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D R Howard

Publications and source records attributed to D R Howard.

At least 19 recordsLinked to original sources
PubMed1999

The effect of the aqueous solubility of xanthine derivatives on the release mechanism from ethylcellulose matrix tablets.

Release data from ethylcellulose (EC) matrix tablets was analyzed to determine which release equation provides the best fit to the data and to observe the effect of drug solubility on the release mechanism(s). Tablets were prepared by direct compression of drug, EC, and lubricant in an appropriate mass ratio to achieve a high and a low drug loading. Theophylline, caffeine, and dyphylline were selected as non-electrolyte xanthine derivatives with solubilities from 8.3 to 330 mg/ml at 25 degrees C. Drug release studies were conducted in 37 degrees C water with UV detection at 272 nm. Several equations to characterize release mechanisms were tested with respect to the release data. Drug diffusion, polymer relaxation, and tablet erosion were the mechanisms considered. Parameters were generated and ANOVA data presented by WinNonlin Pro(R) software. The Akaike Information Criterion was also considered to ascertain the best fit equation. At high drug loading, drug was released by a diffusion mechanism with a rate constant that increased with an increase in aqueous solubility. At low drug loading, polymer relaxation also became a component of the release mechanism. However, its contribution to drug release was less pronounced as solubility decreases, becoming negligible in the case of theophylline.

Algorithms↗
PubMed1999

Open-label comparison of the antiemetic efficacy of single intravenous doses of dolasetron mesylate in pediatric cancer patients receiving moderately to highly emetogenic chemotherapy.

BACKGROUND: Nausea and vomiting are among the most unpleasant adverse side effects of cancer therapy. PROCEDURE: An open-label dose-escalation study was conducted to assess the appropriate intravenous dose of dolasetron for pediatric patients undergoing chemotherapy. Patients received dolasetron in single intravenous doses of 0.6 (n = 10), 1.2 (n = 12), 1.8 (n = 12), or 2.4 (n = 12) mg/kg 30 min before receiving emetogenic chemotherapy. Pharmacokinetic parameters were evaluated at each dose level and efficacy was evaluated over the first 24 hr following the administration of dolasetron. RESULTS: A complete response was achieved in 10% of patients given 0.6 mg/kg, 25% of patients given 1. 2 mg/kg, 67% of patients given 1.8 mg/kg, and 33% of patients given 2.4 mg/kg. Peak plasma concentrations (Cmax) were observed between 0. 33 and 0.75 hr following dolasetron infusion. Cmax and area under plasma concentration-time (AUC) increased with larger doses of dolasetron, while terminal disposition half-life (t1/2) and apparent clearance (Clapp) were not significantly changed with respect to dose. For 1.8-mg/kg dolasetron, the t1/2 was 4.98 hr and the maximum plasma concentration (tmax) 0.47 hr. Adverse events were mild to moderate. No serious events occurred. Conclusions. This study suggests that a single intravenous dose of 1.8 mg/kg is the optimum single intravenous dose for controlling chemotherapy-induced emesis in pediatric patients.

Adolescent↗
PubMed1999

Frequent loss of heterozygosity for chromosome 10 in uterine leiomyosarcoma in contrast to leiomyoma.

Distinction of malignant uterine leiomyosarcomas from benign leiomyomas by morphological criteria is not always possible. Leiomyosarcomas typically have complex cytogenetic abnormalities; in contrast, leiomyomas have simple or no cytogenetic abnormalities. To understand better the biological distinction(s) between these tumors, we analyzed two other potential markers of genomic instability, loss of heterozygosity (LOH) and microsatellite instability. We examined archival materials from 16 leiomyosarcomas and 13 benign leiomyomas by polymerase chain reaction for 26 microsatellite polymorphisms. Markers were selected based on previous reports of cytogenetic or molecular genetic abnormalities in leiomyosarcomas or leiomyomas and surveyed chromosomes 7, 9, 10, 11, 12, 14, 15, 16, 18, 21, and X. LOH for markers on chromosomes 15, 18, 21, and X was infrequent in leiomyosarcomas (1 of 6 tumors for each chromosome) and not observed for markers on chromosomes 7, 9, 11, 12, 14, or 16. Interestingly, 8 of 14 (57.2%) informative leiomyosarcomas had LOH for at least one marker on chromosome 10 and involved both chromosomal arms in 45.5% (5 of 11). In contrast to leiomyosarcomas, LOH for chromosome 10 was not found in 13 benign leiomyomas. Microsatellite instability was found infrequently in leiomyosarcomas and not detected in leiomyoma. Clinicopathological features (eg, atypia, necrosis, and clinical outcome) did not appear to correlate with LOH for chromosome 10. In contrast to other chromosomes studied, LOH on chromosome 10 was frequent in leiomyosarcomas and absent in benign leiomyomas.

