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Howard L McLeod

Publications and source records attributed to Howard L McLeod.

At least 19 recordsLinked to original sources
PubMed2006

Mechanisms of acquired chemoresistance to 5-fluorouracil and tomudex: thymidylate synthase dependent and independent networks.

PURPOSE: Thymidylate synthase (TS) over-expression is widely accepted as a major molecular mechanism responsible for 5-fluorouracil (5-FU) and tomudex (TDX) resistance. In this study, the importance of TS in 5-FU and TDX resistance was evaluated. METHODS: The sensitivity of TS-over-expressing 5-FU (3) and TDX (3) resistant cell lines to 5-FU and TDX was analysed. The cross-resistance between 5-FU and TDX resistant cell lines was determined. The relationship between p53 and NF-kappaB status and the sensitivity to 5-FU and TDX was evaluated. RESULTS: Compared to relevant parental sensitive cell lines, the 5-FU resistant cell lines were highly cross-resistant to TDX (over 20,000-fold). In contrast, over-expression of TS did not significantly confer 5-FU resistance on the TDX resistant cell lines (0.8- to 1.3-fold). Thymidine (20 microM) rescue induced TDX resistance in TDX sensitive cell lines (over 10,000-fold) but only moderately influenced 5-FU sensitivity in 5-FU sensitive cell lines (1.1- to 2.4-fold). Uridine moderately protected one cancer cell line (RKO) from 5-FU-induced, but not TDX-induced, cytotoxicity. NF-kappaB transfected MCF-7 and p53 knockout HCT116 cells were resistant to 5-FU (4.4- and 2.4-fold, respectively) but not to TDX. TS protein expression in NF-kappaB transfected and p53 knockout cell lines was comparable to the relevant parental cell lines. CONCLUSION: In some cancer cell lines, TS-independent molecular events may play a key role in 5-FU resistance. Loss of p53 function and NF-kappaB over-expression may be involved in TS-independent 5-FU chemoresistance in some cancer cell lines.

Antimetabolites, Antineoplastic↗
PubMed2006

A high-resolution map of segmental DNA copy number variation in the mouse genome.

Submicroscopic (less than 2 Mb) segmental DNA copy number changes are a recently recognized source of genetic variability between individuals. The biological consequences of copy number variants (CNVs) are largely undefined. In some cases, CNVs that cause gene dosage effects have been implicated in phenotypic variation. CNVs have been detected in diverse species, including mice and humans. Published studies in mice have been limited by resolution and strain selection. We chose to study 21 well-characterized inbred mouse strains that are the focus of an international effort to measure, catalog, and disseminate phenotype data. We performed comparative genomic hybridization using long oligomer arrays to characterize CNVs in these strains. This technique increased the resolution of CNV detection by more than an order of magnitude over previous methodologies. The CNVs range in size from 21 to 2,002 kb. Clustering strains by CNV profile recapitulates aspects of the known ancestry of these strains. Most of the CNVs (77.5%) contain annotated genes, and many (47.5%) colocalize with previously mapped segmental duplications in the mouse genome. We demonstrate that this technique can identify copy number differences associated with known polymorphic traits. The phenotype of previously uncharacterized strains can be predicted based on their copy number at these loci. Annotation of CNVs in the mouse genome combined with sequence-based analysis provides an important resource that will help define the genetic basis of complex traits.

Animals↗
PubMed2006

Pharmacogenomics: challenges and opportunities.

The outcome of drug therapy is often unpredictable, ranging from beneficial effects to lack of efficacy to serious adverse effects. Variations in single genes are 1 well-recognized cause of such unpredictability, defining the field of pharmacogenetics (see Glossary). Such variations may involve genes controlling drug metabolism, drug transport, disease susceptibility, or drug targets. The sequencing of the human genome and the cataloguing of variants across human genomes are the enabling resources for the nascent field of pharmacogenomics (see Glossary), which tests the idea that genomic variability underlies variability in drug responses. However, there are many challenges that must be overcome to apply rapidly accumulating genomic information to understand variable drug responses, including defining candidate genes and pathways; relating disease genes to drug response genes; precisely defining drug response phenotypes; and addressing analytic, ethical, and technological issues involved in generation and management of large drug response data sets. Overcoming these challenges holds the promise of improving new drug development and ultimately individualizing the selection of appropriate drugs and dosages for individual patients.

