence and metastasis, as well as the prognosis (disease-specific survival), in patients with adenoid cystic carcinoma of the head and neck treated by carbon ion beam radiotherapy.

METHODS

This was a retrospective cohort study of sixty-seven patients who underwent a MET-PET or PET/CT study prior to and one month after the completion of carbon ion radiotherapy (CIRT). The minimum follow-up period for survivors was 12 months. The MET accumulation of the tumor was evaluated using the semiquantitative tumor to normal tissue ratio (TNR). A univariate analysis was conducted using the log-rank method, and the Cox model was used in a multivariate survival regression analysis.

RESULTS

The average TNR prior to and following treatment was 4.8 (±1.5) and 3.0 (±1.3), respectively, showing a significant decrease following treatment. In the univariate analysis, a high TNR prior to treatment (TNRpre) was a significant factor for predicting the occurrence of metastasis and the disease-specific survival. A high TNR following treatment (TNRpost) was a significant factor for predicting the development of local recurrence. The residual ratio of TNR changes (TNRratio) seemed to be less useful than the TNRpre. In the multivariate analysis, the TNRpost and tumor size were the factors found to significantly influence the risk of local recurrence. The TNRpre, TNRratio and tumor size were all significant factors influencing the occurrence of metastasis. Regarding the disease-specific survival, the TNRpre and age were the only factors with a significant influence on the outcome.

CONCLUSIONS

The TNRpre was a factor that was significantly related to the occurrence of metastasis and the disease-specific survival after CIRT for adenoid cystic carcinoma of the head and neck. The TNRpost was a factor that was significantly related to the development of local recurrence. Thus, MET-PET or PET/CT can be useful for predicting or determining the therapeutic efficacy of CIRT.

Prospective study of alcohol consumption and the risk of colorectal cancer before and after folic acid fortification in the United States

PURPOSE

To evaluate the influence of alcohol consumption on the risk of colorectal cancer according to folic acid fortification period in the United States.

METHODS

We evaluated the association between alcohol consumption and colorectal cancer by fortification period (before 1998 vs. after 1998) in 2 prospective cohort studies, the Nurses' Health Study (NHS) of women and the Health Professionals Follow-up Study (HPFS) of men, in which 2793 cases of invasive colorectal cancer were documented.

RESULTS

Alcohol consumption was associated with an increased risk of colorectal cancer. Among nonusers of multivitamins and/or folic acid supplements, the pooled multivariate relative risk for ≥30 g/d drinkers versus nondrinkers was 1.36 (95% confidence interval [95% CI], 1.09-1.70; P for trend, 0.02). The effect of alcohol consumption was slightly stronger in the prefolic acid fortification period (1980 NHS/1986 HPFS-1998) than in the postfortification period (1998-2008); the pooled multivariate relative risks for ≥30 g/d drinkers versus nondrinkers were 1.31 (95% CI, 1.00-1.71; P for trend, 0.10) in the prefortification period and 1.07 (95% CI, 0.69-1.65; P for trend, 0.67) in the postfortification period.

CONCLUSIONS

Folic acid fortification may attenuate the adverse effect of high alcohol consumption on the risk of colorectal cancer.

Epigenetic modulation by methionine deficiency attenuates the potential for gastric cancer cell dissemination

INTRODUCTION

Methionine dependency occurs frequently in tumor cells. Here we have investigated the effect of methionine deficiency on metastatic potential of gastric cancer cells in vitro and in vivo.

MATERIALS AND METHODS

Model of peritoneal carcinomatosis and xenograft was generated by intraperitoneal or subcutaneous implantation of gastric cancer cells in NOD-SCID mice. In comparison to control medium, 3-day culture of MKN45, MKN74, and KATOIII cells in a methionine-deficient medium inhibited cell proliferation, increased the rate of cell apoptosis, and reduced cell adhesion and migration. In the xenograft model induced by implantation of MNK45 and MNK74 cells, two cycles of methionine-deficient diet reduced the tumor growth. Further on, a 10-day cycle of methionine-deficient diet reduced the number of peritoneal nodules in the model of peritoneal carcinomatosis induced by MKN45 cells injection. Finally, a microarray analysis of the methylation of promoter CpG islets demonstrated that methionine deficiency reduced the promoter methylation of E-cadherin whose expression was markedly increased in vivo and in vitro.

