A retrospective review of an epidural blood patch database: the incidence of epidural blood patch associated with obstetric neuraxial anesthetic techniques and the effect of blood volume on efficacy

BACKGROUND

The optimal volume of blood required to treat post-dural puncture headache remains in question. In our institution a target volume of 30mL is used for an epidural blood patch unless the patient experiences pain during injection.

METHODS

The institutional database was retrospectively reviewed for epidural blood patch and delivery statistics over a 15-year period to determine if the volume of blood administered during the procedure directly correlated with the number of epidural blood patches administered. The primary endpoint was defined as the need for a repeat epidural blood patch.

RESULTS

There were 466 epidural blood patches performed on 394 patients, associated with 84 804 obstetric neuraxial procedures. Thirty-two percent (95% CI 28.3 to 34.9%) of patients who had an inadvertent dural puncture with an epidural needle received an epidural blood patch versus 0.19% (0.16% to 0.22%) of patients who received neuraxial anesthesia with no documented dural puncture with an epidural needle. All patients experienced relief of post-dural puncture headache, although 17% required two and 1.5% required three epidural blood patches. The mean±SD volume of blood administered was 20.5±5.4mL and only 35 patients (8.9%) received 30mL.

CONCLUSION

Increasing blood volumes up to 30mL did not reduce the need for repeat epidural blood patch. Although the optimal volume of blood to administer during epidural blood patch placement remains unknown, our institution will continue to administer up to 30mL or until the patient experiences pain during epidural injection.

The MDM2-a splice variant of MDM2 alters transformation in vitro and the tumor spectrum in both Arf- and p53-null models of tumorigenesis

MDM2-A is a common splice variant of murine double minute 2 (MDM2) that is frequently detected in many tumor types. Our previous work has characterized MDM2-A as an activator of p53, and therefore, in a wild-type p53 background, this splice variant would be predicted to confer p53-dependent tumor protection. To test this hypothesis, we used Mdm2-a transgenic mice to assess transformation and tumorigenesis in tumor susceptible murine models. A MDM2-A-dependent decrease in transformation was observed in Arf-null mouse embryonic fibroblasts (MEF) or when wild-type MEFs were exposed to the carcinogen ethylnitrosourea. However, this reduced transformation did not confer tumor protection in vivo; Mdm2-a/Arf-null mice and ethylnitrosourea-treated MDM2-expressing mice developed similar tumor types with equivalent latency compared with their respective controls. Interestingly, when p53 was deleted, MDM2-A expression enhanced transformation of p53-null MEFs and altered tumor spectrum in vivo. In addition, p53-heterozygous mice that expressed MDM2-A developed aggressive mammary tumors that were not observed in p53-heterozygous controls. In conclusion, we found that although MDM2-A expression enhances p53 activity and decreases transformation in vitro, it cannot confer tumor protection. In contrast, MDM2-A seems to exhibit a novel transforming potential in cells where p53 function is compromised. These data show that MDM2 splice variants, such as MDM2-A, may provide protection against transformation of normal tissues having intact p53. However, when such splice variants are expressed in tumors that have defects in the p53 pathway, these isoforms may contribute to tumor progression, which could explain why their expression is often associated with aggressive tumor types.

MDM2-A, a common Mdm2 splice variant, causes perinatal lethality, reduced longevity and enhanced senescence

MDM2 is the predominant negative regulator of p53 that functions to maintain the appropriate level of expression and activity of this central tumor suppressor. Mdm2-a is a commonly identified splice variant of Mdm2; however, its physiological function is unclear. To gain insight into the activity of MDM2-A and its potential impact on p53, an Mdm2-a transgenic mouse model was generated. Mdm2-a transgenic mice displayed a homozygous-lethal phenotype that could be rescued by a reduction in p53 expression, demonstrating a dependence upon p53. Mdm2-a hemizygous mice exhibited reduced longevity, and enhanced senescence was observed in their salivary glands. In addition, the transgenic mice lacked typical, accelerated aging phenotypes. Growth of transgenic mouse embryonic fibroblasts (MEFs) was inhibited relative to wild-type MEFs, and MDM2-A was shown to bind to full-length MDM2 in an interaction that could increase p53 activity via reduced MDM2 inhibition. Evidence of p53 activation was shown in the Mdm2-a transgenic MEFs, including p53-dependent growth inhibition and elevated expression of the p53 target protein p21. In addition, MDM2-A increased senescence in a p21-independent manner. In conclusion, unexpected roles for MDM2-A in longevity and senescence were identified in a transgenic mouse model, suggesting that Mdm2 splice variants might be determinants of these phenotypes in vivo.

MDM2 displays differential activities dependent upon the activation status of NFkappaB

MDM2 is an oncoprotein best characterized for its role in the inactivation and degradation of the p53 tumor suppressor. However, MDM2 has many other binding partners and its p53-independent role in the regulation of cell growth and survival appears to be extremely complex. This report describes the expression of MDM2 in two rhabdomyosarcoma cell lines, both expressing a mutant p53 gene. Expression of MDM2 in Rh30 cells enhanced cell growth whereas expression of MDM2 in RD cells suppressed their growth and enhanced the rate of spontaneous apoptosis. The mechanism for these opposite phenotypes was demonstrated to be due to differential effects on the NFkappaB pathway. Previously MDM2 has been shown to activate NFkappaB through activation of transcription of the p65RelA subunit. In Rh30 cells MDM2 acted similarly to previously described, thereby promoting growth of Rh30 cells. In untreated RD cells p65RelA was constitutively overexpressed resulting in activation of the NFkappaB pathway. Expression of MDM2 in RD cells transcriptionally repressed p65RelA and suppressed NFkappaB activity, resulting in a reduced growth rate and enhanced apoptosis. The MDM2-sensitive region of the p65 promoter was localized to a 225 bp fragment to which MDM2 protein was shown to bind. The observation that MDM2 induces apoptosis under certain circumstances may help to explain the apparently surprising clinical studies that have shown that MDM2 expression in tumors is often associated with a favorable prognosis.

Ceramide-induced G2 arrest in rhabdomyosarcoma (RMS) cells requires p21Cip1/Waf1 induction and is prevented by MDM2 overexpression

The sphingoplipid ceramide is responsible for a diverse range of biochemical and cellular responses including a putative role in modulating cell cycle progression. Herein, we describe that an accumulation of ceramide, achieved through the exogenous application of C(6)-ceramide or exposure to sphingomyelinase, induces a G(2) arrest in Rhabdomyosarcoma (RMS) cell lines. Utilizing the RMS cell line RD, we show that this G(2) arrest required the rapid induction of p21(Cip1/Waf1) independent of DNA damage. This was followed at later time points (48 h) by the commitment to apoptosis. Apoptosis was prevented by Bcl-2 overexpression, but permitted the maintenance of elevated p21(Cip1/Waf1) protein expression and the stabilization of the G(2) arrest response. Inhibition of p21(Cip1/Waf1) protein synthesis with cyclohexamide (CHX) or silencing of p21(Cip1/Waf1) with siRNA, prevented ceramide-mediated G(2) arrest and the late induction of apoptosis. Further, adopting the recent discovery that murine double minute 2 (MDM2) controls p21(Cip1/Waf1) expression by presenting this CDK inhibitor to the proteasome for degradation, RD cells overexpressing MDM2 abrogated ceramide-mediated p21(Cip1/Waf1) induction, G(2) arrest and the late ensuing apoptosis. Collectively, these data further support the notion that ceramide accumulation can modulate cell cycle progression. Additionally, these observations highlight MDM2 expression and proteasomal activity as key determinants of the cellular response to ceramide accumulation.

