Strategies for Utilizing Neuroimaging Biomarkers in CNS Drug Discovery and Development: CINP/JSNP Working Group Report.

Despite large unmet medical needs in the field for several decades, CNS drug discovery and development has been largely unsuccessful. Biomarkers, particularly those utilizing neuroimaging, have played important roles in aiding CNS drug development, including dosing determination of investigational new drugs (INDs). A recent working group was organized jointly by CINP and Japanese Society of Neuropsychopharmacology (JSNP) to discuss the utility of biomarkers as tools to overcome issues of CNS drug development.The consensus statement from the working group aimed at creating more nuanced criteria for employing biomarkers as tools to overcome issues surrounding CNS drug development. To accomplish this, a reverse engineering approach was adopted, in which criteria for the utilization of biomarkers were created in response to current challenges in the processes of drug discovery and development for CNS disorders. Based on this analysis, we propose a new paradigm containing 5 distinct tiers to further clarify the use of biomarkers and establish new strategies for decision-making in the context of CNS drug development. Specifically, we discuss more rational ways to incorporate biomarker data to determine optimal dosing for INDs with novel mechanisms and targets, and propose additional categorization criteria to further the use of biomarkers in patient stratification and clinical efficacy prediction. Finally, we propose validation and development of new neuroimaging biomarkers through public-private partnerships to further facilitate drug discovery and development for CNS disorders.

Combining onartuzumab with erlotinib inhibits growth of non-small cell lung cancer with activating EGFR mutations and HGF overexpression.

Erlotinib, a tyrosine kinase inhibitor of the epidermal growth factor receptor (EGFR-TKI), benefits survival of patients with non-small cell lung cancer (NSCLC) who harbor activating EGFR mutations. However, elevated expression of hepatocyte growth factor (HGF), a ligand of the MET receptor tyrosine kinase, causes erlotinib resistance. Because onartuzumab, a monovalent antibody to MET, blocks HGF-induced MET activation, the addition of onartuzumab to erlotinib may improve therapeutic efficacy. We engineered the human NSCLC cell line PC-9 (MET-positive cells harboring an exon 19 deletion of EGFR) to overexpress hHGF and evaluated the effects of an onartuzumab and erlotinib combination in vitro and in vivo in xenograft models. A stable clone of PC-9/hHGF was less sensitive to erlotinib than the parental PC-9, and the addition of onartuzumab to erlotinib suppressed the proliferation of these cells in vitro. In PC-9/hHGF xenograft tumors, onartuzumab or erlotinib alone minimally inhibited tumor growth; however, combining onartuzumab and erlotinib markedly suppressed tumor growth. The total MET protein level was decreased in PC-9/hHGF cells, because MET is constitutively phosphorylated by autocrine HGF, leading to its ubiquitination and degradation. Onartuzumab reduced phospho-MET levels, inhibited MET ubiquitination, and consequently restored MET protein levels. Moreover, in NSCLC clinical specimens harboring activating EGFR mutations, more than 30% of patients expressed high levels of HGF. Our findings raised the possibility that patients with NSCLC with EGFR mutations who express high levels of HGF may benefit from onartuzumab and erlotinib combination therapy, and that HGF can be a novel biomarker for selecting such patients.

Expression analysis of actin-related genes as an underlying mechanism for mood disorders.

In this study, we explored the newly postulated 'disturbed cytoskeletal' theory of mood disorders. Firstly, we identified Cap1, a gene for important mediator of actin turnover, as a cogent quantitative trait gene for depressive trait of mice by combining the results of our prior genetic and current genome-wide expression analyses. Then we rigorously examined 'core' actin-related gene expression in the frontal cortex of C57BL/6 (B6) (prone to depression) and C3H/He (C3) (resistant to depression) mice. We confirmed that Cap1 was down-regulated at both transcript and protein levels in B6. Other differentially regulated genes included cofilin1 and profilin1 (up-regulated in B6), and a Rho-family GTPase member (Pak1) (down-regulated in B6). Thirdly, we investigated the 'core' actin-pathway components in human postmortem prefrontal cortices, and observed trend for CAP1 reduction in the bipolar brains. These data suggest that the balance of actin dynamics might be altered towards actin depolymerization in mood disorders.

