A crucial step in the drug discovery and development process is the assessment of membrane permeability properties of new chemical entities and researchers are constantly searching for cost-effective, high through-put models with as high as possible predictive value. In addition, a thorough understanding of the membrane permeability pathways and metabolism mechanisms are required when evaluating drug disposition and pharmacokinetics. Various in vitro methods/techniques are available to measure the rate of permeation of compounds across epithelial cell membranes to estimate oral drug absorption in humans. The aim of this study is to compare three in vitro models (i.e. excised rat intestinal tissue, excised pig intestinal tissue and Caco-2 human cell cultures) in terms of drug permeability characteristics by means of different techniques including the Ussing type Sweetana-Grass diffusion chamber apparatus, everted sac glass apparatus and the Transwell® plate apparatus. The transport of abacavir sulphate was determined in two directions (i.e. apical-to-basolateral or AP - BL and basolateral-to-apical or BL - AP) across excised rat intestinal tissue, excised pig intestinal tissue and Caco-2 cell monolayers. The test solution was applied to the donor side and samples (200 μl) were drawn from the acceptor side at 20 min intervals for a period of 2 h. The concentration of abacavir in the samples was then measured by means of a validated high performance liquid chromatography (HPLC) method. The transepithelial electrical resistance (TEER) was measured before and after each transport experiment to give an indication of the integrity of the cell membranes. The apparent permeability coefficient (Papp) and efflux ratio (ER) values were calculated and used to compare the different methods and techniques in terms of drug permeation characteristics. All three of the in vitro methods, in all of the techniques employed, showed higher transport of abacavir in the BL - AP direction than in the AP - BL direction. This indicates that all three in vitro methods had intact active efflux transporters over the entire study period. The excised rat intestinal method showed similar drug permeability characteristics in both techniques compared to that of the Caco-2 cell monolayers. In contrast, the excised pig intestinal method only showed similar drug permeability characteristics in the Sweetana-Grass diffusion apparatus when compared to the Caco-2 cell monolayers. This phenomenon can possibly be explained by the relatively large surface area of the pig tissue used in the everted sac technique where the role of physiological and other factors take effect. These factors may include the thickness of the membrane and mucus layer as well as variables such as diet, age, gender and size of the pigs obtained from the abattoir that cannot be controlled. / MSc (Pharmaceutics), North-West University, Potchefstroom Campus, 2015

A crucial step in the drug discovery and development process is the assessment of membrane permeability properties of new chemical entities and researchers are constantly searching for cost-effective, high through-put models with as high as possible predictive value. In addition, a thorough understanding of the membrane permeability pathways and metabolism mechanisms are required when evaluating drug disposition and pharmacokinetics. Various in vitro methods/techniques are available to measure the rate of permeation of compounds across epithelial cell membranes to estimate oral drug absorption in humans. The aim of this study is to compare three in vitro models (i.e. excised rat intestinal tissue, excised pig intestinal tissue and Caco-2 human cell cultures) in terms of drug permeability characteristics by means of different techniques including the Ussing type Sweetana-Grass diffusion chamber apparatus, everted sac glass apparatus and the Transwell® plate apparatus. The transport of abacavir sulphate was determined in two directions (i.e. apical-to-basolateral or AP - BL and basolateral-to-apical or BL - AP) across excised rat intestinal tissue, excised pig intestinal tissue and Caco-2 cell monolayers. The test solution was applied to the donor side and samples (200 μl) were drawn from the acceptor side at 20 min intervals for a period of 2 h. The concentration of abacavir in the samples was then measured by means of a validated high performance liquid chromatography (HPLC) method. The transepithelial electrical resistance (TEER) was measured before and after each transport experiment to give an indication of the integrity of the cell membranes. The apparent permeability coefficient (Papp) and efflux ratio (ER) values were calculated and used to compare the different methods and techniques in terms of drug permeation characteristics. All three of the in vitro methods, in all of the techniques employed, showed higher transport of abacavir in the BL - AP direction than in the AP - BL direction. This indicates that all three in vitro methods had intact active efflux transporters over the entire study period. The excised rat intestinal method showed similar drug permeability characteristics in both techniques compared to that of the Caco-2 cell monolayers. In contrast, the excised pig intestinal method only showed similar drug permeability characteristics in the Sweetana-Grass diffusion apparatus when compared to the Caco-2 cell monolayers. This phenomenon can possibly be explained by the relatively large surface area of the pig tissue used in the everted sac technique where the role of physiological and other factors take effect. These factors may include the thickness of the membrane and mucus layer as well as variables such as diet, age, gender and size of the pigs obtained from the abattoir that cannot be controlled. / MSc (Pharmaceutics), North-West University, Potchefstroom Campus, 2015

Tocopheryl Polyethylene Glycol Succinate 1000 (TPGS 1000) can inhibit P-glycoprotein (P-gp); TPGS 1000 was not originally designed to inhibit an efflux pump. Recent work from our laboratories demonstrated that TPGS activity has a rational PEG chain length dependency. In other recent work, inhibition mechanism was investigated and appears to be specific to the ATPase providing P-gp energy. Based on these observations, we commenced rational surface-active design. The current work summarizes new materials tested in a validated Caco-2 cell monolayer model; rhodamine 123 (10 μM) was used as the P-gp substrate. These results demonstrate that one may logically construct non-ionic surfactants with enhanced propensity to inhibit in vitro efflux. One new surfactant based inhibitor, Tocopheryl Polypropylene Glycol Succinate 1000 (TPPG 1000), approached cyclosporine (CsA) in its in vitro efflux inhibitory potency. Subsequently, TPPG 1000 was tested for its ability to enhance the bioavailability of raloxifene - an established P-gp substrate - in fasted male rats. Animals dosed with raloxifene and TPPG 1000 experienced an increase in raloxifene oral bioavailability versus a control group which received no inhibitor. These preliminary results demonstrate that one may prepare TPGS analogs that possess enhanced inhibitory potency in vitro and in vivo.