CYP3A4 promoter variant in Saudi, Ghanaian and Scottish Caucasian populations

Pharmacogenetics of Breast Cancer Treatments: A Sub-Saharan Africa Perspective

Breast cancer is the most frequent cause of cancer death in low- and middle-income countries, in particular among sub-Saharan African women, where response to available anticancer treatment therapy is often limited by the recurrent breast tumours and metastasis, ultimately resulting in decreased overall survival rate. This can also be attributed to African genomes that contain more variation than those from other parts of the world. The purpose of this review is to summarize published evidence on pharmacogenetic and pharmacokinetic aspects related to specific available treatments and the known genetic variabilities associated with metabolism and/or transport of breast cancer drugs, and treatment outcomes when possible. The emphasis is on the African genetic variation and focuses on the genes with the highest strength of evidence, with a close look on CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4/5, CYP19A1, UGT1A4, UGT2B7, UGT2B15, SLC22A16, SLC38A7, FcγR, DPYD, ABCB1, and SULT1A1, which are the genes known to play major roles in the metabolism and/or elimination of the respective anti-breast cancer drugs given to the patients. The genetic variability of their metabolism could be associated with different metabolic phenotypes that may cause reduced patients’ adherence because of toxicity or sub-therapeutic doses. Finally, this knowledge enhances possible personalized treatment approaches, with the possibility of improving survival outcomes in patients with breast cancer.

Genetic variants association with cancers in African-based populations: A systematic review

BACKGROUND

Cancer is the single leading cause of human deaths worldwide. The highest incidence and mortality are recorded from Africa. The last two decades have witnessed extensive research which has led to emerging prognosis and new gene therapy technologies. Cancer therapy in Africa is derived with little input from African population data. While a number of cancer studies on African populations have suggested varied susceptible variant, no comprehensive review of these studies has been undertaken to assess their coverage across Africa.

METHODS

This study aimed to undertake a review of all molecular genetic studies that interrogated the genetic variants of cancers in African-based populations. Our search methodology was modelled after the Cochrane systematic review protocol, which included MeSH terms and related keywords.

RESULTS

Ninety-seven articles studying 13 cancer types, were reviewed. 91 articles screened for polymorphisms using PCR-based techniques while three used SNP array, two used whole exome sequencing and one used pyrosequencing. North African (NA) countries undertook 51/97 (53 %) studies on 12/13 (92 %) cancer types while the Sub Saharan Africa (SSA) countries undertook 46/97 (47 %) studies on 7/13 (54 %) cancer types. Twelve out of these thirteen cancer type studies suggested susceptibility to their target polymorphism (p > 0.05). No study replicated or validated variants detected.

CONCLUSION

Research on genetic determinants in African-based population cancer offers translational benefits. We recommended large scale, multi-national genome association studies using high throughput techniques. SSA needs to receive more attention due to the shortage of this type of study and data in the region.

The role of ethnicity on pregnancy outcomes in women with epilepsy: The need for specific research

The role of ethnicity on pregnancy outcomes of women with epilepsy (WWE) has received little research attention but is important to guide management. The aim of this review is to identify and describe current knowledge of ethnicity for WWE giving birth. Literature searches were performed with the following terms: ethnic/race combined with epilepsy/seizure, antiepileptic drugs (AED), and/or pregnancy, and combined them with congenital malformation, birth outcome, or pregnancy complication, with English language restriction in PubMed, EMBASE, and Web of Science. Both primary studies and review articles were included. Ethnicity disparities exist in specific congenital malformations, pregnancy complications, and birth outcomes among the general population. There is also ethnicity-related diversity of AED disposition. Information on ethnicity is rarely considered in studies about pregnant WWE. The association between ethnicity and pregnancy outcomes of WWE remains to be elucidated. The lack of data relating to ethnicity in pregnancy studies among WWE needs addressing. Knowledge of potential effects of ethnicity on pregnancy outcomes in WWE will help inform better clinical care around the world.

