Yok Moi Khoo

Dose- and schedule-dependent protective efficacy of celgosivir in a lethal mouse model for dengue virus infection informs dosing regimen for a proof of concept clinical trial.

Celgosivir (6-O-butanoyl castanospermine), a pro-drug of the naturally occurring castanospermine, is an inhibitor of α-glucosidase I and II that is found to be a potent inhibitor of several enveloped viruses including all four serotypes of dengue virus. We showed previously that the compound fully protected AG129 mice from lethal infection with a mouse adapted dengue virus at a dose of 50mg/kg twice daily (BID) for 5days and was effective even after 48h delayed treatment. Here we show that the protection by celgosivir is dose- and schedule-dependent and that a twice-a-day regimen of 50, 25 or 10mg/kg is more protective than a single daily dose of 100mg/kg. Treatment with 50mg/kg BID castanospermine had comparable efficacy as 25mg/kg BID celgosivir, suggesting that celgosivir is approximately twice as potent as castanospermine with respect to in vivo antiviral efficacy. Pharmacokinetics (PK) studies of celgosivir in mice showed that it rapidly metabolized to castanospermine. Simulation of the PK data with the survival data for the various doses of celgosivir tested suggests that the steady-state minimum concentration is a critical parameter to note in choosing dose and schedule. These results influenced the selection of the dose regimen for a proof-of-concept clinical trial of celgosivir as a treatment against dengue fever.

Extended Evaluation of Virological, Immunological and Pharmacokinetic Endpoints of CELADEN: A Randomized, Placebo-Controlled Trial of Celgosivir in Dengue Fever Patients.

CELADEN was a randomized placebo-controlled trial of 50 patients with confirmed dengue fever to evaluate the efficacy and safety of celgosivir (A study registered at ClinicalTrials.gov, number NCT01619969). Celgosivir was given as a 400 mg loading dose and 200 mg bid (twice a day) over 5 days. Replication competent virus was measured by plaque assay and compared to reverse transcription quantitative PCR (qPCR) of viral RNA. Pharmacokinetics (PK) correlations with viremia, immunological profiling, next generation sequence (NGS) analysis and hematological data were evaluated as exploratory endpoints here to identify possible signals of pharmacological activity. Viremia by plaque assay strongly correlated with qPCR during the first four days. Immunological profiling demonstrated a qualitative shift in T helper cell profile during the course of infection. NGS analysis did not reveal any prominent signature that could be associated with drug treatment; however the phylogenetic spread of patients’ isolates underlines the importance of strain variability that may potentially confound interpretation of dengue drug trials conducted during different outbreaks and in different countries. Celgosivir rapidly converted to castanospermine (Cast) with mean peak and trough concentrations of 5727 ng/mL (30.2 μM) and 430 ng/mL (2.3 μM), respectively and cleared with a half-life of 2.5 (± 0.6) hr. Mean viral log reduction between day 2 and 4 (VLR2-4) was significantly greater in secondary dengue than primary dengue (p = 0.002). VLR2-4 did not correlate with drug AUC but showed a trend of greater response with increasing Cmin. PK modeling identified dosing regimens predicted to achieve 2.4 to 4.5 times higher Cmin. than in the CELADEN trial for only 13% to 33% increase in overall dose. A small, non-statistical trend towards better outcome on platelet nadir and difference between maximum and minimum hematocrit was observed in celgosivir-treated patients with secondary dengue infection. Optimization of the dosing regimen and patient stratification may enhance the ability of a clinical trial to demonstrate celgosivir activity in treating dengue fever based on hematological endpoints. A new clinical trial with a revised dosing regimen is slated to start in 2016 (NCT02569827). Furthermore celgosivir’s potential value for treatment of other flaviruses such as Zika virus should be investigated urgently. Trial Registration: ClinicalTrials.gov NCT01619969

A high-performance liquid chromatography method for the quantification of cysmethynil, an inhibitor of isoprenylcysteine carboxylmethyl transferase, in mouse plasma

Cysmethynil, a newly identified small molecule inhibitor of isoprenylcysteine carboxylmethyl transferase (Icmt) is involved in the post-translational modification of CaaX proteins. Cysmethynil causes cell death in many human cancer cells in vitro, and inhibits tumor growth in the xenograft mouse model in vivo. A HPLC method for the quantification of cysmethynil in mouse plasma was developed and validated. The lower limit of quantification of this method was 0.01microg/ml. Inter- and intra-day variability ranged from 0.38-8.5% and accuracy was between 86% and 98%. This sensitive method was used to quantify cysmethynil in plasma of mice after intraperitoneal dosing for preliminary pharmacokinetic studies.

A simple and sensitive high-performance liquid chromatographic method for quantification of PXD101, a histone deacetylase inhibitor in human plasma

PXD101, a new histone deacetylase inhibitor, is currently undergoing phase I/II clinical trials as an anticancer drug. This study describes a simple and sensitive high-performance liquid chromatography ultraviolet method developed for the quantification of PXD101 in human plasma samples to support such trials. Following solid phase extraction at room temperature, the analytes were separated on a 5 μm C18 150 × 2.1 mm column using gradient elution (mobile phase of acetonitrile and 25 mM NaH2PO4, pH 2.8) at a flow rate of 0.5 mL/min and ultraviolet detection at 268 nm. Oxamflatin was used as an internal standard. PXD101 and the internal standard were eluted at about 7.9 min and 13.6 min, respectively. The lower limit of quantification of PXD101 in plasma was 10 ng/mL. The calibration curves for concentrations in the range of 10 to 2,000 ng/mL gave excellent linearity (r2 = 0.999). The coefficients of variation for intraday and interday assays were all less than 10%. The accuracy of all concentration determinations ranged from 98.0% to 102.0%. There were no problems with PXD101 stability following freeze-thawing, short-term exposure to room temperature, postextraction stability up to 24 hours, and sample storage at −70°C for 3 months. The reported method, with dilution integrity of up to 50 fold, has the requisite sensitivity and is suitable for pharmacokinetic studies of PXD101.

A simple high-performance liquid chromatography method for measuring serum cloxacillin in eight Asian patients.

A simple reversed-phase high-performance liquid chromatography method using probenecid as internal standard was used for the quantitation of serum cloxacillin in eight Asian patients. The method does not require the extraction of the antibiotic from serum and the percentage recovery of cloxacillin was 96–103%. The presence of ampicillin, fusidic acid, benzylpenicillin, and gentamicin in serum appeared not to interfere with the method. The day-to-day coefficient of variation of the method over 6 months for 4–120 mUg/ml ranged between 6.2 and 11.5%. In the eight patients in whom cloxacillin was administered intravenously or orally, there was great interindividual and intra-individual variation in the serum concentrations attained. The highest concentration of 85 mUg/ml was obtained in a sample taken 1.5 h after an intravenous dose of 1 g. The lowest concentration of < 1 mUg/ml was from a sample taken 6 h after an oral dose of 500 mg.

Simple HPLC Determination of the Concentrations of Epiroprim in the Serum and Brains of Mice

Epiroprim, an analogue of trimethoprim, has been shown to potentiate the efficacy of dapsone in experimental parasitic infections. A simple and accurate HPLC method has been developed to estimate epiroprim in serum and brain