Biomedical subjects

Sui Yung Chan

Publications and source records attributed to Sui Yung Chan.

At least 19 recordsLinked to original sources

PubMed2006

Authentication of traditional Chinese medicine using infrared spectroscopy: distinguishing between ginseng and its morphological fakes.

The quality of pharmaceutical products such as ginseng is important for ensuring consumer safety and efficacy. Ginseng is an expensive herb, and adulteration with other cheaper products may occur. Quality assurance of ginseng is needed since many of its commercial products now come in various formulations such as capsules, powder, softgels and tea. Thus traditional means of authentication via smell, taste or physical appearance are hardly reliable. Herbs like ginseng tend to exhibit characteristic infrared fingerprints due to their different chemical constituents. Here we report for the first time a rapid means of distinguishing American and Asian ginsengs from two morphological fakes--sawdust and Platycodon grandiflorum, via pattern differences and principal component analysis of their infrared spectra. Our results show that ginseng can be distinguished from both sawdust and Platycodon grandiflorum, hence there is a potential of using infrared spectroscopy as a novel analytical technique in the authentication of ginseng.

Drugs, Chinese Herbal↗

PubMed2006

The role of the activin system in keloid pathogenesis.

Keloid scars represent a pathological response to cutaneous injury under the regulation of many growth factors. Activin-A, a dimeric protein and a member of the transforming growth factor-beta superfamily, has been shown to regulate various aspects of cell growth and differentiation in the repair of the skin mesenchyme and the epidermis. Thus our aim was to study the role of activin and its antagonist, follistatin, in keloid pathogenesis. Increased mRNA expression for activin was observed in keloid scar tissue by performing RNase protection assay. Immunohistochemistry showed increased localization of both activin-A and follistatin in the basal layer of epidermis of keloid tissue compared with normal tissue. ELISA demonstrated a 29-fold increase in concentration of activin-A and an approximately 5-fold increase in follistatin in conditioned media in keloid fibroblasts compared with normal fibroblasts. Although keloid keratinocytes produced 25% more follistatin than normal keratinocytes, the amounts of activin-A, in contrast, was approximately 77% lower. Proliferation of fibroblasts was stimulated when treated with exogenous activin-A (46% increase in keloids fibroblasts) or following co-culture with hbetaAHaCaT cells (66% increase). Activin-A upregulated key extracellular matrix components, namely collagen, fibronectin, and alpha-smooth muscle actin, in normal and keloid fibroblasts. Co-treatment of follistatin with activin-A blocked the stimulatory effects of activin on extracellular matrix components. These findings emphasize the importance of the activin system in keloid biology and pathogenesis and suggest a possible therapeutic potential of follistatin in the prevention and treatment of keloids.

Activins↗

PubMed2006

St. John's wort attenuates irinotecan-induced diarrhea via down-regulation of intestinal pro-inflammatory cytokines and inhibition of intestinal epithelial apoptosis.

Diarrhea is a common dose-limiting toxicity associated with cancer chemotherapy, in particular for drugs such as irinotecan (CPT-11), 5-fluouracil, oxaliplatin, capecitabine and raltitrexed. St. John's wort (Hypericum perforatum, SJW) has anti-inflammatory activity, and our preliminary study in the rat and a pilot study in cancer patients found that treatment of SJW alleviated irinotecan-induced diarrhea. In the present study, we investigated whether SJW modulated various pro-inflammatory cytokines including interleukins (IL-1beta, IL-2, IL-6), interferon (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) and intestinal epithelium apoptosis in rats. The rats were treated with irinotecan at 60 mg/kg for 4 days in combination with oral SJW or SJW-free control vehicle at 400 mg/kg for 8 days. Diarrhea, tissue damage, body weight loss, various cytokines including IL-1beta, IL-2, IL-6, IFN-gamma and TNF-alpha and intestinal epithelial apoptosis were monitored over 11 days. Our studies demonstrated that combined SJW markedly reduced CPT-11-induced diarrhea and intestinal lesions. The production of pro-inflammatory cytokines such as IL-1beta, IFN-gamma and TNF-alpha was significantly up-regulated in intestine. In the mean time, combined SJW significantly suppressed the intestinal epithelial apoptosis induced by CPT-11 over days 5-11. In particular, combination of SJW significantly inhibited the expression of TNF-alpha mRNA in the intestine over days 5-11. In conclusion, inhibition of pro-inflammatory cytokines and intestinal epithelium apoptosis partly explained the protective effect of SJW against the intestinal toxicities induced by irinotecan. Further studies are warranted to explore the potential for STW as an agent in combination with chemotherapeutic drugs to lower their dose-limiting toxicities.

Animals↗

PubMed2006

A mechanistic study of the intestinal absorption of cryptotanshinone, the major active constituent of Salvia miltiorrhiza.