RESULTS

In summary, we have provided evidence that a methionine-deficient diet modulates the growth of gastric tumor cells and in vitro deficiency of methionine increased apoptosis and decreased cellular adhesion and migration associated to epigenetic change of E-cadherin gene, in vivo and in vitro.

Isocorydine inhibits cell proliferation in hepatocellular carcinoma cell lines by inducing G2/m cell cycle arrest and apoptosis

The treatment of human hepatocellular carcinoma (HCC) cell lines with (+)-isocorydine, which was isolated and purified from Papaveraceae sp. plants, resulted in a growth inhibitory effect caused by the induction of G2/M phase cell cycle arrest and apoptosis. We report that isocorydine induces G2/M phase arrest by increasing cyclin B1 and p-CDK1 expression levels, which was caused by decreasing the expression and inhibiting the activation of Cdc25C. The phosphorylation levels of Chk1 and Chk2 were increased after ICD treatment. Furthermore, G2/M arrest induced by ICD can be disrupted by Chk1 siRNA but not by Chk2 siRNA. In addition, isocorydine treatment led to a decrease in the percentage of CD133(+) PLC/PRF/5 cells. Interestingly, isocorydine treatment dramatically decreased the tumorigenicity of SMMC-7721 and Huh7 cells. These findings indicate that isocorydine might be a potential therapeutic drug for the chemotherapeutic treatment of HCC.

The preclinical discovery of bacterial therapy for the treatment of metastatic cancer with unique advantages

INTRODUCTION

The potential of bacteria as therapeutics for cancer has a long history, dating at least as far back as the early 19(th) Century. Bacteria have a large genome that can be manipulated in order to target and eradicate tumors. Many types of bacteria have been shown to target tumors but most are obligate anaerobes whose growth is confined to the necrotic parts of tumors, thereby limiting their efficacy. Salmonella, on the other hand, are facultative aerobes that can grow aerobically or anaerobically and, therefore, grow on viable tumor tissue as well as necrotic tissue.

AREAS COVERED

The article focuses on the double amino-acid auxotrophs of Salmonella typhimurium. These auxotrophs, which have no attenuating mutations and can grow in both viable and necrotic areas of tumors but not normal tissue, have shown particular effectiveness in mouse models of metastatic cancer. The approach described here is a significant improvement over previous bacterial tumor-therapy strategies which must be combined with toxic chemotherapy in order to be effective. This review uniquely discusses the critical points to optimally engineer Salmonella typhimurium for cancer therapy.

EXPERT OPINION

Bacterial therapy offers significant advantages over chemical or biological drugs or oncolytic viruses. Of these types of bacterial therapy, bacteria that can grow in both viable and necrotic areas of the tumors without growing in normal tissue hold the greatest promise in the treatment of cancer. Salmonella typhimurium shows much promise for this paradigm.

Purification and characterization of a new L-methioninase from solid cultures of Aspergillus flavipes

L-Methioninase was purified to electrophoretic homogeneity from cultures of Aspergillus flavipes using anion-exchange and gel filtration chromatography by 12.1 fold compared to the crude enzyme preparation. The purified enzyme had a molecular mass of 47 kDa under denaturing conditions and an isoelectric point of 5.8 with no structural glycosyl residues. The enzyme had optimum activity at pH 7.8 and pH stability from 6.8-8.0 at 35°C. The enzyme appeared to be catalytically stable below 40°C. The enzyme activity was strongly inhibited by DL-propargylglycine, hydroxylamine, PMSF, 2-mercaptoethanol, Hg(+), Cu(2+), and Fe(2+), with slight inhibition by Triton X-(100). A flavipes L-methioninase has a higher catalytic affinity towards L-methionine (Km, 6.5 mM and Kcat, 14.1 S(-1)) followed by a relative demethiolating activity to L-homo-cysteine (Km, 12 mM and Kcat, 9.3 S(-1)). The enzyme has two absorption maxima at 280 and 420 nm, typical of other PLP-enzymes. Apo-L-methioninase has the ability to reconstitute its structural catalytic state completely upon addition of 0.15 mM PLP. L-Methioninase has neither an appreciable effect on liver function, platelet aggregation, nor hemolysis of human blood. The purified L-methioninase from solid cultures of A. flavipes displayed unique biochemical and catalytic properties over the currently applied Pseudomonad enzyme.