Adult↗
PubMed1997

Time course of 5-HT2A receptor occupancy in the human brain after a single oral dose of the putative antipsychotic drug MDL 100,907 measured by positron emission tomography.

MDL 100,907 is a potent and selective antagonist of 5-HT2A serotonin receptors. Animals studies suggest that MDL 100,907 may behave as an atypical antipsychotic drug. Positron emission tomograph (PET) using [11C]NMSP as the radiotracer was used to define the time course of 5-HT2 receptor occupancy in the human frontal cerebral cortex after a single oral dose of MDL 100,907 (10 or 20 mg) in nine healthy subjects. After the baseline scan each subject was studied three times post dosing at various time points. 5-HT2 occupancies were in the range of 70 and 90% after each dose. While the occupancy remains in this range over 24 hours after 20 mg MDL 100,907, it decreases by about 20% at 24 hours compared to the timepoint at 8 hours, when only 10 mg are administered (p < 0.05). Our results should allow determination of the appropriate dosing regimen for future trials in schizophrenic patients.

Adult↗
PubMed1996

Pharmacokinetics of the active metabolite (MDL 74,156) of dolasetron mesylate after oral or intravenous administration to anesthetized children.

BACKGROUND: Dolasetron mesylate is a selective 5-HT3 receptor antagonist under investigation as an antiemetic in children. Published studies indicate that its antiemetic activity results from the active metabolite (MDL 74,156), which is produced within 10 minutes of administration of dolasetron mesylate. METHODS: The pharmacokinetics of MDL 74,156 and the safety and tolerability of dolasetron mesylate were studied after a single oral or intravenous dose of 1.2 mg.kg-1 dolasetron mesylate to healthy children from 2 to 12 years of age. Oral dolasetron was administered to 12 children 1 to 2 hours before anesthesia. Intravenous dolasteron was administered to 18 children at induction of anesthesia. Serial blood samples were collected for 24 hours after dosing to measure the plasma concentration of MDL 74,156. Indexes of liver and kidney function were determined, and electrocardiograms and adverse events were recorded.

Administration, Oral↗
PubMed1996

Detection of Mycobacterium tuberculosis in respiratory specimens by strand displacement amplification of DNA.

A total of 294 clinical respiratory specimens, including 75 with culture-positive results, were tested for the presence of Mycobacterium tuberculosis by strand displacement amplification (SDA) of DNA. A region of the IS6110 insertion element and an internal control sequence were amplified and then detected by a chemiluminescence assay. Receiver operator-characteristic curves were used to evaluate three methods for declaring specimens positive for M. tuberculosis. By the preferred method, SDA chemiluminescence results were converted to theoretical numbers of M. tuberculosis organisms. A positive threshold (PT) value, above which 95% of the SDA results were judged to be M. tuberculosis positive (sensitivity = 95%), was found to be 2.4 M. tuberculosis organisms per SDA reaction. The analogous PT value for 95% sensitivity on smear-positive specimens was 3.6 M. tuberculosis organisms per reaction. The PT of 2.4 M. tuberculosis organisms per reaction detected 100% of culture-positive, smear-positive specimens (sensitivity = 100%), while 95% sensitivity was achieved with a PT of 15.5 M. tuberculosis organisms per reaction. Specificities, which were calculated with respect to culture- and smear-negative specimens, ranged from 96% at a PT of 15.5 M. tuberculosis organisms to 84% at a PT of 2.4 M. tuberculosis organisms per reaction. The M. tuberculosis-negative specimens were also segregated according to whether the patients received antituberculosis chemotherapy. SDA specificity ranged from 90% (PT = 2.4 M. tuberculosis organisms) to 98% (PT = 15.5 M. tuberculosis organisms) for the M. tuberculosis-negative specimens from patients who had not received chemotherapy. SDA specificity in the M. tuberculosis-negative specimens from patients who received chemotherapy was lower (85 to 94%). This study represents the first large-scale demonstration of M. tuberculosis detection in clinical sputum specimens by isothermal DNA amplification with SDA.

