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P J Burke

Publications and source records attributed to P J Burke.

At least 19 recordsLinked to original sources
PubMed2006

Repeated cycles of Clostridium-directed enzyme prodrug therapy result in sustained antitumour effects in vivo.

The unique properties of the tumour microenvironment can be exploited by using recombinant anaerobic clostridial spores as highly selective gene delivery vectors. Although several recombinant Clostridium species have been generated during the past decade, their efficacy has been limited. Our goal was to substantially improve the prospects of clostridia as a gene delivery vector. Therefore, we have assessed a series of nitroreductase (NTR) enzymes for their capacity to convert the innocuous CB1954 prodrug to its toxic derivative. Among the enzymes tested, one showed superior prodrug turnover characteristics. In addition, we established an efficient gene transfer procedure, based on conjugation, which allows for the first time genetic engineering of Clostridium strains with superior tumour colonisation properties with high success rates. This conjugation procedure was subsequently used to create a recombinant C. sporogenes overexpressing the isolated NTR enzyme. Finally, analogous to a clinical setting situation, we have tested the effect of multiple consecutive treatment cycles, with antibiotic bacterial clearance between cycles. Importantly, this regimen demonstrated that intravenously administered spores of NTR-recombinant C. sporogenes produced significant antitumour efficacy when combined with prodrug administration.

Animals↗
PubMed2005

Microwave transport in metallic single-walled carbon nanotubes.

The dynamical conductance of electrically contacted single-walled carbon nanotubes is measured from dc to 10 GHz as a function of source-drain voltage in both the low-field and high-field limits. The ac conductance of the nanotube itself is found to be equal to the dc conductance over the frequency range studied for tubes in both the ballistic and diffusive limit. This clearly demonstrates that nanotubes can carry high-frequency currents at least as well as dc currents over a wide range of operating conditions. Although a detailed theoretical explanation is still lacking, we present a phenomenological model of the ac impedance of a carbon nanotube in the presence of scattering that is consistent with these results.

Computer Simulation↗
PubMed2004

In vitro cytotoxic activity of Thai medicinal plants used traditionally to treat cancer.

The SRB assay was used to test cytotoxicity against three human cancer cell lines and one normal cell line of 11 Thai medicinal plant species used by traditional doctors in treating cancer patients. The extraction procedures used were similar to those practised by Thai traditional doctors (ethanolic and water extracts). Extracts were tested against the human large cell lung carcinoma cell line COR-L23, the human breast adenocarcinoma cell line MCF-7 and human colon adenocarcinoma cell line LS-174T and normal human keratinocytes SVK-14. The results showed that three plants; Dioscorea membranacea Pierre ex Prain & Burkill, Dioscorea birmanica Prain & Burkill (Dioscoreaceae) and Siphonodon celastrineus Griff. (Celastraceae), exhibited high cytotoxic activity showing a certain degree of selectivity against the different cell types.

Cell Line, Tumor↗
PubMed2002

Long-term follow-up of intensive ara-C-based chemotherapy followed by bone marrow transplantation for adult acute lymphoblastic leukemia: impact of induction Ara-C dose and post-remission therapy.

We report single institution outcome of brief, intensive ara-C-based chemotherapy using bone marrow transplantation as primary intensification for untreated adult patients with acute lymphoblastic leukemia (ALL). Overall disease-free and overall survival were inferior to those reported with prolonged chemotherapy modeled on pediatric protocols. Survival and disease-free survival were superior for patients receiving allogeneic BMT compared with chemopurged autologous transplant or maintenance chemotherapy (patients ineligible for or declining BMT). In multivariate analysis, non-L2-FAB, higher ara-C dose, absence of CNS disease, non-Ph1+ karyotype, allogeneic BMT, T cell phenotype, and younger age were associated with improved disease-free survival. Autologous BMT was not superior to chemotherapy, and appears unlikely to provide adequate curative treatment for most adult ALL patients if not followed by maintenance.

Adult↗
PubMed2001

Formaldehyde in human cancer cells: detection by preconcentration-chemical ionization mass spectrometry.

