TSPAN5, ERICH3 and selective serotonin reuptake inhibitors in major depressive disorder: pharmacometabolomics-informed pharmacogenomics.

Millions of patients suffer from major depressive disorder (MDD), but many do not respond to selective serotonin reuptake inhibitor (SSRI) therapy. We used a pharmacometabolomics-informed pharmacogenomics research strategy to identify genes associated with metabolites that were related to SSRI response. Specifically, 306 MDD patients were treated with citalopram or escitalopram and blood was drawn at baseline, 4 and 8 weeks for blood drug levels, genome-wide single nucleotide polymorphism (SNP) genotyping and metabolomic analyses. SSRI treatment decreased plasma serotonin concentrations (P<0.0001). Baseline and plasma serotonin concentration changes were associated with clinical outcomes (P<0.05). Therefore, baseline and serotonin concentration changes were used as phenotypes for genome-wide association studies (GWAS). GWAS for baseline plasma serotonin concentrations revealed a genome-wide significant (P=7.84E-09) SNP cluster on chromosome four 5' of TSPAN5 and a cluster across ERICH3 on chromosome one (P=9.28E-08) that were also observed during GWAS for change in serotonin at 4 (P=5.6E-08 and P=7.54E-07, respectively) and 8 weeks (P=1.25E-06 and P=3.99E-07, respectively). The SNPs on chromosome four were expression quantitative trait loci for TSPAN5. Knockdown (KD) and overexpression (OE) of TSPAN5 in a neuroblastoma cell line significantly altered the expression of serotonin pathway genes (TPH1, TPH2, DDC and MAOA). Chromosome one SNPs included two ERICH3 nonsynonymous SNPs that resulted in accelerated proteasome-mediated degradation. In addition, ERICH3 and TSPAN5 KD and OE altered media serotonin concentrations. Application of a pharmacometabolomics-informed pharmacogenomic research strategy, followed by functional validation, indicated that TSPAN5 and ERICH3 are associated with plasma serotonin concentrations and may have a role in SSRI treatment outcomes.

Altered interactions of tryptophan metabolites in first-episode neuroleptic-naive patients with schizophrenia.

Schizophrenia is characterized by complex and dynamically interacting perturbations in multiple neurochemical systems. In the past, evidence for these alterations has been collected piecemeal, limiting our understanding of the interactions among relevant biological systems. Earlier, both hyper- and hyposerotonemia were variously associated with the longitudinal course of schizophrenia, suggesting a disturbance in the central serotonin (5-hydroxytryptamine (5-HT)) function. Using a targeted electrochemistry-based metabolomics platform, we compared metabolic signatures consisting of 13 plasma tryptophan (Trp) metabolites simultaneously between first-episode neuroleptic-naive patients with schizophrenia (FENNS, n=25) and healthy controls (HC, n=30). We also compared these metabolites between FENNS at baseline (BL) and 4 weeks (4w) after antipsychotic treatment. N-acetylserotonin was increased in FENNS-BL compared with HC (P=0.0077, which remained nearly significant after Bonferroni correction). N-acetylserotonin/Trp and melatonin (Mel)/serotonin ratios were higher, and Mel/N-acetylserotonin ratio was lower in FENNS-BL (all P-values<0.0029), but not after treatment, compared with HC volunteers. All three groups had highly significant correlations between Trp and its metabolites, Mel, kynurenine, 3-hydroxykynurenine and tryptamine. However, in the HC, but in neither of the FENNS groups, serotonin was highly correlated with Trp, Mel, kynurenine or tryptamine, and 5-hydroxyindoleacetic acid (5HIAA) was highly correlated with Trp, Mel, kynurenine or 3-hydroxykynurenine. A significant difference between HC and FENNS-BL was further shown only for the Trp-5HIAA correlation. Thus, some metabolite interactions within the Trp pathway seem to be altered in the FENNS-BL patients. Conversion of serotonin to N-acetylserotonin by serotonin N-acetyltransferase may be upregulated in FENNS patients, possibly related to the observed alteration in Trp-5HIAA correlation. Considering N-acetylserotonin as a potent antioxidant, such increases in N-acetylserotonin might be a compensatory response to increased oxidative stress, implicated in the pathogenesis of schizophrenia.

