Combinatorial effects of histone deacetylase inhibitors (HDACi), vorinostat and entinostat, and adaphostin are characterized by distinct redox alterations

PURPOSE

Amongst the epigenetically targeted therapies, targeting of the histone deacetylases (HDACs) has yielded numerous drugs for clinical use in hematological malignancies, but none as yet for acute lymphocytic leukemia (ALL). Single agent activity of HDAC inhibitors (HDACi) has been elusive in ALL, and has prompted study of combinatorial strategies. Because several HDACi raise levels of intracellular oxidative stress, we evaluated combinations of two structurally distinct HDACi with the redox active compound adaphostin in ALL.

METHODS

The HDACi vorinostat and entinostat were tested in combination with adaphostin in human ALL cell lines. DNA fragmentation, caspase activation, mitochondrial disruption and levels of  intracellular peroxides, superoxide and glutathione were measured in cells treated with the HDACi/adaphostin combinations. Antioxidant blockade of cell death induction and gene expression profiling of cells treated with vorinostat/adaphostin versus entinostat/adaphostin combinations were evaluated.

RESULTS

Both combinations synergistically induced apoptotic DNA fragmentation, which was preceded by an increase in superoxide levels, a reduction in mitochondrial membrane potential, and an increase in caspase-9 activation. The antioxidant N-acetylcysteine (NAC) blocked superoxide generation and prevented reduction of mitochondrial membrane potential. NAC decreased DNA fragmentation and caspase activity in cells treated with adaphostin and vorinostat, but not in those treated with adaphostin and entinostat. Gene expression arrays revealed differential regulation of several redox genes prior to cell death induction.

CONCLUSIONS

A redox modulatory agent, adaphostin, enhances efficacy of two HDACi, vorinostat or entinostat, but via different mechanisms indicating a point of divergence in the mechanisms of synergy between the two distinct HDACi and adaphostin.

Abstract 3591: Inhibition of heme oxygenase 1 decreases proliferation and resensitizes TKI-resistant Flt3-ITD-positive AML cells

Acute myelogenous leukemia (AML) afflicts ∼12,330 new patients per year in the United States. Regrettably, only 25% of patients will survive five years past diagnosis. The most common mutation in AML is internal tandem duplication (ITD) of the juxtamembrane domain of the fms-like tyrosine kinase receptor-3 (Flt3), which renders it constitutively active. This mutation correlates with poor clinical prognosis and has been targeted therapeutically. Unfortunately, Flt3-directed tyrosine kinase inhibitors (TKI) have shown only modest benefit as single agents. Additionally, relapse and resistance are major factors in the treatment of Flt3-ITD+AML. In addition to its prominent role in regulating proliferative signaling, Flt3-ITD also increases production of reactive oxygen species (ROS) which act as secondary messengers, mediating oncogenesis and drug resistance. Heme oxygenase 1 (HO-1) is a ROS-responsive antioxidant that mediates proliferation and drug resistance in some cancer types. Initial analysis of patient samples from the AML TCGA cohort suggests that HO-1 is up-regulated in a subset of AML patients where its expression correlates with poor prognosis. Interestingly, HO-1 over-expression co-occurs with Flt3 receptor alterations. Thus, we hypothesized that Flt3-ITD-dependent signaling and ROS production increase HO-1, resulting in proliferation and drug resistance in AML. Constitutive expression of HO-1 protein and mRNA was elevated in murine (BaF3/Flt3-ITD) and human (MOLM13 and MV4.11) ITD+ cell lines as compared to Flt3-WT cells. This expression was dependent on Flt3-kinase, as treatment with Flt3-directed TKIs (quizartinib or lestaurtinib) attenuated HO-1 expression. Further, oxygen consumption and respiration analyses, as well as chemical inhibitors revealed a role for non-mitochondrial ROS producing enzymes in HO-1 expression in ITD+ cells. To determine a functional role for HO-1, we inhibited HO-1 with zinc protoporphyrin (ZnPP) or utilized siRNA knockdown of HO-1, both of which resulted in decreased proliferation of ITD+ cells. To determine the contribution of HO-1 in resistance to Flt3-directed TKI, we created a model of acquired resistance to Flt3-directed TKI (ITDR). HO-1 expression was elevated in ITDR compared to parental cells. However, HO-1 was no longer under control of Flt3-kinase signaling, as treatment with Flt3-directed TKI had no effect on HO-1. Similar to parental cells, knockdown of HO-1 or treatment with ZnPP resulted in decreased proliferation of ITDR cells. Further, combined treatment with Flt3-directed TKIs and ZnPP or HO-1 knockdown resulted in increased induction of cell death of ITDR cells. These data provide impetus for direct targeting of HO-1 in TKI resistant ITD+ AML. Together, our data suggest HO-1 as a growth and resistance factor in Flt3-ITD+ AML; therefore, targeting HO-1, or the mechanisms that control its expression, may prove therapeutically valuable.