A rapid and highly sensitive method for the detection of formaldehyde utilizing selected ion flow tube-chemical ionization mass spectrometry is reported. Formaldehyde in aqueous biological samples is preconcentrated by distillation and directly analyzed using gas-phase thermal energy proton transfer from H30+; this procedure can be performed in 30 min. The method detection limit for formaldehyde based on seven replicate measurements of reference water samples (2.5 mL) is 80 nM at the 99% confidence level. Detection is linear up to 130 microM. This technique allows the first measurement of natural formaldehyde levels in human cancer cells in vitro. Elevated levels of formaldehyde relative to the reference water are observed for doxorubicin-sensitive cells (MCF-7 breast cancer, K562 leukemia, HeLa S3 cervical cancer) with estimated intracellular formaldehyde concentrations ranging from 1.5 to 4.0 microM, whereas formaldehyde in doxorubicin-resistant MCF-7/Adr breast cancer cells is essentially at reference level. This trend is inverted for prostate cancer cells LNCaP (sensitive) and DU-145 (resistant). Correlation of natural formaldehyde level with doxorubicin cytotoxicity is a function of the expression of enzymes that neutralize oxidative stress and the drug efflux pump, P-170 glycoprotein.

Formaldehyde↗
PubMed2001

Acute abdomen in infants of adolescent mothers: diagnostic challenges.

Caring for children of adolescent parents presents unique challenges. Because adolescent parents may lack parenting skills and knowledge of medical terminology, symptoms of life-threatening illnesses may be misinterpreted. We present two cases of unexpected acute abdomen in young infants with adolescent mothers. The first case involves midgut volvulus, which was discovered during a routine newborn visit. The second case, involving pyloric stenosis, presented a clinical management challenge when the adolescent mother refused diagnostic studies.

Abdomen, Acute↗
PubMed2000

Evaluation of Apaf-1 and procaspases-2, -3, -7, -8, and -9 as potential prognostic markers in acute leukemia.

Recent studies have suggested that variations in levels of caspases, a family of intracellular cysteine proteases, can profoundly affect the ability of cells to undergo apoptosis. In this study, immunoblotting was used to examine levels of apoptotic protease activating factor-1 (Apaf-1) and procaspases-2, -3, -7, -8, and -9 in bone marrow samples (at least 80% leukemia) harvested before chemotherapy from adults with newly diagnosed acute myelogenous leukemia (AML, 42 patients) and acute lymphocytic leukemia (ALL, 18 patients). Levels of each of these polypeptides varied over a more than 10-fold range between specimens. In AML samples, expression of procaspase-2 correlated with levels of Apaf-1 (R(s) = 0.52, P <.02), procaspase-3 (R(s) = 0.56, P <.006) and procaspase-8 (R(s) = 0.64, P <.002). In ALL samples, expression of procaspases-7 and -9 was highly correlated (R(s) = 0.90, P <.003). Levels of these polypeptides did not correlate with prognostic factors or response to induction chemotherapy. In further studies, 16 paired samples (13 AML, 3 ALL), the first harvested before induction therapy and the second harvested at the time of leukemia regrowth, were also examined. There were no systematic alterations in levels of Apaf-1 or procaspases at relapse compared with diagnosis. These results indicate that levels of initiator caspases vary widely among different leukemia specimens but cast doubt on the hypothesis that this variation is a major determinant of drug sensitivity for acute leukemia in the clinical setting. (Blood. 2000;96:3922-3931)

Acute Disease↗
PubMed2000

Bioactivation of 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB 1954) by human NAD(P)H quinone oxidoreductase 2: a novel co-substrate-mediated antitumor prodrug therapy.