The nature of intestinal absorption of most herbal medicine is unknown. Cryptotanshinone (CTS) is the principal active constituent of the widely used cardiovascular herb Salvia miltiorrhiza (Danshen). We investigated the oral bioavailability of CTS in rats and the mechanism for its intestinal absorption using several in vitro and in vivo models: 1) Caco-2 cell monolayers; 2) monolayers of MDCKII cells overexpressing P-glycoprotein (PgP); and 3) single-pass rat intestinal perfusion with mesenteric vein cannulation. The systemic bioavailabilities of CTS after oral and intraperitoneal administration at 100 mg/kg were 2.05 and 10.60%, respectively. In the perfused rat intestinal model, permeability coefficients based on CTS disappearance from the luminal perfusate (Plumen) were 6.7- to 10.3-fold higher than permeability coefficients based on drug appearance in venous blood (Pblood). Pblood significantly increased in the presence of the P-gP inhibitor, verapamil. CTS transport across Caco-2 monolayers was pH-, temperature- and ATP-dependent. The transport from the apical (AP) to the basolateral (BL) side was 3- to 9-fold lower than that from the BL to the AP side. Inclusion of verapamil (50 microM) in both AP and BL sides abolished the polarized CTS transport across Caco-2 cells. Moreover, CTS was significantly more permeable in the BL to AP than in the AP to BL direction in MDCKII and MDR1-MDCKII cells. The permeability coefficients in the BL to AP direction were significantly higher in MDCKII cells overexpressing PgP. These findings indicate that CTS is a substrate for PgP that can pump CTS into the luminal side.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2006

Relationship between genotype and enzyme activity of glutathione S-transferases M1 and P1 in Chinese.

Glutathione S-transferases (GSTs) are the major detoxifying Phase II enzyme for eliminating electrophilic compounds. Mutations in GSTM1, GSTP1 and GSTT1 in Caucasian and GSTA1 in Chinese have been found to reduce enzyme activity. However, data on the impact of common genetic polymorphisms of GSTM1 and GSTP1 on enzyme activity in Chinese is lacking. This study aimed to investigate the effect of common GSTP1 and GSTM1 polymorphisms on erythrocyte GST activity in healthy Chinese (n = 196). GSTM1 null mutation (GSTM1*0) was analyzed by a PCR-Multiplex procedure, whereas GSTP1 313A-->G polymorphism (resulting in Ile105Val at codon 105) was analyzed by PCR-restriction fragment length polymorphism (RFLP) analysis. Erythrocyte GST activity was measured using 1-chloro-2,4-dinitro-bezene (CDNB) as the model substrate. The frequency of GSTM1 null genotype was 54.3% and the frequency of GSTP1-Ile/Ile, -Ile/Val, and -Val/Val genotype was 60.7%, 35.2% and 4.1%, respectively, with a frequency of 21.7% for the 105 valine allele. Age, gender and smoking did not significantly affect the erythrocyte GST activities. The mean erythrocyte GST enzyme activity for GSTP1*-Ile/Val genotype group (3.53 +/- 0.63U/gHb) was significantly lower than that for subjects with GSTP1-Ile/Ile genotype (4.25 +/- 1.07U/gHb, P = 0.004), while subjects with the GSTP1-Val/Val genotype had the lowest enzyme activity (2.44 +/- 0.67U/gHb). In addition, the GST activity in carriers of GSTM1*0/GSTP1-Ile/Ile was significantly higher than that of subjects inherited GSTM1*0/GSTP1-Ile/Val or GSTM1*0/GSTP1-Val/Val. However, there is no association between GSTM1 null mutation and reduced enzyme activity. GSTP1 codon 105 mutation led to reduced erythrocyte GST activity in Chinese. A combined GSTP1 and GSTM1 null mutations also resulted in significantly reduced GST activity. Further studies are needed to explore the clinical implications of GSTM1 and GSTP1 polymorphisms.

Adult↗

PubMed2006

Limonene GP1/PG organogel as a vehicle in transdermal delivery of haloperidol.

Penetration enhancers are a classical means for improving transdermal drug delivery (TDD). Enhancers permeate into the skin and reversibly decrease the barrier resistance. Basically, our aim is to formulate a transdermal gel containing an appropriate enhancer for a controlled drug release. Terpenes, namely limonene, linalool and cineole, in propylene glycol (PG) were first investigated in vitro for their capacity to enhance the percutaneous release of an anti-psychotic drug, haloperidol (HP). Relative to oxygenated linalool and cineole, hydrocarbon limonene was more effective as a skin enhancer; it increased human skin permeability and decreased lag time. Limonene was thus incorporated in an organogel comprised of gelator GP1 and PG. This skin-friendly gel in a transdermal patch could act as a long-acting formulation that delivers HP at a sustained percutaneous rate. The microscopic framework of the organogel is a branched network of interlocking fibres. Varying the gelator content modulates the fibre density and gel stiffness, and presents different degrees of resistance to drug diffusion on the vehicle side. Rheological and permeation studies demonstrated that an increase in gelator concentration increased gel moduli and decreased drug flux simultaneously. The rheology of the gel matrix influenced drug release rate in a manner described by several experimentally-derived correlations.