Citation Format: Mary E. Irwin, Joya Chandra. Inhibition of heme oxygenase 1 decreases proliferation and resensitizes TKI-resistant Flt3-ITD-positive AML cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3591. doi:10.1158/1538-7445.AM2015-3591

Abstract 960: Targeting Egr-1 is an effective strategy for overcoming kinase inhibitor resistance in CML

The primary oncogene associated with CML is BCR/ABL which controls proliferative and survival signaling and is a potent inducer of reactive oxygen species (ROS). ROS play both positive and negative roles in proliferation and survival; this dual nature has been exploited by leukemia cells to promote growth, genomic instability, and drug resistance. However, the distinct molecular alterations that occur as a result of BCR/ABL-induced ROS are not well described. BCR/ABL-targeted therapeutics have improved clinical response rates, therefore the number of CML patients living with detectable disease burden is rising. Complete hematologic responses to tyrosine kinase inhibitor (TKI) therapy are seen in ∼10-30% of CML patients, so acquired drug resistance and relapse remain major issues. Thus, novel targets for combined therapeutics are needed. We have shown that early growth response 1 (Egr-1) is a BCR/ABL-dependent, redox-responsive transcription factor that modulates expression of the non-receptor tyrosine kinase Fyn in CML leading to proliferation and survival. Tissue microarray analysis of 26 CML patients (10 chronic phase, 6 accelerated phase, and 10 blast crisis), corroborated by western blotting on independent patient samples, showed that Egr-1 protein expression increased as CML progresses from chronic phase to the more treatment resistant accelerated phase and blast crisis. Egr-1 protein expression was also elevated 2.5 fold in a model of acquired pan-TKI resistance (K562-STI) when compared with parental K562 cells. When Egr-1 was genetically inhibited, proliferation of K562-STI cells decreased by 56%. Egr-1 knockdown was also sufficient to sensitize K562-STI cells to growth inhibition caused by first and second generation BCR/ABL-directed TKI, further implicating Egr-1 in acquired TKI resistance. Egr-1 is well known as a redox-responsive transcription factor, and we found that ROS were elevated in K562-STI vs. K562 cells. While analysis of mitochondrial respiration using a Seahorse Bioanalyzer showed no increase in mitochondrial respiration, spare respiratory capacity, nor proton leak in K562-STI vs. K562, there remained a basal level of oxygen consumption from non-mitochondrial sources in both cell lines. Interestingly, fluorigenic and western blotting assays showed increases in NADPH oxidase (NOX) activity (1.35 fold) and p47phox (2 fold), an essential component of the NOX complex, respectively in K562-STI cells, suggesting NOX as a source of ROS in these cells. To this end, inhibition of the NOX complex with diphenyleneiodonium decreased ROS levels and Egr-1 expression by 50% in K562-STI but not K562 cells. These data suggest that K562-STI have altered regulation of Egr-1 controlled, in part, by NOX. Together, our findings suggest that targeting the transcription factor Egr-1 directly, or through the NOX complex, may be beneficial for improving outcomes for CML patients.

Citation Format: Mary E. Irwin, Roxsan Manshouri, Blake Johnson, Hesham M. Amin, Joya Chandra. Targeting Egr-1 is an effective strategy for overcoming kinase inhibitor resistance in CML. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 960. doi:10.1158/1538-7445.AM2014-960

Small molecule ErbB inhibitors decrease proliferative signaling and promote apoptosis in philadelphia chromosome-positive acute lymphoblastic leukemia

The presence of the Philadelphia chromosome in patients with acute lymphoblastic leukemia (Ph⁺ALL) is a negative prognostic indicator. Tyrosine kinase inhibitors (TKI) that target BCR/ABL, such as imatinib, have improved treatment of Ph⁺ALL and are generally incorporated into induction regimens. This approach has improved clinical responses, but molecular remissions are seen in less than 50% of patients leaving few treatment options in the event of relapse. Thus, identification of additional targets for therapeutic intervention has potential to improve outcomes for Ph+ALL. The human epidermal growth factor receptor 2 (ErbB2) is expressed in ∼30% of B-ALLs, and numerous small molecule inhibitors are available to prevent its activation. We analyzed a cohort of 129 ALL patient samples using reverse phase protein array (RPPA) with ErbB2 and phospho-ErbB2 antibodies and found that activity of ErbB2 was elevated in 56% of Ph⁺ALL as compared to just 4.8% of Ph⁻ALL. In two human Ph+ALL cell lines, inhibition of ErbB kinase activity with canertinib resulted in a dose-dependent decrease in the phosphorylation of an ErbB kinase signaling target p70S6-kinase T389 (by 60% in Z119 and 39% in Z181 cells at 3 µM). Downstream, phosphorylation of S6-kinase was also diminished in both cell lines in a dose-dependent manner (by 91% in both cell lines at 3 µM). Canertinib treatment increased expression of the pro-apoptotic protein Bim by as much as 144% in Z119 cells and 49% in Z181 cells, and further produced caspase-3 activation and consequent apoptotic cell death. Both canertinib and the FDA-approved ErbB1/2-directed TKI lapatinib abrogated proliferation and increased sensitivity to BCR/ABL-directed TKIs at clinically relevant doses. Our results suggest that ErbB signaling is an additional molecular target in Ph⁺ALL and encourage the development of clinical strategies combining ErbB and BCR/ABL kinase inhibitors for this subset of ALL patients.

