Phase I Metabolic Stability and Electrophilic Reactivity of 2-Phenylaminophenylacetic Acid Derived Compounds.

Diclofenac and lumiracoxib are two highly analogous 2-phenylaminophenylacetic acid anti-inflammatory drugs exhibiting occasional dose-limiting hepatotoxicities. Prior data indicate that bioactivation and reactive metabolite formation play roles in the observed toxicity, but the exact chemical influence of the substituents remains elusive. In order to elucidate the role of chemical influence on metabolism related toxicity, metabolic stability and electrophilic reactivity were investigated for a series of structurally related analogues and their resulting metabolites. The resulting analogues embody progressive physiochemical changes through varying halogeno- and aliphatic substituents at two positions and were subjected to in vitro human liver microsomal metabolic stability and cell-based GSH depletion assays (to measure electrophilic reactivity). LC-MS/MS analysis of the GSH trapped reactive intermediates derived from the analogues was then used to identify the putative structures of reactive metabolites. We found that chemical modifications of the structural backbone led to noticeable perturbations of metabolic stability, electrophilic reactivity, and structures and composition of reactive metabolites. With the acquired data, the relationships between stability, reactivity, and toxicity were investigated in an attempt to correlate between Phase I metabolism and in vitro toxicity. A positive correlation was identified between reactivity and in vitro toxicity, indicating that electrophilic reactivity can be an indicator for in vitro toxicity. All in all, the effect of substituents on the structures and reactivity of the metabolites, however subtle the changes, should be taken into consideration during future drug design involving similar chemical features.

HPLC-MS/MS coupled with equilibrium dialysis method for quantification of free drug concentration of pazopanib in plasma.

BACKGROUND: The selective occurrence of hepatotoxicity observed with use of pazopanib may be attributed to its high level of plasma protein binding and low hepatic extraction ratio. The primary objective was to investigate changes in free drug concentration amongst patients with varying albumin concentrations. METHODS: A HPLC-MS/MS method using C18 column (4.6 × 150 mm, 5 µm) with ESI source in positive mode had been developed and validated for the quantitative determination of free pazaopanib concentration in human plasma. Prior to sample preparation, patient samples were subjected to 6-hour equilibrium dialysis with molecular weight cut-off set at 8000 Da. RESULTS: The calibration curves were linear over the range of 5-1000 ng/mL, with a lower limit of quantification of 5 ng/mL. The intra-day and inter-day precisions and accuracies were all within ± 15 %, at 3 different quality controls. Higher median fraction unbound of pazopanib were observed in patients (n = 17) with lower than normal albumin concentrations. CONCLUSION: With the developed assay, monitoring of plasma free concentrations may be evaluated as an indicator of pazopanib exposure in patients.

Improved Bioavailability of Levodopa Using Floatable Spray-Coated Microcapsules for the Management of Parkinson's Disease.

Oral administration of levodopa (LD) is the gold standard in managing Parkinson's disease (PD). Although LD is the most effective drug in treating PD, chronic administration of LD induces levodopa-induced dyskinesia. A continuous and sustained provision of LD to the brain could, therefore, reduce peak-dose dyskinesia. In commercial oral formulations, LD is co-administrated with an AADC inhibitor (carbidopa) and a COMT inhibitor (entacapone) to enhance its bioavailability. Nevertheless, patients are known to take up to five tablets a day because of poor sustained-releasing capabilities that lead to fluctuations in plasma concentrations. To achieve a prolonged release of LD with the aim of improving its bioavailability, floatable spray-coated microcapsules containing all three PD drugs were developed. This gastro-retentive delivery system showed sustained release of all PD drugs, at similar release kinetics. Pharmacokinetics study was conducted and this newly developed formulation showed a more plateaued delivery of LD that is void of the plasma concentration fluctuations observed for the control (commercial formulation). At the same time, measurements of LD and dopamine of mice administered with this formulation showed enhanced bioavailability of LD. This study highlights a floatable, sustained-releasing delivery system in achieving improved pharmacokinetics data compared to a commercial formulation.