Administration, Cutaneous↗

PubMed2006

Population pharmacokinetics of tacrolimus in whole blood and plasma in asian liver transplant patients.

OBJECTIVES: The objectives of this study were to develop population pharmacokinetic models of tacrolimus in an Asian population with whole blood and plasma drug concentration data, to compare the variability of the pharmacokinetic parameters in these two matrices and to search for the main patient characteristics that explain the variability in pharmacokinetic parameters. STUDY DESIGN: Prospective pharmacokinetic assessment followed by model fitting. PATIENTS: Whole blood samples from 31 liver transplant patients in a local hospital receiving oral tacrolimus as part of their immunosuppressive therapy were assessed. Plasma samples from 29 of the 31 patients were also evaluated. Concentrations of tacrolimus in whole blood and plasma were determined by an electrospray high-performance liquid chromatography with tandem mass spectrometry. Two hundred and thirteen whole blood and 157 plasma tacrolimus concentrations were used for building two nonlinear mixed-effects population models to describe the disposition of tacrolimus in whole blood and plasma, respectively. Covariates that were investigated included demographic characteristics, biological markers of liver and renal functions, corticosteroid dose and haematological parameter. RESULTS: A one-compartment model was used to describe the whole blood and plasma concentration-time data of tacrolimus after oral administration. For the whole blood population model, the population estimates of the first-order absorption rate constant (k(a)), apparent clearance based on whole blood concentration after oral administration (CL(B)/F) and apparent volume of distribution based on whole blood concentrations after oral administration (V(d,B)/F) were 2.08h(-1), 14.1 L/h and 217L, respectively. The coefficient of variations (CVs) of interpatient variabilities in CL(B)/F and V(d,B)/F were 65.7% and 63.8%, respectively. Bodyweight, liver and renal function influenced CL(B)/F, while height and haematocrit influenced V(d,B)/F. The residual (unexplained) variability was 34.8%. For the plasma population model, the population estimates of the k(a), apparent clearance based on plasma concentrations after oral administration (CL(P)/F) and apparent volume of distribution based on plasma concentrations after oral administration (V(d,P)/F) were 5.21h(-1), 537 L/h and 563L, respectively. The CVs of interpatient variabilities in CL(P)/F and V(d,P)/F were 96.0% and 105.4%, respectively. Bodyweight was found to influence CL(P)/F, while the erythrocyte-to-plasma concentration ratio influenced V(d,P)/F. The residual (unexplained) variability was 49.8% at the mean plasma concentration of 1.1 ng/mL. CONCLUSIONS: Whole blood and plasma population pharmacokinetic models of tacrolimus in Asian adult and paediatric liver transplant patients were developed using prospective data in a clinical setting. This has identified and quantified sources of interindividual variability in CL(B)/F, V(d,B)/F, CL(P)/F and V(d,P)/F of tacrolimus in Asian liver transplant patients. Information derived from the whole blood population model may subsequently be used by clinicians for dosage individualisation through Bayesian forecasting.

Adolescent↗

PubMed2006

Topotecan is a substrate for multidrug resistance associated protein 4.

