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Saye H Khoo

Publications and source records attributed to Saye H Khoo.

At least 19 recordsLinked to original sources
PubMed2006

Pharmacologic optimization of protease inhibitors and nonnucleoside reverse transcriptase inhibitors (POPIN)--a randomized controlled trial of therapeutic drug monitoring and adherence support.

We evaluated the feasibility and effectiveness of therapeutic drug monitoring (TDM) and adherence support (collectively, AT) vs standard of care (SOC) in patients receiving HIV protease inhibitors (PIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs) within a nurse-led clinic. Primary end points were failure to achieve viral load of <50 copies/mL at 24 weeks, viral rebound, or development of treatment limiting toxicity. One hundred twenty-two patients (AT 63 and SOC 59) were followed-up every 12 weeks, for a median of 72 weeks. No difference was observed between arms in risk of reaching a study end point or between groups of patients with abnormal vs "therapeutic" drug concentrations. Interindividual variabilities (coefficient of variation) were the following: efavirenz, 77.5%; nevirapine, 74.5%; lopinavir, 73.4%; nelfinavir, 83.7%; indinavir, 80.8%; saquinavir, 112.4%. Intraindividual variabilities (median coefficient of variation) were the following: NNRTIs, approximately 25%; PIs, 48.4%. Despite persistently abnormal results in 26 of patients in the AT arm (38%), dosage adjustment was only undertaken in 9 patients (35%).A significant proportion of patients had drug concentrations outside the therapeutic range. The Pharmacologic Optimization of PIs and NNRTIs (POPIN) study confirms that TDM trials are complex to interpret and statistically underpowered, with effectiveness better assessed through the clinical utility of a TDM result, whether normal or abnormal. Although TDM of PIs and NNRTIs may be useful in selected patients, routine and unselected use is not supported by current evidence.

Adult↗
PubMed2006

Pharmacogenetics of HIV therapy.

Drug treatment in HIV disease is characterized by variable responses, in terms of both efficacy and toxicity. Both genetic and environmental factors are important determinants of this variability, although the relative contributions are unclear and likely to vary with different drugs. Many of the antiretrovirals are metabolized by polymorphically expressed enzymes (cytochrome P450, CYP450; glucuronyl transferase, GT) and/or transported by drug transporters (ABC and SLC families). Initial studies of antiretroviral efficacy have therefore focused on these genes. For example, it has recently been shown that a CYP2B6 genetic variant predicts higher plasma efavirenz exposure and possibly increased central nervous system toxicity. A large number of studies on ABCB1 genetics with antiretrovirals have also been undertaken; however, as in other therapeutic areas, the data have been contradictory, and currently, no firm conclusions can be reached on the effect of ABCB1 variability as a determinant of efficacy. Indeed, this highlights the need for validation of initial association studies in pharmacogenetic research. By contrast, the clearest association between genetic variants and response relates to the hypersensitivity reaction that occurs with abacavir. The identification that the major histocompatibility complex haplotype 57.1 acts as a strong genetic predisposing factor can be regarded as a prime example of how fundamental research can be translated into a pharmacogenetic test. Nevirapine hypersensitivity has also been related to an HLA gene (HLA-DRB1*0101) but the predictive value does not appear to be sufficient to implement in clinical practice. Much more work needs to be done to define the genetic factors determining response to antiretroviral agents. These studies need to be sufficiently powered and utilize a modern genotyping strategy. Most importantly, the phenotype needs to be carefully characterized. We also need to disseminate this information: a pivotal resource for this can be found at www.HIV-pharmacogenomics.org.

Anti-HIV Agents↗
PubMed2006

Use of nonlinear mixed-effects analysis for improved precision of early pharmacodynamic measures in tuberculosis treatment.

Nonlinear mixed-effects analysis of serial sputum colony-counting data supports the existence of two bacillary subpopulations in sputum, eliminated at different rates. It distinguishes between combination regimens, removes bias, and greatly improves precision, with significant implications for the analysis of surrogate endpoints of "sterilization" in the development of new antituberculosis regimens.

Antitubercular Agents↗
PubMed2005

Modulation of the intracellular accumulation of saquinavir in peripheral blood mononuclear cells by inhibitors of MRP1, MRP2, P-gp and BCRP.