MDM2 splice variants predominantly localize to the nucleoplasm mediated by a COOH-terminal nuclear localization signal

Of the >40 alternative and aberrant splice variants of MDM2 that have been described to date, the majority has lost both the well-characterized nuclear localization signal (NLS1) and the nuclear export signal (NES) sequence. Because cellular localization of proteins provides insight regarding their potential function, we determined the localization of three different MDM2 splice variants. The splice variants chosen were the common variants MDM2-A and MDM2-B. In addition, MDM2-FB26 was chosen because it is one of the few variants described that contains the complete p53-binding site. All three splice variants predominantly localized to the nucleus. Nuclear localization of MDM2-A and MDM2-B was controlled by a previously uncharacterized nuclear localization signal (NLS2), whereas nucleoplasmic localization of MDM2-FB26 was mediated by NLS1. p53 and full-length MDM2 colocalized with the splice variants in the nucleus. MDM2-A and MDM2-B both contain a COOH-terminal RING finger domain, and interaction with full-length MDM2 through this domain was confirmed. MDM2-FB26 was the only splice variant evaluated that contained a p53-binding domain; however, interaction between MDM2-FB26 and p53 could not be shown. p14(ARF) did not colocalize with the splice variants and was predominantly expressed within the nucleoli. In summary, nuclear localization signals responsible for the nucleoplasmic distribution of MDM2 splice variants have been characterized. Colocalization and interaction of MDM2-A and MDM2-B with full-length MDM2 in the nucleus have important physiologic consequences, for example, deregulation of p53 activity.

Stem cell-associated genes are extremely poor prognostic factors for soft-tissue sarcoma patients

Cancer stem cells can play an important role in tumorigenesis and tumor progression. However, it is still difficult to detect and isolate cancer stem cells. An alternative approach is to analyse stem cell-associated gene expression. We investigated the coexpression of three stem cell-associated genes, Hiwi, hTERT and survivin, by quantitative real-time-PCR in 104 primary soft-tissue sarcomas (STS). Multivariate Cox's proportional hazards regression analyses allowed correlating gene expression with overall survival for STS patients. Coexpression of all three stem cell-associated genes resulted in a significantly increased risk of tumor-related death. Importantly, tumors of patients with the poorest prognosis were of all four tumor stages, suggesting that their risk is based upon coexpression of stem cell-associated genes rather than on tumor stage.

Selection for mutations in the cDNAs of transgenic mice upon expression of an embryonic lethal protein

The generation of transgenic mouse models to study in vivo functions of specific proteins has become common practice. In addition, PCR technology allows efficient and rapid identification of founder mice by the analysis of tail tip DNA. Whilst the DNA construct used in the microinjection of one-cell-stage embryos is usually sequenced it is not common practice to sequence the PCR product once the transgene has been inserted into the mouse genome. In this report we describe why sequencing of inserted transgenes is important. Upon generation of transgenic mice expressing a splice variant of MDM2, MDM2-A, three of four founders contained mutations within the Mdm2-a cDNA sequence. The observation that selection against expression of wild-type MDM2-A resulted in the generation of mice expressing mutant transgenes highlights the importance of sequencing the transgenes of founder mice.

Differential cooperation of oncogenes with p53 and Bax to induce apoptosis in rhabdomyosarcoma

Background

Deregulated expression of oncogenes such as MYC and PAX3-FKHR often occurs in rhabdomyosarcomas. MYC can enhance cell proliferation and apoptosis under specific conditions, whereas PAX3-FKHR has only been described as anti-apoptotic.

Results

In order to evaluate how MYC and PAX3-FKHR oncogenes influenced p53-mediated apoptosis, rhabdomyosarcoma cells were developed to independently express MYC and PAX3-FKHR cDNAs. Exogenous wild-type p53 expression in MYC transfected cells resulted in apoptosis, whereas there was only a slight effect in those transfected with PAX3-FKHR. Both oncoproteins induced BAX, but BAX induction alone without expression of wild-type p53 was insufficient to induce apoptosis. Data generated from genetically modified MEFs suggested that expression of all three proteins; MYC, BAX and p53, was required for maximal cell death to occur.

Conclusion

We conclude that cooperation between p53 and oncoproteins to induce apoptosis is dependent upon the specific oncoprotein expressed and that oncogene-mediated induction of BAX is necessary but insufficient to enhance p53-mediated apoptosis. These data demonstrate a novel relationship between MYC and p53-dependent apoptosis, independent of the ability of MYC to induce p53 that may be important in transformed cells other than rhabdomyosarcoma.

MDM2 splice variants and their therapeutic implications

MDM2 splice variants have now been identified in many different tumor types, and their expression has been associated with advanced disease. However, published data concerning their function is contradictory, and therefore their role in tumorigenesis and their potential as a therapeutic target are unclear. Expression of a specific splice variant, MDM2-B, in a transgenic mouse model results in tumor development; and expression of several splice variants has been shown to enhance tumor formation in Emu-myc transgenic mice. However, expression of similar variants in vitro results in growth inhibition, an observation inconsistent with a transformed phenotype. The observed growth inhibition is p53-dependent, resulting from the binding of splice variants with an intact C-terminal RING finger domain to full-length MDM2 protein. In doing so, p53 can no longer bind MDM2, and p53 activity is elevated. Subsequent inactivation of p53 or p53-mediated apoptosis could contribute to the MDM2 splice variant-mediated tumorigenesis observed in vivo. However, MDM2 splice variants, like full-length MDM2, probably display p53-independent activities. Therefore, the potential for MDM2 splice variants as therapeutic targets will be dependent upon their phenotype within specific tumor types.

Epigenetic regulation of O6-methylguanine-DNA methyltransferase gene expression by histone acetylation and methyl-CpG binding proteins

Transcriptional silencing of the DNA repair gene, O6-methylguanine-DNA methyltransferase (MGMT) in a proportion of transformed cell lines is associated with methylated CpG hotspots in the MGMT 5′ flank. The goal of the study was to evaluate the mechanism by which CpG methylation of theMGMT promoter region influenced silencing of the gene. Analysis of histone acetylation status in two regions of the promoter using chromatin immunoprecipitation assay showed that a higher level of histone acetylation was associated with expression in three MGMT-expressing cell lines (HeLa CCL2, HT29, and Raji) compared with three MGMT-silenced cell lines (HeLa S3, BE, and TK6). To determine how the modulation of CpG methylation and histone acetylation influenced MGMT expression, we exposed the cells to 5-aza-2′deoxycytidine (5-Aza-dC), inhibitor of DNA methylation, which strongly up-regulated MGMT expression in three MGMT-silenced cell lines whereas trichostatin A, inhibitor of histone deacetylase, weakly induced MGMT. However, combined treatment with 5-Aza-dC and trichostatin A significantly up-regulated MGMT RNA expression to a greater extent than in cells treated with either agent alone suggesting that histone deacetylation plays a role in MGMT silencing but that CpG methylation has a dominant effect. Consistent with enhanced MGMT expression, 5-Aza-dC increased the association of acetylated histone H3 and H4 bound to the MGMT promoter. Chromatin immunoprecipitation analysis of methyl-CpG binding domain containing proteins detected a greater amount of MeCP2, MBD1, and CAF-1 bound to the MGMT promoter in MGMT-silenced cells. Our findings implicate specific MBD proteins in methylation-mediated transcriptional silencing of MGMT.

Ocular pharmacology of bicyclic hexahydroaporphines

This paper explores the ocular hypotensive actions of bicyclic analogs of hexahydroaporphine (HHA), specifically nor-HHA, in an attempt to shed light on the mechanism(s) by which they lower intraocular pressure (IOP). Studies involving the measurement of IOP and aqueous humor production were conducted in ocular normotensive albino rabbits, while those involving smooth muscle contractility utilized isolated bovine iris. The ability of nor-HHA to produce a sustained drop in IOP is linked to both a functioning adrenergic nervous system and the availability of the products of cyclooxygenase metabolism. Although aqueous flow is not impacted by the bicyclic structures, the significant enhancement of outflow facility points to a probable mechanism of IOP-lowering action. Nor-HHA had no direct contractile or relaxant action on bovine irides, but does cause a concentration-dependent inhibition of carbachol-evoked contractions. This inhibition was reversed by inhibitors of phospholipase A(2) and cyclooxygenase, but not by inhibitors of lipoxygenase, again indicating a role for prostaglandins in the ocular pharmacological action of bicyclic HHAs. Pretreatment with a nitric oxide (NO) scavenger also reversed the ability of nor-HHA to inhibit carbachol-induced contractions, implying a role for NO in the postjunctional actions of HHAs.