The role of biobanks in elucidating prevalent genetic diseases in Saudi Arabia

Biobanking entails large-scale collection of human biological specimens that are linked to the donors' health and personal information, and has several applications in clinical research. Human biological specimens, such as blood, urine and tissue, have become immensely important to medical research: they offer a valuable source of genetic material that researchers can use to identify disease-associated genetic variation and to determine interactions between genes and environmental factors. Identification of genetic contributions to disease can lead to the development of new diagnostic tests and targeted treatments. Over the last decade, both common diseases and rare genetic disorders have been reported in Saudi Arabia. The need to generate extensive genetic data on these diseases has led to the establishment of several Saudi Arabian biobanks. Fortunately, these vital efforts have the support of the Saudi Government and researchers. However, the success of any biobank also requires public support and the willingness of the population to donate their biological material along with information on their medical records. Thus, the Saudi public needs to be informed of the benefits of maintaining biobanks, their participation needs to be encouraged through donation of biological material, and any public concerns regarding the confidential treatment of medical data need to be addressed. This article reviews the most common genetic diseases identified in the Saudi population, it describes biobanks and it examines how biobanks can support biomedical research in the area. Moreover, this article proposes measures that might help to increase public awareness of biobanks and the preparedness of the Saudi Arabian population to donate biological material.

Cytochrome P450 single nucleotide polymorphisms in an indigenous Tanzanian population: a concern about the metabolism of artemisinin-based combinations

BACKGROUND

Artemisinin-based combinations currently recommended for treatment of uncomplicated Plasmodium falciparum malaria in many countries of sub-Saharan Africa are substrates of CYP enzymes. The cytochrome enzyme system is responsible for metabolism of about 80-90% of clinically used drugs. It is, therefore, important to obtain the pharmacogenetics of the population in the region with respect to these combinations and thereby enable practitioners to predict treatment outcomes. The aim of this study was to detect and determine allelic frequencies of CYP2C8*2, CYP2C8*3, CYP3A4*1B, CYP3A5*3 and CYP2B6*6 variant alleles in a Tanzanian indigenous population.

METHODS

Genomic DNA extraction from blood obtained from 256 participants who escorted patients at Karume Health Centre in Mwanza Tanzania, was carried out using the Gene JET™ Genomic DNA purification kit (Thermo Scientific). Genotyping for the cytochrome P450 variant alleles was performed using predesigned primers. Amplification was done by PCR while differentiation between alleles was done by restriction fragment length polymorphism (PCR-RFLP) (for CYP2C8*2, CYP2C8*3) and sequencing (for CYP2B6*6, CYP3A5*3 and CYP3A4*1B).

RESULTS

CYP2C8*2, CYP2C8*3, CYP3A5*3, CYP3A4*1B and CYP2B6*6 variant allelic frequencies were found to be 19,10,16,78 and 36% respectively.

CONCLUSION

Prevalence of CYP2C8*2, CYP3A5*3, CYP3A4*1B and CYP2B6*6 mutations in a Tanzanian population/subjects are common. The impact of these point mutations on the metabolism of anti-malarial drugs, particularly artemisinin-based combinations, and their potential drug-drug interactions (DDIs) needs to be further evaluated.

Frequency distribution of high risk alleles of CYP2C19, CYP2E1, CYP3A4 genes in Haryana population

The genotype of an individual can significantly influence the disposition of a chemical, and determine their susceptibility to its toxicity. Many enzymes involved in either activation or detoxification of chemical carcinogen metabolism are polymorphically expressed, with the alleles presenting different enzymatic activities and some of them having been associated with susceptibility to cancer. Cytochrome P450 (P450 or CYP) constitutes the most important phase I enzyme group responsible for the metabolism of endogenous and exogenous (xenobiotics) substances. The present study was aimed to analyze the frequencies of commonly known polymorphisms of human xenobiotic metabolizing genes (XMG) in the Haryana State population of North India. The study was conducted in 308 healthy Haryana volunteers. DNA was extracted from leucocytes and the genetic polymorphisms in CYP2C19*2, CYP2C19*3, CYP2E1*5B and CYP3A4*1B were determined by digesting the PCR Product with restriction enzymes BamHI, SmaI, PstI and PstI respectively. The genotype frequencies of CYP2C19*2, CYP2C19*3, CYP2E1*5B, and CYP3A4*1B were found to be 22.0%, 0.0%, 2.11% and 2.0% respectively. The North Indian population which is known to be Caucasoid Aryans is ethnically different from South Indians known as Caucasoid Dravidians but no significant difference in genetic polymorphism was found.

