Effective in vitro evaluation of the risk of histamine release related to valemetostat tosylate using MRGPRX2-expressing cells.

Mas-related G-protein-coupled receptor X2 (MRGPRX2), expressed on mast cells, is associated with drug-induced pseudo-allergic reactions. Although it is well known that there are differences of sensitivity between species in the pseudo-allergic reactions, no platform for evaluating a human risk of the pseudo-allergic reactions observed in nonclinical studies has been established. Valemetostat tosylate, developed as an anti-cancer drug, induced histamine release in a nonclinical study with dogs. The purpose of the current study was to identify the mechanism and assess the human risk of valemetostat-tosylate-induced histamine release using dog and human MRGPRX2-expressing cells. In an experiment with human or dog MRGPRX2-expressing cells, valemetostat tosylate caused activation of human and dog MRGPRX2. Importantly, the EC50 for dog MRGPRX2 was consistent with the Cmax value at which histamine release was observed in dogs. Furthermore, the EC50 for human MRGPRX2 was ca. 27-fold higher than that for dog MRGPRX2, indicating a species difference in histamine-releasing activity. In a clinical trial, histamine release was not observed in patients receiving valemetostat tosylate. In conclusion, an in vitro assay using human and animal MRGPRX2-expressing cells would be an effective platform to investigate the mechanism and predict the human risk of histamine release observed in nonclinical studies.

Potent and Selective PTDSS1 Inhibitors Induce Collateral Lethality in Cancers with PTDSS2 Deletion.

SIGNIFICANCE: This study identifies a specific dependency on PTDSS1 for phosphatidylserine synthesis following PTDSS2 deletion and introduces novel PTDSS1 inhibitors as a therapeutic option to induce collateral lethality in cancer with PTDSS2 loss.

Determination of key residues in MRGPRX2 to enhance pseudo-allergic reactions induced by fluoroquinolones.

MAS-related G protein-coupled receptor X2 (MRGPRX2), expressed in human mast cells, is associated with drug-induced pseudo-allergic reactions. Dogs are highly sensitive to the anaphylactoid reactions induced by certain drugs including fluoroquinolones. Recently, dog MRGPRX2 was identified as a functional ortholog of human MRGPRX2, with dog MRGPRX2 being particularly sensitive to fluoroquinolones. The aim of this study was to determine key residues responsible for the enhanced activity of fluoroquinolone-induced histamine release associated with MRGPRX2. Firstly, a structure model of human and dog MRGPRX2 was built by homology modeling, and docking simulations with fluoroquinolones were conducted. This model indicated that E164 and D184, conserved between human and dog, are essential for the binding to fluoroquinolones. In contrast, F78 (dog: Y) and M109 (dog: W) are unconserved residues, to which the species difference in fluoroquinolone sensitivity is attributable. Intracellular calcium mobilisation assay with human MRGPRX2 mutants, in which residues at positions 78 and 109 were substituted to those of dog MRGPRX2, revealed that M109 and F78 of human MRGPRX2 are crucial residues for enhancing the fluoroquinolone-induced histamine release. In conclusion, these key residues have important clinical implications for revealing the mechanisms and predicting the risks of fluoroquinolone-mediated pseudo-allergic reactions in humans.

Biochemical profiles of rat primary cultured hepatocytes following treatment with rotenone, FCCP, or (+)-usnic acid.

The metabolomic profiles of rat primary hepatocytes following treatment with rotenone, FCCP, or (+)-usnic acid were determined using liquid chromatography-mass spectrometry/mass spectrometry and gas chromatography-mass spectrometry. Significant and similar changes in the levels of 283 biochemical metabolites were associated with the three treatments compared with solvent control samples. Overall, the three treatments generated similar global biochemical profiles, with some minor differences associated with rotenone treatment. All three treatments resulted in a shift in energy metabolism as demonstrated by decreased glycogen stores and glycolysis. A reduced antioxidant response was detected in cells following all treatments. In addition, bile acid biosynthesis decreased as a potential consequence of increased oxidative stress by all three treatments. Conversely, rotenone treatment induced a number of changes after 1 hr, which were not detected in FCCP- or (+)-usnic acid-treated samples; these changes were not sustained over time and included increased NAD+ salvage and lysine degradation. In conclusion, these biochemical profiles could provide new insights into the mechanism(s) of mitochondrial toxicity.

Fluoroquinolones suppress gluconeogenesis by inhibiting fructose 1,6-bisphosphatase in primary monkey hepatocytes.