Epigenetic regulation of O6-methylguanine-DNA methyltransferase gene expression by histone acetylation and methyl-CpG binding proteins

Transcriptional silencing of the DNA repair gene, O6-methylguanine-DNA methyltransferase (MGMT) in a proportion of transformed cell lines is associated with methylated CpG hotspots in the MGMT 5' flank. The goal of the study was to evaluate the mechanism by which CpG methylation of theMGMT promoter region influenced silencing of the gene. Analysis of histone acetylation status in two regions of the promoter using chromatin immunoprecipitation assay showed that a higher level of histone acetylation was associated with expression in three MGMT-expressing cell lines (HeLa CCL2, HT29, and Raji) compared with three MGMT-silenced cell lines (HeLa S3, BE, and TK6). To determine how the modulation of CpG methylation and histone acetylation influenced MGMT expression, we exposed the cells to 5-aza-2'deoxycytidine (5-Aza-dC), inhibitor of DNA methylation, which strongly up-regulated MGMT expression in three MGMT-silenced cell lines whereas trichostatin A, inhibitor of histone deacetylase, weakly induced MGMT. However, combined treatment with 5-Aza-dC and trichostatin A significantly up-regulated MGMT RNA expression to a greater extent than in cells treated with either agent alone suggesting that histone deacetylation plays a role in MGMT silencing but that CpG methylation has a dominant effect. Consistent with enhanced MGMT expression, 5-Aza-dC increased the association of acetylated histone H3 and H4 bound to the MGMT promoter. Chromatin immunoprecipitation analysis of methyl-CpG binding domain containing proteins detected a greater amount of MeCP2, MBD1, and CAF-1 bound to the MGMT promoter in MGMT-silenced cells. Our findings implicate specific MBD proteins in methylation-mediated transcriptional silencing of MGMT.

MDM2 and its splice variant messenger RNAs: expression in tumors and down-regulation using antisense oligonucleotides

Alternative splicing has an important role in expanding protein diversity. An example of a gene with more than one transcript is the MDM2 oncogene. To date, more than 40 different splice variants have been isolated from both tumor and normal tissues. Here, we review what is known about the alteration of MDM2 mRNA expression, focusing on alternative splicing and potential functions of different MDM2 isoforms. We also discuss the progress that has been made in the development of antisense oligonucleotides targeted to MDM2 for use as a potential cancer therapy.

MDM2 and Its Splice Variant Messenger RNAs: Expression in Tumors and Down-Regulation Using Antisense Oligonucleotides

Alternative splicing has an important role in expanding protein diversity. An example of a gene with more than one transcript is the MDM2 oncogene. To date, more than 40 different splice variants have been isolated from both tumor and normal tissues. Here, we review what is known about the alteration of MDM2 mRNA expression, focusing on alternative splicing and potential functions of different MDM2 isoforms. We also discuss the progress that has been made in the development of antisense oligonucleotides targeted to MDM2 for use as a potential cancer therapy.

P21Waf1/Cip1 dysfunction in neuroblastoma: a novel mechanism of attenuating G0-G1 cell cycle arrest

In normal cells in which DNA has been damaged, p53 induces the expression of p21(Waf1/Cip1); p21, in turn, binds to cyclin-dependent kinase 2 (cdk2) and inhibits its function. Inhibition of cdk2 results in cell cycle arrest in G(0)-G(1). Although p53 is transcriptionally active and induces p21 expression in neuroblastoma (NB) cells, the G(0)-G(1) checkpoint is attenuated. Here we report that the mechanism that mediates this defect in NB cells is the inability of p21 to bind to, or inhibit the activity of cdk2. However, when recombinant p21 protein was added to NB cell extracts in vitro, the protein inhibited the activity of cdk2. This finding suggests that endogenous p21 protein in NB cells is inactive and may be bound either to a protein complex or in a conformation that precludes its binding to cdk2. The dysfunction of p21 in NB cells represents a novel mechanism by which the G(0)-G(1) cell cycle checkpoint can be inactivated. This mechanism may be important in regulating the growth of NB and potentially other types of tumors. Cdk inhibitors currently being developed for clinical use may be useful therapy for tumors such as NB in which endogenous cdk inhibitors are defective.

p53-mediated regulation of expression of a rabbit liver carboxylesterase confers sensitivity to 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11)

We have exploited the ability of wild-type (wt) p53 to repress gene expression and produce tumor-selective cytotoxicity using viral-directed enzyme prodrug therapy. Vectors containing either the cytomegalovirus or Rous sarcoma virus promoter regulating transcription of a rabbit liver carboxylesterase (CE) have been constructed. Upon transfection of these plasmids into cells expressing either wt or mutant p53, differential expression of the CE has been observed, resulting in sensitization of the cells expressing the latter protein to the anticancer prodrug irinotecan, 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carb- onyloxycamptothecin (CPT-11). Transduction of isogenic cell lines with adenovirus containing CE under control of the Rous sarcoma virus promoter confirmed the decreased sensitization of cells expressing wtp53 to CPT-11. These studies indicate that the inactivation of wtp53 by mutant p53 in human tumor cells may be sufficient enough to generate a therapeutic window for enhanced cytotoxicity with CPT-11.

MDM2 does not influence p53-mediated sensitivity to DNA-damaging drugs

MDM2 inhibits transactivation properties of the tumor suppressor protein p53 by binding to and facilitating proteasomal degradation of p53. Because MDM2 targets p53 for degradation, it was anticipated that cells that overexpress MDM2 would not contain functional wild-type p53 (wtp53). However, p53 and MDM2 in cells with damaged DNA can become phosphorylated, and their binding to each other can become inhibited. Thus, p53 remains functional and induces apoptosis of damaged cells. Here we report the results of experiments designed to investigate whether MDM2 amplification and overexpression can inhibit p53-mediated chemosensitivity to DNA-damaging drugs. Two cell lines in which MDM2 is amplified, NB-1691 and Rh18, were transduced with an adenoviral expression vector for p53 (Ad.p53). Although functional wtp53 was detected, no change in chemosensitivity was observed, suggesting that endogenous wtp53 may have been active in the MDM2-amplified cells. The adenoviral vector Ad.MDM2 was used to generate MDM2 expression in a rhabdomyosarcoma cell line, Rh30-CI.27, engineered to express inducible wtp53. When p53 expression was induced, cells became chemosensitive to actinomycin D in the presence or absence of MDM2 expression; this result suggests that MDM2 cannot inhibit p53-mediated chemosensitivity. There was no evidence of a reduced amount of MDM2-p53 binding after drug exposure, but the remaining unbound wtp53 may be functional and capable of potentiating cytotoxicity. In conclusion, MDM2 expression is important in inhibiting p53 function during tumor development but not during the DNA damage-mediated cytotoxic response.

Novel mdm2 splice variants identified in pediatric rhabdomyosarcoma tumors and cell lines

Mdm2 is an oncogene that binds to and inactivates the tumor suppressor p53. However, the presence of oncogenic splice variants of mdm2 in human tumors that lack the p53 binding site has suggested a p53-independent transforming function for this protein. This report describes expression of 11 different mdm2 splice variants in pediatric rhabdomyosarcoma (RMS) cell lines and tumors at a frequency of 75% and 82%, respectively. Five of these isoforms have previously been described in other tumor histiotypes but six are novel and may be unique to RMS. There was no association between expression of splice variants and mdm2 gene amplification or p53 status. In addition, the frequency of splice variants was much higher than the incidence of mdm2 amplification or p53 mutations. These variants may be important to consider with respect to RMS tumor progression and therapeutic response.

Efficacy and toxicity of a virus-directed enzyme prodrug therapy purging method: preclinical assessment and application to bone marrow samples from neuroblastoma patients

Autologous stem cell transplantation is used to rescue cancer patients from myelosuppression caused by high-dose chemotherapy. However, autologous grafts often contain tumor cells that can contribute directly to relapse. Current purging methods are useful when fewer than 1% tumor cells contaminate the bone marrow, and patients with tumor burdens of >1% are considered ineligible for chemotherapy that necessitates stem cell rescue. Using neuroblastoma (NB) as a model system, we developed a method that is effective even with tumor burdens of 10-25%. Mixtures of NB-1691 NB cells and CD34(+) hematopoietic cells purged by this method showed no evidence of viable tumor cells as assessed by clonogenic assays or reverse transcription-PCR for the NB cell markers tyrosine hydroxylase and N-MYC. The efficacy and lack of toxicity of the method were verified using in vivo mouse models. Severe combined immunodeficient mice that received purged cell preparations containing 10% NB-1691 cells survived without evidence of disease for the observation period (>1 year), whereas mice that received unpurged cells developed disseminated disease requiring euthanasia 73-96 days after injection of cells. No evidence of toxicity to the mice was detected by numerous laboratory values for bone marrow, liver, and kidney function, and no difference was seen in the ability of purged cell mixtures versus unmanipulated CD34(+) cells to reconstitute the marrow of non-obese diabetic severe combined immunodeficient mice. In a pilot study, marrow was obtained from eight patients who had >/=1% metastatic tumor burden. All eight samples were purged to the level of detection by reverse transcription-PCR (samples from seven patients) or clonogenic potential (sample from one patient), whichever assay was used. The described adenovirus/rabbit carboxylesterase/CPT-11 (irinotecan, 7-ethyl-10[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin) virus-directed enzyme prodrug method may be useful for patients whose tumor burdens exceed 1% at the time of stem cell harvest. Assessment of purging efficacy with additional samples from NB patients is ongoing.