Clinical Medicine↗
PubMed2006

Hoosier Oncology Group randomized phase II study of docetaxel, vinorelbine, and estramustine in combination in hormone-refractory prostate cancer with pharmacogenetic survival analysis.

PURPOSE: To determine the safety and efficacy of two docetaxel doublets in hormone-refractory prostate cancer (HRPC) patients and to examine the prognostic role of polymorphisms in host genes important to docetaxel metabolism and transport. EXPERIMENTAL DESIGN: Sixty-four chemotherapy-naive patients with HRPC were randomized to docetaxel and vinorelbine (D, 20 mg/m2 i.v. days 1 and 8; V, 25 mg/m2 i.v. days 1 and 8) or docetaxel and estramustine phosphate (D, 60-70 mg/m2 i.v. day 1; E, 280 mg oral thrice daily days 1-5) administered q21d. Primary end point was clinically significant toxicity. A pharmacogenetic analysis of host genes was done in patients who received at least one cycle of docetaxel therapy. RESULTS: Grade 3/4 toxicity occurred in 15.6% of DV patients and in 28.6% DE patients. Neither arm exceeded the threshold of clinically significant toxicity. In the DV arm, objective response rate was 33%, prostate-specific antigen response rate was 20%, and median survival was 16.2 months. In the DE arm, objective response rate was 67%, prostate-specific antigen response rate was 43%, and median survival was 19.7 months. Pharmacogenetic analyses showed a significant association between survival beyond 15 months and the ABCG2 421 C > A (Q141K) polymorphism compared with the wild-type (C/C) genotype (66% versus 27%; P = 0.05). CONCLUSIONS: DV and DE doublets are active with a tolerable toxicity profile in patients with HRPC; however, efficacy does not seem superior to standard single-agent docetaxel. The ABCG2 421 C > A (Q141K) polymorphism may be an important predictor of response and survival in HRPC patients treated with docetaxel-based chemotherapy.

Adult↗
PubMed2006

DNA repair pathway profiling and microsatellite instability in colorectal cancer.

BACKGROUND: The ability to maintain DNA integrity is a critical cellular function. DNA repair is conducted by distinct pathways of genes, many of which are thought to be altered in colorectal cancer. However, there has been little characterization of these pathways in colorectal cancer. METHOD: By using the TaqMan real-time quantitative PCR, RNA expression profiling of 20 DNA repair pathway genes was done in matched tumor and normal tissues from 52 patients with Dukes' C colorectal cancer. RESULTS: The relative mRNA expression level across the 20 DNA repair pathway genes varied considerably, and the individual variability was also quite large, with an 85.4 median fold change in the tumor tissue genes and a 127.2 median fold change in the normal tissue genes. Tumor-normal differential expression was found in 13 of 20 DNA repair pathway genes (only XPA had a lower RNA level in the tumor samples; the other 12 genes had significantly higher tumor levels, all P<0.01). Coordinated expression of ERCC6, HMG1, MSH2, and POLB (RS>or=0.60) was observed in the tumor tissues (all P<0.001). Apoptosis index was not correlated with expression of the 20 DNA repair pathway genes. MLH1 and XRCC1 RNA expression was correlated with microsatellite instability status (P=0.045 and 0.020, respectively). An inverse correlation was found between tumor MLH1 RNA expression and MLH1 DNA methylation (P=0.003). CONCLUSION: Our study provides an initial characterization of the DNA repair pathways for understanding the cellular DNA damage/repair system in human colorectal cancer.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Applying pharmacogenomics to enhance the use of biomarkers for drug effect and drug safety.

Pharmacogenomics is used to improve patient outcome by maximizing the likelihood of desired effects and minimizing the risk of adverse events using an individual's genetic profile. As such, pharmacogenomics can be used to improve current risk-management strategies (improving the risk-benefit balance). Two areas of great promise for pharmacogenomics in this regard are emerging: (i) the pharmacogenomics of modulating disease biomarkers (to provide insight into novel mechanisms of drug response and to identify the patients most likely to respond to a drug in a favorable way); and (ii) using pharmacogenomics to enhance drug safety. Given that novel biomarkers could enable the earlier detection of many diseases and more-widespread therapies for primary prevention, pharmacogenomics provides the opportunity to identify the patients most likely to respond to these therapies, thereby preserving valuable health-care resources. The use of pharmacogenomics in pharmacovigilance could also be useful for risk-stratifying patients and for helping to identify the mechanisms involved in adverse events.