Dysglycemia is one of the most serious adverse events associated with the clinical use of certain fluoroquinolones. The purpose of this study was to investigate the effects of the representative fluoroquinolones moxifloxacin and gatifloxacin on hepatic gluconeogenesis using primary monkey hepatocytes. Glucose production was induced after the cells were incubated for 4 h with 10 mM sodium lactate and 1 mM sodium pyruvate as gluconeogenic substrates. Under these conditions, moxifloxacin and gatifloxacin dose-dependently suppressed gluconeogenesis at concentrations of 100 µM or higher. Transcriptome analysis of rate-limiting enzymes involved in hepatic gluconeogenesis revealed that moxifloxacin and gatifloxacin at a concentration of 1000 µM did not affect the expression of key gluconeogenic enzymes such as phosphoenolpyruvate carboxykinase, glucose 6-phosphatase, and fructose 1,6-bisphosphatase. Furthermore, metabolome analysis, in vitro glucose production assay using additional gluconeogenic substrates, and fructose 1,6-bisphosphatase assay using the cell extracts showed that fluoroquinolones enzymatically suppressed hepatic gluconeogenesis by inhibiting fructose 1,6-bisphosphatase. These inhibitory effects may involve in the clinically relevant dysglycemia associated with fluoroquinolones in human.

Establishment of an in vitro cytotoxicity assay platform using primary monkey cardiomyocytes.

To establish an in vitro cytotoxicity assay platform using monkey cardiomyocytes, we isolated primary cardiomyocytes from fetal cynomolgus monkeys at different gestation days (from day 39 to 90) using the trypsin and collagenase digestion method, which was identical to the standard procedure for rat cardiomyocytes. Under these conditions, the primary cells obtained from monkeys at gestation day 63 or earlier showed spontaneous beating, with >80% cells being viable from all fetuses. Transcriptome analysis of the monkey cardiomyocytes indicated that the cells have essential components of cardiac functions, such as myosins, α-actin, cardiac troponins, and calcium-related molecules. The susceptibility to doxorubicin-induced cytotoxicity in monkey cardiomyocytes was comparable to that in rat cardiomyocytes, as evaluated based on intracellular ATP levels. Microarray analysis with Ingenuity Pathway Analysis revealed that doxorubicin predominantly increased the expression of several key genes involved in the endoplasmic reticulum stress pathway in monkey cardiomyocytes than in rat cardiomyocytes. In conclusion, we isolated primary monkey cardiomyocytes that showed similar sensitivity to doxorubicin as compared with rat cardiomyocytes. This in vitro monkey cardiomyocyte assay platform would serve as a powerful tool for the investigation of the interspecies differences in drug-induced cardiotoxicity and its underlying mechanism.

Discovery of DS-6930, a potent selective PPARγ modulator. Part I: Lead identification.

The lead identification of a novel potent selective PPARγ agonist, DS-6930 is reported. To avoid PPARγ-related adverse effects, a partial agonist was designed to prevent the direct interaction with helix 12 of PPARγ-LBD. Because the TZD group is known to interact with helix 12, the TZD in efatutazone (CS-7017) was replaced to discover novel PPARγ intermediate partial agonist 8i. The optimization of 8i yielded 13ac with high potency in vitro. Compound 13ac exhibited robust plasma glucose lowering effects comparable to those of rosiglitazone (3 mg/kg) in Zucker diabetic fatty rats. Upon toxicological evaluation, compound 13ac (300 mg/kg) induced hemodilution to a lower extent than rosiglitazone; however, 13ac elevated liver enzyme activities. X-ray crystallography revealed no direct interaction of 13ac with helix 12, and the additional lipophilic interactions are also suggested to be related to the maximum transcriptional activity of 13ac.

Discovery of DS-6930, a potent selective PPARγ modulator. Part II: Lead optimization.

Attempts were made to reduce the lipophilicity of previously synthesized compound (II) for the avoidance of hepatotoxicity. The replacement of the left-hand side benzene with 2-pyridine resulted in the substantial loss of potency. Because poor membrane permeability was responsible for poor potency in vitro, the adjustment of lipophilicity was examined, which resulted in the discovery of dimethyl pyridine derivative (I, DS-6930). In preclinical studies, DS-6930 demonstrated high PPARγ agonist potency with robust plasma glucose reduction. DS-6930 maintained diminished PPARγ-related adverse effects upon toxicological evaluation in vivo, and demonstrated no hepatotoxicity. Cofactor recruitment assay showed that several cofactors, such as RIP140 and PGC1, were significantly recruited, whereas several canonical factors was not affected. This selective cofactor recruitment was caused due to the distinct binding mode of DS-6930. The calcium salt, DS-6930b, which is expected to be an effective inducer of insulin sensitization without edema, could be evaluated clinically in T2DM patients.