Topotecan (TPT) is a semisynthetic water-soluble derivative of camptothecin (CPT) used as second-line therapy in patients with metastatic ovarian carcinoma, small cell lung cancer, and other malignancies. However, both dose-limiting toxicity and tumor resistance hinder the clinical use of TPT. The mechanisms for resistance to TPT are not fully defined, but increased efflux of the drug by multiple drug transporters including P-glycoprotein (PgP), multidrug resistance associated protein 1 (MRP1) and breast cancer resistance protein (BCRP) from tumor cells has been highly implicated. This study aimed to investigate whether overexpression of human MRP4 rendered resistance to TPT by examining the cytotoxicity profiles using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide (MTT) assay and cellular accumulation of TPT in HepG2 cells stably overexpressing MRP4. Two kinds of cell lines, HepG2 with insertion of an empty vector plasmid (V/HepG2), HepG2 cells stably expressing MRP4 (MRP4/HepG2), were exposed to TPT for 4 or 48 hr in the absence or presence of various MRP4 inhibitors including DL-buthionine-(S,R)-sulphoximine (BSO), diclofenac, celecoxib, or MK-571. The intracellular accumulation of TPT and paclitaxel (a PgP substrate) by V/HepG2 and MRP4/HepG2 cells was determined by incubation of TPT with the cells and the amounts of the drug in cells were determined by validated HPLC methods. The study demonstrated that MRP4 conferred a 12.03- and 6.86-fold resistance to TPT in the 4- and 48-hr drug-exposure MTT assay, respectively. BSO, MK-571, celecoxib, or diclofenac sensitised MRP4/HepG2 cells to TPT cytotoxicity and partially reversed MRP4-mediated resistance to TPT. In addition, the accumulation of TPT was significantly reduced in MRP4/HepG2 cells compared to V/HepG2 cells, and one-binding site model was found the best fit for the MRP4-mediated efflux of TPT, with an estimated K(m) of 1.66 microM and V(max) of 0.341 ng/min/106 cells. Preincubation of MRP4/HepG2 cells with BSO (200 microM) for 24 hr, celecoxib (50 microM), or MK-571 (100 microM) for 2 hr significantly increased the accumulation of TPT over 10 min in MRP4/HepG2 cells by 28.0%, 37.3% and 32.5% (P < 0.05), respectively. By contrast, there was no significant difference in intracellular accumulation of paclitaxel in V/HepG2 and MRP4/HepG2 cells over 120 min. MRP4 also rendered resistance to adefovir dipivoxil (bis-POM-PMEA) and methotrexate, two reported MRP4 substrates. MRP4 did not exhibit any significant resistance to other model drugs including vinblastine, vincristine, etoposide, carboplatin, cyclosporine and paclitaxel in both long (48 hr) and short (4 hr) drug-exposure MTT assays. These findings indicate that MRP4 confers resistance to TPT and TPT is the substrate for MRP4. Further studies are needed to explore the role of MRP4 in resistance to, toxicity and pharmacokinetics of TPT in cancer patients.

Antineoplastic Agents↗

PubMed2006

Pharmacokinetic mechanisms for reduced toxicity of irinotecan by coadministered thalidomide.

The clinical use of irinotecan (CPT-11) is hindered by dose-limiting diarrhea and myelosuppression. Recent clinical studies indicate that thalidomide, a known tumor necrosis factor-alpha inhibitor, ameliorated the toxicities induced by CPT-11. However, the mechanisms for this are unknown. This study aimed to investigate whether combination of thalidomide modulated the toxicities of CPT-11 using a rat model and the possible role of the altered pharmacokinetic component in the toxicity modulation using in vitro models. The toxicity model was constructed by treatment of healthy rats with CPT-11 at 60 mg/kg per day by intravenous (i.v.) injection. Body weight, acute and delayed-onset diarrhea, blood cell counts, and macroscopic and microscopic intestinal damages were monitored in rats treated with CPT-11 alone or combined therapy with thalidomide at 100 mg/kg administered by intraperitoneal (i.p.) injection. Single dose and 5-day multiple-dose studies were conducted in rats to examine the effects of concomitant thalidomide on the plasma pharmacokinetics of CPT-11 and its major metabolites SN-38 and SN-38 glucuronide (SN-38G). The effect of CPT-11 on thalidomide's pharmacokinetics was also checked. Rat liver microsomes and a rat hepatoma cell line, H4-II-E cells, were used to study the in vitro metabolic interactions between these two drugs. H4-II-E cells were also used to investigate the effect of thalidomide and its hydrolytic products on the transport of CPT-11 and SN-38. In addition, the effect of thalidomide and its hydrolytic products on rat plasma protein binding of CPT-11 and SN-38 was examined. Administration of CPT-11 by i.v. for 4 consecutive days to rats induced significant body weight loss, decrease in neutrophil and lymphocyte counts, severe acute- and delayed-onset diarrhea, and intestinal damages. These toxicities were alleviated when CPT-11 was combined with thalidomide. In both single-dose and 5-day multiple-dose pharmacokinetic study, coadministered thalidomide significantly increased the area under the plasma concentration-time curve (AUC) of CPT-11, but the AUC and elimination half-life (t(1/2)) of SN-38 were significantly decreased. However, CPT-11 did not significantly alter the pharmacokinetics of thalidomide. Thalidomide at 25 and 250 microM and its hydrolytic products at a total concentration of 10 microM had no significant effect on the plasma protein binding of CPT-11 and SN-38, except for that thalidomide at 250 microM caused a significant increase in the unbound fraction (f(u)) of CPT-11 by 6.7% (P < 0.05). The hydrolytic products of thalidomide (total concentration of 10 microM), but not thalidomide, significantly decreased CPT-11 hydrolysis by 16% in rat liver microsomes (P < 0.01). The formation of both SN-38 and SN-38G from CPT-11, SN-38 glucuronidation, or intracellular accumulation of both CPT-11 and SN-38 in H4-II-E cells followed Michaelis-Menten kinetics with the one-binding site model being the best fit for the kinetic data. Coincubation or 2-hr preincubation of thalidomide at 25 microM and 250 microM and its hydrolytic products at 10 microM did not show any significant effects on CPT-11 hydrolysis and SN-38 glucuronidation. However, preincubation of H4-II-E cells with thalidomide (250 microM), its hydrolytic products (total concentration of 10 microM), or phthaloyl glutamic acid (one major thalidomide hydrolytic product, 10 microM) significantly increased the intracellular accumulation of SN-38, but not CPT-11 (P < 0.01). The dose-limiting toxicities of CPT-11 were alleviated by combination with thalidomide in rats and the pharmacokinetic modulation by thalidomide may partially explain its antagonizing effects on the toxicities of CPT-11. The hydrolytic products of thalidomide, instead of the parental drug, modulated the hepatic hydrolysis of CPT-11 and intracellular accumulation of SN-38, probably contributing to the altered plasma pharmacokinetics of CPT-11 and SN-38. Further studies are needed to explore the role of both pharmacokinetics and pharmacodynamic components in the protective effect of thalidomide against the toxicities of CPT-11.