Bacteriological Techniques↗
PubMed1995

Acetylcholinesterase inhibition by zifrosilone: pharmacokinetics and pharmacodynamics.

OBJECTIVE: To determine the pharmacokinetics, pharmacodynamics and safety of the acetylcholinesterase inhibitor zifrosilone in healthy male volunteers. METHODS: Pharmacokinetics, pharmacodynamics, and tolerance of zifrosilone were studied in a double-blind, sequential, single-escalating-dose, randomized panel design. Each panel consisted of six subjects, with four subjects receiving zifrosilone (10, 30, 60, 90, 120, 150, 200, 250, and 300 mg orally) and two subjects receiving matching placebo. Serial blood samples were obtained for zifrosilone plasma concentrations and red blood cell acetylcholinesterase and butyrylcholinesterase activities. Participating subjects (n = 54) were men between the ages of 18 and 45 years. Each subject had a normal physical examination, electrocardiogram, serum chemistries, hematology, urinalysis, and test for human immunodeficiency virus at screening. RESULTS: A greater than proportionate increase in mean plasma concentration values for area under the curve from time zero to infinity was observed over the 200 to 300 mg dose range groups. Red blood cell acetylcholinesterase showed a dose-inhibition relationship, with a mean maximum inhibition of 20.9% at 10 mg that increased to 62.1% at 300 mg. Butyrylcholinesterase activity was relatively unaffected by zifrosilone (< 20% inhibition at 300 mg). For doses > or = 200 mg, an Emax pharmacodynamic model was used to describe the relationship between zifrosilone plasma concentration and red blood cell acetylcholinesterase inhibition (Emax = 83.8%; EC50 = 0.65 ng/ml). CONCLUSIONS: Zifrosilone showed dose-dependent pharmacokinetics after oral administration and was effective in causing selective inhibition of red blood cell acetylcholinesterase.

Acetophenones↗
PubMed1994

Regulation of Chlamydomonas flagellar dynein by an axonemal protein kinase.

Genetic, biochemical, and structural data support a model in which axonemal radial spokes regulate dynein-driven microtubule sliding in Chlamydomonas flagella. However, the molecular mechanism by which dynein activity is regulated is unknown. We describe results from three different in vitro approaches to test the hypothesis that an axonemal protein kinase inhibits dynein in spoke-deficient axonemes from Chlamydomonas flagella. First, the velocity of dynein-driven microtubule sliding in spoke-deficient mutants (pf14, pf17) was increased to wild-type level after treatment with the kinase inhibitors HA-1004 or H-7 or by the specific peptide inhibitors of cAMP-dependent protein kinase (cAPK) PKI(6-22)amide or N alpha-acetyl-PKI(6-22)amide. In particular, the peptide inhibitors of cAPK were very potent, stimulating half-maximal velocity at 12-15 nM. In contrast, kinase inhibitors did not affect microtubule sliding in axonemes from wild-type cells. PKI treatment of axonemes from a double mutant missing both the radial spokes and the outer row of dynein arms (pf14pf28) also increased microtubule sliding to control (pf28) velocity. Second, addition of the type-II regulatory subunit of cAPK (RII) to spoke-deficient axonemes increased microtubule sliding to wild-type velocity. Addition of 10 microM cAMP to spokeless axonemes, reconstituted with RII, reversed the effect of RII. Third, our previous studies revealed that inner dynein arms from the Chlamydomonas mutants pf28 or pf14pf28 could be extracted in high salt buffer and subsequently reconstituted onto extracted axonemes restoring original microtubule sliding activity. Inner arm dyneins isolated from PKI-treated axonemes (mutant strain pf14pf28) generated fast microtubule sliding velocities when reconstituted onto both PKI-treated or control axonemes. In contrast, dynein from control axonemes generated slow microtubule sliding velocities on either PKI-treated or control axonemes. Together, the data indicate that an endogenous axonemal cAPK-type protein kinase inhibits dynein-driven microtubule sliding in spoke-deficient axonemes. The kinase is likely to reside in close association with its substrate(s), and the substrate targets are not exclusively localized to the central pair, radial spokes, dynein regulatory complex, or outer dynein arms. The results are consistent with a model in which the radial spokes regulate dynein activity through suppression of a cAMP-mediated mechanism.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1994

Uterine smooth-muscle tumors of uncertain malignant potential.

