Boon-Cher Goh

National University Health System, Singapore

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Publications (52)244.52 Total impact

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    ABSTRACT: We aim to evaluate the influence of covariates, including cytochrome P450 3A (CYP3A) genetic polymorphisms, on the pharmacokinetics of midazolam (MDZ) in Asian cancer patients, using a population pharmacokinetic approach. Pharmacokinetic data were obtained from twenty-four adult cancer patients who received an intravenous bolus dose of 1mg MDZ as a CYP3A phenotyping probe, one day before starting FOLFIRI chemotherapy. Concentrations of MDZ and its major metabolites, 1'-hydroxymidazolam (1OHM) and 1'-hydroxymidazolam glucuronide (HMG) were measured using liquid chromatography/mass spectrometry. The population pharmacokinetic study was conducted using NONMEM. Demographics, clinical characteristics and genetic polymorphisms were screened as covariates. A two-compartment model for MDZ and two sequential compartments representing 1OHM and HMG best described the data. The CYP3A5*3 and total bilirubin level significantly influenced MDZ clearance. The population typical MDZ clearance for CYP3A5*3 expressers was 22% lower than non-expressers. Baseline bodyweight was a statistically significant covariate for clearance and distribution volume of 1OHM. Creatinine clearance was positively correlated with HMG clearance. Our data indicate that CYP3A5*3, total bilirubin, bodyweight and creatinine clearance are important predictors of MDZ and metabolite pharmacokinetics. Further studies in more patients are needed to explore the links between the identified covariates and the disposition of MDZ and its metabolites.
    The Journal of Clinical Pharmacology 11/2013; · 2.84 Impact Factor
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    ABSTRACT: This study evaluated the pharmacokinetics of gabapentin in Chinese subjects who received a diet rich in shiitake mushrooms. Shiitake mushrooms have been shown to contain high amount of ergothioneine. In vitro studies have shown that OCTN1-mediated secretion of gabapentin is trans-stimulated by ergothioneine. This study also investigated the levels of ergothioneine in plasma at baseline and following mushroom consumption. Ten healthy male subjects were recruited and received a diet containing no mushrooms (Treatment A) or a high mushroom diet (Treatment B; after at least a 7-day washout period) 1 day prior to administration of a single oral dose of gabapentin 600 mg. Ingestion of shiitake mushrooms produced significant increases in plasma ergothioneine levels that were sustained for more than 48 hours. A statistically significant but modest increase in the renal clearance (CLR ) of gabapentin occurred after intake of the mushroom diet (91.1±25.1 versus 76.9±20.6 mL/min; P=0.031); no significant changes in AUClast of gabapentin were observed (P=0.726). Creatinine clearance did not correlate with CLR of gabapentin at baseline (Treatment A). After ingestion of the mushroom diet, creatinine clearance accounted for 65.3% of the variance in CLR of gabapentin. These data suggest that diet-drug pharmacokinetic interactions may occur during co-exposure to gabapentin and mushroom constituents. However, as it does not affect the AUClast of gabapentin, it may not have clinically important consequences. Shiitake mushrooms can also be used as a source of ergothioneine for future clinical studies.
    British Journal of Clinical Pharmacology 10/2013; · 3.58 Impact Factor
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    ABSTRACT: Epithelial ovarian cancer (EOC) is hallmarked by a high degree of heterogeneity. To address this heterogeneity, a classification scheme was developed based on gene expression patterns of 1538 tumours. Five, biologically distinct subgroups - Epi-A, Epi-B, Mes, Stem-A and Stem-B - exhibited significantly distinct clinicopathological characteristics, deregulated pathways and patient prognoses, and were validated using independent datasets. To identify subtype-specific molecular targets, ovarian cancer cell lines representing these molecular subtypes were screened against a genome-wide shRNA library. Focusing on the poor-prognosis Stem-A subtype, we found that two genes involved in tubulin processing, TUBGCP4 and NAT10, were essential for cell growth, an observation supported by a pathway analysis that also predicted involvement of microtubule-related processes. Furthermore, we observed that Stem-A cell lines were indeed more sensitive to inhibitors of tubulin polymerization, vincristine and vinorelbine, than the other subtypes. This subtyping offers new insights into the development of novel diagnostic and personalized treatment for EOC patients.