A study on the prognostic evaluation of carbon ion radiotherapy for head and neck adenocarcinoma with C-11 methionine PET

PURPOSE

Carbon ion radiotherapy (CIRT) has been developed, and a phase I/II CIRT trial has been conducted in patients with adenocarcinoma in the head and neck region. We evaluated whether the L-methyl [11C]-methionine (MET) uptake could be an early predictor for local recurrence, metastasis, and the prognosis in patients with adenocarcinoma in the head and neck region.

METHODS

Twenty-six patients were prospectively studied by MET-positron emission tomography (PET) before and about 1 month after CIRT. The tumor MET uptake was measured with the semiquantitative tumor to normal tissue ratio (TNR). The tumor TNR and relevant clinical parameters were then evaluated by both univariate and multivariate analyses.

RESULTS

The average TNRs before and after the treatment were 6.2 (± 2.2) and 3.9 (± 1.7), respectively, and significant differences were observed between them. In a univariate analysis, both local recurrence and metastasis were observed more frequently in the group with a higher TNR before and after the treatment than a lower TNR, and the prognosis was also poor. The cut-off values were 9.3, 4.9, and 5.1 before the treatment and 4.9, 4.2, and 4.3 after the treatment, respectively. In the rate of TNR changes before and after the treatment, metastasis was observed more frequently in the group with lower rates of change, and the prognosis was poor. The cut-off values for metastasis and prognosis determination were 18.0% and 16.9%, respectively. In a multivariate analysis, significant differences were observed for all relationships except for the relationship between the TNR before the treatment and local recurrence. Significant differences were observed for metastasis and prognosis in the rate of TNR changes before and after the treatment.

CONCLUSIONS

The determination of treatment effectiveness using TNR in CIRT for head and neck adenocarcinoma is an independent factor for predicting local recurrence, the incidence of metastasis, and the prognosis. MET-PET is therefore considered to be useful for determining the treatment effectiveness in patients with head and neck adenocarcinoma undergoing CIRT.

Imaging with non-FDG PET tracers: outlook for current clinical applications

Apart from the historical and clinical relevance of positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG), various other new tracers are gaining a remarkable place in functional imaging. Their contribution to clinical decision-making is irreplaceable in several disciplines. In this brief review we aimed to describe the main non-FDG PET tracers based on their clinical relevance and application for patient care.

Localization of medullary thyroid carcinoma after surgery using (11)C-methionine PET/CT: comparison with (18)F-FDG PET/CT

Tumor localization is difficult in patients with medullary thyroid carcinoma (MTC) that have persistent hypercalcitoninemia after thyroidectomy. In this study, the (11)C-methionine positron emission tomography/computed tomography (PET/CT) was compared with the (18)F-FDG PET/CT for diagnostic sensitivity in detecting residual or metastatic disease. (11)C-methionine PET/CT and (18)F-FDG PET/CT were performed on 16 consecutive patients with MTC that had persistent hypercalcitoninemia after surgery in this prospective, single-center study. Patient- and lesion-based analyses were performed using a composite reference standard which was the sum of the lesions confirmed by all combined modalities, including neck ultrasonography (US) with or without fine needle aspiration cytology, CT, bone scan, magnetic resonance imaging (MRI), and surgery. By patient-based analysis, the sensitivities of (11)C-methionine PET/CT and (18)F-FDG PET/CT were both 63%. By lesion-based analysis, the sensitivity of (11)C-methionine PET/CT was similar to (18)F-FDG PET/CT (73% vs. 80%). Excluding hepatic lesions, which could not be detected because of physiological uptake of methionine by the liver, the sensitivity of (11)C-methionine PET/CT was better than (18)F-FDG PET/CT especially for detecting cervical lymph node lesions; however, it was not superior to US. All patients with serum calcitonin levels ≥370 pg/mL showed uptake by (11)C-methionine PET/CT and (18)F-FDG PET/CT. This preliminary data showed that despite its similar sensitivity to (18)F-FDG PET/CT for detecting residual or metastatic MTC, (11)C-methionine PET/CT provided minimal additional information compared to combined (18)F-FDG PET/CT and neck US.