Frequency and prognostic significant of CYP3A4-A-290G polymorphism in acute myeloid leukemia

Cytochrome P450 3A4 (CYP3A4) is the most plentiful cytochrome P450 in adult human liver and small intestine and is responsible for detoxification of more than 50% of drugs in addition to the metabolic deactivation and metabolism of many carcinogens. Polymorphism of CYP3A4-A-290G considered the only allele that appears to stimulate CYP3A4 expression and has been associated with a number of clinical phenotypes, including prostate cancer, breast cancer, leukemia and the early onset of puberty. In this study, we analyzed the presence of CYP3A4-A-290G polymorphism in 77 newly diagnosed AML cases and 72 healthy control using PCR/RFLP aiming to show CYP3A4-A-290G polymorphism pattern in acute myeloid leukemia patients, and its role in disease severity and progression. A highly statistically significant difference was found between the control and AML groups as regards the heterozygous genotype (p-value = 0.002) and increases the risk of AML 11.4-fold. Also there was a highly significant difference between the control and AML patients regarding variant allele (G in AG and GG genotypes) (p-value 0.001) and increases the risk of AML 19-fold. No statistically significant association found between the CYP3A4-A-290G polymorphism and different clinical or laboratory parameters as well as an initial response to treatment, overall survival and the disease free survival. We concluded that CYP3A4-A-290G polymorphism is a genotypic factor that increases the CYP3A4 enzymatic activity and increases the risk of AML by 18.9-fold.

CYP3A4*22: promising newly identified CYP3A4 variant allele for personalizing pharmacotherapy

Many studies have attempted to explain the interindividual variability observed in drug metabolism by assessing the impact of SNPs in genes implicated in drug absorption, distribution, metabolism and excretion pathways. Particular attention has been paid to the CYP450s. CYP3A4 is the main CYP isoform in human liver and intestine and is involved in the metabolism of many drugs. Its activity, however, is characterized by widespread variation in the general population, which is thought to have a genetic basis. A new CYP3A4 allele (CYP3A4*22; rs35599367 C>T in intron 6) with a frequency of 5-7% in the Caucasian population was recently discovered through its association with low hepatic CYP3A4 expression and CYP3A4 activity, and showing effects on statin, tacrolimus and cyclosporine metabolism. This review will summarize the current literature on phenotypes linked to this new promising CYP3A4 genetic marker SNP and discusses the potential clinical relevance.

Cytochrome P450 pharmacogenetics in African populations

The Cytochrome P450 (CYP450) family of enzymes is involved in the oxidative metabolism of many therapeutic drugs, carcinogens and various endogenous substrates. These enzymes are highly polymorphic at an inter-individual and inter-ethnic level. Polymorphisms or genetic variations account for up to 30% of inter-individual differences seen in a variety of drug responses. The frequencies of the different metabolizer categories (slow, intermediate, extensive and ultra-rapid), the distribution of genetic variants, genotype-phenotype correlations and the clinical importance of the CYP450 enzymes have been extensively documented in Caucasian and Oriental populations. Limited data exists for African populations, despite the fact that this knowledge is critically important for these populations who experience a heavy burden of communicable and non-communicable diseases. In addition, the costs incurred through adverse drug reactions and non-responsiveness to therapy could be reduced through the wide-scale application of pharmacogenetics. This review provides an overview and investigation of CYP450 genotypic and phenotypic reports published from 1980 to present in African populations. Our findings confirm the high degree of variability that is expected when comparing individuals of African origin to other ethnic groups and also highlight the distribution of clinically relevant CYP450 alleles amongst the various African populations. The notable discordance in genotypic and phenotypic data amongst African populations exemplifies the need for in-depth and well-orchestrated molecular and pharmacological investigations of these populations in the future, for which whole genome sequencing and association studies will be critical.