Abstract 4124: The Antioxidant heme oxygenase 1 promotes proliferation and survival of Flt3-ITD-positive AML

Acute myelogenous leukemia (AML) afflicts ∼12,330 new patients per year in the United States. Regrettably, only 25% of patients will survive five years past diagnosis. The most common mutation in AML is internal tandem duplication (ITD) of the juxtamembrane domain of the fms-like tyrosine kinase receptor-3 (Flt3), which renders it constitutively active. Flt3-ITD regulates proliferation and survival, and also increases the production of reactive oxygen species (ROS), which act as secondary messengers for oncogenic signaling. ROS can cause the induction of a number of molecules, however, one protein, heme oxygenase 1 (HO-1), a well-known antioxidant, has been connected to both proliferation and drug resistance of various cancers. We hypothesized that Flt3-ITD-dependent signaling and ROS production increase constitutive expression of HO-1, leading to the activation of antioxidant and anti-apoptotic pathways, resulting in proliferation and drug resistance in AML. Western blotting revealed a two-fold increase of HO-1 protein in Flt3-ITD+ cells as compared to Flt3-WT; a four-fold up-regulation of HO-1 mRNA was noted by quantitative real-time PCR suggesting transcriptional control. To determine if this up-regulation was due to the altered redox status of Flt3-ITD+ cells, the flavonoid inhibitor diphenylene iodonium (DPI) was used. Consistent with published results implicating the flavonoid protein complex NADPH oxidase (NOX) as a primary source of ROS in these cells, DPI reduced ROS levels as early as two hours post treatment. This ROS reduction coincided with a decrease in HO-1 protein, suggesting that NOX may be involved in HO-1 up-regulation. Our previous results in chronic myeloid leukemia suggest that a Rac1-dependent isoform of NOX controls HO-1 expression, however, in Flt3-ITD+AML, dominant negative inhibition of Rac1 was insufficient to alter HO-1 expression suggesting that either a Rac1-independent NOX isoform is involved or that another flavonoid protein modulates HO-1 expression in this leukemia subtype. Interestingly, when HO-1 expression was knocked down using RNAi, there was a 50% reduction of proliferation and 40% reduction of viability as measured by trypan blue exclusion in Flt3-ITD+AML cells. These data suggest that the function of HO-1 up-regulation is to promote survival and proliferation of Flt3-ITD+AML. Additionally, we have created a model of acquired resistance to lestaurtinib, a Flt3 kinase inhibitor, by treating with increasing doses of the drug over time. Preliminary results suggest that HO-1 is further elevated in these resistant cells as compared to parental Flt3-ITD cells; thus, we will use this model to test the functional role of HO-1 in acquired resistance. Together, our data suggest that HO-1 is a growth and survival factor in Flt3-ITD+AML; therefore, targeting HO-1 or the mechanisms that control its expression may prove therapeutically valuable.

Citation Format: Mary E. Irwin, Joya Chandra. The Antioxidant heme oxygenase 1 promotes proliferation and survival of Flt3-ITD-positive AML. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4124. doi:10.1158/1538-7445.AM2013-4124

Redox control of leukemia: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) play both positive and negative roles in the proliferation and survival of a cell. This dual nature has been exploited by leukemia cells to promote growth, survival, and genomic instability-some of the hallmarks of the cancer phenotype. In addition to altered ROS levels, many antioxidants are dysregulated in leukemia cells. Together, the production of ROS and the expression and activity of antioxidant enzymes make up the primary redox control of leukemia cells. By manipulating this system, leukemia cells gain proliferative and survival advantages, even in the face of therapeutic insults. Standard treatment options have improved leukemia patient survival rates in recent years, although relapse and the development of resistance are persistent challenges. Therapies targeting the redox environment show promise for these cases. This review highlights the molecular mechanisms that control the redox milieu of leukemia cells. In particular, ROS production by the mitochondrial electron transport chain, NADPH oxidase, xanthine oxidoreductase, and cytochrome P450 will be addressed. Expression and activation of antioxidant enzymes such as superoxide dismutase, catalase, heme oxygenase, glutathione, thioredoxin, and peroxiredoxin are perturbed in leukemia cells, and the functional consequences of these molecular alterations will be described. Lastly, we delve into how these pathways can be potentially exploited therapeutically to improve treatment regimens and promote better outcomes for leukemia patients.