A novel prodrug activation system, endogenous in human tumor cells, is described. A latent enzyme-prodrug system is switched on by a simple synthetic, small molecule co-substrate. This ternary system is inactive if any one of the components is absent. CB 1954 [5-(aziridin-1-yl)-2,4-dinitrobenzamide] is an antitumor prodrug that is activated in certain rat tumors via its 4-hydroxylamine derivative to a potent bifunctional alkylating agent. However, human tumor cells are resistant to CB 1954 because they are unable to catalyze this bioactivation efficiently. A human enzyme has been discovered that can activate CB 1954, and it has been shown to be commonly present in human tumor cells. The enzyme is NQO2 [NAD(P)H quinone oxidoreductase 2], but its activity is normally latent, and a nonbiogenic co-substrate such as NRH [nicotinamide riboside (reduced)] is required for enzymatic activity. There is a very large (100-3000-fold) increase in CB 1954 cytotoxicity toward either NQO2-transfected rodent or nontransfected human tumor cell lines in the presence of NRH. Other reduced pyridinium compounds can also act as co-substrates for NQO2. Thus, the simplest quaternary salt of nicotinamide, 1-methyl-3-carboxamidopyridinium iodide, was a co-substrate for NQO2 when reduced to the corresponding 1,4-dihydropyridine derivative. Increased chain length and/or alkyl load at the 1-position of the dihydropyridine ring improved specific activity, and compounds more active than NRH were found. However, little activity was seen with either the 1-benzyl or 1-(2-phenylethyl) derivatives. A negatively charged substituent at the 3-position of the reduced pyridine ring also negated the ability of these compounds to act as cosubstrates for NQO2. In particular, 1-carbamoylmethyl-3-carbamoyl-1,4dihydropyridine was shown to be a co-substrate for NQO2 with greater stability than NRH, with the ability to enter cells and potentiate the cytotoxicity of CB 1954. Furthermore, this agent is synthetically accessible and suitable for further pharmaceutical development. NQO2 activity appears to be related to expression of NQO1 (DT-diaphorase), an enzyme that is known to have a favorable distribution toward certain human cancers. NQO2 is a novel target for prodrug therapy and has a unique activation mechanism that relies on a synthetic co-substrate to activate an apparently latent enzyme. Our findings may reopen the use of CB 1954 for the direct therapy of human malignant disease.

Animals↗
PubMed2000

Mass spectrometric measurement of formaldehyde generated in breast cancer cells upon treatment with anthracycline antitumor drugs.

Selected ion flow tube-chemical ionization mass spectrometry was used to measure formaldehyde levels in human breast cancer cells in comparison with levels in cells treated with the antitumor drugs doxorubicin (DOX) and daunorubicin (DAU) and the daunorubicin-formaldehyde conjugate Daunoform (DAUF). The measurement was performed on cell lysates and showed only background levels of formaldehyde in untreated cells and drug-treated resistant cells (MCF-7/Adr cells) but levels above background in DOX- and DAU-treated sensitive cells (MCF-7 cells). The level of formaldehyde above background was a function of drug concentration (0.5-50 microM), treatment time (3-24 h), cell density (0.3 x 10(6) to 7 x 10(6) cells/mL), and cell viability (0-100%). Higher levels of formaldehyde were observed in lysates of MCF-7 cells treated at higher drug levels, unless the treatment resulted in low cell viability. Elevated levels were directly related to cell density and were observed even with 0.5 microM drug. A lower limit for excess formaldehyde in MCF-7 cells treated with 0.5 microM DAU for 24 h is 0.3 mM. Control experiments showed that formaldehyde was not produced after cell lysis. Lysates of sensitive and resistant cells treated with 0.5 micromolar equiv of the formaldehyde conjugate (DAUF) for 3 h showed only background levels of formaldehyde. The results support a mechanism for drug cytotoxicity which involves drug induction of metabolic processes leading to formaldehyde production followed by drug utilization of formaldehyde to virtually cross-link DNA.

Animals↗
PubMed2000

Reliability and validity of a DSM-IV based ADHD screener.

The Diagnostic Rating Scale (DRS) was completed by the parents and teachers of 82 children referred for clinical evaluations, 73 referred children seen twice, and 218 non-referred children from the community. The DRS, which uses a categorical rather than a dimensional rating approach, was 70% to 90% sensitive to diagnoses of Attention Deficit/Hyperactivity Disorder (ADHD) made by blind clinical teams. In research and clinical applications, the DRS could improve screening efficiency, especially in situations where it would be desirable to exclude all children who might have ADHD or identify all children with Hyperactive-Impulsive symptoms. Because of its objectivity and consistency with the Diagnostic and Statistical Manual (DSM)-IV criteria, the DRS could facilitate comparison of participant samples across studies.

Attention Deficit Disorder with Hyperactivity↗
PubMed1999

Novel inhibitors of carboxypeptidase G2 (CPG2): potential use in antibody-directed enzyme prodrug therapy.

