Biomedical subjects

Howard McLeod

Publications and source records attributed to Howard McLeod.

10 recordsLinked to original sources

PubMed2007

Graying anatomy? Toward molecular tumor characterization.

Will anatomical tumor classification become history as we make way for molecular characterization in oncology? Howard McLeod, Fred Eshelman Distinguished Professor of Pharmacy and Professor of Medicine at the University of North Carolina (NC, USA), is internationally recognized for his work on the pharmacogenomic analysis of cancer treatments. Here, he offers Pharmacogenomics his perspectives on the prospects for practical implementation of PGx in clinical care and the corresponding timescales. He and colleagues have already identified specific genetic components of several drugs that have lead to the US FDA changing the drug package inserts to identify patient groups that are genetically predisposed to risk of severe side effects or inadequate benefit. He is currently working with the large national clinical trials groups--such as Cancer and Leukemia Group B--to confirm that findings from small institutional studies will actually translate into better therapy across the USA.

Humans↗

PubMed2005

Contrasting patterns of Y chromosome and mtDNA variation in Africa: evidence for sex-biased demographic processes.

To investigate associations between genetic, linguistic, and geographic variation in Africa, we type 50 Y chromosome SNPs in 1122 individuals from 40 populations representing African geographic and linguistic diversity. We compare these patterns of variation with those that emerge from a similar analysis of published mtDNA HVS1 sequences from 1918 individuals from 39 African populations. For the Y chromosome, Mantel tests reveal a strong partial correlation between genetic and linguistic distances (r=0.33, P=0.001) and no correlation between genetic and geographic distances (r=-0.08, P>0.10). In contrast, mtDNA variation is weakly correlated with both language (r=0.16, P=0.046) and geography (r=0.17, P=0.035). AMOVA indicates that the amount of paternal among-group variation is much higher when populations are grouped by linguistics (Phi(CT)=0.21) than by geography (Phi(CT)=0.06). Levels of maternal genetic among-group variation are low for both linguistics and geography (Phi(CT)=0.03 and 0.04, respectively). When Bantu speakers are removed from these analyses, the correlation with linguistic variation disappears for the Y chromosome and strengthens for mtDNA. These data suggest that patterns of differentiation and gene flow in Africa have differed for men and women in the recent evolutionary past. We infer that sex-biased rates of admixture and/or language borrowing between expanding Bantu farmers and local hunter-gatherers played an important role in influencing patterns of genetic variation during the spread of African agriculture in the last 4000 years.

Africa↗

PubMed2004

The pharmacogenetics of antiretroviral therapy: a review of studies to date.

Although the ever-expanding armamentarium of antiretroviral drugs has significantly decreased the morbidity and mortality due to human immunodeficiency virus infection, patients and clinicians are increasingly faced with the problems of inadequate or toxic response to therapy that may be genetically mediated. Significant evidence now exists that interindividual differences, such as efficacy of therapy, hypersensitivity reactions, and metabolic complications as a result of antiretroviral therapy, are in part genetically determined. This article reviews the significant studies published to date in the area of the pharmacogenetics of antiretroviral therapy and summarizes current trends, as well as areas where further research is needed.

Anti-HIV Agents↗

PubMed2004

Pharmacogenetics: ethical problems and solutions.

Regulators, drug companies, academic scientists, bioethicists, clinicians and, increasingly, the general public are starting to realize that pharmacogenetics (PGx) will probably have a huge impact on the way in which we treat both common and rare diseases. But how much thought has gone into the ethical issues that the incorportation of phamacogenetic testing into drug discovery, prescription and use will entail? It seems that "quite a bit" is the answer, as the diverse viewpoints of representatives of all of these groups presented here illustrate. However, these views also highlight that now is the time to start formulating and implementing solutions to these potential problems.

Ethics, Medical↗

PubMed2004

CYP3A5 polymorphism and the ethnic differences in cyclosporine pharmacokinetics in healthy subjects.