Analysis of Prostate Deformation during a Course of Radiation Therapy for Prostate Cancer.

PURPOSE: Accurate analysis of the correlation between deformation of the prostate and displacement of its center of gravity (CoG) is important for efficient radiation therapy for prostate cancer. In this study, we addressed this problem by introducing a new analysis approach. METHOD: A planning computed tomography (CT) scan and 7 repeat cone-beam CT scans during the course of treatment were obtained for 19 prostate cancer patients who underwent three-dimensional conformal radiation therapy. A single observer contoured the prostate gland only. To evaluate the local deformation of the prostate, it was divided into 12 manually defined segments. Prostate deformation was calculated using in-house developed software. The correlation between the displacement of the CoG and the local deformation of the prostate was evaluated using multiple regression analysis. RESULTS: The mean value and standard deviation (SD) of the prostate deformation were 0.6 mm and 1.7 mm, respectively. For the majority of the patients, the local SD of the deformation was slightly lager in the superior and inferior segments. Multiple regression analysis revealed that the anterior-posterior displacement of the CoG of the prostate had a highly significant correlation with the deformations in the middle-anterior (p < 0.01) and middle-posterior (p < 0.01) segments of the prostate surface (R2 = 0.84). However, there was no significant correlation between the displacement of the CoG and the deformation of the prostate surface in other segments. CONCLUSION: Anterior-posterior displacement of the CoG of the prostate is highly correlated with deformation in its middle-anterior and posterior segments. In the radiation therapy for prostate cancer, it is necessary to optimize the internal margin for every position of the prostate measured using image-guided radiation therapy.

Bacterial ß-glucuronidase inhibition protects mice against enteropathy induced by indomethacin, ketoprofen or diclofenac: mode of action and pharmacokinetics.

1. We have previously demonstrated that a small molecule inhibitor of bacterial ß-glucuronidase (Inh-1; [1-((6,8-dimethyl-2-oxo-1,2-dihydroquinolin-3-yl)-3-(4-ethoxyphenyl)-1-(2-hydroxyethyl)thiourea]) protected mice against diclofenac (DCF)-induced enteropathy. Here we report that Inh-1 was equally protective against small intestinal injury induced by other carboxylic acid-containing non-steroidal anti-inflammatory drugs (NSAIDs), indomethacin (10 mg/kg, ip) and ketoprofen (100 mg/kg, ip). 2. Inh-1 provided complete protection if given prior to DCF (60 mg/kg, ip), and partial protection if administered 3-h post-DCF, suggesting that the temporal window of mucosal protection can be extended for drugs undergoing extensive enterohepatic circulation. 3. Pharmacokinetic analysis of Inh-1 revealed an absolute bioavailability (F) of 21% and a short t1/2 of <1 h. This low F was shown to be due to hepatic first-pass metabolism, as confirmed with the pan-CYP inhibitor, 1-aminobenzotriazole. 4. Using the fluorescent probe 5 (and 6)-carboxy-2',7'-dichlorofluorescein, we demonstrated that Inh-1 did not interfere with hepatobiliary export of glucuronides in gall bladder-cannulated mice. 5. These data are compatible with the hypothesis that pharmacological inhibition of bacterial ß-glucuronidase-mediated cleavage of NSAID glucuronides in the small intestinal lumen can protect against NSAID-induced enteropathy caused by locally high concentrations of NSAID aglycones.

Isoniazid-induced cell death is precipitated by underlying mitochondrial complex I dysfunction in mouse hepatocytes.