BACKGROUND: The efflux transporters P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRP) and breast cancer resistance protein (BCRP) limit the accumulation of antiretrovirals in cell lines but it is more important to know whether the expression of these transporters in peripheral blood mononuclear cells (PBMC) impacts cellular drug concentrations. OBJECTIVES: To study the transport and accumulation of saquinavir (SQV) in PBMC and the effects of specific inhibitors of MRP1, MRP2, P-gp and BCRP. METHODS: Transport and accumulation of [H]-SQV was measured in PBMC in the absence or presence of specific and non-specific inhibitors of MRP1, MRP2, P-gp and BCRP. Flow cytometric, western blot and real-time PCR assays were used to examine the relative expression of the drug efflux transporters in the same batches of PBMC. RESULTS: MRP2 is present in PBMC. The expression of P-gp, MRP1, MRP2 (mRNA) and BCRP all displayed batch-to-batch variability. Specific and non-specific inhibitors of MRP1, P-gp and MRP2 significantly increased the baseline accumulation of SQV. Accumulation of SQV was not correlated with the expression of any single transporter. CONCLUSIONS: Multiple drug efflux transporters are important in the intracellular accumulation of SQV in PBMC. If drug efflux contributes towards virological failure, then all contributing transporters will need to be inhibited.

Blotting, Western↗
PubMed2005

Intracellular and plasma pharmacokinetics of efavirenz in HIV-infected individuals.

OBJECTIVES: The site of action of efavirenz is inside HIV-infected cells. Measurement of intracellular (IC) concentrations of efavirenz may therefore provide further understanding of therapeutic failure, especially where virological rebound occurs despite adequate plasma levels, and a lack of detectable viral resistance. Here, we determined IC and plasma pharmacokinetics of efavirenz and their relationship with plasma protein binding and P-glycoprotein (P-gp, an active drug efflux transporter) expression. PATIENTS AND METHODS: Venous blood samples from 10 HIV-infected patients receiving efavirenz (600 mg once a day plus two nucleoside reverse transcriptase inhibitors) were collected over the 24 h dosing interval. Plasma and peripheral blood mononuclear cells (PBMCs) were isolated. Plasma protein bound and unbound efavirenz were separated using ultrafiltration. IC (or cell-associated), total plasma and unbound plasma efavirenz levels were quantified using HPLC-UV. P-gp expression was measured by flow cytometry. Area under the concentration-time curves (AUC0-24) were then calculated using non-compartmental analyses and the IC accumulation expressed as a ratio of IC to plasma AUC0-24. RESULTS: The median (range) % unbound and IC accumulation ratio was 0.6% (0.4-1.5%) and 1.3 (0.7-3.3), respectively. There was a linear relationship between IC and total AUC0-24 (r2= 0.59, P = 0.01) but not unbound AUC0-24 (r2= 0.13, P = 0.75). An inverse correlation between IC AUC0-24 and % unbound was observed (r2= 41, P = 0.05). There was no relationship between IC AUC0-24 and P-gp expression on the cell surface (r2< 0.01, P = 0.98). CONCLUSIONS: There was a direct relationship between % bound efavirenz in plasma and IC accumulation implying that the IC accumulation of efavirenz is related to binding to IC proteins or other cellular constituents. Studies investigating the unbound concentration of antiretrovirals inside the cell are now required.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

In vitro synergy and enhanced murine brain penetration of saquinavir coadministered with mefloquine.

Highly active antiretroviral therapy has substantially improved prognosis in human immunodeficiency virus (HIV). However, the integration of proviral DNA, development of viral resistance, and lack of permeability of drugs into sanctuary sites (e.g., brain and lymphocyte) are major limitations to current regimens. Previous studies have indicated that the antimalarial drug chloroquine (CQ) has antiviral efficacy and a synergism with HIV protease inhibitors. We have screened a panel of antimalarial compounds for activity against HIV-1 in vitro. A limited efficacy was observed for CQ, mefloquine (MQ), and mepacrine (MC). However, marked synergy was observed between MQ and saquinavir (SQV), but not CQ in U937 cells. Furthermore, enhancement of the antiviral activity of SQV and four other protease inhibitors (PIs) by MQ was observed in MT4 cells, indicating a class specific rather than a drug-specific phenomenon. We demonstrate that these observations are a result of inhibition of multiple drug efflux proteins by MQ and that MQ also displaces SQV from orosomucoid in vitro. Finally, coadministration of MQ and SQV in CD-1 mice dramatically altered the tissue distribution of SQV, resulting in a >3-fold and >2-fold increase in the tissue/blood ratio for brain and testis, respectively. This pharmacological enhancement of in vitro antiviral activity of PIs by MQ now warrants further examination in vivo.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

Intracellular and plasma pharmacokinetics of nevirapine in human immunodeficiency virus-infected individuals.