Pharmacogenetics in Ghana: reviewing the evidence

Different clinical response of different patients to the same medicine has been recognised and documented since the 1950's. Variability in response of individuals to standard doses of drug therapy is important in clinical practice and can lead to therapeutic failures or adverse drug reactions. Pharmacogenetics seeks to identify individual genetic differences (polymorphisms) in drug absorption, metabolism, distribution and excretion that can affect the activity of a particular drug with the view of improving efficacy and reducing toxicity. Although knowledge of pharmacogenetics is being translated into clinical practice in the developed world, its applicability in the developing countries is low. Several factors account for this including the fact that there is very little pharmacogenetic information available in many indigenous African populations including Ghanaians. A number of genes including Cytochrome P450 (CYP) 2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, MDR1 and TPMT have been genotyped in the Ghanaian population since the completion of the Human genome project. There is however, an urgent need to increase pharmacogenetic research in Ghana to increase availability of data. Introducing Pharmacogenetics into the curriculum of Medical and Pharmacy training institutions will influence translating knowledge of pharmacogenetics into clinical practice. This will also equip health professionals with the skill to integrate genetic information into public health decision making.

Population pharmacokinetic modeling of the association between 63396C->T pregnane X receptor polymorphism and unboosted atazanavir clearance

Atazanavir (ATV) plasma concentrations are influenced by CYP3A4 and ABCB1, which are regulated by the pregnane X receptor (PXR; NR1I2). PXR expression is correlated with CYP3A4 in liver in the absence of enzyme inducers. The PXR single nucleotide polymorphism (SNP) 63396C→T (rs2472677) alters PXR expression and CYP3A4 activity in vitro, and we previously showed an association of this polymorphism with unboosted ATV plasma concentrations. The aim of this study was to develop a population pharmacokinetic analysis to quantify the impact of 63396C→T and diurnal variation on ATV clearance. A population analysis was performed with 323 plasma samples from 182 randomly selected patients receiving unboosted ATV. Two hundred fifty-nine of the blood samples were collected at random time points, and 11 patients had a full concentration-time profile at steady state. Nonlinear mixed effects modeling was applied to explore the effects of PXR 63396C→T, patient demographics, and diurnal variation. A one-compartment model with first-order absorption and lag time best described the data. Population clearance was 19.7 liters/h with interpatient variability or coefficient of variation (CV) of 21.5%. Homozygosity for the T allele for PXR 63396 was associated with a 17.0% higher clearance that was statistically significant. Evening dosing was associated with 34% higher bioavailability than morning dosing. Patient demographic factors had no effect on ATV clearance. These data show an association of PXR 63396C→T and diurnal variation on unboosted ATV clearance. The association is likely to be mediated through an effect on hepatic PXR expression and therefore expression of its target genes (e.g., CYP3A4, SLCO1B1, and ABCB1), which are known to be involved in ATV clearance.

Genetic polymorphisms in MDR1, CYP3A4 and CYP3A5 genes in a Ghanaian population: a plausible explanation for altered metabolism of ivermectin in humans?

BACKGROUND

Ivermectin, a substrate of multidrug resistance (MDR1) gene and cytochrome P450 (CYP) 3A4, has been used successfully in the treatment of onchocerciasis in Ghana. However, there have been reports of suboptimal response in some patients after repeated treatment. Polymorphisms in host MDR1 and CYP3A genes may explain the observed suboptimal response to ivermectin. We genotyped relevant functional polymorphisms of MDR1 and CYP3A in a random sample of healthy Ghanaians and compared the data with that of ivermectin-treated patients with a view to exploring the relationship between suboptimal response to ivermectin and MDR1 and CYP3A allelic frequencies.

METHODS

Using PCR-RFLP, relevant polymorphic alleles of MDR1 and CYP3A4 genes were analysed in 204 randomly selected individuals and in 42 ivermectin treated patients.