Angiogenesis Inhibitors↗

PubMed2005

Monitoring drug-protein interaction.

A variety of therapeutic drugs can undergo biotransformation via Phase I and Phase II enzymes to reactive metabolites that have intrinsic chemical reactivity toward proteins and cause potential organ toxicity. A drug-protein adduct is a protein complex that forms when electrophilic drugs or their reactive metabolite(s) covalently bind to a protein molecule. Formation of such drug-protein adducts eliciting cellular damages and immune responses has been a major hypothesis for the mechanism of toxicity caused by numerous drugs. The monitoring of protein-drug adducts is important in the kinetic and mechanistic studies of drug-protein adducts and establishment of dose-toxicity relationships. The determination of drug-protein adducts can also provide supportive evidence for diagnosis of drug-induced diseases associated with protein-drug adduct formation in patients. The plasma is the most commonly used matrix for monitoring drug-protein adducts due to its convenience and safety. Measurement of circulating antibodies against drug-protein adducts may be used as a useful surrogate marker in the monitoring of drug-protein adducts. The determination of plasma protein adducts and/or relevant antibodies following administration of several drugs including acetaminophen, dapsone, diclofenac and halothane has been conducted in clinical settings for characterizing drug toxicity associated with drug-protein adduct formation. The monitoring of drug-protein adducts often involves multi-step laboratory procedure including sample collection and preliminary preparation, separation to isolate or extract the target compound from a mixture, identification and determination. However, the monitoring of drug-protein adducts is often difficult because of short half-lives of the protein adducts, sampling problem and lack of sensitive analytical techniques for the protein adducts. Currently, chromatographic (e.g. high performance liquid chromatography) and immunological methods (e.g. enzyme-linked immunosorbent assay) are two major techniques used to determine protein adducts of drugs in patients. The present review highlights the importance for clinical monitoring of drug-protein adducts, with an emphasis on methodology and with a further discussion of the application of these techniques to individual drugs and their target proteins.

Biotransformation↗

PubMed2005

Monitoring of immune responses to a herbal immuno-modulator in patients with advanced colorectal cancer.

Many herbal medicines are widely used as immuno-modulators in Asian countries. Ganoderma lucidum (Lingzhi) is one of the most commonly used herbs in Asia and preclinical studies have established that the polysaccharide fractions of G. lucidum have potent immuno-modulating effects. However, clinical evidence for this is scanty. The present open-labeled study aimed to evaluate the effects of G. lucidum polysaccharides on selected immune functions in patients with advanced colorectal cancer. Forty-seven patients were enrolled and treated with oral G. lucidum at 5.4 g/day for 12 weeks. Selected immune parameters were monitored using various immunological methods throughout the study. In 41 assessable cancer patients, treatment with G. lucidum tended to increase mitogenic reactivity to phytohemagglutinin, counts of CD3, CD4, CD8 and CD56 lymphocytes, plasma concentrations of interleukin (IL)-2, IL-6 and interferon (IFN)-gamma, and NK activity, whereas plasma concentrations of IL-1 and tumor necrosis factor (TNF)-alpha were decreased. For all of these parameters, no statistical significance was observed when a comparison was conducted between baseline and those values after a 12-week treatment with G. lucidum. The changes of IL-1 were correlated with those for IL-6, IFN-gamma, CD3, CD4, CD8 and NK activity (p<0.05) and IL-2 changes were correlated with those for IL-6, CD8 and NK activity. The results indicate that G. lucidum may have potential immuno-modulating effect in patients with advanced colorectal cancer. Further studies are needed to explore the benefits and safety of G. lucidum in cancer patients.

Adult↗

PubMed2005

Insights into oxazaphosphorine resistance and possible approaches to its circumvention.