5-Lipoxygenase-Activating Proteins↗
PubMed2006

The cancer and leukemia group B pharmacology and experimental therapeutics committee: a historical perspective.

The Chemotherapy Committee of Cancer and Leukemia Group B (CALGB) was established in the mid-1970s to assemble a group of experts in cancer chemotherapy and pharmacology who could advise the CALGB disease committees about the optimal use of drugs in the fight against cancer and to provide quality assurance for the chemotherapy section of CALGB protocols. Chaired initially by Edward Henderson and then David Van Echo, the committee was also the repository of studies in diseases for which CALGB did not have a formal committee, such as testis cancer and sarcoma. In 1990, following the appointment of Richard Schilsky as Chair, the name of the committee was changed to the Pharmacology and Experimental Therapeutics (PET) Committee to reflect a more specific focus and scientific agenda (i.e., studies of chemotherapy pharmacology and development of new agents). Three PET Committee reference pharmacology laboratories (led by Merrill Egorin, Tony Miller, and Mark Ratain) were established to measure drug concentrations in biological fluids and to perform pharmacokinetic analyses. In addition, the PET Committee embarked on a number of multi-institution phase I studies. These phase I studies included studies of special populations, including the first prospective study of an anticancer agent (paclitaxel) in patients with hepatic dysfunction. In addition, the Committee studied a number of phase I combinations destined for phase II evaluation in disease-specific committees. Following Dr. Schilsky's election as CALGB Group Chair in 1994, Mark Ratain took over as Chair of the PET Committee and continued to emphasize population pharmacology as the primary theme of the Committee's research agenda. In addition, the PET Committee began to develop novel clinical trial designs, including the first completed randomized discontinuation trial of an antineoplastic agent. Most recently, the PET Committee has launched an ambitious research program in pharmacogenetics, facilitated in large part through the recruitment of Howard McLeod as Vice Chair. This area of research is a collaborative effort with the NIH Pharmacogenetics Research Network and has the potential to definitively address the hypothesis that germ line polymorphisms are a significant determinant of the toxicity and efficacy of anticancer therapy. It is anticipated that the results of the current studies will contribute significantly to the goal of individualizing cancer treatment.

Antineoplastic Agents↗
PubMed2006

Identification of candidate alkylator-induced cancer susceptibility genes by whole genome scanning in mice.

Secondary malignancies are a serious adverse consequence of alkylator chemotherapy. The risk of developing an alkylator-associated malignancy is influenced by genetic background, although the relevant genetic factors are poorly understood. To screen for novel susceptibility factors, we established a mouse model of alkylator-induced malignancy. We exposed mice from 20 inbred strains to the prototypical alkylating agent, N-nitroso-N-ethylurea (ENU). ENU was a potent carcinogen in many of the strains tested, inducing 140 tumors in 240 ENU-treated mice (66% incidence of at least one tumor in evaluable mice), compared with a background incidence of 8% spontaneous tumors in 240 strain-, age-, and sex-matched control mice (relative risk, 8.4; P < 0.0001). A wide variety of tumor histologies were noted, including epithelial carcinomas, soft tissue sarcomas, and hematopoietic tumors. Cancer susceptibility was a heritable trait for the most common tumor types, lung adenocarcinoma (H(2) = 0.25), T cell lymphoma (H(2) = 0.19), and myeloid malignancies (H(2) = 0.10). Quantitative trait locus mapping identified regions on chromosomes 3, 6, 9, and 15 containing candidate genes associated with lung adenoma, lung carcinoma, and lymphoma susceptibility. This novel mouse model recapitulates many features of human alkylator-associated cancer and supports the hypothesis that susceptibility to this syndrome is influenced by inherited polymorphisms that could be used to make informed clinical treatment decisions.

Alkylating Agents↗
PubMed2006

Pharmacogenomics: from bedside to clinical practice.

The field of pharmacogenomics has seen some exciting advances in the recent past. The Human Genome Project and International HapMap projects have uncovered a wealth of information for researchers. The discovery of clinically predictive genotypes (e.g. UGT1A1*28, TYMS TSER), haplotypes (e.g. VKORC1 Haplotype A) and somatic mutations (e.g. epidermal growth factor receptor), along with the introduction of FDA approved pharmacogenetic tests (UGT1A1*28) and the initiation of a genotype-guided clinical trial for cancer therapy (TYMS TSER in rectal cancer) have provided the first steps towards the integration of pharmacogenomics into clinical practice. This review describes some of the recent advances in pharmacogenomics research.