Isoniazid (INH) is an antituberculosis drug that has been associated with idiosyncratic liver injury in susceptible patients. The underlying mechanisms are still unclear, but there is growing evidence that INH and/or its major metabolite, hydrazine, may interfere with mitochondrial function. However, hepatic mitochondria have a large reserve capacity, and minor disruption of energy homeostasis does not necessarily induce cell death. We explored whether pharmacologic or genetic impairment of mitochondrial complex I may amplify mitochondrial dysfunction and precipitate INH-induced hepatocellular injury. We found that INH (≤ 3000 µM) did not induce cell injury in cultured mouse hepatocytes, although it decreased hepatocellular respiration and ATP levels in a concentration-dependent fashion. However, coexposure of hepatocytes to INH and nontoxic concentrations of the complex I inhibitors rotenone (3 µM) or piericidin A (30 nM) resulted in massive ATP depletion and cell death. Although both rotenone and piericidin A increased MitoSox-reactive fluorescence, Mito-TEMPO or N-acetylcysteine did not attenuate the extent of cytotoxicity. However, preincubation of cells with the acylamidase inhibitor bis-p-nitrophenol phosphate provided protection from hepatocyte injury induced by rotenone/INH (but not rotenone/hydrazine), suggesting that hydrazine was the cell-damaging species. Indeed, we found that hydrazine directly inhibited the activity of solubilized complex II. Hepatocytes isolated from mutant Ndufs4(+/-) mice, although featuring moderately lower protein expression levels of this complex I subunit in liver mitochondria, exhibited unchanged hepatic complex I activity and were therefore not sensitized to INH. These data indicate that underlying inhibition of complex I, which alone is not acutely toxic, can trigger INH-induced hepatocellular injury.

Uncertainty in patient set-up margin analysis in radiation therapy.

We investigated the uncertainty in patient set-up margin analysis with a small dataset consisting of a limited number of clinical cases over a short time period, and propose a method for determining the optimum set-up margin. Patient set-up errors from 555 registration images of 15 patients with prostate cancer were tested for normality using a quantile-quantile (Q-Q) plot and a Kolmogorov-Smirnov test with the hypothesis that the data were not normally distributed. The ranges of set-up errors include the set-up errors within the 95% interval of the entire patient data histogram, and their equivalent normal distributions were compared. The patient set-up error was not normally distributed. When the patient set-up error distribution was assumed to have a normal distribution, an underestimate of the actual set-up error occurred in some patients but an overestimate occurred in others. When using a limited dataset for patient set-up errors, which consists of only a small number of the cases over a short period of time in a clinical practice, the 2.5% and 97.5% intervals of the actual patient data histogram from the percentile method should be used for estimating the set-up margin. Since set-up error data is usually not normally distributed, these intervals should provide a more accurate estimate of set-up margin. In this way, the uncertainty in patient set-up margin analysis in radiation therapy can be reduced.

Resistance to acetaminophen-induced hepatotoxicity in glutathione S-transferase Mu 1-null mice.

We investigated the role of glutathione S-transferases Mu 1 (GSTM1) in acetaminophen (APAP)-induced hepatotoxicity using Gstm1-null mice. A single oral administration of APAP resulted in a marked increase in plasma alanine aminotransferase accompanied by hepatocyte necrosis 24 hr after administration in wild-type mice, but its magnitude was unexpectedly attenuated in Gstm1-null mice. Therefore, it is suggested that Gstm1-null mice are resistant to APAP-induced hepatotoxicity. To examine the mechanism of this resistance in Gstm1-null mice, we measured phosphorylation of c-jun N-terminal kinase (JNK), which mediates the signal of APAP-induced hepatocyte necrosis, by Western blot analysis 2 and 6 hr after APAP administration. A marked increase in phosphorylated JNK was observed in wild-type mice, but the increase was markedly suppressed in Gstm1-null mice. Therefore, it is suggested that suppressed phosphorylation of JNK may be a main mechanism of the resistance to APAP-induced hepatotoxicity in Gstm1-null mice, although other possibilities of the mechanism cannot be eliminated. Additionally, phosphorylation of glycogen synthase kinase-3ß and mitogen-activated protein kinase kinase 4, which are upstream kinases of JNK in APAP-induced hepatotoxicity, were also suppressed in Gstm1-null mice. A decrease in liver total glutathione 2 hr after APAP administration, which is an indicator for exposure to N-acetyl-p-benzoquinoneimine, the reactive metabolite of APAP, were similar in wild-type and Gstm1-null mice. In conclusion, Gstm1-null mice are considered to be resistant to APAP-induced hepatotoxicity perhaps by the suppression of JNK phosphorylation. This study indicates the novel role of GSTM1 as a factor mediating the cellular signal for APAP-induced hepatotoxicity.

Analysis of the optimum internal margin for respiratory-gated radiotherapy using end-expiratory phase assessments using a motion phantom.