Neuroprotective effects of creatine in a transgenic animal model of amyotrophic lateral sclerosis.

Mitochondria are particularly vulnerable to oxidative stress, and mitochondrial swelling and vacuolization are among the earliest pathologic features found in two strains of transgenic amyotrophic lateral sclerosis (ALS) mice with SOD1 mutations. Mice with the G93A human SOD1 mutation have altered electron transport enzymes, and expression of the mutant enzyme in vitro results in a loss of mitochondrial membrane potential and elevated cytosolic calcium concentration. Mitochondrial dysfunction may lead to ATP depletion, which may contribute to cell death. If this is true, then buffering intracellular energy levels could exert neuroprotective effects. Creatine kinase and its substrates creatine and phosphocreatine constitute an intricate cellular energy buffering and transport system connecting sites of energy production (mitochondria) with sites of energy consumption, and creatine administration stabilizes the mitochondrial creatine kinase and inhibits opening of the mitochondrial transition pore. We found that oral administration of creatine produced a dose-dependent improvement in motor performance and extended survival in G93A transgenic mice, and it protected mice from loss of both motor neurons and substantia nigra neurons at 120 days of age. Creatine administration protected G93A transgenic mice from increases in biochemical indices of oxidative damage. Therefore, creatine administration may be a new therapeutic strategy for ALS.

Induction of a cellular enzyme for energy metabolism by transforming domains of adenovirus E1a.

Brain creatine kinase is a major enzyme of cellular energy metabolism. It is overexpressed in a wide range of tumor cell lines and is used as a tumor marker. We reported recently that the promoter of the human gene has a strong sequence similarity to the adenovirus E2E promoter. This similarity suggested that the brain creatine kinase gene may be regulated by the viral activator E1a. Experiments reported here showed that both enzyme activity and mRNA levels were induced by the oncogenic products of the E1a region of adenovirus type 5, but unlike the viral E2E promoter, which is induced predominantly by E1a domain 3, brain creatine kinase induction required domains 1 and 2. These domains are important for transformation and for the association of E1a with the retinoblastoma gene product and other cellular proteins. The induction by an oncogene of a cellular gene for energy metabolism may be of significance for the metabolic events that take place after oncogenic activation.

The steroid metabolome in women with premenstrual dysphoric disorder during GnRH agonist-induced ovarian suppression: effects of estradiol and progesterone addback.

Clinical evidence suggests that symptoms in premenstrual dysphoric disorder (PMDD) reflect abnormal responsivity to ovarian steroids. This differential steroid sensitivity could be underpinned by abnormal processing of the steroid signal. We used a pharmacometabolomics approach in women with prospectively confirmed PMDD (n=15) and controls without menstrual cycle-related affective symptoms (n=15). All were medication-free with normal menstrual cycle lengths. Notably, women with PMDD were required to show hormone sensitivity in an ovarian suppression protocol. Ovarian suppression was induced for 6 months with gonadotropin-releasing hormone (GnRH)-agonist (Lupron); after 3 months all were randomized to 4 weeks of estradiol (E2) or progesterone (P4). After a 2-week washout, a crossover was performed. Liquid chromatography/tandem mass spectrometry measured 49 steroid metabolites in serum. Values were excluded if >40% were below the limit of detectability (n=21). Analyses were performed with Wilcoxon rank-sum tests using false-discovery rate (q<0.2) for multiple comparisons. PMDD and controls had similar basal levels of metabolites during Lupron and P4-derived neurosteroids during Lupron or E2/P4 conditions. Both groups had significant increases in several steroid metabolites compared with the Lupron alone condition after treatment with E2 (that is, estrone-SO4 (q=0.039 and q=0.002, respectively) and estradiol-3-SO4 (q=0.166 and q=0.001, respectively)) and after treatment with P4 (that is, allopregnanolone (q=0.001 for both PMDD and controls), pregnanediol (q=0.077 and q=0.030, respectively) and cortexone (q=0.118 and q=0.157, respectively). Only sulfated steroid metabolites showed significant diagnosis-related differences. During Lupron plus E2 treatment, women with PMDD had a significantly attenuated increase in E2-3-sulfate (q=0.035) compared with control women, and during Lupron plus P4 treatment a decrease in DHEA-sulfate (q=0.07) compared with an increase in controls. Significant effects of E2 addback compared with Lupron were observed in women with PMDD who had significant decreases in DHEA-sulfate (q=0.065) and pregnenolone sulfate (q=0.076), whereas controls had nonsignificant increases (however, these differences did not meet statistical significance for a between diagnosis effect). Alterations of sulfotransferase activity could contribute to the differential steroid sensitivity in PMDD. Importantly, no differences in the formation of P4-derived neurosteroids were observed in this otherwise highly selected sample of women studied under controlled hormone exposures.

