Analysis of 2-difluoromethyl-DL-ornithine in human plasma, cerebrospinal fluid and urine by cation-exchange high-performance liquid chromatography

Micellar sensitized Resonance Rayleigh Scattering and spectrofluorometric methods based on isoindole formation for determination of Eflornithine in cream and biological samples

α-Difluoromethylornithine or Eflornithine is an FDA-approved drug used for the treatment of Sleeping Sickness (as vials dosage form) and also used for diminishing the unwanted excess facial hair in the hirsutism (as creams dosage form). The proposed work is based on the condensation interaction between the amino moiety of Eflornithine and O-phthalaldehyde/2-mercaptoethanol to form a highly fluorescent isoindole derivative. The fluorescence and the Resonance Rayleigh Scattering (RRS) intensities of the reaction product were greatly augmented upon the addition of hexadecyl-trimethyl ammonium bromide by 153% and 250%, respectively. After optimization of the reaction conditions, the formed isoindole derivative was measured fluorometrically at λ_emission= 429 nm after λ_excitation= 337 nm. Moreover, the significant augmentation in the RRS intensity of the formed product was measured at λ_max= 422 nm. In regards to accuracy, sensitivity, robustness and precision, the proposed methods were validated according to ICH guidelines. Furthermore, the proposed methods were successfully applied for the assay of Eflornithine in various commercial brands of the pharmaceutical cream samples with good recovery. In addition to the current fluorometric method was confirmed to be effective in the assaying of Eflornithine in spiked plasma and urine specimens with good recovery.

Chiral Chromatographic Isolation on Milligram Scale of the Human African Trypanosomiasis Treatment d- and l-Eflornithine

Eflornithine is a recommended treatment against the otherwise fatal parasitic disease late stage human African trypanosomiasis (HAT), also known as Gambian sleeping sickness. It is administered repeatedly as a racemic mixture intravenously (IV) together with oral nifurtimox. Racemic eflornithine has been investigated in clinical trials for oral dosing. However, due to low systemic exposures at a maximum tolerated oral dose, the drug is continued to be administered IV. The eflornithine enantiomers, d- and l-eflornithine, have different affinities to the target enzyme ornithine decarboxylase, suggesting that the pharmacodynamics of the enantiomers may differ. The aim of this study was to develop a method for isolation of d- and l-eflornithine from a racemic mixture. Several chiral stationary phases (CSPs) were evaluated for enantioselectivity using supercritical fluid chromatography (SFC) or high-performance liquid chromatography (HPLC). None of the tested CSPs rendered separation of the enantiomers in SFC mode. Separation of the enantiomers with SFC on the CSP Chiralpak IG was only achieved on an analytical scale after derivatization with ortho-phthalaldehyde (OPA). This was the first reported enantioselective SFC method for an eflornithine derivate. However, due to poor stability, the eflornithine-OPA derivates degraded and no chemically pure enantiomers were obtained. The CSP that showed enantioselectivity in HPLC mode was Chirobiotic R, which resulted in a successful isolation on a semipreparative milligram scale. The isolated eflornithine enantiomers will be tested in nonclinical in vitro and in vivo studies to support and assess the feasibility of a future clinical program with an oral HAT treatment.

A simple and sensitive assay for eflornithine quantification in rat brain using pre-column derivatization and UPLC-MS/MS detection

Eflornithine (α-difluoromethylornithine) has been used to treat second-stage (or meningoencephalitic-stage) human African trypanosomiasis and currently is under clinical development for cancer prevention. In this study, a new ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)-based assay was developed and validated for the quantification of eflornithine in rat brain. To improve chromatographic retention and MS detection, eflornithine was derivatized with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate for 5 min at room temperature prior to injection. Derivatized eflornithine was separated on a reverse-phase C18 UPLC column with a 6-min gradient; elution occurred at approximately 1.5 min. Prior to derivatization, eflornithine was reproducibly extracted from rat brain homogenate by methanol protein precipitation (~70% recovery). Derivatized eflornithine was stable in the autosampler (6 °C) for at least 24 h. This new assay had acceptable intra- and interday accuracy and precision over a wide dynamic range (5000-fold) and excellent sensitivity with a lower limit of quantification of 0.1 µm (18 ng/mL) using only 10 μL of rat brain homogenate. The validated eflornithine assay was applied successfully to determine eflornithine distribution in different regions of rat brain in an in situ rat brain perfusion study.