BACKGROUND AND OBJECTIVE: Plasma concentrations of nevirapine have been linked to human immunodeficiency virus (HIV) treatment outcome. However, because the site of action of nevirapine is within HIV-infected cells, intracellular concentrations may better relate to antiviral exposure. Investigation of factors that alter the intracellular pharmacokinetics of nevirapine may also aid in our understanding of therapeutic failure. Our objective was to determine intracellular (or cell-associated) nevirapine concentrations over the full dosing interval and to relate protein binding and P-glycoprotein (P-gp) expression to intracellular exposure. METHODS: Plasma and peripheral blood mononuclear cells were isolated from blood samples taken from 10 HIV-infected patients at 0, 2, 4, 8, and 12 hours after dosing. Intracellular and plasma (total and unbound) concentrations were determined by liquid chromatography-tandem mass spectrometry, and the ratios of intracellular to total plasma exposure (area under the concentration-time curves) were calculated. P-gp expression was measured by flow cytometry. RESULTS: The median intracellular accumulation ratio was 0.005 (range, 0.001-0.054) and remained unchanged over the dosing interval. There was an association between higher plasma concentrations and lower cellular concentrations of nevirapine (total r(2) = 0.62, P = .007). There was no relationship between percent unbound nevirapine and intracellular nevirapine. There was a correlation between higher plasma nevirapine exposure and higher P-gp expression (r(2) = 0.77, P = .03), whereas intracellular nevirapine exposure decreased with higher P-gp expression (r(2) = 0.62, P = .01). CONCLUSIONS: The intracellular accumulation of nevirapine was low, did not change over the dosing interval, and was not related to protein binding. In this small study, cells with higher P-gp expression had lower cellular concentrations of nevirapine. Further studies are required to explore the influx and efflux transporter profile of this drug.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2004

The relationship between nevirapine plasma concentrations and abnormal liver function tests.

Abnormal liver function tests are frequently observed in HIV-infected individuals receiving nevirapine (NVP). Here we investigate the relationship between total and unbound plasma concentrations of NVP and the liver enzymes alanine aminotransferase (ALT) and gamma-glutamyl transferase (gammaGT). HIV-infected individuals [n = 85, 22 female, 34 hepatitis C or B virus (HCV or HBV(+))] receiving NVP (200 mg bd; median duration 66 weeks, range 3-189) and two nucleoside reverse transcriptase inhibitors (NRTIs) were enrolled into this study. Blood samples were taken at C(trough) (12 hr postdose) for measurement of NVP and liver function tests (ALT and gammaGT). Plasma protein bound and unbound drug was separated using ultrafiltration and NVP concentrations quantified using HPLC-MS/MS. A linear relationship was observed between total and unbound NVP C(trough) (r(2) = 0.77, p < 0.0001). Patients with elevated ALT (>37 IU/liter; n = 31) had higher NVP unbound C(trough) than those with ALT within the normal range (median 2268 vs. 1694 ng/ml, p = 0.04) but there was no difference in total C(trough). Logistic regression revealed no association between higher NVP C(trough) and ALT elevations. Significantly higher NVP total and unbound C(trough) were observed in patients with increased gammaGT (>40 IU/liter; n = 63; total 6747 vs. 4530 ng/ml, p = 0.001; unbound 2113 vs. 1557 ng/ml, p = 0.03). Significantly higher unbound NVP C(trough) was observed in HCV/HBV(+) (median 2275 vs. 1726 ng/ml, p = 0.02) and on bivariate analysis, higher NVP C(trough) was associated with HCV/HBV coinfection (chi(2) = 4.228; p = 0.04). Overall we found no strong association between NVP concentrations and hepatotoxicity. Although in this study NVP was well tolerated in HCV/HBV coinfected patients, higher plasma concentrations were observed.

Alanine Transaminase↗
PubMed2004

Lopinavir protein binding in vivo through the 12-hour dosing interval.