The design and synthesis of potent thiocarbamate inhibitors for carboxypeptidase G2 are described. The best thiocarbamate inhibitor N-(p-methoxybenzenethiocarbonyl)amino-L-glutamic acid 6d, chosen for preliminary investigations of in vitro antibody-directed enzyme prodrug therapy (ADEPT), abrogated the cytotoxicity of a combination of A5B7-carboxypeptidase G2 conjugate and prodrug PGP (N-p-{N,N-bis (2-chloroethyl)amino}phenoxycarbonyl-L-glutamate) toward LS174T cells. This is the first report of a small-molecule enzyme inhibitor proposed for use in conjunction with the ADEPT approach.

Aniline Mustard↗
PubMed1999

Developments with targeted enzymes in cancer therapy.

Cancer therapy based on the delivery of enzymes to tumour sites has advanced in several directions since antibody-directed enzyme/prodrug therapy was first described. It has been shown that methoxypolyethylene glycol (MPEG) can be used to deliver enzyme to a variety of solid tumours. MPEG-enzyme conjugates show reduced immunogenicity and may allow repeated treatment with enzymes of bacterial origin. Enzyme delivery to tumours by polymers can be used to convert a low toxicity prodrug to a potent cytotoxic agent. An example of such a prodrug is CB1954, which can be activated by a human enzyme in the presence of a cosubstrate. Tumour-located enzymes can also be used in conjunction with a combination of antimetabolites and rescue agents. The rescue agent protects normal tissue but is degraded at cancer sites by the enzyme, thus deprotecting the tumour and allowing prolonged antimetabolite action.

Antineoplastic Agents↗
PubMed1999

Cytotoxic activity of indole alkaloids from Alstonia macrophylla.

Thirteen indole alkaloids isolated from the root bark of Alstonia macrophylla and a semisynthetic bisindole O-acetylmacralstonine have been assessed for cytotoxic activity against two human lung cancer cell lines, MOR-P (adenocarcinoma) and COR-L23 (large cell carcinoma), using the SRB assay. Pronounced cytotoxic activity was exhibited by the bisindoles on both cell lines. This suggests that, in comparison with the corresponding monomeric indoles, at least part of both the ring systems present in the bisindoles is essential for cytotoxic activity. The potent alkaloids were further tested against a human normal cell line (breast fibroblasts) and other human cancer cell lines including StMI1 1a (melanoma), Caki-2 (renal cell carcinoma), MCF7 (breast adenocarcinoma), and LS174T (colon adenocarcinoma). The bisindoles O-acetylmacralstonine, villalstonine and macrocarpamine were found to possess pronounced activity against cancer cell lines with IC50 values in the range of 2-10 microM, with no discernible cell-type selectivity. However, O-acetylmacralstonine displayed discernibly less toxicity against the normal breast fibroblasts.

Alkaloids↗
PubMed1999

Targeting enzymes to cancers--new developments.

Two methods of using tumour located enzymes have been described. These are antibody directed enzyme prodrug therapy (ADEPT) and macromolecule directed enzyme prodrug therapy (MDEPT), where the tumour located enzyme converts a non-toxic prodrug into a cytotoxic drug at tumour sites. The alternative use of tumour located enzymes is to inactivate rescue agents that protect cells from antimetabolite action, and is described as 'Antimetabolite with inactivation of rescue agent at cancer sites' (AMIRACS). The leakiness of tumour blood vessels and poor lymphatic drainage allows enzymes to be targeted to many cancers by attachment to polymeric macromolecules (MDEPT), as well as to antibodies and antibody fragments (ADEPT). To avoid systemic toxicity, enzyme activity in blood and normal tissues must be very low before giving a prodrug or rescue agent. Antibodies directed against the enzyme component of macromolecular conjugates have proved to be very efficient at clearing normal tissues. Human enzymes which are over expressed by cancer cells can be exploited particularly if they require co-factors or co-substrates, either in situ or targeted to extracellular sites. Bacterial enzymes have advantages in specificity but require some form of immunological control in view of their immunogenicity. Prodrugs which generate drugs with very short half lives are desirable, and have been developed, including one which has a differential toxicity between prodrug and the active drug of 1000 to 10,000 fold. The range of antimetabolites available for AMIRACS was initially restricted to inhibitors of dihydrofolate reductase but has been greatly extended by the introduction of inhibitors of other enzymes. The limitations of these systems are discussed.