Expression and activity of Fyn mediate proliferation and blastic features of chronic myelogenous leukemia

The BCR-ABL1 oncogene is a tyrosine kinase that activates many signaling pathways, resulting in the induction of chronic myeloid leukemia (CML). Kinase inhibitors, such as imatinib, have been developed for the treatment of CML; however, the terminal, blast crisis phase of the disease remains a clinical challenge. Blast crisis CML is difficult to treat due to resistance to tyrosine kinase inhibitors, increased genomic instability and acquired secondary mutations. Our recent studies uncovered a role for Fyn in promoting BCR-ABL1 mediated cell growth and sensitivity to imatinib. Here we demonstrate that Fyn contributes to BCR-ABL1 induced genomic instability, a feature of blast crisis CML. Bone marrow cells and mouse embryonic fibroblasts derived from Fyn knockout mice transduced with BCR-ABL1 display slowed growth and clonogenic potential as compared to Fyn wild-type BCR-ABL1 expressing counterparts. K562 cells overexpressing constitutively active Fyn kinase were larger in size and displayed an accumulation of genomic abnormalities such as chromosomal aberrations and polyploidy. Importantly, loss of Fyn protected mouse embryonic fibroblast cells from increased number of chromosomal aberrations and fragments induced by BCR-ABL1. Together, these results reveal a novel role for Fyn in regulating events required for genomic maintenance and suggest that Fyn kinase activity plays a role in the progression of CML to blast crisis.

Inhibition of the NADPH oxidase regulates heme oxygenase 1 expression in chronic myeloid leukemia

BACKGROUND

Patients with chronic myelogenous leukemia (CML) in blast crisis have a poor response to tyrosine kinase inhibitors designed to inhibit the breakpoint cluster region-v-Abelson murine leukemia viral oncogene homolog 1 (BCR-ABL1) oncogene. Recent work has demonstrated that heme oxygenase 1 (HO-1) expression is increased in BCR-ABL1-expressing cells and that the inhibition of HO-1 in CML leads to reduced cellular growth, suggesting that HO-1 may be a plausible target for therapy. The objective of the current study was to clarify the mechanism of HO-1 overexpression and the role of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase as a contributor to this mechanism in CML.

METHODS

HO-1 expression was evaluated in bone marrow specimens from patients with CML in various stages of disease, in a transplantation-based model for CML, and in CML cell lines. Chemical and genetic inhibition of the NADPH oxidase was carried out in CML cells.

RESULTS

Specimens from patients with CML in blast crisis displayed higher levels of HO-1 staining than specimens from patients with CML in chronic or accelerated phase. HO-1 up-regulation in BCR-ABL1-expressing cells was suppressed by diphenyleneiodonium (DPI), a chemical inhibitor of the NADPH oxidase. Targeting the NADPH oxidase through RNA interference (RNAi) to Ras-related C3 botulinum toxin substrate 1 (Rac1), a dominant-negative Rac1 construct or an inhibitor of Rac1 activity also blunted HO-1 protein expression. Moreover, inhibition of the NADPH oxidase by RNAi directed toward the 47-kd cytosolic subunit of Nox (p47phox) similarly abrogated HO-1 levels.

CONCLUSIONS

BCR-ABL1 expression up-regulated HO-1, a survival factor for CML cells. This up-regulation was more pronounced in blast crisis CML relative to early stage disease and was mediated by the NADPH oxidase components Rac1 and p47phox. The expression of p47phox was increased in BCR-ABL1-expressing cells.

Src family kinases mediate epidermal growth factor receptor signaling from lipid rafts in breast cancer cells

Activation of the epidermal growth factor receptor (EGFR) regulates cellular proliferation, survival, and migration of breast cancer cells. In particular, EGFR recruits signaling proteins to the cell membrane leading to their phosphorylation and activation. However, EGFR also localizes to other cellular structures, including endosomes, mitochondrion, and nuclei. Recently, we demonstrated that lipid raft localization of EGFR in triple-negative breast cancer cell lines promotes EGFR protein-dependent, EGFR kinase-independent activation of Akt. Here, we further define the mechanism by which lipid rafts regulate EGFR signaling to Akt. Specifically, we show that the non-receptor tyrosine kinase c-Src co-localizes and co-associates with EGFR and lipid rafts. Breast cancer cells resistant to treatment with EGFR inhibitors, were also resistant to treatment with Src family kinase (SFK) inhibitors; however, the combination of EGFR and SFK inhibitors synergistically decreases cell viability. We found that this decrease in cell viability observed with EGFR and SFK inhibitor co-treatment correlates with loss of Akt phosphorylation. In addition, we found that in breast cancer cell lines with EGFR and c-Src co-localized to lipid rafts, phospho-inositide 3 kinase (PI3K) was also associated with lipid rafts. Together, the data herein suggest that lipid rafts provide a platform for the interaction of EGFR, c-Src, and PI3K, leading to activation of cellular survival signaling in breast cancer cells.