    EMBO Molecular Medicine 05/2013; · 7.80 Impact Factor
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    ABSTRACT: A sensitive analytical method has been developed and validated for the quantification of L-ergothioneine in human plasma and erythrocytes by liquid chromatography-tandem mass spectrometry. A commercially available isotope-labeled L-ergothioneine-d9 is used as the internal standard. A simple protein precipitation with acetonitrile is utilized for bio-sample preparation prior to analysis. Chromatographic separation of L-ergothioneine is conducted using gradient elution on Alltime C18 (150 mm × 2.1 mm, 5 µ). The run time is 6 min at a constant flow rate of 0.45 ml/min. The mass spectrometer is operated under a positive electrospray ionization condition with multiple reaction monitoring mode. The mass transitions of L-ergothioneine and L-ergothioneine-d9 are m/z 230 > 127 and m/z 239 > 127, respectively. Excellent linearity [coefficient of determination (r(2) ) ≥ 0.9998] can be achieved for L-ergothioneine quantification at the ranges of 10 to 10 000 ng/ml, with the intra-day and inter-day precisions at 0.9-3.9% and 1.3-5.7%, respectively, and the accuracies for all quality control samples between 94.5 and 101.0%. This validated analytical method is suitable for pharmacokinetic monitoring of L-ergothioneine in human and erythrocytes. Based on the determination of bio-samples from five healthy subjects, the mean concentrations of L-ergothioneine in plasma and erythrocytes are 107.4 ± 20.5 ng/ml and 1285.0 ± 1363.0 ng/ml, respectively. Copyright © 2013 John Wiley & Sons, Ltd.
    Biological Mass Spectrometry 03/2013; 48(3):406-412. · 3.41 Impact Factor
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    ABSTRACT: Belinostat is a hydroxamate class HDAC inhibitor that has demonstrated activity in peripheral T-cell lymphoma and is undergoing clinical trials for non-hematologic malignancies. We studied the pharmacokinetics of belinostat in hepatocellular carcinoma patients to determine the main pathway of metabolism of belinostat. The pharmacokinetics of belinostat in liver cancer patients were characterized by rapid plasma clearance of belinostat with extensive metabolism with more than 4-fold greater relative systemic exposure of major metabolite, belinostat glucuronide than that of belinostat. There was significant interindividual variability of belinostat glucuronidation. The major pathway of metabolism involves UGT1A1-mediated glucuronidation and a good correlation has been identified between belinostat glucuronide formation and glucuronidation of known UGT1A1 substrates. In addition, liver microsomes harboring UGT1A1*28 alleles have lower glucuronidation activity for belinostat compared to those with wildtype UGT1A1. The main metabolic pathway of belinostat is through glucuronidation mediated primarily by UGT1A1, a highly polymorphic enzyme.
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    ABSTRACT: Belinostat is a hydroxamate class HDAC inhibitor that has demonstrated activity in peripheral T-cell lymphoma and is undergoing clinical trials for non-hematologic malignancies. We studied the pharmacokinetics of belinostat in hepatocellular carcinoma patients to determine the main pathway of metabolism of belinostat. The pharmacokinetics of belinostat in liver cancer patients were characterized by rapid plasma clearance of belinostat with extensive metabolism with more than 4-fold greater relative systemic exposure of major metabolite, belinostat glucuronide than that of belinostat. There was significant interindividual variability of belinostat glucuronidation. The major pathway of metabolism involves UGT1A1-mediated glucuronidation and a good correlation has been identified between belinostat glucuronide formation and glucuronidation of known UGT1A1 substrates. In addition, liver microsomes harboring UGT1A1*28 alleles have lower glucuronidation activity for belinostat compared to those with wildtype UGT1A1. The main metabolic pathway of belinostat is through glucuronidation mediated primarily by UGT1A1, a highly polymorphic enzyme. The clinical significance of this finding remains to be determined. TRIAL REGISTRATION: ClinicalTrials.gov NCT00321594.
