Assessing the Value of the Zebrafish Conditioned Place Preference Model for Predicting Human Abuse Potential

Regulatory agencies recommend that centrally active drugs are tested for abuse potential before approval. Standard preclinical assessments are conducted in rats or non-human primates (NHPs). This study evaluated the ability of the zebrafish conditioned place preference (CPP) model to predict human abuse outcomes. Twenty-seven compounds from a variety of pharmacological classes were tested in zebrafish CPP, categorized as positive or negative, and analyzed using standard diagnostic tests of binary classification to determine the likelihood that zebrafish correctly predict robust positive signals in human subjective effects studies (+HSE) and/or Drug Enforcement Administration drug scheduling. Results were then compared with those generated for rat self-administration and CPP, as well as NHP self-administration, using this same set of compounds. The findings reveal that zebrafish concordance and sensitivity values were not significantly different from chance for both +HSE and scheduling. Although significant improvements in specificity and negative predictive values were observed for zebrafish relative to +HSE, specificity without sensitivity provides limited predictive value. Moreover, assessments in zebrafish provided no added value for predicting scheduling. By contrast, rat and NHP models generally possessed significantly improved concordance, sensitivity, and positive predictive values for both clinical measures. Although there may be predictive value with compounds from specific pharmacological classes (e.g., µ-opioid receptor agonists, psychostimulants) for zebrafish CPP, altogether these data highlight that using the current methodology, the zebrafish CPP model does not add value to the preclinical assessment of abuse potential.

Suppression of TGFβ and Angiogenesis by Type VII Collagen in Cutaneous SCC

BACKGROUND

Individuals with severe generalized recessive dystrophic epidermolysis bullosa (RDEB), an inherited blistering disorder caused by mutations in the COL7A1 gene, develop unexplained aggressive squamous cell carcinomas (SCC). Here we report that loss of type VII collagen (Col7) in SCC results in increased TGFβ signaling and angiogenesis in vitro and in vivo.

METHODS

Stable knockdown (KD) of Col7 was established using shRNA, and cells were used in a mouse xenograft model. Angiogenesis was assessed by immunohistochemistry, endothelial tube-forming assays, and proteome arrays. Mouse and zebrafish models were used to examine the effect of recombinant Col7 on angiogenesis. Findings were confirmed in anonymized, archival human tissue: RDEB SCC tumors, non-EB SCC tumors, RDEB skin, normal skin; and two human RDEB SCC cell lines. The TGFβ pathway was examined using immunoblotting, immunohistochemistry, biochemical inhibition, and siRNA. All statistical tests were two-sided.

RESULTS

Increased numbers of cross-cut blood vessels were observed in Col7 KD compared with control xenografts (n = 4 to 7 per group) and in RDEB tumors (n = 21) compared with sporadic SCC (n = 24, P < .001). Recombinant human Col7 reversed the increased SCC angiogenesis in Col7 KD xenografts in vivo (n = 7 per group, P = .04). Blocking the interaction between α2β1 integrin and Col7 increased TGFB1 mRNA expression 1.8-fold and p-Smad2 levels two-fold. Increased TGFβ signaling and VEGF expression were observed in Col7 KD xenografts (n = 4) compared with control (n = 4) and RDEB tumors (TGFβ markers, n = 6; VEGF, n = 17) compared with sporadic SCC (TGFβ markers, n = 6; VEGF, n = 21). Inhibition of TGFβ receptor signaling using siRNA resulted in decreased endothelial cell tube formation (n = 9 per group, mean tubes per well siC = 63.6, SD = 17.1; mean tubes per well siTβRII = 29.7, SD = 6.1, P = .02).

CONCLUSIONS

Type VII collagen suppresses TGFβ signaling and angiogenesis in cutaneous SCC. Patients with RDEB SCC may benefit from anti-angiogenic therapy.