Lipid raft localization of EGFR alters the response of cancer cells to the EGFR tyrosine kinase inhibitor gefitinib

Epidermal growth factor receptor (EGFR) is overexpressed in many cancer types including ~30% of breast cancers. Several small molecule tyrosine kinase inhibitors (TKIs) targeting EGFR have shown clinical efficacy in lung and colon cancers, but no benefit has been noted in breast cancer. Thirteen EGFR expressing breast cancer cell lines were analyzed for response to EGFR TKIs. Seven were found to be EGFR TKI resistant; while shRNA knockdown of EGFR determined that four of these cell lines retained the requirement of EGFR protein expression for growth. Interestingly, EGFR localized to plasma membrane lipid rafts in all four of these EGFR TKI-resistant cell lines, as determined by biochemical raft isolation and immunofluorescence. When lipid rafts were depleted of cholesterol using lovastatin, all four cell lines were sensitized to EGFR TKIs. In fact, the effects of the cholesterol biosynthesis inhibitors and gefitinib were synergistic. While gefitinib effectively abrogated phosphorylation of Akt- and mitogen-activated protein kinase in an EGFR TKI-sensitive cell line, phosphorylation of Akt persisted in two EGFR TKI-resistant cell lines, however, this phosphorylation was abrogated by lovastatin treatment. Thus, we have shown that lipid raft localization of EGFR correlates with resistance to EGFR TKI-induced growth inhibition and pharmacological depletion of cholesterol from lipid rafts decreases this resistance in breast cancer cell lines. Furthermore, we have presented evidence to suggest that when EGFR localizes to lipid rafts, these rafts provide a platform to facilitate activation of Akt signaling in the absence of EGFR kinase activity.

Abstract 269: Disruption of lipid rafts sensitizes EGFR expressing breast cancer cells to EGFR inhibitors

While therapeutic strategies have improved, ∼500,000 women worldwide die from breast cancer each year. Many proteins have been implicated in breast cancer, including the HER family of receptors. Overexpression of epidermal growth factor receptor (EGFR) and one of its family members, HER2, each occur in ∼30% of breast cancers and correlates with poor clinical prognosis. Herceptin, an inhibitor of HER2, has been approved for treatment of breast cancer patients; however small molecule tyrosine kinase inhibitors (TKIs) targeting EGFR have not shown efficacy in breast cancer. To understand why breast cancers do not respond to EGFR tyrosine kinase inhibition, a panel of twenty breast cancer cell lines was characterized for EGFR expression. Thirteen of the twenty cell lines expressed EGFR; seven of which were resistant to EGFR TKIs. Unlike the response of HER2 positive breast cancers to Herceptin, increased expression of EGFR correlated with resistance to EGFR TKIs. One possible mechanism for resistance to EGFR TKIs is that EGFR expression is not required for growth. However, when EGFR expression was knocked down, cell growth was significantly decreased in four of the seven cell lines suggesting that EGFR expression is important for cell growth in a portion of EGFR TKI resistant breast cancers. A second mechanism for resistance to EGFR may be elevated HER2 and HER3 expression as observed in lung cancer. Conversely, in these cell lines, HER2 and HER3 expression levels did not correlate with response to EGFR TKIs. In addition, an EGFR family kinase inhibitor also was unable to abrogate the growth of these cells suggesting that HER2 expression and kinase activity was not a mediator of cell growth in the presence of EGFR TKIs. EGFR is known to localize within many sub-cellular regions including the nucleus, mitochondria, endosomes, and plasma membrane. Localization of EGFR to membrane microdomains (lipid rafts) is known to modulate EGFR signaling. Therefore, a third potential mechanism for EGFR TKI resistance may be localization of EGFR within lipid rafts. Using biochemical raft isolation and immunofluorescence, EGFR was shown to localize to lipid rafts in all four EGFR-dependent, EGFR TKI resistant breast cancer cell lines. To determine if this localization mediates resistance to EGFR TKIs, cholesterol (a main structural component of lipid rafts) was depleted using cholesterol biosynthesis inhibitors. While such inhibitors had no effect on cell growth alone, combinatorial depletion of lipid rafts and inhibition of EGFR-kinase activity resulted in decreased cell growth. Further, the interaction between cholesterol biosynthesis inhibitors and EGFR inhibitors was synergistic. Thus, we have discovered that EGFR expression and localization to lipid rafts correlate with EGFR TKI resistance in breast cancer, and that depletion of lipid rafts can overcome such resistance in EGFR expression-dependent breast cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 269.

Efficiency and cost saving of 7 day per week exercise testing utilizing all electrocardiography technologists

BACKGROUND

In most centers, exercise testing (ET) is performed by one or two trained technologists during the weekdays (0800 hours-1600 hours), leaving a void during evenings and weekends. This leads to unnecessary increased costs due to delays in management of patients. Electrocardiography technologists (ECGT) are often available for extended hours. This project was undertaken to improve the efficiency of the ET laboratory by using ECGT to perform ET during these extended hours.

METHODS

Clinical utility and cost saving of a 7 day per week ET for management of patients with suspected and/or known coronary artery disease utilizing ECGT was assessed after adequate training. Of 4099 patients undergoing ET between January 1995 and December 1997, 810 tests performed by ECGT were reviewed retrospectively.