    PLoS ONE 01/2013; 8(1):e54522. · 3.73 Impact Factor
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    ABSTRACT: AIM: Aldo-ketoreductases have been implicated in the metabolism of doxorubicin. We sought to assess the influence of AKR1C3 genetic variants on doxorubicin metabolism. METHODS: We sequenced AKR1C3 exon 5 and genotyped 7 functional SNPs in CBR3, ABCB1, and SLC22A16 involved in doxorubicin pharmacology in 151 Asian breast cancer patients treated with doxorubicin-containing chemotherapy, and correlated these genotypes with doxorubicin pharmacokinetics and pharmacodynamics. RESULTS: Two previously reported AKR1C3 intronic variants, IVS4-212 C>G and IVS4+218 G>A were detected. AKR1C3 IVS4-212 GG genotype was associated with significantly lower cycle 1 day 15 leucocyte (mean leucocyte 2.49±1.57x10(9) /L vs 3.85±3.42x10(9) /L, p=0.007) and neutrophil count (mean neutrophil 0.70±1.01x10(9) /L vs 1.56±2.80x10(9) /L, p=0.008), and significant improvement of progression-free survival (mean PFS 49.0 [95% CI 42.2-55.8] vs 31.0 [95% CI 20.7-41.2] months, p=0.017) and overall survival (mean OS 64.4 [95% CI 58.3-70.5] vs 46.3 [95% CI 35.1-57.5] months, p=0.006) compared to those carrying at least one C allele. There was no significant association between AKR1C3 IVS4-212 C>G and doxorubicin pharmacokinetics. For the other 7 SNPs genotyped, CBR3 G11A correlated with doxorubicinol AUC and OS, ABCB1 G2677T/A with doxorubicin clearance and platelet toxicity, while ABCB1 IVS26+59T>G correlated with OS. AKR1C3 IVS4-212C>G remained significantly correlated with both PFS and OS on multivariate analysis with clinical prognosticators. CONCLUSION: AKR1C3 IVS4-212 GG genotype was associated with greater hematologic toxicity, longer progression-free and overall survival after doxorubicin-based therapy, suggesting potential interaction of this variant with doxorubicin metabolism.
    British Journal of Clinical Pharmacology 11/2012; · 3.58 Impact Factor
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    ABSTRACT: The mechanism by which cells decide to skip mitosis to become polyploid is largely undefined. Here we used a high-content image-based screen to identify small-molecule probes that induce polyploidization of megakaryocytic leukemia cells and serve as perturbagens to help understand this process. Our study implicates five networks of kinases that regulate the switch to polyploidy. Moreover, we find that dimethylfasudil (diMF, H-1152P) selectively increased polyploidization, mature cell-surface marker expression, and apoptosis of malignant megakaryocytes. An integrated target identification approach employing proteomic and shRNA screening revealed that a major target of diMF is Aurora kinase A (AURKA). We further find that MLN8237 (Alisertib), a selective inhibitor of AURKA, induced polyploidization and expression of mature megakaryocyte markers in acute megakaryocytic leukemia (AMKL) blasts and displayed potent anti-AMKL activity in vivo. Our findings provide a rationale to support clinical trials of MLN8237 and other inducers of polyploidization and differentiation in AMKL.