RESULTS

We recorded significantly higher MDR1 (3435T) variant allele frequency in suboptimal responders (21%) than in patients who responded to treatment (12%) or the random population sample (11%). CYP3A4*1B, CYP3A5*3 and CYP3A5*6 alleles were detected at varied frequencies for the sampled Ghanaian population, responders and suboptimal responders to ivermectin. CYP3A5*1/CYP3A5*1 and CYP3A5*1/CYP3A5*3 genotypes were also found to be significantly different for responders and suboptimal responders. Haplotype (*1/*1/*3/*1) was determined to be significantly different between responders and suboptimal responders indicating a possible role of these haplotypes in treatment response with ivermectin.

CONCLUSION

A profile of pharmacogenetically relevant variants for MDR1, CYP3A4 and CYP3A5 genes has been generated for a random population of 204 Ghanaians to address the scarcity of data within indigenous African populations. In 42 patients treated with ivermectin, difference in MDR1 variant allele frequency was observed between suboptimal responders and responders.

An Interethnic Comparison of Polymorphisms of the Genes Encoding Drug-Metabolizing Enzymes and Drug Transporters: Experience in Singapore

Much of the interindividual variability in drug response is attributable to the presence of single nucleotide polymorphisms (SNPs) in genes encoding drug-metabolizing enzymes and drug transporters. In recent years, we have investigated the polymorphisms in a number of genes encoding phase I and II drug-metabolizing enzymes including CYPIA1, CYP3A4, CYP3A5, GSTM1, NAT2, UGT1A1, and TPMT and drug transporter (MDR1) in three distinct Asian populations in Singapore, namely the Chinese, Malays, and Indians. Significant differences in the frequencies of common alleles encoding these proteins have been observed among these three ethnic groups. For example, the frequency of the variant A2455G polymorphism of CYP1A1 was 28% in Chinese and 31% in Malays, but only 18% in Indians. CYP3A4*4 was detected in two of 110 Chinese subjects, but absent in Indians and Malays. Many Chinese and Malays (61-63%) were homozygous for the GSTM1*0 null genotype compared with 33% of Indians. The frequency of the UGTIA1*28 allele was highest in the Indian population (35%) compared to similar frequencies that were found in the Chinese (16%) and Malay (19%) populations. More importantly, our experience over the years has shown that the pharmacogenetics of these drug-metabolizing enzymes and MDR1 in the Asian populations are different from these in the Caucasian and African populations. For example, the CYP3A4*1B allele, which contains an A-290G substitution in the promoter region of CYP3A4, is absent in all three Asian populations of Singapore studied, but occurs in more than 54% of Africans and 5% of Caucasians. There were no difference in genotype and allelic variant frequencies in exon 12 of MDR1 between the Chinese, Malay, and Indian populations. When compared with other ethnic groups, the distribution of the wild-type C allele in exon 12 in the Malays (34.2%) and Indians (32.8%) was relatively high and similar to the Japanese (38.55%) and Caucasians (41%) but different from African-Americans (15%). The frequency of wild-type TT genotype in Asians (43.5% to 52.1%) and Japanese (61.5%) was much higher than those found in Caucasians (13.3%). All the proteins we studied represent the primary hepatic or extrahepatic enzymes, and their polymorphic expression may be implicated in disease risk and the disposition of drugs or endogenous substances. As such, dose requirements of certain drugs may not be optimal for Asian populations, and a second look at the factors responsible for this difference is necessary.

Pharmacogenetic analysis of paclitaxel transport and metabolism genes in breast cancer

Paclitaxel is commonly used in the treatment of breast cancer. Variability in paclitaxel clearance may contribute to the unpredictability of clinical outcomes. We assessed genomic DNA from the plasma of 93 patients with high-risk primary or stage IV breast cancer, who received dose-intense paclitaxel, doxorubicin and cyclophosphamide. Eight polymorphisms in six genes associated with metabolism and transport of paclitaxel were analyzed using Pyrosequencing. We found no association between ABCB1, ABCG2, CYP1B1, CYP3A4, CYP3A5 and CYP2C8 genotypes and paclitaxel clearance. However, patients homozygous for the CYP1B1*3 allele had a significantly longer progression-free survival than patients with at least one Valine allele (P=0.037). This finding could reflect altered paclitaxel metabolism, however, the finding was independent of paclitaxel clearance. Alternatively, the role of CYP1B1 in estrogen metabolism may influence the risk of invasive or paclitaxel resistant breast cancer in patients carrying the CYP1B1*3 allele.