Selective chemosensitization of rhabdomyosarcoma cell lines following wild-type p53 adenoviral transduction

Rhabdomyosarcoma (RMS) cell lines were transduced with an adenoviral vector containing the wild-type p53 (wtp53) cDNA (Ad-p53) and then exposed to four cytotoxic agents: actinomycin D, vincristine, 5-fluorouracil and bleomycin. Potentiation of cytotoxicity following wild-type p53 expression varied from 0- to 20-fold for different drugs and between cell lines. It appeared that alveolar RMS cells (n = 2) were more susceptible to p53-mediated chemosensitization than embryonal RMS cells (n = 3), although this was independent of pax3-FKHR expression. Overall, cells that were most chemosensitive prior to Ad-p53 exposure were those that were most susceptible to p53 potentiation of cytotoxicity. The different results obtained with these RMS cell lines does not appear to be related to expression of pax3-FKHR, p21, Bax or Bcl-2 but may in part be due to differential regulation of p53 target genes, such as MDM2. In conclusion, exogenous wild-type expression selectively chemosensitizes RMS cells to cytotoxic agents. However, expression of transcriptionally active wtp53 does not predict a chemosensitive phenotype.

Alternative and aberrant splicing of MDM2 mRNA in human cancer

MDM2 has been characterized as a protein that binds to and facilitates degradation of the tumor suppressor p53. Interestingly, more than 40 different splice variants of MDM2 transcripts have been identified both in tumors and normal tissues, and the majority of these variants do not contain sequence encoding the p53 binding site. This review describes the different splice forms, the tissues in which they have been identified, and their association with tumor progression and prognosis. In addition, we discuss the potential functions of these variants and how they interact with full-length MDM2 protein.

Hypoxia-induced [(3)H]D-aspartate release from isolated bovine retina: modulation by calcium-channel blockers and glutamatergic agonists and antagonists

PURPOSE

The aim of the present study was two-fold: (a) to examine the effect of hypoxia on [(3)H]D-aspartate release from isolated bovine and human retinae, and (b) to investigate the regulation of hypoxia-induced neurotransmitter release by glutamate receptor agonists and antagonists.

METHODS

Isolated neural retinae were incubated in oxygenated Krebs buffer solution containing [(3)H]D-aspartate and then prepared for studies of neurotransmitter release using the superfusion method. Release of [(3)H]D-aspartate was evoked by K(+) (50 mM) applied at 90 minutes (S(1)) and hypoxia (induced by exposure of tissues to solutions pregassed with 95%N(2): 5% CO(2) for 60 minutes) at 108 minutes (S(2)) after onset of superfusion.

RESULTS

Under hypoxic conditions, pO(2) in normal Krebs buffer solution was reduced from 14.53 +/- 0.26 ppm (n = 6) to 0.54 +/- 0.04 ppm (n = 9) after one hour of gassing with 95% N(2): 5% CO( 2). Exposure to hypoxia elicited an overflow of [(3)H]D-aspartate yielding S(2)/S(1) ratios of 0.62 +/- 0.06 (n = 12) and 0.54 +/- 0.03 (n = 8) in bovine and human tissues respectively. In isolated bovine retinae, L- and N-calcium-channel antagonists diltiazem, nitrendipine, verapamil and omega-conotoxin significantly (p < 0.01 or higher) attenuated hypoxia-induced [(3)H]D-aspartate release. L-glutamate (30 microM) significantly (p < 0.001) potentiated hypoxia-induced [(3)H]D-aspartate release whereas kainate (30 microM) inhibited this response. NMDA (in concentrations up to 1 mM) had no effect on hypoxia-induced [(3)H]D-aspartate release. Antagonists of glutamate receptors and the polyamine site on the NMDA receptor inhibited hypoxia-induced release of [(3)H]D-aspartate in bovine retina with the following rank order of activity: ifenprodil congruent with MCPG > L-AP3 > MK-801. At an equimolar concentration (10 microM), L-AP3 but not ifenprodil, MCPG, MK 801 or arcaine, caused a significant (p < 0.001) inhibition of hypoxia-induced [(3)H]D-aspartate release from human retinae.

CONCLUSIONS

Hypoxia can induce the release of [( 3)H]D-aspartate from isolated bovine retinae by a calcium-dependent process. Hypoxia-induced [(3)H]D-aspartate release from isolated bovine retinae can be regulated by glutamate receptor agonists/antagonists and blockers of polyamine site on the NMDA receptor.

Potentiation of sympathetic neurotransmission in bovine isolated irides by isoprostanes

Isoprostanes (IsoP) are formed by free radical catalyzed peroxidation of arachidonic acid independent of the cyclooxygenase enzyme. In the present study, we examined the effect of IsoP on norepinephrine (NE) release from the bovine isolated iris. Furthermore, we studied the role of IsoP's in hydrogen peroxide (H2O2)-induced enhancement of NE release from this tissue. Isolated bovine irides were prepared for studies of [3H]NE release using the superfusion method. Release of [3H]NE was induced via electrical field stimulation. Both 8-iso-prostaglandin E2 (E2-IsoP) and 8-iso-prostaglandin F2 alpha (F2-IsoP) produced a concentration-related enhancement of field-stimulated [3H]NE release from isolated bovine irides, an effect that was mimicked by the thromboxane (Tx) receptor agonist, U46619 and by H2O2. The Tx-receptor antagonist, SQ 29548 inhibited responses to E2-IsoP (10 microM) with an IC50 of 370 +/- 50 nM. SQ 29548 (10 microM) also blocked the enhancement of electrically-evoked [3H]NE release induced by U46619 (10 microM) but not that caused by H2O2 (300 microM). The Tx synthetase inhibitor, carboxyheptylimidazole (10 microM) prevented the stimulatory effect of E2-IsoP on evoked [3H]NE release without affecting responses induced by H2O2. We conclude that IsoP's can enhance sympathetic neurotransmission in the bovine isolated iris, an effect that can be blocked by a Tx-receptor antagonist. Furthermore, endogenously produced Tx's mediate the stimulatory effect of IsoP's on NE release. However, endogenously generated IsoP's or Tx's are not involved in H2O2-induced potentiation of sympathetic neurotransmission.

A virus-directed enzyme prodrug therapy approach to purging neuroblastoma cells from hematopoietic cells using adenovirus encoding rabbit carboxylesterase and CPT-11

Tumor cells that contaminate hematopoietic cell preparations contribute to the relapse of neuroblastoma patients who receive autologous stem cell rescue as a component of therapy. Therefore, effective purging methods are needed. This study details in vitro experiments to develop a viral-directed enzyme prodrug purging method that specifically targets neuroblastoma cells. The approach uses an adenovirus to deliver the cDNA encoding a rabbit liver carboxylesterase that efficiently activates the prodrug irinotecan,7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11). The data show that an adenoviral multiplicity of infection of 50 transduces 100% of cultured neuroblastoma cells and primary tumor cells, irrespective of the level of tumor cell line contamination. Exposure of neuroblastoma cell lines or of mixtures of these cell lines with CD34(+) cells at a ratio of 10:90 to replication-deficient AdRSVrCE for 24 h and subsequent exposure of cells to 1-5 microM CPT-11 for 4 h increased the toxicity of CPT-11 to three neuroblastoma cell lines (SJNB-1, NB-1691, and SK-N-SH) from approximately 20-50-fold and eradicated their clonogenic potential. Also, after "purging," RNA for neuroblastoma cell markers (tyrosine hydroxylase, synaptophysin, and N-MYC) was undetectable by reverse transcription-PCR. In contrast, the purging protocol did not affect the number or type of colonies formed by CD34(+) cells in an in vitro progenitor cell assay. No bystander effect on CD34(+) cells was observed. The method described is being investigated for its potential clinical utility, particularly its efficacy for use with patients having relatively high tumor burdens, because no published methods have been shown to be efficacious when the tumor burden exceeds 1%.