OBJECTIVE: To determine whether tumors meeting the criteria of Hendrickson and Kempson for uterine smooth-muscle tumors of uncertain malignant potential have a natural history different from those of leiomyomas and leiomyosarcomas. METHODS: Tumors with five to ten mitoses per ten high-power fields and with mild or moderate cellular atypia were classified as tumors of uncertain malignant potential. Tumors with two to four mitoses per ten high-power fields and severe cellular atypia would also be classified as tumors of uncertain malignant potential, but we had no tumors that fell into this latter group. Forty-seven women with leiomyosarcoma or smooth-muscle tumors of uncertain malignant potential were identified. Paraffin-embedded blocks were recut, and hematoxylin and eosin-stained sections were studied for mitotic counts and cellular atypia. Statistical analysis used chi 2, Fisher exact test, Student t test, and Kaplan-Meier life table analysis. RESULTS: Fifteen tumors were classified as uncertain malignant potential and 32 as leiomyosarcomas. The patients with leiomyosarcoma were significantly older and more likely to present with extrauterine disease. Those with tumors of uncertain malignant potential had a 5-year disease-free survival of 66% and overall survival of 92%, compared to 28 and 40%, respectively, for leiomyosarcomas; these differences were statistically significant. Patients with tumors of uncertain malignant potential tended to have a protracted clinical course after development of recurrence, and several survived longer than 5 years with metastatic disease. CONCLUSIONS: Patients with five to ten mitoses per ten high-power fields and mild to moderate cellular atypia had a prognosis significantly better than that of patients with leiomyosarcomas. In this group, only 27% developed a recurrence, and after recurrence they tended to have a protracted course. Some of these tumors do have a very aggressive course, and the term "uncertain malignant potential" is appropriate.

Adult↗
PubMed1992

Deoxyribonucleic acid analysis by flow cytometry of uterine leiomyosarcomas and smooth muscle tumors of uncertain malignant potential.

OBJECTIVES: The histologic distinction of uterine benign leiomyomas from leiomyosarcomas is difficult. Ploidy analysis and measurement of the proliferative rate were examined to determine if they could distinguish malignant from benign tumors and if they were independent prognostic factors. STUDY DESIGN: Paraffin-embedded blocks were recut and prepared for flow cytometry with the technique of Hedley. Mitotic counts and tumor grading were performed on an adjacent hematoxylin and eosin-stained section. Statistical analysis was carried out with chi 2 life-table, and Cox model analysis. RESULTS: There were 33 patients with deoxyribonucleic acid histograms that were acceptable for analysis. Fourteen tumors were diploid and 19 were aneuploid. There were no significant differences in the clinical characteristics between the patients with diploid tumors and those with aneuploid tumors. Aneuploid tumors were more likely to have cellular atypia (p = 0.085). There was a strong correlation between the percentage of cells in the S phase and the mitotic count (p = 0.0001). Increasing mitotic count, increasing S phase, presence of extrauterine disease, and postmenopausal status were all adverse prognostic factors. However, when multivariant analysis with a Cox model was used, only S phase and presence of extrauterine disease were adverse factors. Diploid tumors have a better overall survival (p = 0.0658) but a similar disease-free survival. In those patients who ultimately have relapses, diploid tumors have a significantly longer interval from relapse to death (p = 0.0045). CONCLUSIONS: Neither ploidy analysis nor measurement of the proliferative rate will distinguish a benign from a malignant course in an individual patient; however, ploidy is predictive of survival from time of disease progression and proliferative rate is the strongest predictor of overall survival. The time-proven reliability of mitotic count in the diagnosis of smooth muscle tumors reflects its ability to predict proliferative rate.

DNA, Neoplasm↗
PubMed1992

Kinetochore-staining of spermatid micronuclei: studies of mice treated with X-radiation or acrylamide.

The rodent spermatid micronucleus (MN) assay was used in conjunction with immunofluorescent techniques to distinguish kinetochores in MN following exposure of mice to X-radiation or acrylamide. After either treatment, modest increases in kinetochore-positive MN were observed. Spermatids which had been exposed during meiotic prophase to X-rays (400 cGy) had approximately 10-fold increases in MN compared to controls; up to 15% of the MN observed were kinetochore-positive. Following acrylamide treatment of meiotic prophase cells, there was a doubling of spermatid MN over baseline levels, approximately one-third of which were kinetochore-positive.