Evaluation of creatine analogues as a new class of anticancer agents using freshly explanted human tumor cells.

BACKGROUND: The creatine kinase (CK) isozymes and their substrates, creatine and creatine phosphate, are believed to play a pivotal role in energy transduction in tissues with large, fluctuating energy demands, such as skeletal muscle, heart, and brain. This enzyme system may also be involved in the process of cellular transformation. Inhibition of tumor cell growth by creatine analogues has been observed and may be due to the ability of these analogues to impair cellular energy generation and utilization. PURPOSE: An in vitro human tumor colony-forming assay was used to predict the clinical usefulness of creatine analogues as anticancer agents. METHODS: The ability of cyclocreatine (1-carboxymethyl-2-iminoimidazolidine) and homocyclocreatine (1-carboxyethyl-2-iminoimidazolidine) to inhibit the growth of cells prepared from tumor samples taken directly from patients was evaluated by quantitative measurement of colony formation in a soft-agar cell culture assay system. Cyclocreatine was tested in this human tumor colony-forming assay at concentrations ranging from 0.067 to 20 mM against 128 tumor samples, 51 of which formed colonies in the assay and were considered evaluable. Homocyclocreatine was similarly tested at concentrations from 0.2 to 20 mM against 139 tumor samples; 54 were considered evaluable. The colony-forming assay was also used to compare the efficacy of the creatine analogues to representatives from the six major classes of standard chemotherapeutics (alkylating agents, antimetabolites, DNA intercalators, platinum compounds, topoisomerase inhibitors, and tubulin-interacting agents). In addition, CK levels were measured in 192 tumor samples that were taken from 166 patients. RESULTS: Cyclocreatine and homocyclocreatine, at concentrations previously achieved in animal tissues (7-20 mM), had antitumor activity against 19% and 50%, respectively, of tumor samples that formed colonies in the assay. Cyclocreatine was effective against a subset of tumors sensitive to homocyclocreatine (P = .023; Fisher's exact test), which was the more potent creatine analogue in this assay (P < .001; McNemar's test). No relationships were seen between tumor samples sensitive to the creatine analogues and those sensitive to standard chemotherapeutics. Pairwise Wilcoxon rank sum tests indicated that CK activity was significantly higher in tumors with any growth in the colony assay compared with tumors that did not grow (P < .025). CONCLUSIONS: The creatine analogues, cyclocreatine and homocyclocreatine, effectively reduced colony formation of freshly explanted human tumor cells. The mechanism of action or resistance to these compounds seems to differ from those of standard chemotherapeutics. IMPLICATIONS: Creatine analogues that may alter the energy status of the tumor cell potentially represent promising new anticancer agents that function through a unique mechanism.

Cell cycle studies of cyclocreatine, a new anticancer agent.

