Page - (000123) - in Biomedical Chemistry: Current Trends and Developments

compounds and main metabolites were extracted from biological samples by a solid-phase extraction (SPE) procedure. The same chiral column and similar SPE protocols were employed to analyze plasma samples from clinical studies (Falcão 2008; Almeida 2008) but with MS/MS detection instead of UV. Moreover, Lv et al. (2013) developed an effective screening strategy to select new agents for brain tumor chemotherapy from a series of low molecular weight anticancer agents [ON123x] by combining several in vitro studies. These studies aimed to evaluate compound metabolic stability in mouse and human liver microsomes, predict their BBB permeability using MDCK-MDR1 cell monolayers and estimate their binding to plasma proteins and brain tissue. In vivo cassette dosing studies were then conducted in mice for the 12 compounds, permitting the examination of in vitro/in vivo relationships to confirm the suitability of the in vitro assays. The same bioanalytical technique was employed for the analysis of all in vitro and in vivo samples, utilizing a C18-reversed-phase column and MS/MS detection after a simple protein precipitation to clean-up the samples. It is noteworthy that the majority of the in vivo studies which quantify parent drug and/or metabolites in biological samples require more demanding and complex sample preparation protocols than in vitro techniques, resorting to validated analytical techniques which guarantee the acquisition of precise and accurate data (Table 2.1.6). Indeed, it is well known that besides chromatographic separation, sample preparation is essential to reduce the effect of the endogenous and exogenous compounds that exist in biological samples and to concentrate the analytes to consequently enhance the method sensitivity. In current practice, SPE seems to be the most widespread used procedure to extract drugs and metabolites from biological samples (Table 2.1.6), probably because it is versatile, very efficient and easily automated. Similarly to HPLC column packing materials, SPE cartridges utilize a wide range of silica-based and polymer-based sorbents and the extraction procedure follows the generic chromatographic protocol. A novel 96-well SPE plate format is being widely employed, conferring a unique design that makes the use of the sorbents higher efficiency and allows elution of target compounds with small quantities of solvent. This