Genome-wide expression analysis detects eight genes with robust alterations specific to bipolar I disorder: relevance to neuronal network perturbation.

The limited number of genome-wide transcriptome analyses using the postmortem brains of bipolar disorder sufferers has not produced a clear consensus on the molecular pathways affected by the disorder. To expand the knowledge in this area, we examined the expression levels of more than 12 000 genes in Brodmann's Area (BA), 46 (dorsolateral prefrontal cortex) from bipolar I disorder and control samples using Affymetrix GeneChips. This analysis detected 108 differentially expressed genes in bipolar brains. Validation studies using quantitative RT-PCR on the two original diagnostic cohorts plus tissue from schizophrenic subjects, confirmed the differential expressions of eight genes (RAP1GA1, SST, HLA-DRA, KATNB1, PURA, NDUFV2, STAR and PAFAH1B3) in a bipolar-specific manner and one gene (CCL3) which was downregulated in both bipolar and schizophrenic brains. Of these, protein levels of RAP1GA1 (RAP1 GTPase activating protein 1) showed a trend of increase in BA46 from bipolar brains, in keeping with mRNA transcript levels. Transmission disequilibrium analysis of the nine genes using 43 single nucleotide polymorphisms (SNPs) in 229 National Institute of Mental Health bipolar trios exposed nominal SNP association and modest empirical haplotypic association (P=0.033) between SST (somatostatin) and disease. Finally, gene network analysis using the currently obtained expression data highlighted cellular growth and nervous system development pathways as potential targets in the molecular pathophysiology of bipolar disorder.

Distinguishable haplotype blocks in the HTR3A and HTR3B region in the Japanese reveal evidence of association of HTR3B with female major depression.

BACKGROUND: Genetic variations in the serotonin receptor 3A (HTR3A) and 3B (HTR3B) genes, positioned in tandem on chromosome 11q23.2, have been shown to be associated with psychiatric disorders in samples of European ancestry. But the polymorphisms highlighted in these reports map to different locations in the two genes, therefore it is unclear which gene exerts a stronger effect on susceptibility. METHODS: To determine the haplotype block structure in the genomic regions of HTR3A and HTR3B, and to examine whether genetic variations in the region show evidence of association with schizophrenia and affective disorder in the Japanese, we performed haplotype-based case-control analysis using 29 polymorphisms. RESULTS: Two haplotype blocks each were revealed for HTR3A and HTR3B in Japanese samples. In HTR3B, haplotype block 2 that included a nonsynonymous single nucleotide polymorphism (SNP), yielded evidence of association with major depression in females (global p = .0023). Analysis employing genome-wide SNPs using the STRUCTURE program did not detect population stratification in the samples. CONCLUSIONS: Our results suggest an important role for HTR3B in major depression in women and also raise the possibility that previously proposed disease-associated SNPs in the HTR3A/B region in Caucasians are in linkage disequilibrium with haplotype block 2 of HTR3B in the Japanese.

Altered RNA editing of serotonin 2C receptor in a rat model of depression.

Altered RNA editing of serotonin 2C receptor (HTR2C) has been suggested to be involved in the pathophysiology of major depression. Here we examined RNA editing status of HTR2C in the learned helplessness (LH) rats, one of well-established animal models of depression. LH rats showed the significantly increased RNA editing of site E, and tendency for increased RNA editing of other editing sites. Treatment with fluoxetine, a selective serotonin reuptake inhibitor, or imipramine, a tricyclic antidepressant, affected the RNA editing status of the LH rats. Although, these antidepressants differentially altered RNA editing status, they commonly reduced RNA editing efficiency of site E. We further revealed that altered RNA editing in the LH rats and by antidepressants was not explained by altered expression of RNA editing enzymes or their substrates (adenosine deaminases that act on RNA, HTR2C, and spliced form of HTR2C). These results suggest that alteration of RNA editing of HTR2C may play a role in the pathophysiology of depression and action of antidepressants.