Most protease inhibitors available for the treatment of human immunodeficiency virus (HIV) infection are highly bound to plasma proteins, mainly alpha-1 acid glycoprotein. Therapeutic drug monitoring (TDM) of total protease inhibitor (PI) concentrations has been increasing in the past few years; however, the pharmacological activity of the PIs is dependent on unbound drug entering cells harboring HIV. There is little information available on unbound drug concentrations of these drugs in vivo. The aim of the study was to measure unbound plasma concentrations of lopinavir (LPV) and to relate them to the total plasma concentrations to establish the unbound percentage in vivo during a full dosage interval. A pharmacokinetic study was performed in HIV-infected subjects (n = 23; median CD4 cell count = 290 x 10(6) cells x L(-1); viral load < 50 copies x mL(-1)) treated with a LPV/ritonavir (RTV)-containing regimen. Ultrafiltration was used to separate unbound LPV in all plasma samples (n = 115). Equilibrium dialysis was also used to compare with ultrafiltration measurements in 10/23 patients at baseline and 2 hours after drug intake. Total and unbound LPV concentrations were measured by a fully validated method using high-performance liquid chromatography-mass spectometry (HPLC-MS/MS). Based on a comparison of AUC(unbound)AUC(total), the mean (+/- SD) unbound percentage of LPV from all the samples studied (n = 115) was 0.92% (+/- 0.22) when measured with ultrafiltration and 1.32% (+/- 0.44) when equilibrium dialysis was used (n = 20), showing a higher drug recovery (P = 0.048). The unbound percentage of LPV was found to be significantly higher after 2 h than at baseline (P < 0.05 with both methods), suggesting a concentration-dependent binding of LPV that has not been observed in vitro. However, the clinical significance of such phenomena is still unclear.

Adult↗
PubMed2004

Functional correlation of P-glycoprotein expression and genotype with expression of the human immunodeficiency virus type 1 coreceptor CXCR4.

The aim of this study was to investigate the relationship between lymphocyte P-glycoprotein (P-gp) expression and genotype in vivo and the expression of lymphocyte receptors critical in the life cycle of human immunodeficiency virus type 1 (HIV-1), i.e., CD4, CCR5, and CXCR4. Using flow cytometry to quantify each membrane receptor/transporter, we demonstrate a highly significant correlation between P-gp protein expression and the expression of CXCR4 (rho = 0.874; P < 0.0001). Furthermore, confocal microscopy showed colocalized expression of CXCR4 and P-gp in the lymphocyte membrane. This significant relationship was also apparent at the mRNA level by use of reverse transcription-PCR (rho = 0.61; P < 0.005) and was present in both phytohemagglutinin-stimulated and unstimulated peripheral blood mononuclear cells. Genotypic analysis of the C3435T single-nucleotide polymorphism of P-gp confirmed significantly higher levels of P-gp in C (range, 2.45 to 11.00 relative fluorescence units [RFU])- than in T (range, 0.25 to 5.00 RFU)-homozygous individuals (P = 0.0088; 95% confidence interval [95% CI], 0.7 to 6.3 RFU). An equivalent association between CXCR4 levels and C (range, 12.7 to 44.1 RFU) versus T (range, 3 to 18.9 RFU) genotype was also demonstrated (P = 0.0019; 95% CI, 5.4 to 23.7). Functionally, although these correlates had no impact on HIV-1 production from either X4- or R5-tropic virus, expression correlated significantly with the activity of the HIV-1 protease inhibitor (PI) saquinavir for both P-gp (rho = 0.75; P = 0.0019) and CXCR4 (rho = 0.71; P = 0.0041). This study defines an association between P-gp (expression and genotype) and CXCR4 that may have implications for the selection of viral tropism and the access of drugs to protease for specific tropic types. The interplay between these two proteins may also influence the viral genotypes which escape effective chemotherapy and which therefore have the opportunity to evolve resistance to PIs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Intracellular and plasma pharmacokinetics of nelfinavir and M8 in HIV-infected patients: relationship with P-glycoprotein expression.

