In Silico Methods for Unraveling the Mechanistic Complexities of Intestinal Absorption: Metabolism-Efflux Transport Interactions

Garmire, Lana X.; Hunt, C. Anthony

doi:10.1124/dmd.107.020164

Cited by 14 publications

(16 citation statements)

References 23 publications

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“…The logic used by each CYP and PGP along with their function verification was reported in Lam and Hunt (2008). We have used, reused, verified, and validated several variations of CYP and PGP (Garmire and Hunt, 2008;). Different model uses and different referent data can call for different capabilities.…”

Section: Methodsmentioning

confidence: 99%

Mechanistic Insight from In Silico Pharmacokinetic Experiments: Roles of P-glycoprotein, Cyp3A4 Enzymes, and Microenvironments

Lam

Hunt²

2009

J Pharmacol Exp Ther

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Saquinavir exhibits paradoxical transport across modified Caco-2 cell monolayers (doi: 10.1124/jpet.103.056390) expressing P-glycoprotein and Cyp3A4. The data implicate complicated intracellular transport mechanisms. Drawing on recent discrete event modeling and simulation advances, we built an in silico analog of the confluent, asymmetric cell monolayer used in the cited work. We call it in silico experimental Caco-2 (cell monolayer) culture (ISECC). Concrete, working, hypothesized spatial mechanisms were implemented. Validation was achieved when in silico experimental results met similarity measure (SM) expectations that targeted 16 wet-lab experimental conditions. Initial mechanistic hypotheses turned out to be necessary parts of a more complicated explanation. We progressed through four stages of an iterative refinement and validation protocol that enabled and facilitated discovery of plausible, new mechanistic details. The process exercised abductive reasoning, a primary means of scientific knowledge creation and creative cognition. The ISECC that survived the most stringent SM challenge produced transport data that was statistically indistinguishable from referent wet-lab observations. It required a 7:1 ratio of apical transporters to metabolizing enzymes, a 97% reduction of efflux activity by an inhibitor, a biased distribution of metabolizing enzymes, heterogeneous intracellular spaces, and restrictions on intracellular drug movement. Experimenting on synthetic analogs such as ISECC provides a former unavailable means of discovering new mechanistic details and testing their plausibility. The approach thus provides a powerful new expansion of the scientific method: an independent, scientific means to challenge, explore, better understand, and improve any inductive mechanism and, importantly, the assumptions on which it rests. et al. (2004) reported paradoxical observations after a vectorial study of saquinavir transport across a monolayer of modified P-glycoprotein (P-gp) and Cyp3A4-expressing Caco-2 cells: there were higher intracellular levels of saquinavir, yet less metabolite formation after apical compared with basal dosing. The data clearly indicated that the intracellular mechanisms during transport were more complicated than anticipated. Mouly

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Section: Methodsmentioning

confidence: 99%

Mechanistic Insight from In Silico Pharmacokinetic Experiments: Roles of P-glycoprotein, Cyp3A4 Enzymes, and Microenvironments

Lam

Hunt²

2009

J Pharmacol Exp Ther

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“…Although the total amount of intestinal CYP3A is relatively low compared with that in the liver, its strategic colocalization with P-gp in the villous tip of the enterocyte may provide a highly effective barrier against drug absorption. In view of the extensive overlap in their substrates, it has been hypothesized that, for many drugs, it is the combination of back-transport by P-gp in the intestinal epithelial cell and the presence of CYP3A-mediated metabolism within the same cell that makes for efficient first-pass metabolism of orally administered drugs (9)(10)(11)(12)(13)(14). The idea is that, by lowering the intracellular drug concentration, P-gp might help to prevent saturation of enterocyte CYP3A.…”

Section: Introductionmentioning

confidence: 99%

Absence of Both Cytochrome P450 3A and P-glycoprotein Dramatically Increases Docetaxel Oral Bioavailability and Risk of Intestinal Toxicity

et al. 2009

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Docetaxel is one of the most widely used anticancer drugs. A major problem with docetaxel treatment, however, is the considerable interpatient variability in docetaxel exposure. Another disadvantage of the drug is that it has a very low oral bioavailability and can therefore only be administered i.v. The drug-metabolizing enzyme cytochrome P450 3A (CYP3A) and the drug transporter P-glycoprotein (P-gp; MDR1) are considered to be major determinants of docetaxel pharmacokinetics. It has been hypothesized that CYP3A and P-gp work synergistically in limiting the systemic exposure to many orally ingested drugs. However, it has been difficult to examine this interplay in vivo. We therefore generated mice lacking all CYP3A and P-gp genes. Although missing two primary detoxification systems, Cyp3a/Mdr1a/1b