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.

Prospective Evaluation of Body Surface Area as a Determinant of Paclitaxel Pharmacokinetics and Pharmacodynamics in Women with Solid Tumors

PURPOSE

To study a fixed dose (360 mg) of paclitaxel given i.v. over 3 hours to female patients, and to evaluate prospectively the relationships between the following: body surface area and toxicity; body surface area and pharmacokinetics; and pharmacokinetics and toxicity.

EXPERIMENTAL DESIGN

The eligibility criteria included the following: female sex; solid tumors; no more than one prior chemotherapy regimen; no prior paclitaxel; performance status of 0 to 2; and normal organ function. Paclitaxel plasma concentrations were quantified by high-performance liquid chromatography. The area under the curve, total body clearance, and hours above 0.05 micromol/L (T > 0.05) were calculated.

RESULTS

Thirty-two patients were enrolled, and 29 patients received the correct dose and regimen. For statistical analyses, 26 patients had complete follow-up blood counts, 23 patients had complete data to correlate blood counts and area under the curve, and 25 patients had data to correlate blood counts and T > 0.05. The main toxicity was neutropenia of grade 3 and 4 severity in 21% and 25% of patients, respectively, in cycle 1. The worst grade of any toxicity, nadir WBC and absolute neutrophil count, and survival fractions were assessed; no significant relationship was found between body surface area and any measure of toxicity. Body surface area correlated inversely with area under the curve (r = -0.67; P < 0.001) and correlated with total body clearance (r = 0.69; P < 0.001), but body surface area did not correlate with T > 0.05. Neither area under the curve nor total body clearance were correlated with nadir absolute neutrophil count or survival fractions, but a significant correlation was found between T > 0.05 and log(nadir absolute neutrophil count; r = -0.41; P = 0.04).

CONCLUSIONS

These results suggest that fixed dosing of paclitaxel is feasible in women, which would simplify the administration of this drug.

Factors Affecting Cytochrome P-450 3A Activity in Cancer Patients

PURPOSE

The purpose is to identify the demographic, physiologic, and inheritable factors that influence CYP3A activity in cancer patients.

EXPERIMENTAL DESIGN

A total of 134 patients (62 females; age range, 26 to 83 years) underwent the erythromycin breath test as a phenotyping probe of CYP3A. Genomic DNA was screened for six variants of suspected functional relevance in CYP3A4 (CYP3A4*1B, CYP3A4*6, CYP3A4*17, and CYP3A4*18) and CYP3A5 (CYP3A5*3C and CYP3A5*6).

RESULTS

CYP3A activity (AUC(0-40 min)) varied up to 14-fold in this population. No variants in the CYP3A4 and CYP3A5 genes were a significant predictor of CYP3A activity (P > 0.2954). CYP3A activity was reduced by approximately 50% in patients with concurrent elevations in liver transaminases and alkaline phosphatase or elevated total bilirubin (P < 0.001). In a multivariate analysis, CYP3A activity was not significantly influenced by age, sex, and body size measures (P > 0.05), but liver function combined with the concentration of the acute-phase reactant, alpha-1 acid glycoprotein, explained approximately 18% of overall variation in CYP3A activity (P < 0.001).

CONCLUSIONS

These data suggest that baseline demographic, physiologic, and chosen genetic polymorphisms have a minor impact on phenotypic CYP3A activity in patients with cancer. Consideration of additional factors, including the inflammation marker C-reactive protein, as well as concomitant use of other drugs, food constituents, and complementary and alternative medicine with inhibitory and inducible effects on CYP3A, is needed to reduce variation in CYP3A and treatment outcome to anticancer therapy.