The oxazaphosphorines cyclophosphamide, ifosfamide and trofosfamide remain a clinically useful class of anticancer drugs with substantial antitumour activity against a variety of solid tumors and hematological malignancies. A major limitation to their use is tumour resistance, which is due to multiple mechanisms that include increased DNA repair, increased cellular thiol levels, glutathione S-transferase and aldehyde dehydrogenase activities, and altered cell-death response to DNA damage. These mechanisms have been recently re-examined with the aid of sensitive analytical techniques, high-throughput proteomic and genomic approaches, and powerful pharmacogenetic tools. Oxazaphosphorine resistance, together with dose-limiting toxicity (mainly neutropenia and neurotoxicity), significantly hinders chemotherapy in patients, and hence, there is compelling need to find ways to overcome it. Four major approaches are currently being explored in preclinical models, some also in patients: combination with agents that modulate cellular response and disposition of oxazaphosphorines; antisense oligonucleotides directed against specific target genes; introduction of an activating gene (CYP3A4) into tumor tissue; and modification of dosing regimens. Of these approaches, antisense oligonucleotides and gene therapy are perhaps more speculative, requiring detailed safety and efficacy studies in preclinical models and in patients. A fifth approach is the design of novel oxazaphosphorines that have favourable pharmacokinetic and pharmacodynamic properties and are less vulnerable to resistance. Oxazaphosphorines not requiring hepatic CYP-mediated activation (for example, NSC 613060 and mafosfamide) or having additional targets (for example, glufosfamide that also targets glucose transport) have been synthesized and are being evaluated for safety and efficacy. Characterization of the molecular targets associated with oxazaphosphorine resistance may lead to a deeper understanding of the factors critical to the optimal use of these agents in chemotherapy and may allow the development of strategies to overcome resistance.

Animals↗

PubMed2005

Simultaneous determination of the lactone and carboxylate forms of irinotecan (CPT-11) and its active metabolite SN-38 by high-performance liquid chromatography: application to plasma pharmacokinetic studies in the rat.

Irinotecan (CPT-11) and its main metabolite SN-38 are potent anticancer derivatives of camptothecin (CPT), with active lactone and inactive carboxylate forms coexisting. A simple and sensitive HPLC method using the ion-pairing reagent tetrabutylammonium hydrogen sulfate (TBAHS) was developed to simultaneously determine all four analytes in rat plasma samples. Camptothecin (CPT) was used as internal standard. The mobile phase was 0.1M potassium dihydrogen phosphate containing 0.01 M TBAHS (pH 6.4)-acetonitrile (75:25, v/v). Separation of the compounds was carried out on a Hypersil C18 column, monitored at 540 nm (excitation wavelength at 380 nm). All four compounds gave linear response as a function of concentration over 0.01-10 microM. The limit of quantitation in rat plasma was 0.01, 0.008, 0.005 and 0.005 microM for CPT-11 lactone, CPT-11 carboxylate, SN-38 lactone and SN-38 carboxylate, respectively. The method was successfully used in the study on the effect of coadministered thalidomide on the plasma pharmacokinetics of CPT-11 and SN-38 in rats. Coadministered thalidomide (100mg/kg body weight by intraperitoneal injection) significantly increased the AUC(0-10h) values of CPT-11 lactone and CPT-11 carboxylate by 32.6% and 30.3 %, respectively, (P < 0.01), but decreased the values by 19.2% and 32.4% for SN-38 lactone and carboxylate, respectively, (P < 0.05). Accordingly, the value of total body clearance (CL) of CPT-11 lactone was significantly lower in combination group compared to the control (1.329 versus 1.837 L/h/kg, P = 0.0002). Plasma t(1/2beta) values for SN-38 lactone and carboxylate were significantly (P < 0.01) smaller in rats with coadministered thalidomide, as compared to rats receiving CPT-11 alone. Further studies are needed to explore the underlying mechanisms for the observed kinetic interaction between CPT-11 and thalidomide.

Animals↗

PubMed2005

St. John's Wort modulates the toxicities and pharmacokinetics of CPT-11 (irinotecan) in rats.

CPT-11 is a DNA topoisomerase I inhibitor for the therapy of colorectal cancer, whereas St. John's Wort (Hypericum perforatum, SJW) is a widely used herbal anti-depressant. This study aimed to investigate the effects of co-administered SJW on the toxicities and pharmacokinetics of CPT-11 and the underlying mechanisms. The body weight loss, gastrointestinal and hematological toxicities induced by CPT-11, and the pharmacokinetic parameters of CPT-11 were evaluated in rats pretreated with SJW or vehicle. Rats treated with CPT-11 alone experienced rapid decrease in body weight, whereas co-administration of SJW with CPT-11 resulted in lesser body weight loss. The gastrointestinal and hematological toxicities following CPT-11 injection were both alleviated in the presence of SJW. The rat pharmacokinetics of both CPT-11 and its metabolite SN-38 were significantly altered in presence of SJW. In conclusion, co-administered SJW significantly ameliorated the toxicities induced by CPT-11. The protective effect of SJW may be partially due to pharmacokinetic interaction between CPT-11 and SJW.