We aimed to optimize internal margin (IM) determination for respiratory-gated radiotherapy using end-expiratory phase assessments using a motion phantom. Four-dimensional computed tomography (4D CT) data were acquired using a GE LightSpeed RT CT scanner, a respiratory-gating system, and a motion phantom designed to move sinusoidally. To analyze the accuracy of 4D CT temporal resolution, a 25.4 mm diameter sphere was inserted into the motion phantom, and we measured the differences in sphere diameters between static and end-exhalation phase images. In addition, the IM obtained from the maximum intensity projection within the gating window (MIP(GW)) image was compared to theoretical value. Cranial-caudal motion displacement ranged from 5.0 to 30.0 mm, and the respiratory period ranged from 2.0 to 6.0 sec. Differences in sphere diameters between static and end-exhalation phase images ranged from 0.37 to 4.6 mm, with 5.0-mm and 30 mm target displacements, respectively. Differences between the IM obtained from the MIP(GW) and the theoretical values ranged from 1.12 to 6.23 mm with 5.0mm and 30 mm target displacements, respectively. These differences increased in proportion to the target velocity due to a motion artifact generated during tube rotation. In this study, the IMs obtained using the MIPGW image were overestimated in all cases. We therefore propose that the internal target volume (ITV) for respiratory-gated radiotherapy should be determined by adding the calculated value to the end-exhalation phase image. We also demonstrate a methodology for subtracting motion artifacts from the ITV using a motion phantom.

Analysis of post-exposure density growth in radiochromic film with respect to the radiation dose.

The post-exposure density growth (PEDG) is one of the characteristics of radiochromic film (RCF). In film dosimetry using RCF and a flatbed scanner, pixel values read out from the RCF are converted to dose (hereafter, film dose) by using a calibration curve. The aim of this study is to analyze the relationship between the pixel value read out from the RCF and the PEDG, and that between the film dose converted from the RCF and the PEDG. The film (GAFCHROMIC EBT) was irradiated with 10-MV X-rays in an ascending 11-dose-step arrangement. The pixel values of the irradiated EBT film were measured at arbitrary hours using an Epson flatbed scanner. In this study, the reference time was 24 h after irradiation, and all dose conversions from the pixel values read out from the EBT film were made using a calibration curve for 24 h after irradiation. For delivered doses of 33 and 348 cGy, the measured pixel values at 0.1 and 16 h after irradiation represented ranges of -9.6% to -0.7% and -3.9% to -0.3%, respectively, of the reference value. The relative changes between the pixel values read out from the EBT film at each elapsed time and that at the reference time decreased with increasing delivered dose. However, the difference range for all the film doses had a width of approximately -10% of the reference value at elapsed times from 0.1 to 16 h, and it showed no dependence on the delivered dose.

Evaluation of hepatic glutathione transferase Mu 1 and Theta 1 activities in humans and mice using genotype information.

We investigated the impact of glutathione transferases Mu 1 (GSTM1)- and glutathione transferase Theta 1 (GSTT1)-null genotypes on hepatic GST activities in humans and compared the results with those of Gstm1- and Gstt1-null mice. In liver with GSTM1/Gstm1-null genotype, GST activity toward p-nitrobenzyl chloride (NBC) was significantly decreased in both humans and mice. In addition, in liver with GSTT1/Gstt1-null genotype, GST activity toward dichloromethane (DCM) was significantly decreased in both humans and mice. Therefore, null genotypes of GSTM1/Gstm1 and GSTT1/Gstt1 are considered to decrease hepatic GST activities toward NBC and DCM, respectively, in both humans and mice. This observation shows the functional similarity between humans and mice for GSTM1 and GSTT1 toward some substrates. In the case of NBC and DCM, Gst-null mice would be relevant models for humans with GST-null genotype. In addition, decreases in GST activities toward 1,2-dichloro-4-nitrobenzene, trans-4-phenyl-3-buten-2-one, and 1-chloro-2,4,-dinitrobenzene were observed in Gstm1-null mice, and a decrease in GST activity toward 1,2-epoxy-3-(p-nitrophenoxy)propane was observed in Gstt1-null mice. However, an impact of GST-null genotypes on GST activities toward these substrates was not observed in humans. In the case of these mouse-specific substrates, Gst-null mice may be relevant models for humans regardless of GST genotype, because GST activities, which are higher in wild-type mice than in humans, were eliminated in Gst-null mice. This study shows that comparison of hepatic GST activities between humans and mice using genotype information would be valuable in using Gst-null mice as human models.

In vitro cytotoxicity assay to evaluate the toxicity of an electrophilic reactive metabolite using glutathione-depleted rat primary cultured hepatocytes.