Mice heterozygous for germ-line mutations in methylthioadenosine phosphorylase (MTAP) die prematurely of T-cell lymphoma

Large homozygous deletions of 9p21 that inactivate CDKN2A, ARF, and MTAP are common in a wide variety of human cancers. The role for CDKN2A and ARF in tumorigenesis is well established, but whether MTAP loss directly affects tumorigenesis is unclear. MTAP encodes the enzyme methylthioadenosine phosphorylase, a key enzyme in the methionine salvage pathway. To determine if loss of MTAP plays a functional role in tumorigenesis, we have created an MTAP-knockout mouse. Mice homozygous for a MTAP null allele (Mtap(lacZ)) have an embryonic lethal phenotype dying around day 8 postconception. Mtap/Mtap(lacZ) heterozygotes are born at Mendelian frequencies and appear indistinguishable from wild-type mice during the first year of life, but they tend to die prematurely with a median survival of 585 days. Autopsies on these animals reveal that they have greatly enlarged spleens, altered thymic histology, and lymphocytic infiltration of their livers, consistent with lymphoma. Immunohistochemical staining and fluorescence-activated cell sorting analysis indicate that these lymphomas are primarily T-cell in origin. Lymphoma-infiltrated tissues tend to have reduced levels of Mtap mRNA and MTAP protein in addition to unaltered levels of methyldeoxycytidine. These studies show that Mtap is a tumor suppressor gene independent of CDKN2A and ARF.

S-adenosylmethionine stabilizes cystathionine beta-synthase and modulates redox capacity

The transsulfuration pathway converts homocysteine to cysteine and represents the metabolic link between antioxidant and methylation metabolism. The first and committing step in this pathway is catalyzed by cystathionine beta-synthase (CBS), which is subject to complex regulation, including allosteric activation by the methyl donor, S-adenosylmethionine (AdoMet). In this study, we demonstrate that methionine restriction leads to a >10-fold decrease in CBS protein levels, and pulse proteolysis studies reveal that binding of AdoMet stabilizes the protein against degradation by approximately 12 kcal/mol. These observations predict that under pathological conditions where AdoMet levels are diminished, CBS, and therefore glutathione levels, will be reduced. Indeed, we demonstrate this to be the case in a mouse model for spontaneous steatohepatitis in which the gene for the MAT1A isoenzyme encoding AdoMet synthetase has been disrupted, and in human hepatocellular carcinoma, where MAT1A is silenced. Furthermore, diminished CBS levels are associated with reduced cell viability in hepatoma cells challenged with tert-butyl hydroperoxide. This study uncovers a mechanism by which CBS is allosterically activated by AdoMet under normal conditions but is destabilized under pathological conditions, for redirecting the metabolic flux toward methionine conservation. A mechanistic basis for the coordinate changes in redox and methylation metabolism that are a hallmark of several complex diseases is explained by these observations.

Physicochemical and Pharmacokinetic Characterization of Highly Potent Recombinant l-Methionine γ-Lyase Conjugated with Polyethylene Glycol as an Antitumor Agent

A highly potent recombinant L-methionine gamma-lyase (METase) conjugated with polyethylene glycol (PEG) was characterized physicochemically and pharmacokinetically in vivo and in vitro. Pegylated METase (PEG-METase), which contains pyridoxal 5'-phosphate (PLP) as a cofactor in the molecule, is a potent anticancer agent that can deplete L-methionine from plasma. Although pegylation decreased its specific activity, dithiothreitol (DTT) treatment increased it over three times with the detachment of one PEG moiety modified with a cysteine residue. We can produce DTT-treated PEG-METase on a large scale in sufficient quality for therapeutic use. The superiority of DTT-treated PEG-METase was confirmed by the enhancement of L-methionine depletion and amelioration of pharmacokinetics in mice. The holoenzyme of DTT-treated PEG-METase gave a several times larger area under the plasma concentration curve than that of DTT-untreated PEG-METase, not because of an increase of the half-life but because of high specific activity. Conversely, simultaneous PLP infusion led to a greatly increased half-life of the holoenzyme. DTT-treated PEG-METase administration with PLP infusion was the most useful combination for maximizing the potency of the enzyme. We showed that serum albumin interfered with holoenzyme activity in vitro. The decrease of holoenzyme activity was dependent on the type of serum albumin. We concluded that PLP was released from PEG-METase by serum albumin in vivo and in vitro. The deleterious effect of PLP dissociation from PEG-METase could be improved by supplementing PLP and oleic acid. Their synergistic effect in preventing a decrease of the holoenzyme activity was also observed.