Investigation of the effect of plasma albumin levels on regorafenib-induced hepatotoxicity using a validated liquid chromatography-tandem mass spectrometry method.

Regorafenib is an oral multikinase inhibitor indicated for metastatic colorectal cancer and gastrointestinal stromal tumour. Due to its extensive plasma protein binding and low calculated hepatic extraction ratio, the hepatotoxicity observed with usage of the drug may be related to its plasma exposure. To investigate the highly dynamic free:bound drug concentration for regorafenib in the plasma, a bioanalytical liquid chromatography-tandem mass spectrometric assay was developed and validated in human plasma. The concentration range of the assay was 2-1000ng/mL. Sample preparation was via protein precipitation using acetonitrile with sorafenib as the internal standard. The supernatant was injected into an ultra-performance liquid chromatographic system coupled to a triple quadrupole mass spectrometer. The analytes were separated on an AQUITY UPLC BEH C18 column (120Å, 1.7µm, 2.1mm×50mm) and eluted with a gradient elution system. The ions were detected in multiple reaction monitoring mode. The linearity, lower limit of quantification, intra-day and inter-day precision and accuracy conformed to FDA guidelines. The validated method was successfully applied to determine the effect of albumin levels in plasma on the extent of protein binding of regorafenib. The results indicated that physiologically-relevant levels of albumin were found to have no significant effect on the extent of protein binding of regorafenib, hence imposing minimal effect on drug disposition.

Finely Tuned Asymmetric Platinum(IV) Anticancer Complexes: Structure-Activity Relationship and Application as Orally Available Prodrugs.

Platinum(IV) bis-carboxylates are highly versatile prodrug scaffolds with different axial ligands that can be functionalized while keeping the platinum(II) pharmacophore intact. Using a sequential acylation strategy, we developed a class of PtIV prodrugs of cisplatin with contrasting lipophilic and hydrophilic ligands. We investigated their stability, reduction rates, lipophilicity, aqueous solubility, and antiproliferative efficacies, and assessed for correlations among the parameters that could be useful in drug design. We showed that compounds with high lipophilicity result in better antiproliferative effects in vitro and in vivo, with one of the three compounds tested showing better efficacy than satraplatin against an animal model of colorectal cancer, owing to its higher solubility and lower reduction rates. Our asymmetric PtIV prodrugs may pave the way for a highly predictable, fine-tuned class of orally available PtIV prodrugs for the treatment of colorectal cancer.

Structure-toxicity relationship and structure-activity relationship study of 2-phenylaminophenylacetic acid derived compounds.

2-Phenylaminophenylacetic acid is a widely-exploited chemical scaffold whereby notable NSAIDs such as diclofenac and lumiracoxib were derived. Yet, their clinical usage has been associated with toxicities in the liver. While some studies have attributed toxicities to the bioactivation of both drugs to reactive intermediates, the structural predisposition for toxicity, as well as relationship between this toxicity and COX inhibitory activity has not been elucidated. In this study, we aimed to address their intricate link by synthesizing compounds that possess the 2-phenylaminophenylacetic acid backbone with varying alkyl and halogen substituents at three positions critical to the COX inhibitory pharmacophore. These compounds were subjected to cytotoxicity testing on two liver cell lines of contrasting metabolic competencies. We observed higher toxicity in the more metabolically competent cell line, supporting the role of bioactivation as a prerequisite for toxicity. We have also shown that structural changes on the chemical scaffold exerted pronounced effect on liver cytotoxicity. The most lipophilic and brominated compound (24) was identified as the most cytotoxic of all the compounds. A concurrent determination of their pharmacological activity using COX inhibition assays allowed us to derive a safety profile, which showed that selectivity towards COX-2 negatively affected activity and toxicity.