Primary cell providers

For in vitro toxicity studies and assessment of the barrier function, drug transport, cell physiology, and metabolism as well as the development of delivery systems, cell culture models provide powerful systems for scientific research. As the corneal epithelium is the main barrier for ocular penetration, various corneal epithelial cell cultures were established besides the corneal constructs that mimic the whole cornea and serve as reductionist models for the ocular barrier. In general, two types of cell culture models are available primary cell cultures and immortalized, continuous cell lines. 

Whole cells (for example, primary hepatocytes or genetically engineered cells) provide the simplest intact system for the study of xenobiotic metabolism (Ratanasavanh et al., 1986 Daujat et al., 1991 Berry et al.,... 

The assessment of the number of experimental metastases, typically pulmonary metastases, following i.v. injection of a single cell suspension of tumor cells or collagenase-digested primary tumor provides the most common outcomes. Multiple strategies may be used for this enumeration including... 

The primary cell culture model is a more valid model for the study of absorption and transport processes of a drug via the pulmonary route. It provides a tight epithelial barrier with morphological and functional properties resembling those of the in-vivo condition. Primary alveolar epithelial cells from rats [39], rabbits [40] and humans [41] which display morphological and biochemical characteristics similar to the native epithelium have been isolated and can be used for drug transport studies. 

Use of an endothelial cell line should not be considered a substitute for primary endothelial cells such as HUVEC, as different endothelial cell lines may vary in the type and level of adhesion molecules expressed as well as their response to various stimuli such as cytokines. Endothelial cell lines provide a convenient, homogenous, and defined (if not necessarily relevant) cell mono-layer through which leukocytes must migrate in the chemotaxis assay. We find that use of an endothelial cell line to reduce the background migration of primary cells not only improves the signal-to-noise ratio of the assay but also the reproducibility of the assay as compared to HUVEC. 

Products that may have the potential to stimulate growth or induce proliferation or clonal expansion of cell types, in particular, transformed cells, all processes that may eventually lead to neoplasia should be evaluated with respect to receptor expression in various malignant and normal human cells that are relevant to the patient population under study [27], In such cases normal human cell lines and multiple human cancer cell lines expressing the relevant receptor, as well as primary cells derived from human tumor explants, should be used for in vitro assessment. When in vitro data demonstrate enhanced growth, further studies in relevant in vivo xenograft animal models with receptor expressing tumor cell lines may be needed. In addition incorporation of sensitive indexes of cellular proliferation in long-term repeat-dose toxicity studies may provide useful information. 

Many commercial suppliers (Table 10.3) have established protocols and procedures that address many of these issues. Primary human and animal cells of a variety of types are often available, sometimes as ready-to-use frozen stock aliquots or already added to 96-or 384-well plates. Specific culturing medium and detailed protocols for the correct maintenance of the cell line in culture are usually provided as well. This should facilitate the use of primary cells for primary HTS and compound validation. 

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