A family-based association study and gene expression analyses of netrin-G1 and -G2 genes in schizophrenia.

BACKGROUND: The netrin-G1 (NTNG1) and -G2 (NTNG2) genes, recently cloned from mouse, play a role in the formation and/or maintenance of glutamatergic neural circuitry. Accumulating evidence strongly suggests that disturbances of neuronal development and the N-methyl-d-aspartate receptor-mediated signaling system might represent a potential pathophysiology in schizophrenia. We therefore set out to examine the genetic contribution of human NTNG1 and NTNG2 to schizophrenia. METHODS: Twenty-one single nucleotide polymorphisms (SNPs) from NTNG1 and 10 SNPs from NTNG2 were analyzed in 124 schizophrenic pedigrees. All genotypes were determined with the TaqMan assay. The expression levels of NTNG1 and NTNG2 were examined in the frontal (Brodmann's Area [BA]11 and BA46) and temporal (BA22) cortices from schizophrenic and control postmortem brains. The isoform-specific expression of NTNG1 splice variants was assessed in these samples. RESULTS: Specific haplotypes encompassing alternatively spliced exons of NTNG1 were associated with schizophrenia, and concordantly, messenger ribonucleic acid isoform expression was significantly different between schizophrenic and control brains. An association between NTNG2 and schizophrenia was also observed with SNPs and haplotypes that clustered in the 5' region of the gene. CONCLUSIONS: The NTNG1 and NTNG2 genes might be relevant to the pathophysiology of schizophrenia.

[Approaches for identifying depression-related genes using animal models].

The pathophysiology of psychiatric diseases including depression is characterized by the involvement of many genes contributing a small effect. This genetic complexity means larger amounts of information can be gathered by studying the disease process as a single entity, in an animal model. A number of genetically modified animals showing both depressive and anti-depressive phenotypes have been generated. Approximately ten of these models are in current use for screening novel antidepressants. The development of new therapies is intimately linked to the elucidation of mechanisms via which the drugs work and therefore the mechanisms of disease. It is now possible to combine the information from animal models with sophisticated technology including DNA microarray analysis. In this setting, the animal models can provide information about genes altered in both the depressive state and after anti-depressive treatment, whilst DNA microarrays can identify these genes, as well as the direction of change. This information will eventually lead to the discovery of new mechanisms involved in disease pathology. Here we summarize approaches for identifying genes related to depression.

Identification of multiple genetic loci linked to the propensity for "behavioral despair" in mice.

The forced swim test (FST) and tail suspension test (TST) are widely used and well established screening paradigms for antidepressants. A variety of antidepressive agents are known to reduce immobility time in both FST and TST. To identify genetic determinants of immobility duration in both tests, we analyzed 560 F2 mice from an intercross between C57BL/6 (B6) and C3H/He (C3) strains. Composite interval mapping revealed five major loci (suggestive and significant linkage) affecting immobility in the FST, and four loci for the TST. The quantitative trait loci (QTL) on chromosomes 8 and 11 overlap between the two behavioral measures. Genome-wide interaction analysis, which was developed to identify locus pairs that may contribute epistatically to a phenotype, detected two pairs of chromosomal loci for the TST. The QTL on chromosome 11 and its associated epistatic TST-QTL on chromosome X encode gamma-aminobutyric acid type A (GABA(A)) receptor subunits as candidates. Sequence and expression analyses of these genes from the two parental strains revealed a significantly lower expression of the alpha1 subunit gene in the frontal cortex of B6 mice compared to C3 mice. The present quantitative trait study should open up avenues for identifying novel molecular targets for antidepressants and unraveling the complex genetic mechanisms of depressive and anxiety disorders.