Cyclocreatine (CCr), a substrate analogue of creatine kinase (CK), exhibits antitumor activity in vitro and in vivo. To address its mechanism of action, we have examined its effects on tumor cell proliferation, viability, and cell cycle progression. Complete inhibition of proliferation of ME-180 cervical carcinoma cells was observed within 8 h of exposure to CCr and was characterized by an inhibition of progression out of all phases of the cell cycle. This initial effect was partially reversible on drug removal. Increased cytotoxicity was observed after several days of drug exposure and was most specific to cells in S. Previous studies have shown that CCr supports ATP regeneration through the CK system less efficiently than the natural substrate creatine and that CCr is active against tumor cell lines with elevated levels of CK. We propose here that the general inhibition of cell cycle progression reflects an effect of CCr on tumor cell energy availability through CK and that impaired energy homeostasis for several days leads to tumor cell death. Our results point out the unique nature of CCr as an anticancer agent that inhibits progression out of all phases of the cell cycle.

Cyclocreatine (1-carboxymethyl-2-iminoimidazolidine) inhibits growth of a broad spectrum of cancer cells derived from solid tumors.

In an effort to investigate the role of creatine kinase and its substrates in malignancy we have tested the effect of cyclocreatine [1-carboxymethyl-2-iminoimidazolidine (CCr)] on the growth of tumor cells in vitro and in vivo. CCr is phosphorylated by creatine kinase to yield a synthetic phosphagen [(N-phosphorylcyclocreatine (CCr approximately P)] with thermodynamic and kinetic properties distinct from those of creatine phosphate. We show that CCr accumulates as CCr approximately P in tumor cells expressing a high level of creatine kinase, and that the accumulation of this phosphagen is detrimental to tumor cell growth. Tumor cell lines expressing a low level of creatine kinase accumulate much less CCr approximately P, and consequently are growth inhibited only at higher concentrations of CCr. When these resistant cells are transfected with a creatine kinase B expression vector, they express creatine kinase, accumulate CCr approximately P, and are growth inhibited. In vivo, in nude mouse xenografts, the rate of growth of a high creatine kinase expressing tumor cell line is inhibited in animals fed 1% CCr. Our results indicate that CCr inhibits the growth of tumor cells in vitro and in vivo.

Metabolomic signatures of drug response phenotypes for ketamine and esketamine in subjects with refractory major depressive disorder: new mechanistic insights for rapid acting antidepressants.

Ketamine, at sub-anesthetic doses, is reported to rapidly decrease depression symptoms in patients with treatment-resistant major depressive disorder (MDD). Many patients do not respond to currently available antidepressants, (for example, serotonin reuptake inhibitors), making ketamine and its enantiomer, esketamine, potentially attractive options for treatment-resistant MDD. Although mechanisms by which ketamine/esketamine may produce antidepressant effects have been hypothesized on the basis of preclinical data, the neurobiological correlates of the rapid therapeutic response observed in patients receiving treatment have not been established. Here we use a pharmacometabolomics approach to map global metabolic effects of these compounds in treatment-refractory MDD patients upon 2 h from infusion with ketamine (n=33) or its S-enantiomer, esketamine (n=20). The effects of esketamine on metabolism were retested in the same subjects following a second exposure administered 4 days later. Two complementary metabolomics platforms were used to provide broad biochemical coverage. In addition, we investigated whether changes in particular metabolites correlated with treatment outcome. Both drugs altered metabolites related to tryptophan metabolism (for example, indole-3-acetate and methionine) and/or the urea cycle (for example, citrulline, arginine and ornithine) at 2 h post infusion (q<0.25). In addition, we observed changes in glutamate and circulating phospholipids that were significantly associated with decreases in depression severity. These data provide new insights into the mechanism underlying the rapid antidepressant effects of ketamine and esketamine, and constitute some of the first detailed metabolomics mapping for these promising therapies.

Metabolomic Signatures for Drug Response Phenotypes: Pharmacometabolomics Enables Precision Medicine.