Animals↗

PubMed2005

Determination of thalidomide by high performance liquid chromatography: plasma pharmacokinetic studies in the rat.

A sensitive and simple high performance liquid chromatography (HPLC) method was developed and validated for the determination of thalidomide in rat plasma. Chromatography was accomplished with a reversed-phase Hypersil C18 column. Mobile phase consisted of acetonitrile-10 mM ammonium acetate buffer (pH 5.50) (28:72, v/v), at a flow rate of 0.8 ml/min. Thalidomide was monitored by ultraviolet detector at 220 nm and it gave a linear response as a function of concentration over 0.02-50 microM. The limit of quantitation in rat plasma was 0.50 ng (0.02 microM plasma concentration) with an aliquot of 20 microl. Results from a 3-day validation study indicated that this method allows for simple and rapid quantitation of thalidomide with excellent accuracy and reliability. Using this validated assay, the effect of coadministered irinotecan (CPT-11) on the plasma pharmacokinetics of thalidomide in rats was determined. Coadministration of CPT-11 (intravenously, 60 mg/kg) increased the maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC(0-10h)) of thalidomide by 32.29 and 11.66%, respectively, as compared to the control, but none of the effect of CPT-11 was of statistical significance (P > 0.05). Concomitant CPT-11 also caused a 10.04% decrease in plasma clearance (CL) and 14.51% decrease in volume of distribution (V(d)) (P > 0.05). These results suggest that coadministered CPT-11 did not significantly alter the plasma pharmacokinetics of thalidomide in rats. Further studies are warranted to explore the pharmacokinetic and pharmacodynamic interactions between CPT-11 and thalidomide.

Animals↗

PubMed2005

Human multidrug resistance associated protein 4 confers resistance to camptothecins.

PURPOSE: The multidrug resistance associated protein (MRP) 4 is a member of the adenosine triphosphate (ATP)-binding cassette transporter family. Camptothecins (CPTs) have shown substantial anticancer activity against a broad spectrum of tumors by inhibiting DNA topoisomerase I, but tumor resistance is one of the major reasons for therapeutic failure. P-glycoprotein, breast cancer resistance protein, MRP1, and MRP2 have been implicated in resistance to various CPTs including CPT-11 (irinotecan), SN-38 (the active metabolite of CPT-11), and topotecan. In this study, we explored the resistance profiles and intracellular accumulation of a panel of CPTs including CPT, CPT-11, SN-38, rubitecan, and 10-hydroxy-CPT (10-OH-CPT) in HepG2 cells with stably overexpressed human MRP4. Other anticancer agents such as paclitaxel, cyclophosphamide, and carboplatin were also included. METHODS: HepG2 cells were transfected with an empty vehicle plasmid (V/HepG2) or human MRP4 (MRP4/HepG2). The resistance profiles of test drugs in exponentially growing V/HepG2 and MRP4/HepG2 cells were examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide (MTT) assay with 4 or 48 h exposure time of the test drug in the absence or presence of various MRP4 inhibitors. The accumulation of CPT-11, SN-38, and paclitaxel by V/HepG2 and MRP4/HepG2 cells was determined by validated high-performance liquid chromatography methods. RESULTS: Based on the resistance folds from the MTT assay with 48 h exposure time of the test drug, MRP4 conferred resistance to CPTs tested in the order 10-OH-CPT (14.21) > SN-38 carboxylate (9.70) > rubitecan (9.06) > SN-38 lactone (8.91) > CPT lactone (7.33) > CPT-11 lactone (5.64) > CPT carboxylate (4.30) > CPT-11 carboxylate (2.68). Overall, overexpression of MRP4 increased the IC50 values 1.78- to 14.21-fold for various CPTs in lactone or carboxylate form. The resistance of MRP4 to various CPTs tested was significantly reversed in the presence of dl-buthionine-(S,R)-sulfoximine (BSO, a gamma-glutamylcysteine synthetase inhibitor), MK571, celecoxib, or diclofenac (all MRP4 inhibitors). In addition, the accumulation of CPT-11 and SN-38 over 120 min in MRP4/HepG2 cells was significantly reduced compared to V/HepG2 cells, whereas the addition of celecoxib, MK571, or BSO significantly increased their accumulation in MRP4/HepG2 cells. There was no significant difference in the intracellular accumulation of paclitaxel in V/HepG2 and MRP4/HepG2 cells, indicating that P-glycoprotein was not involved in the observed resistance to CPTs in this study. MRP4 also conferred resistance to cyclophosphamide and this was partially reversed by BSO. However, MRP4 did not increase resistance to paclitaxel, carboplatin, etoposide (VP-16), 5-fluorouracil, and cyclosporine. CONCLUSIONS: Human MRP4 rendered significant resistance to cyclophosphamide, CPT, CPT-11, SN-38, rubitecan, and 10-OH-CPT. CPT-11 and SN-38 are substrates for MRP4. Further studies are needed to explore the role of MRP4 in resistance, toxicity, and pharmacokinetics of CPTs and cyclophosphamide.