Genotype↗
PubMed2006

The kinetics and tissue distribution of protein transduction in mice.

Protein transduction domains (PTDs) offer an exciting therapeutic opportunity for the treatment of many diseases. An 11-amino acid fragment of human immunodeficiency type 1 (HIV-1) TAT-protein can transduce large, biologically active proteins into mammalian cells; recent evidence has shown an in vivo PTD for the 116 kDa beta-galactosidase protein. However, there is little information on the in vivo distribution of the TAT fusion protein to define the viability of PTDs for human studies. In this study we examined the tissue kinetics and tissue distribution of the PTD-transduced TAT fusion protein in mice. Low (100 microg) or high (500 microg) doses of TAT-beta-galactosidase fusion protein were administrated to mice through four routes (portal vein, i.v., i.p., and oral). Tissues were harvested 15 min, 1h, 6h, 10h, and 24h after treatment. Distribution of beta-galactosidase in various tissues was analysed by in situ staining, enzymatic activity assay, and Western blot analysis. Beta-galactosidase enzyme activity was observed in all tissues (liver, kidney, spleen, lung, bowel, and brain). Beta-galactosidase activity peaked at 15 min in most tissues after portal vein, i.v., and i.p. administration and at 1h after oral dosing in all tissues. Beta-galactosidase activity in the liver at 15 min after portal vein injection (67 milliunits [mU]/mg) was higher than after i.v. (9.8 mU/mg), i.p. (4.4 mU/mg), and oral (0.3 mU/mg) dosing. In situ staining and Western blot results correlated closely with beta-galactosidase enzyme activity assay. The median initial half-life for activity was 2.2h, ranging from 1.2h to 3.4h (coefficient of variation=28.9%). The bioavailability of beta-galactosidase activity after an orally administered PTD was 24%. This study details the kinetics and tissue distribution of delivering of a model TAT fusion protein into the mouse via PTD. These data allow rational selection of delivery route and schedules for therapeutic PTD and will aid the use of TAT fusion protein transduction in the development of protein therapies.

Administration, Oral↗
PubMed2006

Disposition of 9-nitrocamptothecin and its 9-aminocamptothecin metabolite in relation to ABC transporter genotypes.

PURPOSE: The source of the pharmacokinetic variability of 9-nitrocamptothecin (9NC) and its 9-aminocamptothecin (9AC) metabolite is unknown. ATP-binding cassette (ABC) transporters have been reported to modulate camptothecin analogues, are associated with camptothecin resistance, and might also affect 9NC and 9AC pharmacokinetics. The aim of this study was to evaluate the functional consequence of known single nucleotide polymorphisms in the transporter genes ABCB1, ABCC2, and ABCG2 on the pharmacokinetic disposition of 9NC and 9AC. EXPERIMENTAL DESIGN: Pharmacokinetic and genotyping studies were performed in 55 patients as part of two phase I studies of 9NC in patients with refractory solid tumors, a phase II study of 9NC in patients with advanced colon cancer, and a study evaluating the disposition of 9NC after administration of a single dose under fasting conditions. DNA was isolated from plasma and analyzed for variants in ABCB1, ABCC2, and ABCG2 genes. The ABCB1 1236C>T (n = 43), ABCB1 2677G>T/A (n = 43), ABCB1 3435C>T (n = 43), ABCC2 3972C>T (n = 39), and ABCG2 421C>A (n = 42) variants were analyzed using Pyrosequencing. RESULTS: The ABCG2 421C>A genotype significantly affected the pharmacokinetics of 9AC. The mean 9AC lactone AUC/dose for wild-type (n = 25) and heterozygous (n = 2) patients were 14.3 ng/mL x h and 51.1 ng/mL x h, respectively (P = 0.032). The mean +/- SD 9AC total AUC/dose for wild-type (n = 39) and heterozygous (n = 3) patients were 91.9 +/- 78.3 ng/mL x h and 129.0 +/- 90.5 ng/mL x h, respectively (P = 0.40). 9NC and 9AC disposition were not significantly influenced by variants in ABCB1, ABCC2, and ABCG2, and ABCB1 and ABCC2, respectively (P > 0.05). CONCLUSION: These findings suggest that inter-individual variability in 9AC disposition, but not 9NC, may be influenced, in part, by ABCG2 genotype. In contrast, there was no evidence for a relationship between ABCG2 and the disposition of 9NC, or for relationships between ABCB1 and ABCC2 genotypes and the disposition of 9NC or 9AC.