Antisense inhibition of methylenetetrahydrofolate reductase reduces cancer cell survival in vitro and tumor growth in vivo

PURPOSE

Many cancer lines are methionine dependent and decrease proliferation when methionine supply is limited. Methylenetetrahydrofolate reductase (MTHFR) generates the folate derivative for homocysteine remethylation to methionine. We investigated the effect of antisense-mediated inhibition of MTHFR on survival of human cancer cells.

EXPERIMENTAL DESIGN

We examined the in vitro and in vivo anticancer effects of a combination of MTHFR antisense and standard cytotoxic drugs.

RESULTS

Specific antisense against MTHFR (EX5) showed significant inhibitory effects on growth of human colon, lung, breast, prostate, and neuroblastoma tumor cells in vitro compared with that of the control oligonucleotide. Cytotoxic drugs (5-fluorouracil, cisplatin, or paclitaxel) potentiated the effect of EX5. In vivo, antisense alone or in combination with cytotoxic drugs inhibited the growth of human colon and lung carcinoma xenografts. In comparison with control oligonucleotide, treatment with EX5 inhibited growth of colon tumors and lung tumors by 60% and 45%, respectively. EX5 with 5-fluorouracil decreased growth of colon tumors by an additional 30% compared with EX5 alone, and EX5 with cisplatin decreased growth of lung tumors by an additional 40% compared with cisplatin alone. Growth inhibition by EX5 was associated with decreased amounts of MTHFR protein and with increased amounts of an apoptosis marker.

CONCLUSIONS

Our results confirm that MTHFR inhibition decreases tumor growth and suggest that inhibition of MTHFR by antisense or small molecules may be a novel anticancer approach.

Expression profiling of homocysteine junction enzymes in the NCI60 panel of human cancer cell lines

Methionine metabolism provides two key cellular reagents: S-adenosylmethionine and glutathione, derived from the common intermediate, homocysteine. A majority of cancer cells exhibit a methionine-dependent phenotype whereby they are unable to grow in medium in which methionine is replaced by its precursor, homocysteine. Additionally, CpG island hypermethylation of tumor suppressor gene promoters is observed in a background of global hypomethylation in cancerous cells. In this study, we have profiled the expression levels of the homocysteine junction enzymes, methionine synthase (MS), MS reductase (MSR), and cystathionine beta-synthase (CBS) in the NCI60 panel of cancer cell lines. The doubling time of non-small lung cell cancer lines, which exhibit the lowest levels of MS within the panel, was significantly correlated with expression of MS. The ratio of MS to MSR varied over a 5-fold range in the different cell types, which may modulate methionine synthesis. Interestingly, markedly reduced CBS expression was seen in the methionine-dependent prostate cancer cell line, PC-3, but not in the methionine-independent cell line, DU-145. However, neither provision of the transsulfuration pathway product, cysteine, nor overexpression of CBS rescued the growth impairment, indicating that reduced CBS was not responsible for the methionine-dependent phenotype in this cell line.

Prospective Study of Alcohol Drinking and Renal Cell Cancer Risk in a Cohort of Finnish Male Smokers

Of the few studies that have examined alcohol consumption in relation to risk of renal cell cancer (RCC), most are case-control studies. The extent to which alcohol affects RRC risk is unclear. We prospectively examined the association between total alcohol intake as well as specific types of alcoholic beverage and RCC in a large cohort of Finnish male smokers. Men from the Alpha-Tocopherol, BetaCarotene (ATBC) Cancer Prevention Study were followed for 12 years and RCC cases were identified. Alcohol consumption was assessed at baseline using a questionnaire previously shown to be both reproducible and valid. Cox proportional hazards modeling was used to adjust simultaneously for known or suspected risk factors for RCC. We ascertained 195 incident cases of RCC. In multivariate analysis, the relative risks and 95% confidence intervals (CI) of RCC according to increasing quartiles of total alcohol intake were 1.0, 0.91 (0.62-1.33), 0.94 (0.64-1.38), and 0.53 (0.34-0.83), respectively (P value for trend = 0.005); for spirit consumption, 1.0, 0.93 (0.63-1.Fspiait39), 0.84 (0.58-1.20), and 0.55 (0.36-0.85) (P for trend = 0.02); and for beer intake, 1.0, 1.22 (0.85-1.76), 0.83 (0.57-1.22), and 0.55 (0.36-0.85) (P for trend = 0.003). Too few people in this cohort drank wine to assess its association with risk of RCC. These data suggest that alcohol consumption is associated with decreased risk of RCC in male smokers. Because most of the risk reductions were seen at the highest quartile of alcohol intake and alcohol is a risk factor for a number of cancers particularly among smokers, these data should be interpreted with caution.