Acrylamide↗
PubMed1991

Evidence that methanol inhalation does not induce chromosome damage in mice.

Mice were exposed by inhalation to 800 or 4000 ppm methanol for 5 days, and cytogenetic effects were analyzed in blood erythrocytes, lung cells, and testicular germ cells. The results were uniformly negative; no increased frequencies of micronuclei in blood cells, of sister-chromatid exchanges, chromosome aberrations, or micronuclei in lung cells, or of synaptonemal complex damage in spermatocytes were found. From the standpoint of risk assessment, these experimental studies do not reveal any evidence of a cytogenetic hazard associated with inhalation of methanol.

Administration, Inhalation↗
PubMed1990

Transfection of a human alpha-(1,3)fucosyltransferase gene into Chinese hamster ovary cells. Complications arise from activation of endogenous alpha-(1,3)fucosyltransferases.

In order to isolate a human gene encoding an alpha-(1,3)fucosyltransferase (alpha-(1,3)Fuc-T), genomic DNA from HL-60 cells was transfected by several methods into Chinese hamster ovary (CHO) cells. Colonies expressing alpha-(1,3)Fuc-T activity were identified by their ability to bind a monoclonal antibody (anti-SSEA-1) that recognizes the carbohydrate product of alpha-(1,3)Fuc-T action. CHO cells do not express alpha-(1,3)Fuc-T activity but contain at least two, silent alpha-(1,3)Fuc-T genes previously identified by their activation in the rare, dominant mutants LEC11 and LEC12. These CHO enzymes were shown to be distinguishable from the alpha-(1,3)Fuc-T activity of HL-60 cells by the latter's comparative inability to transfer fucose to paragloboside and fetuin. Based on these criteria, only 11 isolates from more than 70 putative transfectants examined were found to stably express an alpha-(1,3)Fuc-T activity typical of HL-60 cells. Genomic DNA from two of these isolates was used to generate five independent secondary transfectants with HL-60-like alpha-(1,3)Fuc-T activity. Southern analysis revealed a common DNA fragment that hybridized to an Alu probe in each secondary, providing evidence that a human alpha-(1,3)Fuc-T gene had been transfected. However, in all transfection experiments, isolates that expressed alpha-(1,3)Fuc-T activities similar to CHO-encoded enzymes were also obtained. Several lines of evidence indicated that these cells arose from activation of endogenous CHO alpha-(1,3)Fuc-T genes as a consequence of DNA transfection. These false positives complicated the identification of transfectants expressing a human alpha-(1,3)Fuc-T gene and represent an important consideration in experiments to transfect other glycosyltransferase genes.

Animals↗
PubMed1990

Genotoxicity of inhibitors of DNA topoisomerases I (camptothecin) and II (m-AMSA) in vivo and in vitro.

The present study was designed to determine and compare the clastogenicity of m-AMSA and camptothecin (CAMP) in vivo in mouse bone marrow and peripheral blood lymphocytes (PBLs), and in vitro in mouse lymphoma L5178Y cells. m-AMSA interferes with topoisomerase II to induce double-strand DNA breaks. CAMP interferes with topoisomerase I to induce single-strand DNA breaks. Thus, we expected the two drugs to induce different types of chromosomal aberrations (CAs). However, both drugs produced quantitatively and qualitatively similar numbers and types of aberrations under similar experimental conditions. In mouse bone marrow exposed over and 18-h period, both drugs (3 mg/kg) induced approximately 30 damaged cells, with an average of 0.4 chromatid breaks per cell (in 100 cells analyzed/mouse). In addition, both drugs induced only chromatid-type aberrations in mouse bone marrow in vivo when exposure occurred during G2. Cell cycle specificity was indicated by the absence of CAs when exposure to the drugs occurred in vivo in mouse PBLs during G0. In L5178Y cells, m-AMSA was considerably more potent for the induction of mutations and somewhat more potent for the induction of CAs than CAMP was. In contrast to the in vivo bone marrow results, the drugs induced high levels of both chromatid- and chromosome-type aberrations in vitro. The ultimate types of chromosomal damage induced by m-AMSA and CAMP result from a complex interaction of (i) cell cycle specific variations in topoisomerase enzyme levels, (ii) the abilities of these drugs to interfere with the orderly DNA breakage/reunion associated with topoisomerase activity, and (iii) the processing of the damage resulting from these interactions.

Amsacrine↗