The key to the cells: The N‐terminal organometallic complex shown greatly improves cellular uptake of a bioconjugate containing the NLS peptide (NLS=nuclear localization sequence) and cobaltocenium carboxylic acid. Nuclear localization of this novel organometallic bioconjugate in HepG2 cells is demonstrated by live‐cell fluorescence microscopy (see picture). FITC=fluorescein isothiocyanate.

Integrated approaches using different in vitro methods in combination with bioinformatics can (i) increase the success rate and speed of drug development; (ii) improve the accuracy of toxicological risk assessment; and (iii) increase our understanding of disease. Three-dimensional (3D) cell culture models are important building blocks of this strategy which has emerged during the last years. The majority of these models are organotypic, i.e., they aim to reproduce major functions of an organ or organ system. This implies in many cases that more than one cell type forms the 3D structure, and often matrix elements play an important role. This review summarizes the state of the art concerning commonalities of the different models. For instance, the theory of mass transport/metabolite exchange in 3D systems and the special analytical requirements for test endpoints in organotypic cultures are discussed in detail. In the next part, 3D model systems for selected organs--liver, lung, skin, brain--are presented and characterized in dedicated chapters. Also, 3D approaches to the modeling of tumors are presented and discussed. All chapters give a historical background, illustrate the large variety of approaches, and highlight up- and downsides as well as specific requirements. Moreover, they refer to the application in disease modeling, drug discovery and safety assessment. Finally, consensus recommendations indicate a roadmap for the successful implementation of 3D models in routine screening. It is expected that the use of such models will accelerate progress by reducing error rates and wrong predictions from compound testing.

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Tissue engineering of human liver cells in a three dimensional cell culture system could improve pharmacological studies in terms of drug metabolism, drug toxicity or adverse drug effects by mimicking the in vivo situation. In this study, we produced 3D organotypic cultures of HepG2 cells using the hanging drop method. 250 -8000 seeded cells formed organotypic cultures within 2-3 days which increased in size during the first week. Viability and metabolic parameters (glucose, lactate) were analyzed during almost three weeks of cultivation. Liver specific albumin production was higher in the organotypic cultures as compared to both monolayer and collagen-sandwich cultures. Amino acid quantification revealed high production of glutamate as well as uptake of glutamine, alanine and branched-chain amino acids. CYP1A induction capacity was significantly improved by organotypic cultivation. The acute toxicity (24 h) of tamoxifen, an anti-cancer drug, was lower in the 3D cultures as compared to monolayer and collagen-sandwich cultures. This could be explained by a higher drug efflux through membrane transporter (MRP-2). We conclude that the engineered HepG2 cultures could be used for the investigation of CYP450 induction, anti-cancer drug effects and for the study of chemotherapy resistance. Applied to other cell types such as the human primary cells these 3D organotypic cultures may have potential in long term toxicity screening of compounds.

Die N‐terminale Organometallverbindung 1 sorgt für die ungewöhnlich leichte zelluläre Aufnahme eines Biokonjugats aus NLS‐Peptid und Cobaltoceniumcarbonsäure. Eine Anreicherung im Zellkern wurde durch Fluoreszenzmikroskopie an lebenden HepG2‐Zellen nachgewiesen (siehe Bild). NLS=Kernlokalisierungssignal (nuclear localization signal), FITC=Fluoresceinisothiocyanat.