[(3)H]-serotonin release from bovine iris-ciliary body: pharmacology of prejunctional serotonin (5-HT(7)) autoreceptors

In the present study, we investigated the pharmacological characteristics of electrically stimulated [(3)H]-serotonin release from mammalian iris-ciliary bodies. Isolated bovine and human iris-ciliary bodies were loaded with [(3)H]-serotonin, superfused with Krebs buffer solution and then stimulated with trains of 300 direct current (d.c.) pulses to initiate the release of the transmitter. The modification of this [(3)H]-serotonin release process by various serotonergic agonists and antagonists was studied in order to define the pharmacology of serotonin receptor(s) present in the iris-ciliary body. In bovine iris-ciliary body, electrically-evoked [(3)H]-serotonin release was calcium-dependent, tetrodotoxin-sensitive and was enhanced by serotonin (EC(50) = 200 n M) and 5-carboxmidotryptamine (EC(50) = 4 n M). The rank order of potency of agonists in enhancing field-stimulated [(3)H]-serotonin release was: 5-carboamidotryptamine > m-chlorophenylbiguanide > 2-methyl-5-hydroxytryptamine = 5-methoxy-dimethyltryptamine > serotonin > 5-methoxy-tryptamine > L-694,247 = alpha-methyl-5-hydroxytryptamine > CGS 12066A = 8-hydroxy-2-(di- n -propylamino)tetraline. Serotonin and m-chlorophenylbiguanide also enhanced electrically-evoked [(3)H]-serotonin release from human iris-ciliary bodies with EC(50)s of 3 microM and 30 n M, respectively. The pharmacological profile displayed by serotonin receptor agonists was supported by the potent antagonism of the serotonin-induced enhancement of [(3)H]-serotonin release by 5HT(7)receptor antagonists SB-258718 (IC(50) = 18.6 +/- 1.2 nM; n = 4) and mesulergine (IC(50) = 0.26 +/- 0.05 nM; n = 4). However, antagonists at 5HT(6)and 5HT(3)receptors exhibited a relatively weak blockade of serotonin induced enhancement of field-stimulated [(3)H]-serotonin release. These studies have shown the presence of functionally active prejunctional 5HT(7)autoreceptors regulating the release of [(3)H]-serotonin from bovine iris-ciliary bodies. Excitatory prejunctional 5-HT autoreceptors also exist in human iris-ciliary bodies. It is possible that these serotonin autoreceptors may have relevance to the regulation of aqueous humor dynamics in the anterior uvea.

Sensitization of human tumor cells to CPT-11 via adenoviral-mediated delivery of a rabbit liver carboxylesterase

Irinotecan, 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) is activated by carboxylesterases (CE) to yield the potent topoisomerase I inhibitor, SN-38. We have demonstrated previously that a rabbit liver CE is approximately 100-1000-fold more efficient at drug activation than a highly homologous human CE. In an attempt to use rabbit CE expression in combination with CPT-11 for gene therapy approaches for the treatment of cancer, we have developed an adenoviral vector expressing this intracellular CE. After transduction, this virus produces very high levels of CE activity in a panel of human tumor cell lines and results in marked sensitization to CPT-11 of all of the transduced cells. Reductions in IC(50) values for this drug ranged from 11-127-fold. Additionally, comparison with an adenovirus expressing a secreted form of the rabbit CE indicated that a collateral effect could be achieved with reductions in the IC(50) values ranging from 4-19-fold. These data suggest that the described reagents may be suitable for use in vivo in a viral-directed enzyme prodrug therapy approach using CPT-11.

Use of a modified ornithine decarboxylase promoter to achieve efficient c-MYC- or N-MYC-regulated protein expression

One of the advantages of viral-directed enzyme prodrug therapy (VDEPT) is its potential for tumor-specific cytotoxicity. However, the viruses used to deliver cDNAs encoding prodrug-activating enzymes transduce normal cells as well as tumor cells, and several approaches to achieve tumor-specific expression of the delivered cDNAs are being investigated. One such approach is to regulate transcription of the prodrug-activating enzyme with a promoter that is preferentially activated by tumor cells. Published data suggest that the most promising transcription factor/promoter/enhancer combinations are those activated by a tumor-specific transcription factor to retain tumor cell specificity but that are equal in strength to nonspecific viral promoters in their ability to up-regulate target cDNAs. This report identifies MYC-responsive, modified ornithine decarboxylase (ODC) promoter/enhancer sequences that up-regulate target protein expression in tumor cells overexpressing either N-MYC or c-MYC protein. The most efficient of the four constructs assessed contained six additional CACGTG MYC binding sites 5' to the endogenous ODC promoter (R6ODC). Reporter assays with this chimeric promoter/enhancer regulating expression of chloramphenicol acetyltransferase demonstrated 50-250-fold more activity in MYC-expressing cells compared with similar assays with promoterless plasmids. The R6ODC regulatory sequence was approximately equivalent to the CMV promoter in inducing expression of the neomycin resistance gene in c-MYC-expressing SW480 and HT-29 colon carcinoma cells and in N-MYC-expressing NB-1691 neuroblastoma cells. The modified ODC promoter may, therefore, be useful in achieving tissue-specific expression of target proteins in tumor cells that overexpress c- or N-MYC.

P53 mutation and MDM2 amplification frequency in pediatric rhabdomyosarcoma tumors and cell lines

BACKGROUND

The p53 tumor suppressor gene is the most commonly mutated gene in human cancer, and mutations arise in a wide variety of tumor types. Wild-type p53 functions as a regulator of apoptosis, so mutations in the p53 gene are generally associated with aggressive tumors and a poor prognosis.

PROCEDURE

We have investigated the p53 mutation and MDM2 amplification frequencies in biopsies from pediatric rhabdomyosarcoma (RMS) tumors and cell lines by SSCP and Southern analyses.

RESULTS

A mutation was detected in only 1 of 20 tumor specimens (5%), whereas the frequency in established RMS cell lines was significantly higher (6/10, 60%). p53 Mutations were more common in cell lines derived from tumors previously exposed to chemotherapy compared to those derived from tumors at di-agnosis, and it is likely that these mutations enhanced the probability of successful long-term culture. The frequency of MDM2 gene amplification in patient biopsies was also low (2/20, 10%). Interestingly, complete responses to treatment were obtained in the two patients with tumors that demonstrated amplification of MDM2. The response to treatment of patients with tumors wild-type for p53 and without MDM2 amplification was quite varied, indicating that expression of a wild-type p53 gene at diagnosis cannot always facilitate a favorable outcome.

CONCLUSIONS

p53 mutation and MDM2 gene amplification frequencies are extremely low in RMS tumors, but a wild-type p53 genotype is not always associated with a favorable prognosis.

Construction of adenovirus for high level expression of small RNAs in mammalian cells. Application to a Bcl-2 ribozyme

A series of plasmid vectors have been generated to allow the rapid construction of adenoviral vectors designed to express small RNA sequences. A truncated human U6 gene containing convenient restriction sites has been shown to be expressed at high levels following electroporation into a series of human cell lines. This gene was ligated into a promoterless adenoviral plasmid, and we have generated high titer virus by homologous recombination with adenoviral Addl327 DNA in 293 cells. Recombinant adenovirus containing a hammerhead ribozyme sequence targeted toward the Bcl-2 mRNA has been used to transduce a panel of human tumor cell lines. We have demonstrated high level expression of the recombinant U6 gene containing the ribozyme and reduction of Bcl-2 protein in transduced cells. These plasmids are suitable for the development of adenoviral vectors designed to express both ribozymes and antisense RNA in human cells.