ATP-Binding Cassette Transporters↗
PubMed2006

Comprehensive evaluation of variability in nicotine metabolism and CYP2A6 polymorphic alleles in four ethnic populations.

Human cytochrome P450 (CYP) 2A6 metabolizes nicotine to cotinine and is a possible modulator of nicotine addiction. Quantitative and qualitative differences in nicotine addiction have been observed between ethnic groups. However, there are few data on the ethnic influences of the CYP2A6-nicotine metabolism relationship, particularly with regard to black subjects. We determined the nicotine metabolism and CYP2A6 genotype in 176 white subjects and 160 black subjects, comparing them with our previous data from 209 Korean subjects and 92 Japanese subjects. Large interindividual differences were observed in the cotinine/nicotine ratios in plasma calculated as an index of nicotine metabolism in white subjects (range, 0.6-36.5) and in black subjects (range, 0.9-30.4). No ethnic difference in the metabolic ratio was observed among white subjects (mean, 7.2 +/- 5.0), black subjects (mean, 7.1 +/- 4.7), and Korean subjects (mean, 8.7 +/- 11.9), whereas Japanese subjects showed a significantly (P < .005) lower metabolic ratio (mean, 3.8 +/- 3.1) compared with the other populations. Women showed significantly (P < .05) higher metabolic ratios than men in the black population (8.0 +/- 5.3 versus 6.0 +/- 3.7). Obvious ethnic differences in the CYP2A6 alleles were observed among these 4 populations. The combined frequencies of the alleles lacking or showing reduced enzymatic activity (CYP2A6*2, CYP2A6*4, CYP2A6*5, CYP2A6*7, CYP2A6*9, CYP2A6*10, CYP2A6*11, CYP2A6*17, CYP2A6*19, and CYP2A6*20) were 9.1%, 21.9%, 42.9%, and 50.5% in white, black, Korean, and Japanese subjects, respectively. These CYP2A6 alleles were associated with reduced nicotine metabolism. Among the homozygotes of CYP2A6*1, interindividual and ethnic differences in the metabolic ratio were still observed. Thus some factors other than genetic ones might also contribute to the interindividual and ethnic differences. This comprehensive study of 4 populations extends our understanding of nicotine metabolism and the impact of genetic polymorphisms of the CYP2A6 gene.

Adolescent↗
PubMed2006

Pharmacokinetics after endovascular lung perfusion with Cisplatin.

PURPOSE: Endovascular lung perfusion (ELP) is a technique designed to deliver high doses of cisplatin via the pulmonary artery for the treatment of lung tumors. The purpose of the current study was to evaluate variables that affect adduct formation. MATERIALS AND METHODS: Thirteen swine underwent ELP. The first group (n = 6) underwent infusion of 150 mg cisplatin diluted to 0.5 mg/mL via a balloon occlusion catheter in the left pulmonary artery. Uptake was compared with that seen with systemic infusion. A second group (n = 7) underwent bilateral sequential infusion of the left pulmonary artery, followed by the right. Cisplatin (150 mg) was infused at one of three concentrations: 1 mg/mL (n = 5 lungs), 0.67 mg/mL (n = 5 lungs), or 0.5 mg/mL (n = 4 lungs). The Pearson coefficient was used to correlate uptake with infusion time, infusate concentration, animal weight, and initial mean pulmonary artery pressure. RESULTS: In the first group, cisplatin uptake in the control lung was less than 8% of that in the study lung. Infusion times for both groups ranged from 3 minutes to 56 minutes. Increases in infusion time correlated with increased adduct levels (r = 0.831; P < .0001). Mean uptake at concentrations of 0.5, 0.67, and 1 mg/mL were 25.79, 12.43, and 13.12 fmol/mug, respectively. There was no significant correlation between pulmonary adduct levels and infusate concentration (r = 0.106; P = .72). Animal weight and initial mean pulmonary artery pressure were not correlated with adduct formation. CONCLUSIONS: ELP with longer infusions of cisplatin may lead to greater adduct formation in pulmonary tissues. Changes in concentration of the infusate do not affect uptake of cisplatin. Hemodynamic parameters do not affect cisplatin uptake.

Animals↗