Determination of eflornithine enantiomers in plasma, by solid-phase extraction and liquid chromatography with evaporative light-scattering detection

A bioanalytical method for determination of eflornithine (DFMO) in 1000 microL human plasma has been developed and validated. DFMO and the internal standard (IS) were analysed by liquid chromatography with evaporative light-scattering detection (ELSD). Separation was performed on a Chirobiotic TAG (250 mm x 4.6 mm) column with ethanol (99.5%):0.01 mol/L acetic acid-triethylamine buffer at the rate of 25:75% (v/v) with flow rate of 1.0 mL/min. For d-DFMO in plasma the inter-assay precision was 6.5% at 75 micromol/L, 6.6% at 375 micromol/L and 5.8% at 750 micromol/L. For l-DFMO in plasma the inter-assay precision was 10.4% at 75 micromol/L, 6.5% at 375 micromol/L and 5.0% at 750 micromol/L. The lower limit of quantification (LLOQ) was determined to 25 micromol/L where the precision was 4.3% and 5.7%, respectively.

High-performance liquid chromatographic method for determination of 2-difluoromethyl-DL-ornithine in plasma and cerebrospinal fluid

A simple, sensitive, selective and reproducible method based on anion-exchange liquid chromatography with post-column derivatisation was developed for the determination of eflornithine (2-difluoromethyl-DL-ornithine; DFMO) in human plasma and cerebrospinal fluid. The 1-alkylthio-2-alkyl-isoindoles fluorescent derivative of the drug was separated from the internal standard (MDL 77246A) on an anion-exchange column (PRP-X300, 250x2.1 mm, 7-microm particle size: Hamilton, USA), with retention times of 6.9 and 10.7 min, respectively. Fluorescence detection was set at 430/340 nm (emission/excitation wavelength). The elution solvent consisted of a solution of 30 mM potassium dihydrogen phosphate buffer (pH 2.2) and acetonitrile (50:50, v/v), running through the column at a flow-rate of 0.3 ml/min. The chromatographic analysis was operated at 37 degrees C. Sample preparation for either plasma or CSF (100 microl) was done by single-step protein precipitation with 20% trichloroacetic acid after incubation at 4 degrees C for 1 h. Calibration curves for plasma (100, 200, 400, 600, 800 and 1200 nmol/100 microl, and 10, 20, 40, 80, 120 and 160 nmol/100 microl for the high and low concentration range curves, respectively) and CSF (1, 2, 4, 8, 16, 32 nmol/100 microl) were all linear with correlation coefficients better than 0.999. The precision of the method based on within-day repeatability and reproducibility (day-to-day variation) at high concentration range was below 15%, whereas at low concentration range was below 20% (% coefficient of variations: %C.V.) Good accuracy was observed for both the intra-day or inter-day assays, as indicated by the minimal deviation of mean values found with measured samples from that of the theoretical values (below +/-15 and +/-20% at high and low concentration range, respectively. The limit of quantification was accepted as 0.1 nmol using 100-microl samples. The mean recovery for DFMO and the internal standard were greater than 95%. The method was free from interference from commonly used drugs including antimalarials and antihelminthics. The method appears to be robust and has been applied to a pharmacokinetic study of DFMO in patients with African trypanosomiasis following oral doses of Ornidyl (Aventis Pharma, Frankfurt, Germany) at 500 mg/kg body weight (125 mg q.i.d.) for 14 days.