Journal Article↗
PubMed1998

Elevated expression of the apoptotic regulator Mcl-1 at the time of leukemic relapse.

Bcl-2, Bcl-xL, and Mcl-1 are three related intracellular polypeptides that have been implicated as negative regulators of apoptosis. In contrast, the partner protein Bax acts as a positive regulator of apoptosis. Based on the observation that all four of these polypeptides are expressed in a variety of acute myelogenous leukemia (AML) and acute lymphocytic leukemia (ALL) cell lines, cellular levels of these polypeptides were examined by immunoblotting in bone marrow samples harvested from 123 adult AML patients and 36 adult ALL patients before initial antileukemic therapy. Levels of Bcl-2, Mcl-1, Bcl-xL, and Bax each varied over a more than 10-fold range in different pretreatment leukemia specimens. When the 54 AML and 23 ALL samples that contained greater than 80% malignant cells were examined in greater detail, it was observed that pretreatment levels of Bcl-2 and Mcl-1 correlated with each other (R = .44, P < .001 for AML and R = .79, P < .0001 for ALL). In addition, a weak negative correlation between Bax expression and age was observed in AML samples (R = -0.35, P < .02) but not ALL samples. There was no relationship between pretreatment levels of these polypeptides and response to initial therapy. However, examination of 19 paired samples (the first harvested before chemotherapy and the second harvested 23 to 290 days later at the time of leukemic recurrence) revealed a greater than or equal to twofold increase in Mcl-1 levels in 10 of 19 pairs (7 of 15 AML and 3 of 4 ALL) at recurrence. In contrast, 2 of 19 pairs contained twofold less Mcl-1 at the time of recurrence. Approximately equal numbers of samples showed twofold increases and decreases in Bcl-2 (5 increases, 3 decreases) and Bcl-xL (1 increase, 4 decreases) at recurrence. Bax levels did not show a twofold decrease in any patient. these results, coupled with recent observations that cells overexpressing Mcl-1 are resistant to a variety of chemotherapeutic agents, raise the possibility that some chemotherapeutic regimens might select for leukemia cells with elevated levels of this particular apoptosis inhibitor.

Adult↗
PubMed1998

Inhibited apoptosis and drug resistance in acute myeloid leukaemia.

Despite extensive investigation into mechanisms of drug resistance in acute myeloid leukaemia (AML), the aetiology of therapeutic resistance is unclear. We found that five leukaemia cell lines (K562, HL-60, CEM. CEM induced to overexpress bcl-2, and REH) displayed parallel sensitivity to four antileukaemia drugs with different mechanisms of action, with K562 generally being the least sensitive and REH being the most sensitive. The amount of spontaneous apoptosis in the cell lines after serum-free culture paralleled their drug sensitivity: K562 cells displayed the least apoptosis at 24h (2.50 +/- 0.24%) and REH the most (24.47 +/- 8.22%). The extent of spontaneous apoptosis of leukaemic blasts from 39 patients with newly diagnosed de novo AML also correlated with the success of the intensive, infusional cytarabine-based induction therapy. There was a median of 19.5% (range 3.6-64%) apoptotic AML cells after 24 h of serum-free culture in patients who entered a complete remission compared with 4.2% (1.8-7.0%) apoptotic AML cells in patients who did not achieve a complete remission (P = 0.0007). Thus, inhibited apoptosis was associated with both in vitro and in vivo pan-resistance to antileukaemic chemotherapy. The cause of inhibited apoptosis in AML is probably a function of interactions among multiple signals that influence apoptosis. Assessment of spontaneous apoptosis may serve as an important prognostic factor for AML.

Acute Disease↗
PubMed1998

Topoisomerase II and the response to antileukemic therapy.

A number of recent studies have investigated the expression of topoisomerase II in clinical leukemia specimens. Here we outline the rationale for these studies, identify potential pitfalls, summarize recent results, and discuss unanswered questions in this area.

Acute Disease↗