The scaling up of data in clinical pharmacology and the merger of systems biology and pharmacology has led to the emergence of a new discipline of Quantitative and Systems Pharmacology (QSP). This new research direction might significantly advance the discovery, development, and clinical use of therapeutic drugs. Research communities from computational biology, systems biology, and biological engineering--working collaboratively with pharmacologists, geneticists, biochemists, and analytical chemists--are creating and modeling large data on drug effects that is transforming our understanding of how these drugs work at a network level. In this review, we highlight developments in a new and rapidly growing field--pharmacometabolomics--in which large biochemical data-capturing effects of genome, gut microbiome, and environment exposures is revealing information about metabotypes and treatment outcomes, and creating metabolic signatures as new potential biomarkers. Pharmacometabolomics informs and complements pharmacogenomics and together they provide building blocks for QSP.

Pharmacometabolomic Assessments of Atenolol and Hydrochlorothiazide Treatment Reveal Novel Drug Response Phenotypes.

Achieving hypertension (HTN) control and mitigating the adverse health effects associated with HTN continues to be a global challenge. Some individuals respond poorly to current HTN therapies, and mechanisms for response variation remain poorly understood. We used a nontargeted metabolomics approach (gas chromatography time-of-flight/mass spectrometry gas chromatography time-of-flight/mass spectrometry) measuring 489 metabolites to characterize metabolite signatures associated with treatment response to anti-HTN drugs, atenolol (ATEN), and hydrochlorothiazide (HCTZ), in white and black participants with uncomplicated HTN enrolled in the Pharmacogenomic Evaluation of Antihypertensive Responses study. Metabolite profiles were significantly different between races, and metabolite responses associated with home diastolic blood pressure (HDBP) response were identified. Metabolite pathway analyses identified gluconeogenesis, plasmalogen synthesis, and tryptophan metabolism increases in white participants treated with HCTZ (P < 0.05). Furthermore, we developed predictive models from metabolite signatures of HDBP treatment response (P < 1 × 10(-5)). As part of a quantitative systems pharmacology approach, the metabolites identified herein may serve as biomarkers for improving treatment decisions and elucidating mechanisms driving HTN treatment responses.

Enhancement of the recovery of rat hearts after prolonged cold storage by cyclocreatine phosphate.

The present study determined whether the administration of cyclocreatine phosphate (CCrP) prior to ischemia can enhance the recovery of rat hearts hypothermically preserved for a prolonged period. Rats (n = 6 per group) were injected intravenously with 1 ml saline or CCrP (500 mg/kg). After 2 hr, hearts were excised and arrested by an infusion of University of Wisconsin solution. Saline hearts were then incubated in 40 ml UW, while CCrP hearts were incubated in 40 ml UW containing 100 mg CCrP; a mixture that is now referred to as Hartford Hospital (HH) solution. After 6 hr of storage at 4 degrees C, hearts were reperfused in the Langendorff mode for 15 min and then in the working heart mode for 30 min. Results indicated that the recovery of cardiac function--measured as aortic flow, coronary flow, cardiac output, stroke volume, and stroke work--was significantly better in CCrP group (50-55% baseline) compared with that of saline hearts (20-25%). Although no difference in enzyme leakage (i.e., creatine kinase) or lactate was detected between the two groups, the increase in heart weight after the initial 6-hr storage was significantly higher in saline hearts compared with that of CCrP hearts. Results of this study support the conclusion that CCrP treatment provides improved functional recovery after prolonged hypothermic preservation.

Cyclocreatine (1-carboxymethyl-2-iminoimidazolidine) inhibits the replication of human herpes viruses.