To determine the relationship between CYP3A5 polymorphism and cyclosporine pharmacokinetic parameters among healthy volunteers, an oral cyclosporine (CsA) pharmacokinetic study was performed in 16 healthy subjects. Blood CsA concentrations were measured by high-performance liquid chromatography. Concentration-versus-time data were analyzed by a noncompartmental method using WinNonLin, and the blood samples were genotyped for the CYP3A5 using the polymerase chain reaction and pyrosequencing. CsA pharmacokinetic parameters were dichotomized and compared using the 1-way ANOVA test according to the CYP3A5*3C genotype. There were 6 homozygous A/A (wild type), 6 homozygous G/G (variant), and 4 heterozygous A/G genotypes for CYP3A5*3 C in these 16 healthy volunteers. All whites were G/G group, and all African Americans except 1 were either A/A or A/G group. The mean AUC (ng x h/mL) of CsA for the 3 genotype groups were 4962 +/- 1074 (A/A), 6677 +/- 1153 (G/G), and 5416 +/- 1817 (A/G), (A/A versus G/G, P = 0.03), and the mean CL/F (mL/min/kg) were 15.6 +/- 3.1 (A/A), 12.0 +/- 2.3 (G/G), and 14.7 +/- 5.9 (A/G), (A/A versus G/G, P = 0.04). None of the other parameters were significantly different among the 3 genotypes. In conclusion, the CYP3A5*3C polymorphism appears to affect AUC and CL/F of oral CsA significantly in healthy subjects, which may partly explain some of the differences of pharmacokinetics in CsA between African Americans and whites.

Adolescent↗

PubMed2004

Pharmacogenomic profiling of the PI3K/PTEN-AKT-mTOR pathway in common human tumors.

The protein synthetic machinery is activated by a variety of genetic alterations during tumor progression and represents an attractive target for cancer therapy. The mammalian target of rapamycin (mTOR) plays an important role in regulating protein translation through phosphorylation of p70 S6 kinase 1 (S6K1), a protein involved in ribosome biogenesis, and 4E-BP1 (eIF-4E binding protein), a translation repressor. It has been shown that mTOR has a direct linkage to the phosphatidylinositol-3'-kinase (PI3K)/PTEN-AKT survival pathway. Recent studies have demonstrated that mTOR inhibition by rapamycin or its analogues have remarkable activity against a wide range of human cancers in vitro and in human tumor xenograft models. Phase I clinical evaluations also suggested an anti-tumor effect of rapamycin analogue such as CCI-779. The clinical challenge for the application of this class of anticancer drug is the ability to prospectively identify which tumors will be sensitive to mTOR inhibition. Recent studies have identified cellular markers that are associated with the in vitro activity of rapamycin or CCI-779. However, there have been no reports on how these cellular markers are expressed together in human tumor specimen. In this study, multiple components of the PI3K/PTEN-AKT-mTOR pathway were evaluated by immunohistochemistry in tissue arrays containing 124 tumors from 8 common tumor types. The results show variable expression of all the signaling proteins. For example, mTOR expression was low in brain tumors, but high in the rest of tumors. High levels of 4E-BP1 were seen in colonic adenocarcinoma and low levels in lymphoma. Phospho-AKT (p-AKT) and phospho-S6K1 (p-S6K1) were the only proteins that had significantly correlated protein expression (rs=0.51, p<0.001). Since low PTEN, high p-AKT and high p-S6K1 expression render tumors sensitive to mTOR inhibition in vitro, these criteria were used to model tumor sensitivity. Overall, 26% of tumors (32/124) are predicted to be sensitive to mTOR inhibition, with variable rates for different tumors (melanoma 0% vs ovarian 41%). This is the first report on the PI3K/PTEN-AKT-mTOR pathway in common human tumors and evaluation of the coordinated expression of different signaling proteins. This study should provide a useful tool for selecting future targeted phase II and III clinical trials in the development of this exciting class of agents.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Irinotecan and carboplatin in metastatic or recurrent NSCLC: an update.

The 1-year survival for patients with metastatic non-small-cell lung cancer is only around 35%. We are evaluating the combination of irinotecan (Camptosar) and carboplatin (Paraplatin) in patients with stage IIIB and IV non-small-cell lung cancer. The first five patients received irinotecan, 250 mg/m2 over 90 minutes followed by carboplatin at an area under the concentration-time curve of 5 over 1 hour1 The dose of irinotecan was subsequently reduced to 200 mg/m2 in view of febrile neutropenia in one of five patients. Chemotherapy cycles are repeated every 21 days. Patients are reevaluated every two cycles. Of a planned 42 patients, 37 have been enrolled so far. Of the 37 enrolled patients, 25 received at least two cycles, 20 received at least four cycles, and 12 received all six planned cycles. Grade 4 neutropenia (absolute neutrophil count <500) occurred in 10 patients and 19 treatment cycles. Two of these patients also had grade 4 diarrhea. Thirty-six cycles (30%) were delayed for neutropenia, six of which occurred among the first five patients who received irinotecan at 250 mg/m2. Best response to therapy included 7 partial responses (23%), 11 stable disease (37%), with 12 patients having progressive disease (40%). The regimen of irinotecan and carboplatin administered once every 3 weeks is tolerable and convenient, with early evidence of activity. The main toxicity is hematologic. This study is ongoing and actively accruing patients.