Adenine↗

PubMed2005

Metabolism and transport of oxazaphosphorines and the clinical implications.

The oxazaphosphorines including cyclophosphamide (CPA), ifosfamide (IFO), and trofosfamide represent an important group of therapeutic agents due to their substantial antitumor and immuno-modulating activity. CPA is widely used as an anticancer drug, an immunosuppressant, and for the mobilization of hematopoetic progenitor cells from the bone marrow into peripheral blood prior to bone marrow transplantation for aplastic anemia, leukemia, and other malignancies. New oxazaphosphorines derivatives have been developed in an attempt to improve selectivity and response with reduced toxicity. These derivatives include mafosfamide (NSC 345842), glufosfamide (D19575, beta-D-glucosylisophosphoramide mustard), NSC 612567 (aldophosphamide perhydrothiazine), and NSC 613060 (aldophosphamide thiazolidine). This review highlights the metabolism and transport of these oxazaphosphorines (mainly CPA and IFO, as these two oxazaphosphorine drugs are the most widely used alkylating agents) and the clinical implications. Both CPA and IFO are prodrugs that require activation by hepatic cytochrome P450 (CYP)-catalyzed 4-hydroxylation, yielding cytotoxic nitrogen mustards capable of reacting with DNA molecules to form crosslinks and lead to cell apoptosis and/or necrosis. Such prodrug activation can be enhanced within tumor cells by the CYP-based gene directed-enzyme prodrug therapy (GDEPT) approach. However, those newly synthesized oxazaphosphorine derivatives such as glufosfamide, NSC 612567 and NSC 613060, do not need hepatic activation. They are activated through other enzymatic and/or non-enzymatic pathways. For example, both NSC 612567 and NSC 613060 can be activated by plain phosphodiesterase (PDEs) in plasma and other tissues or by the high-affinity nuclear 3'-5' exonucleases associated with DNA polymerases, such as DNA polymerases and epsilon. The alternative CYP-catalyzed inactivation pathway by N-dechloroethylation generates the neurotoxic and nephrotoxic byproduct chloroacetaldehyde (CAA). Various aldehyde dehydrogenases (ALDHs) and glutathione S-transferases (GSTs) are involved in the detoxification of oxazaphosphorine metabolites. The metabolism of oxazaphosphorines is auto-inducible, with the activation of the orphan nuclear receptor pregnane X receptor (PXR) being the major mechanism. Oxazaphosphorine metabolism is affected by a number of factors associated with the drugs (e.g., dosage, route of administration, chirality, and drug combination) and patients (e.g., age, gender, renal and hepatic function). Several drug transporters, such as breast cancer resistance protein (BCRP), multidrug resistance associated proteins (MRP1, MRP2, and MRP4) are involved in the active uptake and efflux of parental oxazaphosphorines, their cytotoxic mustards and conjugates in hepatocytes and tumor cells. Oxazaphosphorine metabolism and transport have a major impact on pharmacokinetic variability, pharmacokinetic-pharmacodynamic relationship, toxicity, resistance, and drug interactions since the drug-metabolizing enzymes and drug transporters involved are key determinants of the pharmacokinetics and pharmacodynamics of oxazaphosphorines. A better understanding of the factors that affect the metabolism and transport of oxazaphosphorines is important for their optional use in cancer chemotherapy.

Animals↗

PubMed2005

Overview on the analytical tools for quality control of natural product-based supplements: a case study of ginseng.

The quality of pharmaceutical products like ginseng is important for ensuring consumer safety and efficacy. Many ginseng products sold today are in various formulations such as powder, capsules, tablets, soft-gels, liquid extracts, and tea. This renders ginseng less identifiable by smell, taste, or physical appearance. Furthermore, as ginseng is expensive, adulteration with other cheaper products occurs. Hence quality assurance of ginseng is needed. This paper reviews the major techniques for ascertaining the level of ginsenosides, the primary active ingredients for ginseng, and covers high-performance liquid, gas, and thin-layer chromatographies, infrared and nuclear magnetic resonance spectroscopies, enzyme immunoassays, and other molecular methods. Supporting techniques such as ultraviolet, fluorescence, diode array and evaporative light scattering detections, and mass spectrometry will also be touched upon. This review also discusses the principles and applications of biosensors-in particular fiber optic-based sensors-and their feasibility in ginseng analysis based on preliminary studies. Despite their potential, there is currently no or limited commercial exploitation of fiber optic-based sensors to perform ginseng quality analysis. The opportunity for biosensors to be used for the rapid quality surveillance of ginseng is appealing, but several key issues still need to be addressed before they find widespread applications in the traditional Chinese medicine industry.

Biosensing Techniques↗