The receptor tyrosine kinase Axl regulates cell-cell adhesion and stemness in cutaneous squamous cell carcinoma

Axl is a receptor tyrosine kinase (RTK) upregulated in various tumors including cutaneous squamous cell carcinoma (SCC). Axl expression correlates with poor prognosis and induction of epithelial-mesenchymal transition (EMT), hence we hypothesized that Axl is involved in the disruption of cell-cell adhesion to allow invasion and chemotherapy resistance of the cancer stem cell population. Cutaneous SCC cell lines with stable knockdown of Axl were generated using retroviral vectors. Axl depletion altered expression of intercellular junction molecules increasing cell-cell adhesion with downregulation of Wnt and TGFβR signaling. Furthermore, Axl expression correlated with the expression of putative cancer stem cell markers, CD44 and ALDH1, increased resistance to chemotherapy drugs, enhanced sphere formation ability and expression of EMT features by cancer stem cells. Axl depletion resulted in loss of tumor formation in an in vivo zebrafish xenograft model. In conclusion, these data suggest that abrogation of Axl results in loss of cancer stem cell properties indicating a role for Axl as a therapeutic target in chemotherapy-resistant cancer.

Effects of n-3 fatty acids on the NMR profile of plasma lipoproteins

The effects of fish oil supplementation (14.5 g n-3 fatty acids/day) on plasma lipoprotein particles in healthy volunteers were assessed by high resolution 13C and 1H nuclear magnetic resonance (NMR) spectroscopy. Resonances not previously observed in the 13C and 1H spectra of plasma and isolated lipoproteins were detected after fish oil ingestion. The 13C resonances, centered at 14.3, 127.1, and 131.6 ppm, have been assigned to specific carbon groups (CH3-CH2-CH = CH-, CH3-CH2-CH = CH-CH2-, CH3-CH2-CH = CH-CH2-, respectively) in eicosapentaenoic acid (C20:5n-3) and docosahexaenoic (C22:6n-3) DHA. The new lipid resonance observed in the 1H spectra of plasma (0.941 ppm) is consistent with the incorporation of these n-3 fatty acids into lipoprotein particles. The presence of increased EPA and DHA in plasma lipids was confirmed by gas-liquid chromatography. A marked reduction in the intensity of the methylene signal from very low density lipoproteins (VLDL) was also observed with fish oil. This reduction arises from a decrease in plasma triglyceride concentration (ca. 18%) and a reduction in the number of VLDL particles. Transverse relaxation studies of isolated VLDL and low density lipoprotein (LDL) showed significant elevation in the T2 of the -(CH2)n- and CH3- signals from non-n-3 fatty acids. The relaxation characteristics and signal intensity of the novel 1H peak (0.941 ppm) point to the existence of n-3 enriched microenvironments within lipoprotein particles. These findings suggest that incorporation of EPA and DHA into VLDL and LDL, after fish oil ingestion, leads to significant alteration in the molecular architecture of lipoprotein particles.

The AMP-activated protein kinase gene is highly expressed in rat skeletal muscle. Alternative splicing and tissue distribution of the mRNA

The AMP-activated protein kinase (AMPK) phosphorylates, and thereby inactivates, a number of enzymes involved in the regulation of lipid metabolism. We have studied the expression of the AMPK gene in a variety of rat tissues. The gene is transcribed into a message of approximately 9.5 kb as detected by Northern blotting. Highest expression of the AMPK message was found in skeletal muscle, which contained 20 amol/micrograms total RNA as determined by competitive reverse-transcription/polymerase chain reaction (RT-PCR). In liver, kidney, brain, mammary glands, heart and lung, AMPK mRNA levels ranged over 1-4 amol/micrograms total RNA. Adipose tissue contained less than 1 amol/microgram total RNA. A second AMPK mRNA form was detected by RT-PCR that was 142 bases shorter than the functional transcript. This transcript was apparently generated by alternative splicing of a single exon within the 5'-coding region. The shorter of the two messages, which is not translated into AMPK protein, contributed between 35-60% of AMPK mRNA in most tissues, but only 15-20% in skeletal muscle and heart. As a result, functional AMPK mRNA was sevenfold higher in skeletal muscle than in liver, although AMPK activity was much lower. By Western blotting, relatively large amounts of AMPK protein were detected in skeletal muscle compared to liver. AMPK isolated from skeletal muscle was not activated by treatment with AMPK kinase under conditions where liver AMPK was fully activated. A single 63-kDa polypeptide was immunoprecipitated from rat skeletal muscle using anti-peptide IgG against AMPK. In contrast, two additional polypeptides with apparent molecular masses of 38 kDa and 36 kDa co-precipitated with the 63-kDa AMPK protein from rat liver. These results indicate that the muscle enzyme has a different subunit organization compared to the liver enzyme, which may account for its low catalytic activity. Together, our results indicate a physiological role for AMPK in muscle, in addition to its previously described role in lipid metabolism.