One of the targets of antiretroviral therapy is within cells infected with HIV. In order to improve therapeutic efficacy, it is therefore important that the intracellular pharmacokinetics of drugs, such as nelfinavir mesylate and its active metabolite M8, are studied in addition to plasma pharmacokinetics. Previously, the intracellular accumulation of protease inhibitors has been reported in vivo, displaying the following hierarchy: nelfinavir > saquinavir > ritonavir > indinavir. Multidrug resistance transporters, such as P-glycoprotein (P-gp), may result in a lower intracellular concentration of drug via an efflux mechanism, thus contributing to sanctuary site formation. The objective of this study was to determine concentrations of nelfinavir and M8 in plasma and peripheral blood mononuclear cells from HIV-infected patients, and to ascertain the relationship between intracellular accumulation and lymphocyte P-gp expression. Venous blood samples from 12 HIV-infected patients (viral load <50 copies/ml) receiving nelfinavir (1250 mg twice daily) and dual nucleoside reverse transcriptase inhibitor therapy were collected over a full dosage interval (0, 2, 4, 8 and 12 h). Plasma and intracellular (cell-associated) drug concentrations were measured by HPLC-MS/MS. Drug exposure in plasma and cells was expressed as the area under the concentration-time curve (AUC(0-12h)), derived from non-compartmental modelling. The ratio of intracellular AUC(0-12h)/total plasma AUC(0-12h) was calculated to determine cellular drug accumulation. P-gp expression on lymphocytes was determined by flow cytometry. The median (range) AUC(0-12h) of nelfinavir in plasma and cellular compartments was 21.8 mg x h x l(-1) (5.64-50.8) and 104.6 mg x h x l(-1) (23.1-265.7), respectively. Corresponding values for M8 in plasma and cells were 6.60 mg x h x l(-1) (2.16-17.3) and 19.6 mg x h x l(-1) (5.14-60.8). A ratio of plasma M8/plasma nelfinavir (AUC(0-12h)) and intracellular M8/intracellular nelfinavir (AUC(0-12h)) gave median values of 0.32 and 0.17, respectively. The cellular accumulations [median; (range)] of nelfinavir and M8 were 5.30 (2.28-16.2) and 2.32 (1.01-10.7), respectively. A significant correlation between plasma and intracellular nelfinavir minimum concentration (Cmin) (r2=0.34; P=0.049), but not between plasma and intracellular M8 Cmin was observed. C(0h) concentrations were higher than C(12h) for both nelfinavir and M8. No relationship was observed between nelfinavir or M8 accumulation and lymphocyte cell surface expression of P-gp. This study illustrates that intracellular concentrations were higher than plasma concentrations for both nelfinavir and M8, suggesting lymphocyte accumulation. The mechanism of differential intracellular accumulation of nelfinavir and M8 remains to be elucidated. It may be that affinities for influx transporters or fundamental drug characteristics play a major role in the greater accumulation of nelfinavir than M8.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Expression of pregnane-X-receptor transcript in peripheral blood mononuclear cells and correlation with MDR1 mRNA.

P-glycoprotein (P-gp) limits bioavailability and accumulation of HIV protease inhibitors (PIs). PIs are ligands for the pregnane-X-receptor (PXR), which regulates P-gp expression. This occurs when ligands activate the receptor, initiating binding to response elements in the MDR1 promoter. PXR also activates cytochrome P4503A4 (CYP3A4) and a correlation between hepatic PXR and CYP3A4 mRNA has been reported. We have examined the relationship between MDR1 and PXR mRNA in peripheral blood cells and demonstrate a significant correlation in 18 volunteers (R2=0.4; P<0.005). PXR was approximately 250-fold lower in peripheral blood mononuclear cells than in liver (1.6+/-1.2 vs 450+/-298; n=6; P<0.01).

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Intracellular pharmacokinetics of antiretroviral agents.

Apart from fusion inhibitors, 'conventional' antiretrovirals such as nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs) act on intracellular targets. Intracellular concentrations of these agents may be an important determinant of antiviral activity, and the pharmacokinetics of intracellular drug accumulation (including binding to cytosolic proteins, intracellular-free fraction, influx and efflux kinetics and intracellular drug metabolism) are likely to impact upon efficacy and toxicity. To date, intracellular drug accumulation has been poorly studied in vivo, due to methodological difficulties and the relatively large volumes of blood required. NRTIs require intracellular conversion to their active phosphorylated metabolites: interactions between these agents, or with other drugs may impact upon efficacy. PIs are metabolised by cytochrome P450 enzymes in gut and liver; some intracellular metabolism by P450 isoforms is also possible. PIs are also substrates for drug efflux transporters such as P-gp and MRP1. We have previously observed a hierarchy of intracellular accumulation of PIs, most probably related to physiochemical characteristics of these drugs such as lipophilicity and plasma protein binding. Comparatively, little is known about the intracellular pharmacokinetics of NNRTIs. These drugs probably do not accumulate inside cells to any significant degree. The study of intracellular pharmacokinetics of HIV drugs is central to investigating putative sanctuary sites where HIV may replicate with little selective pressure. However, stringent methodological procedures need to be applied, and techniques for measuring intracellular drug are in their infancy. Moreover, failure to differentiate between truly intracellular drug and drug bound to cell membranes render results difficult to interpret.

Anti-HIV Agents↗