Use of the ornithine decarboxylase promoter to achieve N-MYC-mediated overexpression of a rabbit carboxylesterase to sensitize neuroblastoma cells to CPT-11

Overexpression of specific transcription factors by tumor cells can be exploited to regulate expression of proteins that induce apoptosis or activate prodrugs, thereby producing tumor-selective toxicity. A majority of advanced-stage neuroblastomas overexpress the transcription factor N-MYC, and this overexpression is associated with poor prognosis. This study describes regulation of expression by N-MYC, via the ornithine decarboxylase (ODC) promoter, of a rabbit liver carboxylesterase (CE) that activates the prodrug CPT-11. Chloramphenicol acetyltransferase reporter assays and CE activity assays in transiently transfected neuroblastoma cell lines (SJNB-1, SJNB-4, NB-1691) and rhabdomyosarcoma cell lines (JR1neo20, JR1Nmyc6, JR1Nmyc9) support this approach as a potential method for sensitizing tumor cells to CPT-11. Clonogenic assays with IMR32 human neuroblastoma cells which express N-MYC and that had been stably transfected with a plasmid containing an ODC promoter/CE cassette corroborated results of enzyme activity assays. Specifically, IMR32.ODC.CE cells expressed approximately eightfold more CE activity than IMR32.CMV.neo cells; and 5 microM CPT-11 reduced the clonogenic potential of IMR32.ODC.CE cells to zero, while 50 microM CPT-11 was required to produce the same effect with IMR32.CMV.neo cells. Current experiments focus on adenoviral delivery of an ODC promoter/CE cDNA cassette for potential virus-directed enzyme prodrug therapy applications.

Effect of inhibition of cyclooxygenase on pre- and postjunctional actions of peroxides in the iris-ciliary body

In the present study, we investigated the effect of inhibition of cyclooxygenase (COX) with flurbiprofen (FBF) on peroxide-induced enhancement of field-stimulated [3H]norepinephrine ([3H]NE) release from bovine isolated irides. Furthermore, the effect of FBF was examined on peroxide-induced attenuation of contractions evoked by carbachol on this tissue. Irides were prepared for studies of neurotransmitter release and for measurement of contractile tension in vitro. Pretreatment of tissues with FBF (10 microM) caused significant (P < 0.001) rightward shifts of concentration-response curves to H2O2 and also decreased cumene hydroperoxide (cuOOH)-induced enhancement of evoked [3H]NE release. FBF (10 microM) partially prevented the attenuation of carbachol-induced contractions induced by H2O2 (300 microM) and cuOOH (300 microM). We conclude that inhibition of the biosynthesis of prostanoids reduced both the prejunctional stimulatory effects of H2O2 and cuOOH on sympathetic neurotransmission and inhibitory effects of peroxides on carbachol-induced contractions the in the bovine isolated iris.

Effect of isoprostanes on sympathetic neurotransmission in the human isolated iris-ciliary body

Isoprostanes (IsoP's) are prostaglandin-like compounds that are derived from free-radical catalyzed peroxidation of arachidonic acid independent of the cyclcooxygenase enzyme. In the present study, we investigated the effect of IsoP's on norepinephrine (NE) release from human isolated iris-ciliary bodies. Isolated human iris-ciliary bodies were prepared for studies of [3H]NE release using the superfusion method. Both 8-iso-prostaglandin F2alpha (F2-IsoP) and the thromboxane (Tx) receptor agonist, U46619 enhanced field-stimulated [3H]NE release from isolated, superfused human iris-ciliary bodies without affecting basal tritium efflux. On the other hand, an equimolar concentration (10 microM) of 8-iso-prostaglandin E2 (E2-IsoP) inhibited evoked [3H]NE overflow. The Tx-receptor antagonist, SQ 29548 blocked the enhancements of electrically-evoked [3H]NE release induced by F2-IsoP and U46619. However, the inhibitory responses elicited by E2-IsoP was not antagonized by SQ 29548. We conclude that IsoP's can produce both excitatory and inhibitory effects on sympathetic neurotransmission in human isolated iris-ciliary bodies. The stimulatory effects of IsoP's on NE release may be mediated by Tx-receptors.

Wild-type p53 can induce p21 and apoptosis in neuroblastoma cells but the DNA damage-induced G1 checkpoint function is attenuated

p53 is a tumor suppressor protein important in the regulation of apoptosis. Because p53 functions as a transcription factor, cellular responses depend upon activity of p53 localized in the nucleus. Cytoplasmic sequestration of p53 has been proposed as a mechanism by which the function of this protein can be suppressed, particularly in tumor types such as neuroblastoma in which the frequency of mutations of p53 is low. Data presented here demonstrate that nuclear p53 protein is expressed in a panel of neuroblastoma cell lines, and after exposure to DNA damage, transcriptionally active p53 expression can be induced. After exposure to both equitoxic IC80 and 10-Gy doses of ionizing radiation, both p53 and p21 were induced, but G1 cell cycle arrest was attenuated. To investigate whether the DNA damage signaling pathway was incapable of inducing sufficient p53 in these cells, we expressed additional wild-type p53 after adenoviral vector transduction. This exogenous p53 expression also resulted in p21 induction but was unable to enhance the G1 arrest, suggesting that the pathway downstream from p53 is nonfunctional. Although p53-mediated G1 arrest is attenuated in neuroblastoma cells, the ability of p53 to induce apoptosis appears functional, consistent with its chemosensitive phenotype. This work demonstrates that p53 is expressed in the nucleus of neuroblastoma cells and can mediate induction of p21. However, this cell type appears to have an attenuated ability to mediate a DNA damage-induced G1 cell cycle arrest.

Wild-type p53 induction mediated by replication-deficient adenoviral vectors

Replication-deficient E1-/E3-deleted adenoviral vectors are commonly used to introduce transgenes into cells in vitro and have been used for certain kinds of gene therapy protocols in vivo. We have demonstrated that transduction of cells using these vectors can induce p53 expression in cells containing a wild-type p53 gene. This response is different from p53 induction observed after DNA damage because the time course of induction is slower and because it occurs in cells with an attenuated DNA damage response. However, this vector-induced p53 is transcriptionally active and, therefore, p53 function is not inactivated by viral proteins. The mechanism of induction appears to be an increased rate of protein translation because immunoprecipitation analyses demonstrated increased levels of 35S-labeled p53 protein, even after a short 15-min labeling time. Induction of p53 by adenoviral vectors may have various effects on transduced cells, including apoptosis and altered chemotherapy chemosensitivity. Therefore, the influence of the vector might confound the impact of any particular gene used in a gene therapy application.

Suicidal ideation in Sudanese women

A literature review indicated that suicidal behavior in Sudan was very infrequent. However, an assessment of suicidal ideation in two Sudanese groups of women demonstrated high levels, particularly in women in a displaced-persons area. In addition, the recent establishment of a Befrienders International volunteer service allowed anecdotal evidence of substantial suicidal behavior to be collated. These findings highlight the need for further professional and volunteer assistance with continuing evaluation and research concerning programs for this vulnerable population.

Bax is an important determinant of chemosensitivity in pediatric tumor cell lines independent of Bcl-2 expression and p53 status

Susceptibility of a tumor cell to undergo chemotherapy-induced apoptosis appears to be dependent upon the balance of proapoptotic and survival factors that are expressed within any given cell. We have chosen to evaluate how expression of several of these proteins influences chemosensitivity of a panel of 10 pediatric tumor cell lines chosen from three tumor histiotypes: neuroblastoma, rhabdomyosarcoma, and pediatric glial tumors. The proteins evaluated were p53 and six members of the Bax/Bcl-2 family: three proapoptotic proteins (Bax, Bak, and Bcl-xS) and three survival factors (Bcl-2, Bcl-xL, and Mcl-1). We investigated whether there was any relationship between endogenous expression of these proteins and chemosensitivity (or resistance) to three chemotherapeutic agents that directly damage DNA (doxorubicin, actinomycin D, and topotecan) and a mitotic spindle poison (vincristine). Even though exogenous overexpression of wild-type p53 has been associated with a chemosensitive phenotype in several model systems we demonstrated no such relationship in these studies. In addition, expression levels of Bcl-2, Bcl-xL, Bcl-xS, Bak, or Mcl-1 did not correlate with sensitivity or resistance to the four drugs. However, there was a statistically significant correlation between endogenous levels of Bax protein and sensitivity to both doxorubicin and actinomycin D. We conclude that even though many proteins such as p53 and Bcl-2 have been shown to influence drug response when exogenously overexpressed in model systems, in unmodified cell lines endogenous protein levels may not generate the same results. We have demonstrated that endogenous Bax expression was the only protein found to be associated with chemosensitivity across the three different tumor histiotypes and propose that analysis of Bax may be a more useful prognostic indicator for tumor response to therapy than either p53 or Bcl-2.