Aged↗

PubMed2004

Cisplatin, fluorouracil, celecoxib, and RT in resectable esophageal cancer: preliminary results.

Esophageal cancer frequently expresses cyclooxygenase-2 (COX-2) enzyme. In preclinical studies, COX-2 inhibition results in decreased cell proliferation and potentiation of chemotherapy and radiation. We report preliminary results of a phase II study conducted by the Hoosier Oncology Group in patients with potentially resectable esophageal cancer. All patients received cisplatin at 75 mg/m2 given on days 1 and 29 and fluorouracil (5-FU) at 1000 mg/m2 on days 1 to 4 and 29 to 32 with radiation (50.4 Gy beginning on day 1). Celecoxib (Celebrex) was administered at 200 mg orally twice daily beginning on day 1 until surgery and then at 400 mg orally twice daily until disease progression or unexpected toxicities, or for a maximum of 5 years. Esophagectomy was performed 4 to 6 weeks after completion of chemoradiation. The primary study endpoint was pathologic complete response (pCR). Secondary endpoints included response rate, toxicity, overall survival, and correlation between COX-2 expression and pCR. Thirty-one patients were enrolled from March 2001 to July 2002. Respective grade 3/4 toxicities were experienced by 58%/19% of patients, and consisted of granulocytopenia (16%), nausea/vomiting (16%), esophagitis (10%), dehydration (10%), stomatitis (6%), and diarrhea (31%). Seven patients (24%) required initiation of enteral feedings. There have been seven deaths so far, resulting from postoperative complications (2), pulmonary embolism (1), pneumonia (1), and progressive disease (3). Of the 22 patients (71%) who underwent surgery, 5 had pCR (22%). We conclude that the addition of celecoxib to chemoradiation is well tolerated. The pCR rate of 22% in this study is similar to that reported with the use of preoperative chemoradiation in other trials. Further follow-up is necessary to assess the impact of maintenance therapy with celecoxib on overall survival.

Adult↗

PubMed2003

A pilot study of high-throughput, sequence-based mutational profiling of primary human acute myeloid leukemia cell genomes.

In this pilot study, we used primary human acute myeloid leukemia (AML) cell genomes as templates for exonic PCR amplification, followed by high-throughput resequencing, analyzing approximately 7 million base pairs of DNA from 140 AML samples and 48 controls. We identified six previously described, and seven previously undescribed sequence changes that may be relevant for AML pathogenesis. Because the sequencing templates were generated from primary AML cells, the technique favors the detection of mutations from the most dominant clones within the tumor cell mixture. This strategy represents a viable approach for the detection of potentially relevant, nonrandom mutations in primary human cancer cell genomes.

Case-Control Studies↗

PubMed2002

Evaluation of NQO1 gene expression and variant allele in human NSCLC tumors and matched normal lung tissue.

NQO1 gene expression was evaluated by RT-PCR and SNP status by RFLP in matched samples of lung tumors and adjacent normal tissue. NQO1 was found to be overexpressed in lung tumors when compared to matched normal lung tissue. The mean expression in normal lung tissue was 28.26 x 10(-14) ng/microl +/- 44.9 SD and 61.46 x 10(-14) ng/microl +/- 103.2 SD in lung tumors. NQO1 gene expression was higher in the tumor than in the matched normal lung tissue in 27/50 (59%) patients (p=0.014). In the normal samples, 25 (50%) were wild-type, 16 were heterozygotes (32%) and 8 had the SNP (16%). In the matched tumor samples 14 were wild-type (28%), 16 were heterozygous (32%) and 19 (38%) had the SNP (p=0.0043). The genomic NQO1 mutation was associated with survival in a pilot study of stage II/III NSCLC patients. Patients with a homozygous SNP genotype had a significantly shorter survival (median 12 months), than heterozygous or homozygous wild-type patients (median 41 months) (p=0.007), suggesting NQO1 may be important in chemosensitivity as well as the pathogenesis of lung cancer and NQO1 genotyping may be a useful component of pharmacogenetic strategies for the treatment of NSCLC.

Aged↗