    Cell 08/2012; 150(3):575-89. · 31.96 Impact Factor
  • Ying-Kiat Zee, Boon-Cher Goh, Soo-Chin Lee
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    ABSTRACT: Drug interactions may be exploited to overcome pharmacokinetic issues in order to improve the therapeutic index of a drug, with clinical goals of reducing the dose of the active drug while preserving efficacy or reducing toxicity. This strategy has been used in infectious disease and transplant medicine, and, more recently, in oncology. Pharmacologic modulation strategies range from coadministration of either a drug that inhibits a metabolizing enzyme that would inactivate the drug of interest, a drug that induces an enzyme that activates the drug of interest or a drug that inhibits transporters that affect the uptake or elimination of the drug of interest. This review will discuss pharmacologic modulation strategies that have been tested clinically in order to increase systemic drug exposure. Important examples include ketoconazole inhibition of hepatic CYP3A4 in order to increase systemic exposure to docetaxel, irinotecan and etoposide, and cyclosporine inhibition of intestinal ATP-binding cassette transporters in order to decrease the toxicity of irinotecan and increase the bioavailability of oral docetaxel, paclitaxel and topotecan.
    Future Oncology 06/2012; 8(6):731-49. · 3.20 Impact Factor
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    ABSTRACT: Uridine diphosphoglucuronosyltransferases (UGTs) 1A6 is the only UGT1A isoform expressed in lung tissue. It is responsible for the detoxification of carcinogens such as benezo[a]pyrene from cigarette smoke. The purpose of this study was to evaluate the association of UGT1A6 polymorphisms and haplotypes with lung cancer risk and to evaluate the functional significance of UGT1A6 polymorphisms. Genomic DNA was isolated from leukocytes. Eight UGT1A6 polymorphisms were sequenced in a test set of 72 Chinese lung cancer patients and 62 healthy controls. Potential risk modifying alleles were validated in a separate set of 95 Chinese lung cancer patients and 100 healthy controls. UGT1A6 19T>G, 541A>G and 552A>C showed significant association with increased lung cancer risk, while UGT1A6 105C>T and IVS1+130G>T were significantly associated with reduced lung cancer risk. Multivariate logistic regression analysis demonstrated a significant association of lung cancer with UGT1A6 541A>G (OR: 3.582, 95% CI: 1.27-10.04, p = 0.015), 552A>C (OR: 5.364, 95% CI: 1.92-14.96, p = 0.001) and IVS1+130G>T (OR: 0.191, 95% CI: 0.09-0.36, p<0.001). Functional test demonstrated that UGT1A6 105C>T increased mRNA stability, providing a plausible explanation of its association with reduced lung cancer risk. Thus UGT1A6 polymorphisms may be used to identify people with increased risk of developing lung cancer.
    PLoS ONE 01/2012; 7(8):e42873. · 3.73 Impact Factor
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    ABSTRACT: A novel and specific liquid chromatography-tandem mass spectrometric method (LC-MS/MS) was developed and validated for the quantification of hydroxychloroquine in human blood using its stable labeled isotope, hydroxychloroquine-d4 as the internal standard. Chromatographic separation of analytes was achieved using an Agilent ZORBAX Eclipse XDB - C8 analytical HPLC column (50 mm × 2.1 mm, 5 μm). The mobile phase comprising water containing 0.1% formic acid-acetonitrile (94:6, v/v) was delivered isocratically at a flow rate of 0.5 mL/min. The column effluent was detected by API 4000 triple quadrupole mass spectrometer using electrospray ionization (ESI) and monitored by multiple reaction monitoring with positive mode. The precursor to product ion transitions of m/z 336 → 247 and m/z 340 → 251 were used to measure the analyte and IS, respectively. The assay demonstrated a good linear dynamic range of 5-2000 ng/mL for hydroxychloroquine in human blood, with coefficient of determination (r(2)) of =0.9999. The values for intra-day and inter-day precisions of hydroxychloroquine were ≤ 7.86% with the accuracies ranged from 93.8% to 107.6%. The chromatographic run time was 3 min, making it possible to achieve a high throughput analysis. This method was used as a bio-analytical tool in a phase I clinical trial to quantify blood hydroxychloroquine concentrations in patients with non-small cell lung cancer receiving both hydroxychloroquine and gefitinib in their treatment.