Methionine cytotoxicity in the human breast cancer cell line MCF-7

Among the first nutrients to be linked to cancer were methyl group containing nutrients including methionine. Methionine and its metabolic derivatives are essential components in several indispensable biological reactions including protein synthesis, polyamine synthesis, and many transmethylation reactions. The purpose of this study was to determine the extent to which methionine excess affects the proliferation and gene expression of the human breast cancer cell line MCF-7. Cells were first grown in control medium; the medium was then replaced with either control or methionine-supplemented treatment media. We found that 5 and 10 g/L methionine significantly suppressed cell growth on day 1, and no further growth was detected after 3 d of treatment. Cell proliferation in the methionine treated group was significantly lower than that of the control group. Northern analysis revealed that expression of p53 in methionine-treated MCF-7 cells was approximately 70% lower than that of control cells. p53 is a key cell cycle regulatory protein that has been implicated in tumorigenesis and cancer progression. Alteration of the p53 tumor suppressor gene is the most common genetic change found in a wide variety of malignancies, including cancer. This study shows that excess methionine (5 g/L) inhibited proliferation of MCF-7 breast cancer cells, and down regulation of p53 is correlated with this inhibition. These findings may aid in the development of nutritional strategies for breast cancer therapy.

PEGylation Confers Greatly Extended Half-Life and Attenuated Immunogenicity to Recombinant Methioninase in Primates

Methionine depletion by recombinant methioninase (rMETase) has been demonstrated previously to be highly effective in tumor-bearing mouse models. However, the therapeutic potential of rMETase has been limited by its short plasma half-life and immunologic effects, including high antibody production in mice and monkeys and anaphylactic reactions in monkeys. To overcome these limits of rMETase, the enzyme has been coupled to methoxypolyethylene glycol succinimidyl glutarate (MEGC-PEG-5000). In this study, we evaluated the pharmacokinetics, antigenicity and toxicity of MEGC-PEG-rMETase in Macaca fascicularis monkeys using an escalating-dose strategy. Dose ranging studies at 1,000, 4,000, and 8,000 units/kg i.v. determined that a single dose of 4,000 units/kg was sufficient to reduce plasma methionine to <5 micromol/L for 12 hours. Pharmacokinetic analysis with the single 4,000 units/kg dose showed that MEGC-PEG-rMETase holoenzyme activity was eliminated with a biological half-life of 1.3 hours, and the MEGC-PEG-rMETase apoenzyme was eliminated with a biological half-life of 90 hours, an approximately 36-fold increase compared with non-PEGylated rMETase. A single dose at 2,000 units/kg of MEGC-PEG-rMETase resulted in an apoenzyme half-life of 143 hours. A seven-day i.v. administration of 4,000 units/kg every 12 hours resulted in a steady-state depletion of plasma methionine to <5 micromol/L. The only manifest toxicity was decreased food intake and slight weight loss. Red cell values and hemoglobin declined transiently during treatment but recovered after cessation of treatment. Subsequent challenges on days 29, 50 and, 71 did not result in any immunologic reactions. This result is in contrast to non-PEGylated rMETase, which elicited anaphylactic reactions in monkeys. Anti-MEGC-PEG-rMETase antibodies (at 10(-2)) were found on day 29, and these increased to 10(-3) to 10(4) on day 71, 100 to 1,000-fold less than antibodies elicited by naked rMETase. Although anti-MEGC-PEG-rMETase antibodies were produced, no neutralizing antibody was identified, and each challenge dose was effective in depleting plasma methionine levels. The results of the present study demonstrate that PEGylation greatly prolongs serum half-life of the rMETase apoenzyme and eliminated anaphylactic reactions. The results indicate a profile with respect to serum half-life, toxicity, and antigenicity that suggest clinical potential of MEGC-PEG-rMETase.