Differences in epitope accessibility of p53 monoclonal antibodies suggest at least three conformations or states of protein binding of p53 protein in human tumor cell lines

The p53 tumor suppressor gene is deleted or mutated in over 50% of human tumors. Mutations frequently extend the half-life of the p53 protein; and a high level of nuclear p53 expression, detected by immunohistochemistry, has been used to predict the p53 status of tumors. We compared the sensitivity and reactivity of five frequently used, commercially available monoclonal antibodies (1801, DO1, DO7, BP53.12 and 421) in immunoblot and immunofluorescence assays, and found that results differed among the antibodies. Comparison of immunoblot analysis of denatured nuclear and cytoplasmic p53 protein were consistent with antibodies DO1, DO7 and BP53.12, each of which generated a strong specific signal in both cell fractions. However, in situ analysis demonstrated that although all antibodies recognized nuclear p53, only BP53.12 and 421 recognized p53 protein in the cytoplasm. In addition, 1801 produced a signal in p53-negative tumor cell lines. Differences in situ among the antibodies were probably due to the accessibility of their respective epitopes and suggested that nuclear and cytoplasmic p53 either have different three-dimensional conformations or are bound to different proteins. A third p53 protein conformation was also suggested by the observation that only two of the five antibodies (BP53.12 and DO7) detected induced levels of p53 in situ following exposure to ionizing radiation. In summary, except for the fact that DO7 does not recognize cytoplasmic p53 in situ, we found it to be the most specific, versatile, and reliable antibody. We conclude that the p53 antibody of choice depends upon the specific goal of a study and the method used to detect this protein.

Cytoplasmic sequestration of an O6-methylguanine-DNA methyltransferase enhancer binding protein in DNA repair-deficient human cells

O6-Methylguanine-DNA methyltransferase (MGMT), an enzyme that repairs adducts at O6 of guanine in DNA, is a major determinant of susceptibility to simple methylating carcinogens or of tumor response to anticancer chloroethylating drugs. To investigate the mechanisms underlying cellular expression of this DNA repair enzyme, we focused on the role of a 59-bp enhancer of the human MGMT gene in the regulation of its expression. By using chloramphenicol acetyltransferase reporter assays, we found that the enhancer activity, which was present in both MGMT-expressing (Mer+) and -deficient (Mer-) cells, correlated with the endogenous MGMT activity in Mer+ cell lines. Band-shift assays and deletion analysis of the 59-bp sequence defined a minimal 9-mer cis element (5'-CTGGGTCGC-3') for specific trans factor binding. The MGMT enhancer binding protein (MEBP), 45 kDa by Southwestern blot analysis, was present in the nuclei of all Mer+ cells tested but was apparently restricted to the cytoplasm of Mer- cells. We conclude that the MEBP-enhancer interaction plays an important role in regulating constitutive MGMT expression in Mer+ cells and that MEBP exclusion from the nucleus may account for the down-regulation of MGMT in Mer- cells.

The risk of peripheral vein phlebitis associated with chlorhexidine-coated catheters: a randomized, double-blind trial

OBJECTIVE

To evaluate the risk of phlebitis associated with chlorhexidine-coated polyurethane catheters in peripheral veins.

DESIGN

A randomized, double-blinded trial comparing chlorhexidine-coated polyurethane catheters with uncoated polyurethane catheters.

SETTING

A university hospital.

PATIENTS

Adult medicine and surgery patients.

INTERVENTIONS

Certified registered nurse anesthetists or an infusion team consisting of nurses and physicians inserted the catheters. Catheter insertion sites were scored twice daily for evidence of phlebitis. At the time catheters were removed, a quantitative blood culture was performed, and catheters were sonicated for quantitative culture.

RESULTS

Of 221 evaluable catheters, phlebitis developed in 18 (17%) of 105 coated catheters, compared to 27 (23%) of 116 uncoated catheters (relative risk [RR], 0.74; 95% confidence interval [CI95], 0.43-1.26; P = .32). By survival analysis, chlorhexidine-coated catheters had a lower risk of phlebitis during the first 3 days (P = .06), but not when all catheters were considered in both patient groups (P = .31). In the absence of catheter colonization, the incidence of phlebitis was 21% (16/76) and 24% (20/86) for coated and uncoated catheters, respectively (P = .85), whereas in the presence of catheter colonization, the incidence of phlebitis was 14% (1/7) and 80% (4/5) for coated and uncoated catheters, respectively (RR, 0.18; CI95, 0.03-1.15; P = .07).

CONCLUSION

The risk of phlebitis in the presence of catheter colonization was 82% lower for chlorhexidine-coated polyurethane catheters compared to otherwise identical uncoated catheters.

Retroviral transfer of a bacterial alkyltransferase gene (ada) into human bone marrow cells protects against O6-benzylguanine plus 1, 3-bis(2-chloroethyl)-1-nitrosourea cytotoxicity

The antitumor activity of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) is limited by the O6-alkylguanine-DNA alkyltransferase (ATase) in tumor cells and by delayed myelosuppression. Inactivation of neoplastic ATase by O6-benzylguanine (BG) improves the therapeutic index for BCNU. We have demonstrated previously that BG + BCNU-induced myelosuppression in mice is reduced by expression of the BG-resistant ATase ada in murine bone marrow. We have now generated an amphotropic retrovirus containing the ada gene and tested the effectiveness of ada expression in preventing BG + BCNU cytotoxicity in human hematopoietic progenitor cells. A retroviral producer clone with a biological titer of 6.5 x 10(4) colony-forming units/ml and 4.4 pmol ATase/mg protein was used for transduction of bone marrow. Cocultivation of these ada producer cells with progenitor cells from six normal individuals resulted in 1.9-3. 9-fold protection against BG + BCNU-induced cytotoxicity in committed progenitor cell assays. Furthermore, this cytoprotective effect was associated with a high transduction efficiency (40%) and a 2-fold increase of ATase activity in the surviving committed progenitor cell colonies. These data provide a basis for testing the clinical effectiveness of retroviral ada gene transfer into hematopoietic cells to increase the therapeutic index of BG + BCNU.

Oxygen administration during transport and recovery after outpatient surgery does not prevent episodic arterial desaturation

STUDY OBJECTIVE

To compare the efficacy of two different oxygen (O2) delivery systems in preventing episodic arterial desaturation in the immediate postoperative period.

STUDY DESIGN

Randomized, prospective, nonblinded comparison in patients.

SETTING

Operating room and postanesthesia care unit (PACU) of a university outpatient surgery center.

PATIENTS

100 ASA status I and II adults, male and female, age greater than 18 years, undergoing outpatient surgical procedures not involving the upper airway.

INTERVENTIONS

Group I received supplemental O2 administered by bag-valve-mask during transport, followed by 40% face shield in the PACU. Group 2 received supplemental O2 by nasal cannula at 4 L/min both during transport and during PACU stay.

MEASUREMENTS AND MAIN RESULTS

Arterial O2 saturation (SpO2) was collected by computer from a recording pulse oximeter at 15-second intervals beginning before extubation and continuing until O2 administration was discontinued in PACU. Neither mode of therapy was successful in completely eliminating arterial desaturation defined as SpO2 less than 90%, nor was there any difference in efficacy between the two treatment groups. Group 1 had 8 patients desaturate on 9 different occasions (5 times during transport, 4 times in PACU). Group 2 had 5 patients desaturate on 9 different occasions (4 times during transport, 5 times in PACU).

CONCLUSION

Routine O2 administration during transport and PACU stay did not abolish episodic desaturation, even in healthy patients undergoing minor surgical procedures. Given the marked difference in acquisition cost, it would appear that O2 administration by nasal cannula is a more cost-effective alternative for routine postoperative O2 administration in certain groups of patients undergoing general anesthesia for outpatient surgery.

Wild-type p53 suppresses transcription of the human O6-methylguanine-DNA methyltransferase gene

High-level expression of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) correlates with cellular resistance to the chloroethylnitrosourea (CENU) class of alkylating agents. Consequently, tumors expressing low levels of MGMT are sensitive to CENU chemotherapy, and any mechanism that can be used to reduce MGMT levels could sensitize resistant tumors. We have demonstrated that transient transfection of wild-type, but not mutant, p53 protein into a p53-null cell line, Saos-2, suppresses MGMT promoter activity in a reporter gene system. In addition, following a 24-h transduction of IMR90 fibroblasts with a wild-type p53-adenoviral vector, endogenous MGMT protein is down-regulated and is no longer detectable 5 days following infection. Because p53 is inducible by ionizing radiation, we propose that existing cancer therapy regimens that combine radiotherapy with CENU chemotherapy may be improved by altering scheduling and allowing enough time between the two therapies for the relatively stable MGMT protein to degrade.