RESULTS

Of the 810 patients (age mean 58.4 +/- 0.44 yrs; range 16-88; males: 508, females: 302), 806 (99.5%) underwent the Bruce protocol. The indications were: diagnostic, 61.3%, predischarge acute myocardial infarction (AMI), 17.7%, evaluation of angina, 19.6%, other, 1.4%. Only 8 (0.1%) patients had complications (prolonged chest pain, 6; nonsustained ventricular tachycardia, 2) with no AMIs or deaths. This strategy resulted in a savings of 158 bed days (Can189,600 dollars) on inpatients and 15 bed days (Can18,000 dollars) on those presenting to the emergency department.

CONCLUSIONS

This study demonstrates the feasibility and safety of utilizing ECGT for ET thus extending the hours of service. This resulted in efficient patient management, with a considerable cost-saving to the hospital.

Two-locus modeling of asthma in a Hutterite pedigree via Markov chain Monte Carlo

Bayesian Markov chain Monte Carlo (MCMC) segregation analysis for asthma was performed on the whole 1,544-member Hutterite pedigree. Heterogeneous and epistatic two-locus models and complex one-locus models were investigated, with trait loci postulated to be linked to markers in regions previously found to be possibly linked to asthma or atopy. The epistatic two-locus dominant-dominant model provided the best estimates, among the models investigated, in terms of prediction of population prevalence and relative risk for sibs of the affected.

Mitigating epidemics caused by non-persistently transmitted aphid-borne viruses: the role of the pliant environment

Using Soybean mosaic virus as a model system, the rate, magnitude and timing of epidemics caused by non-persistently transmitted, aphid-borne viruses are examined under various field conditions. Emphasis is placed on the behavioural responses of vectors to environmental cues, although all three biotic components (host plant, vector and virus) are considered. Both single and double manipulations of the cropping system environment are explored using a computer model developed earlier by Ruesink and Irwin (Plant Virus Epidemics: Monitoring, Modelling and Predicting Outbreaks.

Coupling Disease-Progress-Curve and Time-of-Infection Functions for Predicting Yield Loss of Crops

ABSTRACT A general approach was developed to predict the yield loss of crops in relation to infection by systemic diseases. The approach was based on two premises: (i) disease incidence in a population of plants over time can be described by a nonlinear disease progress model, such as the logistic or monomolecular; and (ii) yield of a plant is a function of time of infection (t) that can be represented by the (negative) exponential or similar model (zeta(t)). Yield loss of a population of plants on a proportional scale (L) can be written as the product of the proportion of the plant population newly infected during a very short time interval (X'(t)dt) and zeta(t), integrated over the time duration of the epidemic. L in the model can be expressed in relation to directly interpretable parameters: maximum per-plant yield loss (alpha, typically occurring at t = 0); the decline in per-plant loss as time of infection is delayed (gamma; units of time(-1)); and the parameters that characterize disease progress over time, namely, initial disease incidence (X(0)), rate of disease increase (r; units of time(-1)), and maximum (or asymptotic) value of disease incidence (K). Based on the model formulation, L ranges from alphaX(0) to alphaK and increases with increasing X(0), r, K, alpha, and gamma(-1). The exact effects of these parameters on L were determined with numerical solutions of the model. The model was expanded to predict L when there was spatial heterogeneity in disease incidence among sites within a field and when maximum per-plant yield loss occurred at a time other than the beginning of the epidemic (t > 0). However, the latter two situations had a major impact on L only at high values of r. The modeling approach was demonstrated by analyzing data on soybean yield loss in relation to infection by Soybean mosaic virus, a member of the genus Potyvirus. Based on model solutions, strategies to reduce or minimize yield losses from a given disease can be evaluated.

Higher-level phylogeny of the Therevidae (Diptera: insecta) based on 28S ribosomal and elongation factor-1 alpha gene sequences

Therevidae (stilleto flies) are a little-known family of asiloid brachyceran Diptera (Insecta). Separate and combined phylogenetic analyses of 1200 bases of the 28S ribosomal DNA and 1100 bases of elongation factor-1alpha were used to infer phylogenetic relationships within the family. The position of the enigmatic taxon Apsilocephala Kröber is evaluated in light of the molecular evidence. In all analyses, molecular data strongly support the monophyly of Therevidae, excluding Apsilocephala, and the division of Therevidae into two main clades corresponding to a previous classification of the family into the subfamilies Phycinae and Therevinae. Despite strong support for some relationships within these groups, relationships at the base of the two main clades are weakly supported. Short branch lengths for Australasian clades at the base of the Therevinae may represent a rapid radiation of therevids in Australia.

Guidelines for pacemaker follow-up in Canada: a consensus statement of the Canadian Working Group on Cardiac Pacing

A survey on Canadian pacing practices conducted in 1997 revealed a widespread desire for national guidelines on pacemaker follow-up. The present guidelines for pacemaker follow-up are a consensus statement of the Canadian Working Group on Cardiac Pacing. Direct patient follow-up rather than transtelephonic monitoring is desirable. Patients should be assessed at a minimum of within 72 h of implantation, at two to 12 weeks and at six months following implantation, and annually thereafter. More frequent assessments may be required for some patients. This depends on associated cardiovascular problems and specific devices. A typical follow-up visit should include a targeted cardiovascular assessment, interrogation of the pacing system, review of telemetered data, assessment of the underlying rhythm, assessment of pacing and sensing thresholds, and appropriate reprogramming of pacing parameters to optimize device function and longevity.

