Promoter mutation is a common variant in GJC2-associated Pelizaeus-Merzbacher-like disease

Pelizaeus-Merzbacher-like disease (PMLD) is a clinically and genetically heterogeneous neurological disorder of cerebral hypomyelination. It is clinically characterised by early onset (usually infantile) nystagmus, impaired motor development, ataxia, choreoathetoid movements, dysarthria and progressive limb spasticity. We undertook autozygosity mapping studies in a large consanguineous family of Pakistani origin in which affected children had progressive lower limb spasticity and features of cerebral hypomyelination on MR brain imaging. SNP microarray and microsatellite marker analysis demonstrated linkage to chromosome 1q42.13-1q42.2. Direct sequencing of the gap junction protein gamma-2 gene, GJC2, identified a promoter region mutation (c.-167A>G) in the non-coding exon 1. The c.-167A>G promoter mutation was identified in a further 4 individuals from two families (who were also of Pakistani origin) with clinical and radiological features of PMLD in whom previous routine diagnostic screening of GJC2 had been reported as negative. A common haplotype was identified at the GJC2 locus in the three mutation-positive families, consistent with a common origin for the mutation and likely founder effect. This promoter mutation has only recently been reported in GJC2-PMLD but it has been postulated to affect the binding of the transcription factor SOX10 and appears to be a prevalent mutation, accounting for ~29% of reported patients with GJC2-PMLD. We propose that diagnostic screening of GJC2 should include sequence analysis of the non-coding exon 1, as well as the coding regions to avoid misdiagnosis or diagnostic delay in suspected PMLD.

Ex-vivo analysis of the isoform selective histone deacetylase inhibitor entinostat in triple-negative breast cancer tumors

e14597

Background: Triple-negative (ER, PR, HER2 negative) breast cancer represents an unmet need for which novel agents and approaches are essential. Entinostat is an orally available, class 1 isoform selective histone deacetylase inhibitor currently in multiple phase 2 clinical studies including advanced NSCLC and breast cancer. Studies in vitro and in vivo in the triple negative cell line model MDA-MB-231 have established single agent activity of entinostat in inhibiting tumor growth as well preventing bone metastases. In addition, entinostat induces expression of ERα in MDA-MB-231 in vivo and is synergistic with endocrine therapy agents to inhibit tumor growth of ER negative cancer cells. The aim of these studies was to confirm the activity of entinostat in triple negative breast cancers using human breast tumor explants. Methods: Cytotoxicity of entinostat was determined by the Oncotech Extreme Drug Resistance (EDR) proliferation assay using ten cryopreserved breast tumor explants known to lack estrogen receptor, progesterone receptor and HER2/neu expression (i.e. Triple negative) by immunohistochemistry. Results: Dose response curves of entinostat were analyzed and compared to paclitaxel at 2.45 μM in ten triple negative breast tumor explants in the EDR assay. Entinostat was broadly effective in all of the tumors tested, with most samples showing dose-dependent response for the range of concentrations analyzed (0.003 - 10 μM). Two of the breast tumors that were most sensitive to entinostat (IC50 30- 100nM) were also sensitive to paclitaxel. In contrast, entinostat effectively inhibited (IC50 10–270nM) the growth of eight of the tumors that were resistant to paclitaxel (i.e. < 50% growth inhibition). Overall, all breast tumors tested were sensitive to entinostat at clinically achievable concentrations regardless of paclitaxel resistance indicating entinostat may improve the treatment outcome of triple negative breast cancer patients. Conclusions: Entinostat is an effective agent at inhibiting the growth of triple negative breast tumors with clinically relevant IC50's ranging from 10nM to 270nM. A pre-surgical clinical study to assess the activity of entinostat in triple negative breast cancer patients is planned.

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Long-term NSAID use in primary care: changes over a decade and NICE risk factors for gastrointestinal adverse events

OBJECTIVES

To examine prescribing of non-steroidal anti-inflammatory drugs (NSAIDs) in general practice and to compare the results with a 1993 study. To assess numbers at risk of gastrointestinal adverse events using the National Institute for Clinical Excellence (NICE) guidance on the use of cyclo-oxygenase (Cox) II selective drugs.