The creatine kinase/creatine phosphate (CK/CrP) system plays an important role in cellular energy homeostasis. CK isoenzymes, which reversibly generate ATP from CrP, are compartmentalized at cellular sites where energy is produced or utilized. It has been noted that the expression of CK is induced in cells infected by several DNA viruses, implicating a role for cellular energy modulation as an important step for efficient viral replication. A CK substrate analog, 1-carboxymethyl-2-iminoimidazolidine (cyclocreatine; CCr), was tested in vitro for antiviral activity against a variety of herpes viruses and RNA viruses. Several members of the human herpes virus family were found to be sensitive to CCr, including herpes simplex types 1 and 2 (HSV-1 and HSV-2). varicella-zoster virus, and cytomegalovirus. When administered to mice infected vaginally with HSV-2, CCr significantly reduced mortality, reduced vaginal lesion scores, and lowered the titers of recoverable virus. This treatment combined with acyclovir appeared to enhance the antiviral effects of acyclovir. In a second model, mice infected intraperitoneally with HSV-2 and treated with CCr showed a significant increase in survival compared to placebo. We conclude that CCr is the first example of a new class of antiviral compounds that target the CK/CrP system.

Cyclocreatine in cancer chemotherapy.

Cyclocreatine, an analog of creatine, is an efficient substrate for creatine kinase, but its phosphorylated form is a poor phosphate donor in comparison with creatine phosphate. Cyclocreatine was not very cytotoxic upon 24 h of exposure of human SW2 small-cell lung cancer cells to concentrations of up to 5 mM. However, combinations of cyclocreatine (0.5 mM, 24 h) with each of four antitumor alkylating agents, cis-diamminedichloroplatinum(II), melphalan, 4-hydroperoxycyclophosphamide, and carmustine, resulted in additive to greater-than-additive cytotoxicity toward exponentially growing SW2 cells. The greatest levels of synergy were seen at higher concentrations of 4-hydroperoxycyclophosphamide and carmustine as determined by isobologram analysis. In vivo cyclocreatine (0.5 or 1 g/kg) was more effective if given i.v. rather than i.p. The longest tumor-growth delays, up to 10 days, were produced by extended regimens of cyclocreatine. Cyclocreatine was an effective addition to therapy with standard anticancer agents including cis-diamminedichloroplatinum(II), cyclophosphamide, Adriamycin, or 5-fluorouracil. No additional toxicity was observed when 10 days of cyclocreatine treatment was given with full standard-dose regimens of each drug. The resultant increases in tumor-growth delay were 1.7- to 2.4-fold as compared with those obtained for each of the drugs alone. These results indicate that cyclocreatine may be an effective single agent and an effective addition to combination chemotherapy regimens.

Neuroprotective effects of creatine administration against NMDA and malonate toxicity.

We examined whether creatine administration could exert neuroprotective effects against excitotoxicity mediated by N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainic acid. Oral administration of 1% creatine significantly attenuated striatal excitotoxic lesions produced by NMDA, but had no effect on lesions produced by AMPA or kainic acid. Both creatine and nicotinamide can exert significant protective effects against malonate-induced striatal lesions. We, therefore, examined whether nicotinamide could exert additive neuroprotective effects with creatine against malonate-induced lesions. Nicotinamide with creatine produced significantly better neuroprotection than creatine alone against malonate-induced lesions. Creatine can, therefore, produce significant neuroprotective effects against NMDA mediated excitotoxic lesions in vivo and the combination of nicotinamide with creatine exerts additive neuroprotective effects.

Creatine and phosphocreatine analogs: anticancer activity and enzymatic analysis.

The brain isoform of creatine kinase has been implicated in cellular transformation processes. Cyclocreatine, a creatine kinase substrate analog, was previously shown to be cytotoxic to a broad spectrum of solid tumors. We have synthesized, enzymatically characterized, and evaluated the antitumor activity of a series of substrate analogs of creatine kinase. Using in vitro assays, we demonstrate that several of these analogs are cytotoxic to the human ME-180 cervical carcinoma, the MCF-7 breast adenocarcinoma and the HT-29 colon adenocarcinoma cell lines at low mM concentrations. Analogs that were active in vitro delayed the growth of a subcutaneously implanted rat 13,762 mammary adenocarcinoma. Tumor growth delays of 6-8 days were achieved, which is comparable to effects seen with standard regimens of currently used anticancer drugs. These studies further establish the creatine kinase system as a promising and novel target for anticancer chemotherapy drug design.