A multiple locus analysis of the collaborative study on the genetics of alcoholism data set

Parametric and nonparametric statistical methods have been applied to the alcohol dependence data set collected in the Collaborative Study on the Genetics of Alcoholism (COGA). Our nonparametric linkage analyses (NPL) were based on the S(all) statistic of GENEHUNTER [Kruglyak et al., 1996] and the improved NPL statistic of GENEHUNTER-PLUS [Kong and Cox, 1997]. Based on likely regions for alcohol susceptibility genes identified from our nonparametric analyses, we reanalyzed the data using several two-locus models. We used the TMLINK program [Lathrop and Ott, 1990] in the LINKAGE package for these parametric analyses.

Feasibility of direct discharge from the coronary/intermediate care unit after acute myocardial infarction

OBJECTIVES

This investigation was designed to determine the feasibility and cost-effectiveness of direct discharge from the coronary/intermediate care unit (CICU) in 497 consecutive patients with an acute myocardial infarction (AMI).

BACKGROUND

Although patients with an AMI are traditionally treated in the CICU followed by a period on the medical ward, the latter phase can likely be incorporated within the CICU.

METHODS

All patients were considered for direct discharge from the CICU with appropriate patient education. The 6-week postdischarge course was evaluated using a structured questionnaire by a telephone interview.

RESULTS

There were 497 patients (men = 353; women = 144; age 63.5 +/- 0.6 years) in the study, with 29 in-hospital deaths and a further 11 deaths occurring within 6 weeks of discharge. The mode length of CICU stay was 4.0 days (mean 5.1 +/- 0.2 days): 1 to 2 (12%), 3 (19%), 4 (21%), 5 (14%), 6 to 7 (19%) and > or = 7 (15%) days, respectively with 87.2% discharged home directly. Of the 425 patients surveyed, 119 (28.0%) indicated that they had made unscheduled return visits (URV) to a hospital or physician's office: 10.6% to an emergency room, 9.4% to a physician's office and 8.0% readmitted to a hospital. Of these URV, only 14.3% occurred within 48 h of discharge. Compared to historical controls, the present management strategy resulted in a cost savings of Cdn. $4,044.01 per patient.

CONCLUSIONS

Direct discharge from CICU is a feasible and safe strategy for the majority of patients that results in considerable savings.

Cardiac pacing in Canada in 1998: working towards optimal pacing therapy. Canadian Working Group on Cardiac Pacing

The Canadian Working Group on Cardiac Pacing (CWGCP) was formed in 1996 with the primary goal of promoting optimal pacing therapy in Canada. In 1997, the CWGCP conducted a survey of pacing practices across Canada. Ninety-two of 125 implanting programs (74%) responded. Implant rates vary by province--from 39 per 100,00 population in Ontario to 63 per 100,000 population in Nova Scotia and Prince Edward Island. Variations in regional implant rates persist even after correcting for the age of the population. Physiological pacing was used for 35% of all implants in Canada in 1996/97. There were marked differences across Canada in the mode of pacing selected. In western Canada, 39.5% of pacing systems implanted were physiological compared with 18.2% in Atlantic Canada and 29% in Quebec. There were also differences in follow-up practices. Approximately 40% of centres follow patients with single chamber pacemakers annually, whereas most other centres still follow these patients every six months. Economic constraints, the size of pacing programs and the involvement of committed pacing physicians are factors that may influence the regional differences in cardiac pacing across Canada.

NASPE expert consensus document: use of i.v. (conscious) sedation/analgesia by nonanesthesia personnel in patients undergoing arrhythmia specific diagnostic, therapeutic, and surgical procedures

Use of IV (Conscious) Sedation/Analgesia by Nonanesthesia Personnel in Patients Undergoing Arrhythmia Specific Diagnostic, Therapeutic, and Surgical Procedures. This article is intended to inform practitioners, payers, and other interested parties of the opinion of the North American Society of Pacing and Electrophysiology (NASPE) concerning evolving areas of clinical practice or technologies or both, that are widely available or are new to the practice community. Expert consensus documents are so designated because the evidence base and experience with the technology or clinical practice are not yet sufficiently well developed, or rigorously controlled trials are not yet available that would support a more definitive statement. This article has been endorsed by the American College of Cardiology, October 1997.

An evaluation of a dentifrice containing salivary peroxidase elements for the control of gingival disease in patients with irradiated head and neck cancer

Patients who have undergone irradiation for head and neck tumors commonly have xerostomia. Loss of the protective constituents normally found in saliva leaves patients at greater risk for development of significant dental pathologic disorders, including gingival and periodontal disease. Periodontal disease and tooth extractions are currently accepted as etiologic factors for the development of osteoradionecrosis. This double-blind crossover trial was conducted to assess the efficacy of a dentifrice containing salivary peroxidase elements in the reduction of gingivitis in a population of patients with irradiated cancer. Subjects were instructed to brush with the dentifrice provided. Plaque and gingival index values were obtained and statistically compared with baseline values. A weak positive effect was found between use of the dentifrice and a reduction in gingival inflammation. Patient compliance was a limiting factor in this treatment effect. The results suggest possible efficacy for the dentifrice in augmenting traditional measures of postradiation oral health maintenance.