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“…We would start with TRANSPORTER agents that have been used in other models of this class. To date, TRANSPORTER agents have been validated and used within analogs of cell cultures used in transport studies (Garmire et al, 2007;Lam and Hunt, 2008), including hepatocytes (Sheikh-Bahae and and an in an analog of the small intestine (Garmire and Hunt, 2008).…”

Section: Discussionmentioning

confidence: 99%

Computational Strategies Unravel and Trace How Liver Disease Changes Hepatic Drug Disposition

Ropella¹,

Kim²,

Roberts³

et al. 2008

J Pharmacol Exp Ther

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Liver disease changes the disposition properties of drugs, complicating drug therapy management. We present normal and "diseased" versions of an abstract, agent-oriented In Silico Livers (ISLs), and validate their mechanisms against disposition data from perfused normal and diseased rat livers. Dynamic tracing features enabled spatiotemporal tracing of differences in dispositional events for diltiazem and sucrose across five levels, including interactions with representations of lobular microarchitectural features, cells, and intracellular factors that sequester and metabolize. Differences in attributes map to measures of histopathology. We measured disease-causing differences in local, intralobular ISL effects, obtaining until now unavailable views of how and where hepatic drug disposition may differ in normal and diseased rat livers from diltiazem's perspective. Exploration of disposition in less and more advanced stages of disease is feasible. The approach and technology represent an important step toward unraveling the complex changes from normal to disease states and their influences on drug disposition.Changes in drug disposition properties caused by liver disease complicate drug selection and therapy management. Recent advances in computational biology are providing new, broadly applicable strategies to unravel such complexities. How does cirrhosis (Hung et al., 2002a,b) cause observed changes in hepatic drug disposition? More detailed understanding of precisely how drugs behave in diseased relative to normal livers requires new modeling strategies in which events at different levels can be observed and measured in both space and time. We address this need and provide a novel means of creating and testing real, working representations of hypothesized mechanisms. We present and validate a plausible explanation for structural and functional differences in the normal and diseased rat livers from the perspective of a specific drug, diltiazem (Hung et al., 2001), a cationic compound known to interact with hepatic components at all levels. We then show how those changes may have caused the observed differences in diltiazem's disposition.The In Silico Liver (ISL) Yan et al., 2008a,c) in Fig. 1 is an abstract analog built in software using discrete, object-oriented methods. It is an advanced example of what has been referred to as executable biology (Fisher and Henzinger, 2007;Hunt et al., 2008). ISLs are physiologically based, multilevel analogs of livers undergoing perfusion. They are not intended to be accurate, precise descriptions of how we think the liver works nor are they intended to provide precise, accurate predictions. Rather, they help us reduce uncertainties about hepatic mechanisms enabling us to refine, explore, and test hypotheses about the mechanistic details of hepatic drug disposition. In depicting three-dimensional hepatic morphology at a cellular level, it uses quasiautonomous components that recognize and interact uniquely with mobile objects representing different compounds. The...

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In Silico Methods for Unraveling the Mechanistic Complexities of Intestinal Absorption: Metabolism-Efflux Transport Interactions

Cited by 14 publications

References 23 publications

Mechanistic Insight from In Silico Pharmacokinetic Experiments: Roles of P-glycoprotein, Cyp3A4 Enzymes, and Microenvironments

Mechanistic Insight from In Silico Pharmacokinetic Experiments: Roles of P-glycoprotein, Cyp3A4 Enzymes, and Microenvironments

Absence of Both Cytochrome P450 3A and P-glycoprotein Dramatically Increases Docetaxel Oral Bioavailability and Risk of Intestinal Toxicity

Computational Strategies Unravel and Trace How Liver Disease Changes Hepatic Drug Disposition

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