Mammalian AMP-activated protein kinase is homologous to yeast and plant protein kinases involved in the regulation of carbon metabolism

In mammals, an AMP-activated protein kinase (AMPK) phosphorylates both acetyl-CoA carboxylase and 3-hydroxy-3-methylglutaryl-CoA reductase in vitro and has been proposed to play a major role in the regulation of lipid metabolism in vivo. We report here the primary sequence of rat AMPK and show that antibodies raised against synthetic peptides based on the deduced sequence of AMPK immunoprecipitate AMPK activity from rat liver extracts. AMPK has a remarkable degree of sequence identity to the proteins encoded by the yeast SNF1 gene and the plant RKIN1 gene. SNF1 protein kinase activity is essential for release of genes from glucose repression in Saccharomyces cerevisiae. Expression of cRKIN1 in yeast snf1 mutants restores SNF1 function. These results indicate that AMPK, SNF1, and RKIN1 form part of a family of protein kinases that have been highly conserved throughout evolution. Our results suggest that AMPK may be involved in the regulation of a wide range of metabolic pathways.

Chronic exposure to anxiolytic drugs, working by different mechanisms causes up-regulation of dihydropyridine binding sites on cultured bovine adrenal chromaffin cells

Exposure of bovine adrenal chromaffin cells to ethanol [50 mM], alprazolam [10(-7) M] and buspirone [10(-7) M] inhibited basal and carbachol-induced release of catecholamines from these cells. The inhibition produced by alprazolam was prevented, and that produced by ethanol inhibited, by the presence of the benzodiazepine receptor antagonist, flumazenil [10(-8) M]. The inhibition produced by buspirone was unaffected by flumazenil, but was mimicked by the selective 5-HT1A receptor agonist, 8-OH DPAT and prevented by the 5-HT receptor antagonist spiperone [10(-6) M]. These results suggest that bovine adrenal chromaffin cells express GABAA receptors, containing a benzodiazepine recognition site and also 5-HT1A receptors. Ethanol and alprazolam appear to inhibit the excitability of bovine adrenal chromaffin cells by an action related to the former, while buspirone probably inhibits these cells through the latter. Maintaining bovine adrenal chromaffin cells for several days in culture medium, containing inhibitory concentrations of ethanol alprazolam or buspirone, produced a marked increase in binding sites for a [3H]dihydropyridine [DHP] calcium channel antagonist, on cell membranes. The increase in binding sites produced by alprazolam was greater than that produced by the other two agents and was almost completely prevented by the concomitant presence of flumazenil. The effects of ethanol and buspirone on the binding of DHP were not prevented by flumazenil. The results suggest that drugs which decrease excitability of bovine adrenal chromaffin cells by different mechanisms, may evoke a similar adaptive response involving an increase in DHP-sensitive calcium channels.

Second messengers involved in genetic regulation of the number of calcium channels in bovine adrenal chromaffin cells in culture

Bovine adrenal chromaffin cells in culture show an increased formation of [3H]inositol phosphates (after preloading with [3H]inositol) on depolarisation with increased extracellular K+. This increased breakdown of inositol lipid is further increased by the dihydropyridine Ca2+ channel activator BAY K 8644 at nM concentrations, implying that proteins which bind dihydropyridines are involved in this mechanism. Further, pretreatment of adrenal cells with pertussis toxin (100 ng ml-1) prevented the K(+)-induced breakdown of inositol lipids, arguing the involvement of a pertussis toxin-sensitive G protein in the effect. Chronic exposure of bovine adrenal chromaffin cells to a concentration of ethanol which inhibits K(+)-induced breakdown of inositol phospholipid, caused a 70-100% increase in the binding of [3H]DHP sites. In these experiments it was found that excess extracellular Ca2+ would considerably reduce this up-regulation, whereas growth of cells in pertussis toxin closely mimicked the up-regulation obtained by growth of cells in ethanol. These experiments suggest that inhibition of membrane Ca2+ flux, through a G protein-associated channel, is closely involved in the ethanol-induced regulation of [3H]dihydropyridine binding sites. The inositol lipid-protein kinase C second messenger system is also implicated in this regulation, by experiments in which inhibitors of protein kinase C (chronic treatment with phorbol myristyl acetate, or with sphingosine) up-regulated binding sites for [3H]dihydropyridine to a similar extent as that seen with growth in ethanol.