Randomized controlled trial of selective bowel decontamination for prevention of infections following liver transplantation

Nonabsorbable antibiotics for selective bowel decontamination (SBD) sometimes are administered to liver transplant patients to prevent postoperative infections, but the efficacy of SBD is not known. Accordingly, we prospectively studied 69 patients randomly assigned to receive conventional prophylaxis with systemic antibiotics (control patients) or conventional prophylaxis plus oral nonabsorbable antibiotics for SBD (SBD patients). Overall rates of bacterial and/or yeast infections were nearly equal among control patients (42%) and SBD patients (39%). However, the infection rate at SBD key sites (abdomen, bloodstream, surgical wound, and lungs) was lower among patients who received the SBD regimen > or = 3 days before transplantation (23%) than among control patients (36%). Administration of the SBD regimen was complicated by gastrointestinal intolerance and noncompliance but not by increased stool colonization with antibiotic-resistant gram-negative bacilli. Practical problems associated with administering an SBD regimen to patients awaiting cadaver liver transplants limit the regimen's usefulness, but we found a trend toward reduced key site infection when the regimen was given > or = 3 days before transplantation.

Report of the NASPE Policy Conference on antibradycardia pacemaker follow-up: effectiveness, needs, and resources. North American Society of Pacing and Electrophysiology

On May 4-5, 1993, a policy conference was held in San Diego, California, under the sponsorship of the North American Society of Pacing and Electrophysiology (NASPE) to identify the fundamental goals of antibradycardia pacemaker follow-up, evaluate the effectiveness with which it achieves those goals, and formulate specific recommendations as to how it can be made more effective. The conference addressed clinical, administrative, and educational objectives, focusing on existing and potential resources for follow-up testing and the appropriate frequency of their application. The training of physicians and associated professionals engaged in follow-up also was addressed, as were regulatory and reimbursement issues. This report summarizes the conclusions and recommendations arrived at during the conference and subsequently approved by the NASPE Board of Trustees.

Outcomes of an ambulatory cardiac pacing program: indications, risks, benefits, and outcomes

The purpose of this review was to evaluate the economical benefits and outcomes of an ambulatory pacing system implantation program that began in 1991 for new and replacement pacing system implantations. Patient access, incidence of complications, hospital bed day utilization, economic impact, safety, and practicality of the Ambulatory Pacing System Implantation Program was retrospectively reviewed from August 1991 to March 1994. The Ambulatory Pacing System Implantation Program includes pre-operative outpatient assessment in the pacemaker clinic, admission to the Day Medical Unit followed by same day pacing system implantation, discharge home after a short period of observation, and, in selected cases, cardiac monitoring, followed by pacemaker clinic visit 24-hours postimplantation.

RESULTS

Two hundred four cardiac pacing systems, 154 new and 50 replacements (pulse generator/leads), were implanted under the guidelines of the Ambulatory Pacing System Implantation Program between August 1991 and March 1994. Eighty-seven percent of the patients were implanted with passive fixation leads, the remaining with active fixation leads; all but four of which were leads implanted in the atria. Preprocedure wait time was decreased from 16 to 2 days for elective pacing system implantation. The incidence of lead dislodgment in the first, second, and third year of the Ambulatory Pacing System Implantation Program was 20%, 12%, 5%, respectively; compared to 11% for a similar number of cases in previous years done as inpatients. The incidence of new infection was 2.4% compared to < 1% in previous years. Six of the 204 (2%) cases required admission overnight. A total savings of 1,456 bed days ($1,275,450.00; Canadian) has been realized for an equivalent number of cases when compared with previous years. The operational cost was reduced by $3,976.00 per case.

CONCLUSION

It has been shown that the Ambulatory Pacing System Implantation Program has improved client access, and is a safe and economical approach to implantation of cardiac pacing systems.

Genetic studies on an Alzheimer clinic population

All patients attending the Clinic for Alzheimer Disease and Related Disorders have detailed family histories taken by a geneticist. To date, genetic histories are available for 446 consecutive, unrelated individuals. Of these, 151 (33.9%) are diagnosed as having "probable" (N = 141) or "autopsy-confirmed" (N = 10) Alzheimer disease according to recognized criteria. This data base represents a relatively unselected population with respect to more than one person in the family having dementia. Seventy-one of these 151 index cases (47.0%) have a positive family history of dementia, of which 8 (5.3%) may represent the familial (autosomal dominant) form of Alzheimer disease (FAD). Age-corrected empiric recurrence risks for Alzheimer disease/dementia were calculated for first-degree relatives of these 151 index cases using the Kaplan-Meier lifetable method.