Changes in O6-methylguanine-DNA methyltransferase expression during immortalization of cloned human fibroblasts

Suppressed expression of the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT), characterized as the Mer- phenotype, occurs only in malignant or transformed cell lines. To investigate the relationship between the transformation process and loss of MGMT expression, we derived 20 cloned lines of IMR90 normal fibroblasts transfected with the plasmid pSV3neo expressing the SV40 large-T antigen. Of the five lines that were grown until crisis phase, four emerged as continuously proliferating immortal lines. Of these, only one retained MGMT, the other three having become Mer-. In every case the loss of MGMT coincided with the final phase of immortalization following crisis. Because these were cloned cell lines it is clear that the phenotypic change to Mer- is not merely due to selection of a Mer- cell from the initial population, but must involve a cellular change in MGMT regulation. It is not clear if increased mutation rate associated with loss of MGMT results in increased frequency of an immortalization event or if an immortalization event, such as telomere disruption, results in MGMT suppression. In addition, we have shown that, consistent with previous observations, both hypermethylation in promoter sequences and hypomethylation of downstream sequences in the body of the gene were closely associated with loss of MGMT expression. These studies also illustrate the utility of these new cloned cell lines for characterizing molecular events associated with transformation and immortalization.

Retroviral transfer of a bacterial alkyltransferase gene into murine bone marrow protects against chloroethylnitrosourea cytotoxicity

The chloroethylnitrosoureas (CENUs) are important antineoplastic drugs for which clinical utility has been restricted by the development of severe delayed myelosuppression in most patients. To investigate the potential of DNA repair proteins to reduce bone marrow sensitivity to the CENUs, we transferred the Escherichia coli ada gene, which encodes a Mr 39,000 O6-alkylguanine-DNA alkyltransferase (ATase), into murine bone marrow cells by the use of a high-titer ecotropic retrovirus. The ada-encoded ATase is resistant to O6-benzylguanine (O6-BG), a potent inhibitor of the mammalian ATases, thus affording the bone marrow an additional level of protection against CENUs. In methylcellulose cultures, ada-infected hematopoietic progenitor cells were twice as resistant as uninfected cells to the toxic effects of 1, 3-bis(2-chloroethyl)-1-nitrosourea (BCNU) following treatment with O6-BG. Although showing no obvious protective effects against leukopenia, overexpression of the bacterial ATase activity reduced the severity of anemia and thrombocytopenia in mice treated with O6-BG and BCNU. These effects, which were maximal at a BCNU dose of 12.5 mg/kg, were associated with improved survival when BCNU was given at this dose. At lower BCNU doses cytotoxicity was limited in both transduced and control mice, and at higher doses the protective effect was saturated due to cytotoxicity. These results suggest that ada gene therapy may be a feasible approach to amelioration of delayed myelosuppression following O6-BG plus CENU combination chemotherapy.

Identification of a 59 bp enhancer located at the first exon/intron boundary of the human O6-methylguanine DNA methyltransferase gene

The DNA repair enzyme, O6-methylguanine DNA methyltransferase (MGMT) is responsible for repair of damage induced by alkylating agents that produce adducts at O6-guanine in DNA. Although the MGMT gene promoter has housekeeping gene promoter characteristics, unlike these genes which are expressed at a constant level, MGMT transcriptional activity varies between cell types. During an attempt to identify regions of the MGMT regulatory sequence sensitive to variations in transcription factors between cell types, we have identified a 59 bp enhancer which is required for efficient MGMT promoter function. This fragment produced increased transcriptional activity in reporter gene constructs containing either the MGMT or UMP-synthase promoter when transfected into either of two cell lines; it seems therefore that this enhancer may interact with relatively common trans-acting factors. Functional activity is only detected when the enhancer is in 'cis' with respect to the promoter, suggesting that complexes are formed between proteins bound to the enhancer and promoter sequences. We propose that the enhancer-binding protein may be a novel transcription factor since there are no obvious consensus sequences within the 59 bp sequence for known DNA-binding proteins.

In vitro methylation of the human O6-methylguanine-DNA methyltransferase promoter reduces transcription

Approx. 20% of human tumor cell lines (termed Mer-) are deficient in the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT; E.C.2.1.1.63). Such cells possess the MGMT gene and promoter sequences but have virtually no mRNA or protein. Cytosine methylation of gene sequences has been proposed as a mechanism by which MGMT could be suppressed in Mer- cells; however, the experimental evidence does not uniformly support this idea. We therefore investigated the effect of in vitro methylation of the MGMT promoter in a reporter gene construct transfected into cultured human cells. DNA methylation by HpaII or HhaI methylases suppressed the activity of the promoter, although the effect was not absolute. The occurrence of partial intracellular demethylation of promoter sequences may account for the incomplete inhibition of transcription. A model that attempts to reconcile the opposing views on the role of cytosine methylation in MGMT gene expression is presented.

Expression in mammalian cells of the Escherichia coli O6 alkylguanine-DNA-alkyltransferase gene ogt reduces the toxicity of alkylnitrosoureas

V79 Chinese hamster cells expressing either the O6-alkylguanine-DNA-alkyltransferase (ATase) encoded by the E. coli ogt gene or a truncated version of the E. coli ada gene have been exposed to various alkylnitrosoureas to investigate the contribution of ATase repairable lesions to the toxicity of these compounds. Both ATases are able to repair O6-alkylguanine (O6-AlkG) and O4-alkylthymine (O4-AlkT) but the ogt ATase is more efficient in the repair of O4-methylthymine (O4-MeT) and higher alkyl derivatives of O6-AlkG than is the ada ATase. Expression of the ogt ATase provided greater protection against the toxic effects of the alkylating agents then the ada ATase particularly with N-ethyl-N-nitrosourea (ENU) and N-butyl-N-nitrosourea (BNU) to which the ada ATase expressing cells were as sensitive as parent vector transfected cells. Although ogt was expressed at slightly higher levels than the truncated ada in the transfected cells, this could not account for the differential protection observed. For-N-methyl-N-nitrosourea (MNU) the increased protection in ogt-transfected cells is consistent with O4-MeT acting as a toxic lesion. For the longer chain alkylating agents and chloroethylating agents, the protection afforded by the ogt protein may be a consequence of the more efficient repair of O6-AlkG, O4-AlkT or both of these lesions in comparison with the ada-encoded ATase.

Performance characteristics and interanalyzer variability of PO2 measurements using tonometered human blood

We performed a side-by-side comparison of the ability of four blood gas analyzers (IL-1312, Corning-178, AVL-995, and ABL-330) to measure PO2 across a wide range under controlled laboratory conditions. Samples of fresh whole human blood, tonometered with analytic quality gas, were prepared with partial pressures of oxygen from 0 to 283 mm Hg. Fifteen determinations were made at 16 levels of tonometric PO2 (tPO2) on each of the four blood gas analyzers. The bias, precision, and root mean squared error (RMSE) of the PO2 measurement relative to tPO2 were determined for each analyzer at each tPO2 level. Mean bias and precision across the range tested were 2.78 +/- 1.29 mm Hg (IL), -0.35 +/- 1.91 (Corning), 2.14 +/- 1.43 (AVL), and 3.00 +/- 1.47 (ABL). RMSE was 3.28, 2.61, 3.57, and 2.41 for IL, AVL, ABL, and Corning, respectively. Percent RMSE (RMSE/tPO2 x 100%), ranged from 0.9% (AVL at 75 mm Hg PO2 and IL at 283 mm Hg tPO2) to 9.1% (IL at 29 mm Hg tPO2). Three analyzers (AVL, ABL, and Corning) showed a statistically significant (p < 0.0001) correlation between RMSE and tPO2, and no correlation between percent RMSE and tPO2. This demonstrates that, for these instruments, accuracy is a function of the magnitude of the tPO2 value. IL did not show a significant correlation between RMSE and tPO2 but did demonstrate a significant negative correlation (r = -0.78, p > 0.001) between percent RMSE and tPO2, indicating that, for this analyzer, accuracy is not a function of tPO2. The differences in PO2 measurements between pairs of analyzers were also examined.(ABSTRACT TRUNCATED AT 250 WORDS)