Genetic regulation of dihydropyridine-sensitive calcium channels in brain may determine susceptibility to physical dependence on alcohol

Experiments utilising rodents in vivo and cultures of adrenal cells in vitro have suggested that genetic regulation of dihydropyridine-sensitive calcium channels may be involved in dependence on alcohol. Selection of mouse lines for either a very severe ethanol-withdrawal syndrome (withdrawal seizure prone) or a very mild syndrome (withdrawal seizure resistant), has produced lines which differ very markedly in these characteristics. In these experiments, mice bred selectively for these symptoms for 26 generations, were compared for the severity of withdrawal from alcohol after inhalation of ethanol (plus injections of pyrazole) for 3 days. A proportion of animals from each line was killed before withdrawal and membranes from whole brain were analysed by radioligand binding for binding sites for [3H] nitrendipine. Mice which were withdrawal seizure prone showed a markedly greater severity of the ethanol-withdrawal syndrome, and also showed a significantly greater up-regulation of binding sites for [3H]nitrendipine with no significant difference in binding affinity. The results suggest a relationship between genetic susceptibility to dependence on alcohol and genetic regulation of neuronal calcium channels in brain.

Membrane receptors, involved in up-regulation of calcium channels in bovine adrenal chromaffin cells, chronically exposed to ethanol

Release of catecholamines, induced by carbachol, from bovine adrenal chromaffin cells, maintained in culture, is potently inhibited by the presence of ethanol (50 mM). This inhibition is prevented by the concomitant presence of bicuculline (1 microM) or by the inverse agonist at the benzodiazepine receptor, Ro 15 4513 (50 nM), arguing that the effect of ethanol is, at least, partly due to potentiation of endogenous GABA at the GABAA receptor sites on these cells. Exposing cells to medium containing ethanol (200 mM) for 4 days results in an approximately 100% increase in binding sites for [3H]dihydropyridine on membranes of adrenal chromaffin cells. This increase in binding sites was largely prevented by the presence in the culture medium of Ro 15 4513 (50 nM), the dihydropyridine calcium channel agonist BAY K 8644 (50 nM) or the calcium channel antagonist, nitrendipine (50 nM). The results strongly suggest that the increase in binding sites for [3H]dihydropyridine represents an adaptation of cells to overcome the inhibitory effect of ethanol on the excitability of cells (which is, at least partly, due to some action at the GABAA receptor). The protein containing the receptor site for dihydropyridine drugs is clearly also involved in controlling its up-regulation by ethanol, but this is probably not directly related to its channel function, since both activators and inhibitors of the dihydropyridine-sensitive channel prevented ethanol-induced up-regulation of binding sites for [3H]dihydropyridine.

Genetic up-regulation of calcium channels in a cellular model of ethanol dependence

Bovine adrenal chromaffin cells were maintained in culture medium containing ethanol (200 mM) for 6 days. Cultures maintained in ethanol were viable and were morphologically similar to controls. There was a greater than 100% increase in the number of [3H]dihydropyridine calcium channel antagonist binding sites on the cell membranes from ethanol-treated cultures, which could be prevented by concomitant exposure to cycloheximide (5 micrograms.ml-1) and the mRNA synthesis inhibitor, anisomycin (10 micrograms.ml-1) implicating de novo synthesis of protein and genetic regulation, respectively. Release of catecholamines, induced by 18 mM K+, from cultures grown in ethanol was enhanced. The increased release of catecholamines was inhibited by nM concentrations of dihydropyridine calcium channel antagonists, implying that an increase in the number of dihydropyridine-sensitive calcium channels accounts for this functional alteration.