Glutathione plays an important role as not only a scavenger of reactive oxygen species but also in the conjugation or detoxification of electrophilic reactive metabolites, which has been thought to be one of the causes for idiosyncratic drug toxicity (IDT). Therefore, toxic responses to the reactive metabolites have been expected to be expressed more strongly in a glutathione-depleted condition. In the present study, we attempted to establish an in vitro cytotoxicity assay method to evaluate the toxicity of the reactive metabolite using rat primary cultured hepatocytes with cellular glutathione depletion by l-buthionine-S,R-sulfoximine. Also, we investigated whether the IDT risk is predictable by comparing the cytotoxic sensitivity between glutathione-depleted hepatocytes and untreated hepatocytes. Consequently, 10 drugs of 42 approved drugs, which were classified into 4 IDT categories (Withdrawn, Black box warning, Warning, and Safe), demonstrated higher cytotoxic sensitivity in the glutathione-depleted hepatocytes. Furthermore, a correlation was observed between the incidence of drugs with higher cytotoxic sensitivity in the glutathione-depleted hepatocytes and the IDT risk. The incidence was 50% in the Withdrawn category, 38% in the Black box warning category, 22% in the Warning category, and 8% in the Safe category. These results suggest that the IDT risk of some drugs may be predicted by comparing the cytotoxic sensitivity between them. Additionally, this method may be useful as a screening in the early stage of drug development where leads/candidates are optimized.

Methemoglobinemia induced by 1,2-dichloro-4-nitrobenzene in mice with a disrupted glutathione S-transferase Mu 1 gene.

A specific substrate to Mu class glutathione S-transferase (GST), 1,2-dichloro-4-nitrobenzene (DCNB), was administered to mice with a disrupted GST Mu 1 gene (Gstm1-null mice) to investigate the in vivo role of murine Gstm1 in toxicological responses to DCNB. A single oral administration of DCNB at doses of 500 and 1000 mg/kg demonstrated a marked increase in blood methemoglobin (MetHB) in Gstm1-null mice but not in wild-type mice. Therefore, Gstm1-null mice were considered to be more predisposed to methemoglobinemia induced by a single dosing of DCNB. In contrast, 14-day repeated-dose studies of DCNB at doses up to 600 mg/kg demonstrated a marked increase in blood MetHB in both wild-type and Gstm1-null mice. However, marked increases in the blood reticulocyte count, relative spleen weight, and extramedullary hematopoiesis in the spleen were observed in Gstm1-null mice compared with wild-type mice. In addition, microarray and quantitative reverse transcription-polymerase chain reaction analyses in the spleen showed exclusive up-regulation of hematopoiesis-related genes in Gstm1-null mice. These changes were considered to be adaptive responses to methemoglobinemia and attenuated the higher predisposition to methemoglobinemia observed in Gstm1-null mice in the single-dose study. In toxicokinetics monitoring, DCNB concentrations in plasma and blood cells were higher in Gstm1-null mice than those in wild-type mice, resulting from the Gstm1 disruption. In conclusion, it is suggested that the higher exposure to DCNB due to Gstm1 disruption was reflected in methemoglobinemia in the single-dose study and in adaptive responses in the 14-day repeated-dose study.

Identification of genes related to heart failure using global gene expression profiling of human failing myocardium.

Although various management methods have been developed for heart failure, it is necessary to investigate the diagnostic or therapeutic targets of heart failure. Accordingly, we have developed different approaches for managing heart failure by using conventional microarray analyses. We analyzed gene expression profiles of myocardial samples from 12 patients with heart failure and constructed datasets of heart failure-associated genes using clinical parameters such as pulmonary artery pressure (PAP) and ejection fraction (EF). From these 12 genes, we selected four genes with high expression levels in the heart, and examined their novelty by performing a literature-based search. In addition, we included four G-protein-coupled receptor (GPCR)-encoding genes, three enzyme-encoding genes, and one ion-channel protein-encoding gene to identify a drug target for heart failure using in silico microarray database. After the in vitro functional screening using adenovirus transfections of 12 genes into rat cardiomyocytes, we generated gene-targeting mice of five candidate genes, namely, MYLK3, GPR37L1, GPR35, MMP23, and NBC1. The results revealed that systolic blood pressure differed significantly between GPR35-KO and GPR35-WT mice as well as between GPR37L1-Tg and GPR37L1-KO mice. Further, the heart weight/body weight ratio between MYLK3-Tg and MYLK3-WT mice and between GPR37L1-Tg and GPR37L1-KO mice differed significantly. Hence, microarray analysis combined with clinical parameters can be an effective method to identify novel therapeutic targets for the prevention or management of heart failure.