METHODS

Patients currently prescribed a NSAID for 2 months or more were identified from practice records. Demographic information, indications, previous gastrointestinal disease, serious co-morbidity and concomitant prescriptions were recorded. Data were compared with the 1993 survey and the NICE guidance.

RESULTS

Seven thousand nine hundred and fifty-eight patients were registered with the practice in 2003. Two hundred and four patients were receiving repeat prescriptions for conventional NSAIDs and 63 for Cox II selective drugs. As in 1993 diclofenac (38%) and ibuprofen (24%) were the commonest individual agents and the main indication was regional pain. Seventy-three per cent of patients prescribed Cox II selective drugs and 64% of patients prescribed conventional NSAIDs had at least one NICE risk factor for gastrointestinal adverse events. Frequency of co-prescription of aspirin or antacids was similar for conventional NSAIDs and Cox II selective drugs, but prescription of antacids was higher with NICE risk factors.

CONCLUSION

The indications for NSAIDs have not changed since 1993. Cox II selective drug prescribing was within the NICE guidance but a substantial proportion of patients taking other NSAIDs had risk factors for gastrointestinal adverse events. Discussion with the GPs highlighted the difficulties of balancing perceived risk of gastrointestinal adverse events with cardioprotection and further guidance is urgently needed.

The DNA sequence and comparative analysis of human chromosome 20

The finished sequence of human chromosome 20 comprises 59,187,298 base pairs (bp) and represents 99.4% of the euchromatic DNA. A single contig of 26 megabases (Mb) spans the entire short arm, and five contigs separated by gaps totalling 320 kb span the long arm of this metacentric chromosome. An additional 234,339 bp of sequence has been determined within the pericentromeric region of the long arm. We annotated 727 genes and 168 pseudogenes in the sequence. About 64% of these genes have a 5' and a 3' untranslated region and a complete open reading frame. Comparative analysis of the sequence of chromosome 20 to whole-genome shotgun-sequence data of two other vertebrates, the mouse Mus musculus and the puffer fish Tetraodon nigroviridis, provides an independent measure of the efficiency of gene annotation, and indicates that this analysis may account for more than 95% of all coding exons and almost all genes.

Overexpression of P-glycoprotein is associated with a decreased mitochondrial transmembrane potential in doxorubicin-selected K562 human leukemia cells

We tested the hypothesis of whether overexpression of P-glycoprotein (Pgp) could be coupled with changes in specific mechanisms of antioxidant defense (in particular, transition of mitochondrial transmembrane potential, MTP) in tumor cells chronically exposed to anticancer drugs known to exert their cytotoxicity via oxidative stress. We show elevation of Pgp associated with decreased MTP in doxorubicin-selected K562Dox subline as compared with parental K562 cells. The low MTP was not due to a fewer number of mitochondria in K562Dox cells, nor was it associated with altered content of Bcl-XL protein. We discuss a model for coordinated up-regulation of Pgp and MTP transition in cells that survived chemotherapy-induced oxidative stress.

Altered expression of the MYCN oncogene modulates MRP gene expression and response to cytotoxic drugs in neuroblastoma cells

We have recently shown a close correlation between expression of the Multidrug Resistance-associated Protein (MRP) gene and the MYCN oncogene and provided evidence that high MRP expression is a powerful independent predictor of poor outcome in neuroblastoma (Norris et al., New Engl. J. Med., 334, 231-238, 1996). The effect of MYCN down-regulation on MRP expression and response to cytotoxic drugs was investigated in NBL-S neuroblastoma cells transfected with MYCN antisense RNA constructs. Concomitant with MYCN down-regulation, the level of MRP expression was decreased in the NBAS-4 and NBAS-5 antisense transfectants. These cells demonstrated significantly increased sensitivity to the high affinity MRP substrates vincristine, doxorubicin, sodium arsenate and potassium antimony tartrate, but not to the poor MRP substrates, taxol or cisplatin. Similarly, transfection of full-length MYCN cDNA into SH-EP neuroblastoma cells resulted in increased MRP expression and significantly increased resistance specifically to MRP substrates. The results provide evidence for the MYCN oncogene influencing cytotoxic drug response via regulation of MRP gene expression. Our data also provide a link between the malignant and chemoresistant phenotypes of this childhood malignancy.

