A highly sensitive and rapid LC-MS/MS method for quantification of bexarotene in mouse plasma and brain tissue: Application to mice pharmacokinetic study.

Emerging evidence has suggested that bexarotene, a nearly 20-year-old skin cancer drug, may be a potential drug candidate to treat Alzheimer's disease (AD) and other neurodegenerative disorders. As described in this study, a highly sensitive and rapid method, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) to determine bexarotene in mouse plasma and brain tissue, was established and validated for the first time. Single-step protein precipitation utilizing methanol solution (containing 0.05 % acetic acid) as precipitation agent was employed to prepare the samples of plasma and brain tissue. Chromatographic separation in gradient elution mode was conducted via an Agilent ZORBAX SB-C18 column (50 mm × 4.6 mm, 5 µm) employing methanol-ammonium acetate buffer (5 mM, pH adjusted to 4.6 with acetic acid) as mobile phase which flowed at 0.45 mL/min. The total run time was 6 min for each sample. Detection through mass spectrometric technique was operated by selected reaction monitoring (SRM) in negative electrospray ionization mode. The method was linear within the range of 10.0-15000 ng/mL for plasma and 10.0-600 ng/mL for brain tissue homogenate with the lower limit of quantification of 10.0 ng/ml. The plasma or tissue homogenate was only required 20 µL. The intra- and inter-day precision were less than 13.8 %, and the RE was between -7.4 % and 3.4 %. The method was applied to investigate the plasma pharmacokinetics and brain distribution of bexarotene in mice after being intragastrically administered with bexarotene at the dosage of 100 mg/kg. The results showed that both brain and plasma concentrations of bexarotene peaked at 1.0 h. Bexarotene was rapidly eliminated with a half-life of 2.0 h.

Quantitative Prediction of Oral Bioavailability of a Lipophilic Antineoplastic Drug Bexarotene Administered in Lipidic Formulation Using a Combined In Vitro Lipolysis/Microsomal Metabolism Approach.

For performance assessment of the lipid-based drug delivery systems (LBDDSs), in vitro lipolysis is commonly applied because traditional dissolution tests do not reflect the complicated in vivo micellar formation and solubilization processes. Much of previous research on in vitro lipolysis has mostly focused on rank-ordering formulations for their predicted performances. In this study, we have incorporated in vitro lipolysis with microsomal stability to quantitatively predict the oral bioavailability of a lipophilic antineoplastic drug bexarotene (BEX) administered in LBDDS. Two types of LBDDS were applied: lipid solution and lipid suspension. The predicted oral bioavailability values of BEX from linking in vitro lipolysis with microsomal stability for lipid solution and lipid suspension were 34.2 ± 1.6% and 36.2 ± 2.6%, respectively, whereas the in vivo oral bioavailability of BEX was tested as 31.5 ± 13.4% and 31.4 ± 5.2%, respectively. The predicted oral bioavailability corresponded well with the oral bioavailability for both formulations, demonstrating that the combination of in vitro lipolysis and microsomal stability can quantitatively predict oral bioavailability of BEX. In vivo intestinal lymphatic uptake was also assessed for the formulations and resulted in <1% of the dose, which confirmed that liver microsomal stability was necessary for correct prediction of the bioavailability.

Lipophilic activated ester prodrug approach for drug delivery to the intestinal lymphatic system.

The intestinal lymphatic system plays an important role in the pathophysiology of multiple diseases including lymphomas, cancer metastasis, autoimmune diseases, and human immunodeficiency virus (HIV) infection. It is thus an important compartment for delivery of drugs in order to treat diseases associated with the lymphatic system. Lipophilic prodrug approaches have been used in the past to take advantage of the intestinal lymphatic transport processes to deliver drugs to the intestinal lymphatics. Most of the approaches previously adopted were based on very bulky prodrug moieties such as those mimicking triglycerides (TG). We now report a study in which a lipophilic prodrug approach was used to efficiently deliver bexarotene (BEX) and retinoic acid (RA) to the intestinal lymphatic system using activated ester prodrugs. A range of carboxylic ester prodrugs of BEX were designed and synthesised and all of the esters showed improved association with chylomicrons, which indicated an improved potential for delivery to the intestinal lymphatic system. The conversion rate of the prodrugs to BEX was the main determinant in delivery of BEX to the intestinal lymphatics, and activated ester prodrugs were prepared to enhance the conversion rate. As a result, an 4-(hydroxymethyl)-1,3-dioxol-2-one ester prodrug of BEX was able to increase the exposure of the mesenteric lymph nodes (MLNs) to BEX 17-fold compared to when BEX itself was administered. The activated ester prodrug approach was also applied to another drug, RA, where the exposure of the MLNs was increased 2.4-fold through the application of a similar cyclic activated prodrug. Synergism between BEX and RA was also demonstrated in vitro by cell growth inhibition assays using lymphoma cell lines. In conclusion, the activated ester prodrug approach results in efficient delivery of drugs to the intestinal lymphatic system, which could benefit patients affected by a large number of pathological conditions.