Antiproliferative effects of cyclocreatine on human prostatic carcinoma cells.

Creatine kinase (CK; EC 2.7.3.2) isoenzymes and their substrates have an important function in cellular energy generation and utilization. The brain isoform (CK-BB) has been implicated in cellular transformation processes involving the oncogenic products of the Ela virus and the p53 tumor suppressor gene. Cyclocreatine, an analogue of creatine, has been previously shown to inhibit the growth of a broad spectrum of cancer cells derived from solid tumors. Results reported herein indicate an increased level of creatine kinase activity in human prostate carcinoma cell lines and inhibitory effects of cyclocreatine alone and in combination with adriamycin on the growth of these cells in vitro and in vivo, in immune-deprived mice. Our results suggest the possible use of cyclocreatine in the treatment of prostatic carcinoma.

The synthetic phosphagen cyclocreatine phosphate inhibits the growth of a broad spectrum of solid tumors.

BACKGROUND: The brain isoform of creatine kinase (CKBB), an enzyme involved in energy metabolism, has been implicated in cellular transformation process. Cyclocreatine (CCr), a creatine kinase (CK) substrate analogue, was shown to inhibit the growth of a broad spectrum of solid tumors expressing high levels of CK. Cyclocreatine phosphate (CCrP) generated by CK, was proposed to be the active form responsible for growth inhibition. MATERIALS AND METHODS: We synthesized CCrP and tested its cellular uptake and anti tumor activity in stem cell assays and in athymic mouse models. RESULTS: CCrP seems to be taken up by cells and inhibits the growth of solid tumors with high levels of CK. CCr and CCrP have similar specificity and potency. CONCLUSION: The observation that only high-CK cell lines were responsive to CCrP, similar to CCr, indicates that the enzyme requirement was not bypassed. We propose that CK is a target for CCrP, and is involved in mediating its antiproliferative activity.

Antitumor activity of creatine analogs produced by alterations in pancreatic hormones and glucose metabolism.

When rats bearing the 13,762 mammary carcinoma were treated with intravenously administered creatine analogs, cyclocreatine, beta-guanidinopropionic acid or creatine phosphate on days 4 through 8 and 14 through 18 post tumor implantation, the tumor growth delay produced varied with whether the animals were drinking water or sugar water over the course of the study. The tumor growth delays increased when the animals drank sugar water from 9.3, 1.6 and 7.6 days for cyclocreatine, beta-guanidinopropionic acid and creatine phosphate, respectively, to 15.0, 6.3 and 12.6 days. Blood glucose was decreased over the course of the creatine analog treatment regimen and the skeletal muscle transport protein GLUT-4 increased 1.5 to 2-fold with the creatine analog treatments. Plasma insulin was profoundly decreased to 20-25% of normal by the creatine analog treatment while plasma glucagon levels were increased. Plasma somatostatin increased 3- to 4-fold during the administration of the creatine analogs. These results implicate alterations in pancreatic hormone balance in the antitumor activity of these creatine analogs.

Pharmacometabolomics: implications for clinical pharmacology and systems pharmacology.

Metabolomics, the study of metabolism at an "omic" level, has the potential to transform our understanding of mechanisms of drug action and the molecular basis for variation in drug response. It is now possible to define metabolic signatures of drug exposure that can identify pathways involved in both drug efficacy and adverse drug reactions. In addition, the "metabotype," the metabolic "signature" of a patient, is a unique identity that contains information about drug response and disease heterogeneity. The application of metabolomics for the study of drug effects and variation in drug response is creating "pharmacometabolomics," a discipline that will contribute to personalized drug therapy and will complement pharmacogenomics by capturing environmental and microbiome-level influences on response to drug therapy. This field has the potential to transform pharmacology and clinical pharmacology in significant ways and will contribute to efforts for personalized therapy. This overview highlights developments in the new discipline of pharmacometabolomics.