CYP3A4 and MDR1 alleles in a Portuguese population

Polymorphisms in cytochrome P450 CYP3A4 and multidrug resistance (MDR) 1 genes coding for the important drug-metabolising CYP3A4 and the ATP-binding cassette (ABC) transporter P-glycoprotein (Pgp) are poorly documented in the Portuguese population. In this study we have determined the frequencies of CYP3A4 and MDR1 alleles in Portuguese Caucasians. Both genes were simultaneously analysed as these genes are known to be frequently co-induced and their products to show a pronounced overlap of substrates. CYP3A4 A-392G (CYP3A4*1B), T673C (CYP3A4*2) and MDR1 T-129C, G2677T and C3435T single nucleotide polymorphisms (SNPs) were analysed in 100 individuals from the southern region of the country. We observed a frequency of 4.0% for CYP3A4*1B, not significantly different from that reported on other Caucasian European populations. CYP3A4*2 was found at an allele frequency of 4.5%, constituting the first report of the presence of this allele outside the Finnish population. Significant differences were found concerning the MDR1 C3435T SNP frequency (64.5%) compared with other European populations, while no differences were found concerning G2677T (47.5%) or T-129C (5%) SNPs. Linkage between the C3435T and G2677T SNPs was observed, although not as evidently as documented in other Caucasian populations. No preferential associations were detected between CYP3A4 and MDR1 alleles.

Ethnic differences in the frequency of prostate cancer susceptibility alleles at SRD5A2 and CYP3A4

OBJECTIVES

Ethnic differences in prostate cancer incidence are well documented, with African-Americans having among the highest rates in the world. Ethnic differences in genotypes for genes associated with androgen metabolism including SRD5A2 and CYP3A4 also may exist. The aim of this study was to evaluate differences in these genotypes by ethnicity.

METHODS

We studied cancer-free controls representative of four groups: 147 African Americans, 410 Caucasian-Americans, 129 Ghanaians, and 178 Senegalese. PCR-based genotype analysis was undertaken to identify two alleles (V89L, A49T) at SRD5A2 and *1B allele at CYP3A4.

RESULTS

Differences were observed for V89L (variant frequency of 30% in Caucasians, 27% in African Americans, 19% in Ghanaians, and 18% in Senegalese, p = 0.002) and were observed for CYP3A4*1B (variant frequencies of 8% in Caucasians, 59% in African Americans, 81% in Ghanaians, and 78% in Senegalese, p = 0.0001). Pooled data combining the present data and previously published data from from Asian, Hispanic, and Arab cancer-free controls showed significant ethnic differences for SRD5A2 and CYP3A4 polymorphisms. Overall, Asians were least likely to have alleles associated with increased prostate cancer risk, while Africans were most likely to have those alleles.

CONCLUSIONS

These results suggest that ethnicity-specific differences in genotype frequencies exist for SRD5A2 and CYP3A4. Africans and African-Americans have the highest frequency of those alleles that have previously been associated with increased prostate cancer risk. Future studies should address whether allele frequency differences in part explain differences in prostate cancer incidence in these populations.

CYP3A4*1B and NAT2*14 alleles in a native African population

Single nucleotide polymorphisms were examined in the cytochrome 450 3A4 (CYP3A4) and N-acetyltransferase 2 (NAT2) genes, which code for major mediators of the metabolism of a wide variety of therapeutic drugs, as well as xenobiotics. We determined, in a population from Guinea-Bissau, the frequencies of CYP3A4 and NAT2 variants expected to be prevalent among Africans, due to the high frequency previously observed in African Americans. The observed frequencies were 72% for CYP3A4*1B and 19.2% for the NAT2 191 G>A variant. The high frequency found for these potentially function-altering polymorphisms suggests the possibility of impaired metabolism through CYP3A4 and NAT2 in this population. Strikingly, the frequency observed for the NAT2 191 G>A single nucleotide polymorphism (SNP), associated with the slow acetylator phenotype, was significantly higher than found in other African populations, suggesting the existence of a west to east gradient across Sub-Saharan Africa. The prevalence of these variants may be relevant with regard to therapeutic efficacy in African populations for it may potentially affect drug clearance and consequently, increase the incidence of side effects and drug-drug interactions.