    Journal of pharmaceutical and biomedical analysis 12/2011; 61:86-92. · 2.45 Impact Factor
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    ABSTRACT: Raltegravir is a potent inhibitor of HIV integrase. Persistently high intracellular concentrations of raltegravir may explain sustained efficacy despite high pharmacokinetic variability. We performed a pharmacokinetic study of healthy volunteers. Paired blood samples for plasma and peripheral blood mononuclear cells (PBMCs) were collected predose and 4, 8, 12, 24, and 48 h after a single 400-mg dose of raltegravir. Samples of plasma only were collected more frequently. Raltegravir concentrations were determined using liquid chromatography-mass spectrometry. The lower limits of quantitation for plasma and PBMC lysate raltegravir were 2 nmol/liter and 0.225 nmol/liter, respectively. Noncompartmental analyses were performed using WinNonLin. Population pharmacokinetic analysis was performed using NONMEM. Six male subjects were included in the study; their median weight was 67.4 kg, and their median age was 33.5 years. The geometric mean (GM) (95% confidence interval shown in parentheses) maximum concentration of drug (C(max)), area under the concentration-time curve from 0 to 12 h (AUC(0-12)), and area under the concentration-time curve from 0 h to infinity (AUC(0-∞)) for raltegravir in plasma were 2,246 (1,175 to 4,294) nM, 10,776 (5,770 to 20,126) nM · h, and 13,119 (7,235 to 23,788) nM · h, respectively. The apparent plasma raltegravir half-life was 7.8 (5.5 to 11.3) h. GM intracellular raltegravir C(max), AUC(0-12), and AUC(0-∞) were 383 (114 to 1,281) nM, 2,073 (683 to 6,290) nM · h, and 2,435 (808 to 7,337) nM · h (95% confidence interval shown in parentheses). The apparent intracellular raltegravir half-life was 4.5 (3.3 to 6.0) h. Intracellular/plasma ratios were stable for each patient without significant time-related trends over 48 h. Population pharmacokinetic modeling yielded an intracellular-to-plasma partitioning ratio of 11.2% with a relative standard error of 35%. The results suggest that there is no intracellular accumulation or persistence of raltegravir in PBMCs.
    Antimicrobial Agents and Chemotherapy 09/2011; 55(9):4090-5. · 4.57 Impact Factor
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    ABSTRACT: Vorinostat, a histone deacetylase inhibitor being actively evaluated in solid tumors, is metabolized by UGT2B17. UGT2B17 null genotype (UGT2B17*2) has been shown in vitro to reduce UGT2B17 activity. This variant is common in Asians but rare in Caucasians, and we studied its impact on vorinostat pharmacokinetics and pharmacodynamics in a clinical study in Asian patients with metastatic breast cancer. Eligible patients received 400 mg of vorinostat monotherapy daily in a lead-in phase I followed by a phase II study. Patients were genotyped for UGT2B17*2, which was correlated with vorinostat pharmacokinetics and clinical outcomes. Twenty-six patients were treated with no complete response, one partial response, six stable disease lasting for 12 weeks or more, and 19 progressive disease. Sixteen patients (62%) were UGT2B17*2 homozygotes and had significantly lower mean area under the curve ratio of vorinostat-O-glucuronide/vorinostat (1.84 vs. 2.51 on day 1, P=0.02; 1.63 vs. 2.38 on day 15, P=0.028), and trended toward having higher vorinostat area under the curve (399.02 vs. 318.40, P=0.188), more serious adverse events (31 vs. 0%, P=0.121), higher clinical benefit rate (40 vs. 10%, P=0.179), and longer median progression-free survival (3.0 vs. 1.5 months, P=0.087) than patients with at least one wild-type allele. UGT2B17*2 genotype reduces vorinostat glucuronidation and may increase vorinostat efficacy and toxicity. These observations are important in the development of vorinostat, and may have clinical implications on other cancer and noncancer drugs that are UGT2B17 substrates such as exemestane and ibuprofen.