Activation of the LRP (lung resistance-related protein) gene by short-term exposure of human leukemia cells to phorbol ester and cytarabine

Treatment-induced secondary drug resistance of tumor cells is a major cause of relapsed disease and therapeutic failure in cancer patients. It has been shown that the expression of the multidrug resistance MDR1/P-glycoprotein gene could be induced by short-term in vitro exposure of cells to protein kinase C (PKC) agonists or different chemotherapeutic drugs. We studied whether other genes involved in drug resistance are regulated by similar signaling pathways. Transient (up to 24 h) treatment of HL-60 or K562 leukemia cells with phorbol 12-myristate 13-acetate (TPA) resulted in increased steady-state level of LRP (lung resistance-related protein) mRNA and protein. Among conventional chemotherapeutic drugs tested, only cytarabine (Ara C) induced the LRP mRNA expression though no increase in LRP protein was detected. LRP gene activation was not detectable in either H9 T-cell leukemia or in solid carcinoma cell lines (BT-20, ZR-75-1, and SW 1573). None of the agents influenced the levels of MRP (multidrug resistance-associated protein) mRNA in any cell line tested. In HL-60 cells, the LRP activation by TPA or Ara C was sustained for at least 23 days after withdrawal of inducing agents. bis-Indolylmaleimide I, a potent PKC inhibitor, attenuated TPA-induced LRP activation. In contrast, the inhibitor had no effect on the LRP induction by Ara C. These data indicate that the LRP gene can be activated by different mechanisms, some of which involve PKC.

Transcriptional- and post-transcriptional-dependent regulation of glutathione S-transferase expression in rat hepatocytes as a function of culture conditions

Transcriptional activity of the glutathione S-transferase (GST) alpha (subunits 1 and 2), mu (subunits 3 and 4) and pi (subunit 7) gene families has been analyzed using the nuclear 'run-on' technique on adult rat hepatocytes maintained for 4 days in conventional culture and for 4 and 12 days in co-culture with rat liver epithelial cells. Several medium conditions are included in this study, namely with or without fetal calf serum and with nicotinamide or dimethylsulphoxide. Hepatocytes co-cultured for 4 days maintain approximately 30-70% of the alpha gene family transcriptional activity, whatever the medium conditions, when compared to freshly isolated hepatocytes. A marked decrease is observed after 12 days of co-culture or when hepatocytes are maintained in conventional culture. The transcriptional activity of the mu gene family is maintained at 40-160% when hepatocytes are cultured with or without fetal calf serum, and is inducible by nicotinamide (approximately 4-fold) and dimethylsulphoxide (approximately 2-fold) in conventional culture and/or in co-culture. In contrast to freshly isolated hepatocytes, GST pi gene transcriptional activity is observed in conventional and co-cultured hepatocytes, irrespective of the medium conditions. Dimethylsulphoxide treatment however, represses the expression of GST 7 in vitro. These results demonstrate that the expression of GST alpha, mu and pi genes in conventional and co-cultured rat hepatocytes is controlled primarily at the level of transcription. It cannot be excluded, however, that dimethylsulphoxide stabilizes the GST mRNA levels in vitro.

Regulation of glutathione S-transferase gene expression by phenobarbital in cultured adult rat hepatocytes

Previous studies, by using Northern blotting analyses, showed that phenobarbital (PB) affects the steady-state mRNA levels of glutathione S-transferase (GST) subunits 1/2, 3/4 and 7 in both conventional cultures of adult rat hepatocytes and co-cultures, with rat liver epithelial cells [Vandenberghe et al., 1989, FEBS Lett. 251, 59-64; Morel et al., 1989, FEBS Lett. 258, 99-102]. To determine whether PB acts at the transcriptional level, nuclear 'run on' experiments using cDNA probes hybridizing to GST subunits 1/2, 3/4 and 7 mRNA were performed on purified nuclei isolated from control and PB treated hepatocytes seeded under conventional and co-culture conditions. Data from this study demonstrate that the increase in steady-state mRNA levels observed in both conventional culture and co-culture after 4 days PB exposure results from an increased transcriptional activity of the GST genes. However, a substantial increase in steady-state mRNA levels in the absence of a commensurate increase in transcriptional activity at 12 days of co-culture, indicates that the barbiturate has also a stabilizing effect in vitro on the GST mRNAs.