CYP3A4 and VDR gene polymorphisms and the risk of prostate cancer in men with benign prostate hyperplasia

Prostate cancer (PRCa) is one of the most common causes of cancer death in men and determinants of PRCa risk remain largely unidentified. Benign prostatic hyperplasia (BPH) is found in the majority of ageing men and has been associated with PRCa. Many candidate genes have been suggested to be involved in PRCa, such as those that are central to cellular growth and differentiation in the prostate gland. The vitamin D receptor (VDR) and CYP3A4 have been shown to be involved in the regulation of cell proliferation and differentiation in prostate cells. Genetic variations of these genes have been associated with PRCa in case-control studies and may be useful to detect BPH patients that have a higher risk of developing PRCa. The association between CYP3A4 and VDR TaqI SNPs and the risk of developing PRCa have been investigated in this study by determining the variant genotype frequencies of both SNPs in 400 patients with BPH who have been followed clinically for a median of 11 years. The results of this study showed that the incidence rate of PRCa was higher in BPH patients having CYP3A4 variant genotype compared to those with wild type (relative risk (RR)=2.7; 95% CI=0.77-7.66). No association between variant genotype and risk of developing PRCa was observed with the VDR TaqI variant genotype. In addition, the results of combined genotype analysis of these two SNPs showed a borderline significant association between CYP3A4 and VDR TaqI combined variant genotypes and PRCa risk (RR=3.43; 95% CI=0.99-11.77). While independent confirmation is required in further studies, these results provide a potential tool to assist prediction strategies for this important disease.

Randomized cross-over evaluation of body-surface area-based dosing versus flat-fixed dosing of paclitaxel

PURPOSE

Despite dose calculation using body-surface area (BSA), pharmacokinetics of most anticancer drugs show wide interindividual variability. In this study, we evaluated the role of BSA in paclitaxel disposition.

PATIENTS AND METHODS

Paclitaxel pharmacokinetics were prospectively studied in 12 patients that were treated in a randomized cross-over design with paclitaxel (3-hour infusion at a 3-week interval) at 175 mg/m2 in cycle 1 (A) and a flat-fixed dose of 300 mg in cycle 2 (B), or vice versa. Blood samples were collected up to 24 hours after dosing and analyzed for total and unbound paclitaxel.

RESULTS

The area under the curves (AUC) of unbound paclitaxel were similar in both dosing groups, with mean values +/- SD (A v B) of 1.34 +/- 0.158 versus 1.30 +/- 0.329 microM x h, indicating that BSA-based dosing reduced the coefficient of variation by 53.3%. Unbound and total paclitaxel clearance was also significantly related to various body-size measures, including BSA (R > or = 0.617; P < or =.033), weight (R >or = 0.621; P < or =.031), and lean-body mass (r > or = 0.630; P < or = .028). We hypothesize that this is caused by the association of paclitaxel in the circulation with Cremophor EL, the distribution of which is linked to total blood volume, and thus to BSA.

CONCLUSION

This study indicates that paclitaxel disposition is significantly related to BSA. This provides a pharmacokinetic rationale for BSA-based dosing of this drug.

Molecular basis of ethnic differences in drug disposition and response

Ethnicity is an important demographic variable contributing to interindividual variability in drug metabolism and response. In this rapidly expanding research area many genetic factors that account for the effects of ethnicity on pharmacokinetics, pharmacodynamics, and drug safety have been identified. This review focuses on recent developments that have improved understanding of the molecular mechanisms responsible for such interethnic differences. Genetic variations that may provide a molecular basis for ethnic differences in drug metabolizing enzymes (CYP 2C9, 2C19, 2D6, and 3A4), drug transporter (P-glycoprotein), drug receptors (adrenoceptors), and other functionally important proteins (eNOS and G proteins) are discussed. A better understanding of the molecular basis underlying ethnic differences in drug metabolism, transport, and response will contribute to improved individualization of drug therapy.