    Pharmacogenetics and Genomics 08/2011; 21(11):760-8. · 3.61 Impact Factor
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    ABSTRACT: Nasopharyngeal carcinoma is endemic in Asia and angiogenesis is important for growth and progression. We hypothesized that pazopanib would have antiangiogenic activity in nasopharyngeal carcinoma. A single arm monotherapy study of pazopanib in patients with WHO type II/III nasopharyngeal carcinoma who had metastatic/recurrent disease and failed at least one line of chemotherapy. A Simon's optimal 2-stage design was used. Patients with Eastern Cooperative Oncology Group (ECOG) 0-2 and adequate organ function were treated with pazopanib 800 mg daily on a 21-day cycle. The primary endpoint was clinical benefit rate (CR/PR/SD) achieved after 12 weeks of treatment. Secondary endpoints included toxicity and progression-free survival. Exploratory studies of dynamic-contrast enhanced computed tomography (DCE-CT) paired with pharmacokinetics (PK) of pazopanib was done. Thirty-three patients were accrued. Patients were ECOG 0-1 with median age of 50 years (range 36-68). There were 2 (6.1%) partial responses, 16 (48.5%) stable disease, 11 (33.3%) progressive disease, 4 (12.1%) were not evaluable for response. The clinical benefit rate was 54.5% (95% CI: 38.0-70.2). Ten patients (30.3%) received more than 6 cycles (4 months) of treatment and 7 (21.2%) had PR/SD that lasted at least 6 months. One patient each died from epistaxis and myocardial infarction. Common grade 3/4 toxicities included fatigue (15.2%), hand-foot syndrome (15.2%), anorexia (9.1%), diarrhea (6.1%), and vomiting (6.1%). Serial DCE-CT scans show significant reductions in tumor blood flow, permeability surface area product, and fractional intravascular blood volume. Pazopanib showed encouraging activity in heavily pretreated nasopharyngeal carcinoma with an acceptable toxicity profile.
    Clinical Cancer Research 06/2011; 17(16):5481-9. · 7.84 Impact Factor
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    ABSTRACT: A novel, rapid and specific liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed and validated for the simultaneous quantification of gefitinib and its predominant metabolite, O-desmethyl gefitinib in human plasma. Chromatographic separation of analytes was achieved on an Alltima C18 analytical HPLC column (150 mm × 2.1 mm, 5 μm) using an isocratic elution mode with a mobile phase comprised acetonitrile and 0.1% formic acid in water (30:70, v/v). The flow rate was 300 μL/min. The chromatographic run time was 3 min. The column effluents were detected by API 4000 triple quadrupole mass spectrometer using electrospray ionization (ESI) in positive mode. Linearity was demonstrated in the range of 5-1000 ng/mL for gefitinib and 5-500 ng/mL for O-desmethyl gefitinib. The intra- and inter-day precisions for gefitinib and O-desmethyl gefitinib were ≤10.8% and the accuracies ranged from 89.7 to 104.7% for gefitinib and 100.4 to 106.0% for O-desmethyl gefitinib. This method was used as a bioanalytical tool in a phase I clinical trial to investigate the possible effect of hydroxychloroquine on the pharmacokinetics of gefitinib. The results of this study enabled clinicians to ascertain the safety of the combination therapy of hydroxychloroquine and gefitinib in patients with advanced (Stage IIIB-IV) non-small cell lung cancer (NSCLC).
    Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 06/2011; 879(22):2155-61. · 2.78 Impact Factor
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    ABSTRACT: SB939 is an oral histone deacetylase (HDAC) inhibitor currently in phase II clinical trials potently inhibiting class I, II, and IV HDACs with favorable pharmacokinetic properties, resulting in tumor tissue accumulation. To show target efficacy, a Western blot assay measuring histone H3 acetylation (acH3) relative to a loading control was developed, validated on cancer cell lines, peripheral blood mononuclear cells (PBMC), and in animal tumor models. Exposure of cells to 60 nmol/L (22 ng/mL) SB939 for 24 hours was sufficient to detect an acH3 signal in 25 μg of protein lysate. AcH3 levels of liver, spleen, PBMCs, bone marrow and tumor were measured in BALB/c mice, HCT-116 xenografted BALB/c nude mice, or in SCID mice orthotopically engrafted with AML (HL-60) after oral treatment with SB939. AcH3 could only be detected after treatment. In all tissues, the highest signal detected was at the 3-hour time point on day 1. On day 15, the signal decreased in normal tissues but increased in cancerous tissues and became detectable in the bone marrow of leukemic mice. In all tissues, acH3 correlated with SB939 dose levels (r(2)=0.76-0.94). When applied to PBMCs from 30 patients with advanced solid malignancies in a phase I clinical trial, a dose-dependent (10-80 mg) increase in relative acH3 was observed 3-hour postdose on day 1, correlating with C(max) and AUC of SB939 concentrations in plasma (r=0.97, P=0.014). Our data show that the favorable pharmacokinetic and pharmacodynamic properties of SB939 are translated from preclinical models to patients.
    Molecular Cancer Therapeutics 05/2011; 10(7):1207-17. · 5.60 Impact Factor
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    ABSTRACT: S-1 is an oral fluoropyrimidine anti-neoplastic agent that is converted by CYP2A6 to 5-fluorouracil (5FU). We prospectively studied the pharmacokinetics and pharmacodynamics of S-1 in two groups of East Asian and Caucasian patients with solid malignancy refractory to standard chemotherapy, or for which 5FU was indicated, to elucidate differences in relation to CYP2A6 genotype and phenotype. S-1 was given orally at 30 mg/m(2) b.i.d. for 14 days every 21 days. Dose normalized AUC(0-48 h) for tegafur (P = 0.05) and gimeracil (P = 0.036) were higher in East Asians; conversely, AUC(0-48 h) of fluoro-β-alanine was higher in Caucasians (P = 0.044). Exposure to 5FU was similar in both groups (P = 0.967). Mean cotinine:nicotine ratio was 54% higher in the Caucasian group (P = 0.03), and correlated with oral clearance of tegafur (r = 0.59; P = 0.002). Grade 3/4 gastrointestinal toxicities were more common in Caucasians than Asians (21%vs 0%). Treatment with S-1 yields no significant difference in 5FU exposure between Caucasians and East Asians.
    Cancer Science 02/2011; 102(2):478-83. · 3.48 Impact Factor
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    ABSTRACT: Raltegravir is a highly efficacious inhibitor of HIV integrase. Large pharmacokinetic variability has been reported in clinical trials and this could be due to glucuronidation of raltegravir, the only reported metabolism pathway. In order to precisely evaluate and monitor the raltegravir and raltegravir glucuronide simultaneously, a novel, sensitive and robust liquid chromatography-tandem mass spectrometric method was developed and validated for simultaneous determination of raltegravir and raltegravir glucuronide in human plasma. A simple protein precipitation with acetonitrile was utilized for plasma sample preparation prior to analysis. Baseline chromatographic separation was achieved on a ZORBAX Eclipse XDB-C8 using gradient elution mode. The run time was 9 min at a constant flow rate of 0.4 ml/min. The mass spectrometer was operated under a positive electrospray ionization condition. Excellent linearity (r(2) ≥ 0.9997) was achieved for raltegravir and raltegravir glucuronide in the range of 2-2000 nmol/l. The average recovery of raltegravir and raltegravir glucuronide was 105.8% and 102.2%, respectively. The precision (coefficient of variation) was 1.6-6.6% for raltegravir and 2.1-6.9 for raltegravir glucuronide, respectively. The accuracy was 98.6-106.1% for raltegravir and 96.3-100.3% for raltegravir glucuronide. The plasma samples were tested to be stable after nine freeze-thaw cycles and exposure to room temperature for 24 h. This well-validated assay was applied for the quantification of raltegravir and raltegravir glucuronide in plasma samples within 24 h after a single oral dose of 400 mg raltegravir in six healthy subjects.
    Biological Mass Spectrometry 02/2011; 46(2):202-8. · 3.41 Impact Factor
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    ABSTRACT: Gemcitabine/carboplatin is efficacious in breast cancer but results in significant hematologic toxicities. We employed a multi-gene approach to identify variants to predict its toxicities. Twenty-six gemcitabine and platinum-based DNA repair pathway polymorphisms were correlated with gemcitabine pharmacokinetics, hematologic toxicities, response and survival in 41 Asian breast cancer patients receiving gemcitabine/carboplatin. The combined effects of solute carrier family (SLC)28A1+1528C>T and thymidylate synthetase (TYMS)+1494del6 significantly influenced hematologic toxicities: 89% of patients who possessed either SLC28A1+1528TT or TYMS+1494ins6/ins6 (n=9) developed grade 4 thrombocytopenia, versus 14% with neither genotype (n=29; p<0.001). In concordance, all patients who possessed either genotype developed grade 3/4 neutropenia, compared to 38% with neither genotype (p=0.001). None of the other genetic variants analyzed correlated with drug pharmacokinetics and pharmacodynamics. Approximately one-quarter of our Asian cohort carried SLC28A1+1528TT or TYMS+1494ins6/ins6, which are associated with increased myelotoxicity from gemcitabine/carboplatin. This has potential utility in treatment selection and genotype-based dosing strategies.
    Cancer genomics & proteomics. 01/2011; 8(5):255-9.
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    ABSTRACT: A novel, sensitive and reliable liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed and validated for the determination of belinostat (PXD101) in human plasma. Oxamflatin was used as the internal standard. Liquid-liquid extraction of the plasma sample was performed using tert-butyl methyl ether as the organic solvent. Chromatographic separation was achieved on a BDS Hypersil C18 column (2.1 mm x1 00 mm, 5 microm) using gradient elution mode using 0.05% formic acid in water and 0.05% formic acid in acetonitrile as solvents A and B, respectively, 60/40. The run time was 6 min. The mass spectrometer was operated under a positive electrospray ionization condition and a multiple reaction monitoring mode. An excellent linear calibration was achieved in the range of 0.5-1000 ng/mL. An average recovery of belinostat for four quality controls was 72.6% and the recovery of the internal standard at 1000 ng/mL was 67.8%. The intra-day and inter-day precisions for belinostat were <or=8.0 and <or=10.3%, respectively, and their accuracy ranged from 100.2 to 106.7%. No significant matrix effect was identified. In analysis of patient samples, belinostat glucuronide was identified and baseline separated from belinostat. This well-validated assay has been applied for quantification of belinostat in plasma samples within 24h after the start of infusion for Asian hepatocellular carcinoma patients in a dose escalation study.
    Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 09/2010; 878(26):2409-14. · 2.78 Impact Factor

Publication Stats

767 Citations
244.52 Total Impact Points

Institutions

  • 2013
    • National University Health System
      Singapore
  • 2012
    • National University Cancer Institute
      Tumasik, Singapore
  • 2006–2011
    • National University of Singapore
      • • Department of Pharmacology
      • • Division of Haematology & Oncology
      Tumasik, Singapore
  • 2009
    • University of North Carolina at Chapel Hill
      North Carolina, United States
  • 2002–2009
    • National University Hospital - NUH
      Singapore