Traditional screening paradigms often focus on single targets. To facilitate drug discovery in the more complex physiological environment of a cell or organism, powerful cellular imaging systems have been developed. The emergence of these detection technologies allows the quantitative analysis of cellular events and visualization of relevant cellular phenotypes. Cellular imaging facilitates the integration of complex biology into the screening process, and addresses both high-content and high-throughput needs. This review describes how cellular imaging technologies contribute to the drug discovery process.

The signal transduction pathways connecting cell surface receptors to the activation of muscle-specific promoters and leading to myogenesis are still largely unknown. Recently, a contribution of the p38 mitogen-activated protein kinase (MAPK) pathway to this process was evoked through the use of pharmacological inhibitors. We used several mutants of the kinases composing this pathway to modulate the activity of the muscle-specific myosin light chain and myogenin promoters in C2C12 cells by transient transfections. In addition, we show for the first time, using a stable C2C12 cell line expressing a dominant-negative form of the p38 activator MAPK kinase (MKK)3, that a functional p38 MAPK pathway is indeed required for terminal muscle cell differentiation. The most obvious phenotype of this cell line, besides the inhibition of the activation of p38, is its inability to undergo terminal differentiation. This phenotype is accompanied by a drastic inhibition of cell cycle and myogenesis markers such as p21, p27, MyoD, and troponin T, as well as a profound disorganization of the cytoskeleton.

Sorsby's fundus dystrophy (SFD) is an autosomal dominant degenerative disease of the macula caused by mutations in the tissue inhibitor of metalloproteinase-3 (TIMP-3) gene. Choroidal neovascularization is a hallmark of this disease, which closely resembles the exudative form of age-related macular degeneration. However, the mechanism by which TIMP-3 mutations induce the disease phenotype in SFD remains unknown. To address this question we established human retinal pigment epithelial cell lines expressing wild type or S156C (Ser 156 changed to cysteine) mutant TIMP-3. S156C TIMP-3 had reduced matrix metalloproteinase (MMP) inhibitory activity in retinal pigment epithelial cells and resulted in increased secretion and activation of gelatinase A and B. The conditioned medium from these cells induced angiogenesis in "in vivo" chick chorioallantoic membrane assays that could be reversed with recombinant wild type TIMP-3. Our data indicate that the choroidal neovascularization in SFD may be a result of increased MMP activity, which could lead to the stimulation of angiogenesis. These results also suggest the potential therapeutic use of TIMP-3 or synthetic MMP inhibitors in this disease.Sorsby's fundus dystrophy (SFD), 1 a fully penetrant, autosomal dominant, degenerative disease of the macula (1), is manifested by symptoms of night blindness or sudden loss of acuity usually in the third to fourth decades of life due to submacular neovascularization (2-5). Clinically, early mid-peripheral drusen and color vision deficits are found (4, 5). SFD is a relatively rare disease, but it has generated significant interest because it closely resembles the exudative or "wet" form of age-related macular degeneration, the most common cause of blindness in the elderly population of the western world. SFD is characterized by accumulation of extracellular deposits (drusen) in Bruch's membrane, the five-layered sheet of connective tissue that separates the retinal pigment epithelium (RPE) from the choriocapillaris (6). The predominant histopathological feature in the eyes of a 63-year-old patient with SFD was a confluent 30-m thick, lipid-containing amorphous deposit found between the basement membrane of the RPE and the inner collagenous layer of Bruch's membrane (6). This is distinct from the basal linear deposits seen in age-related macular degeneration that consist of filamentous fine granular material and may represent a thickened basement membrane of the RPE (6). The subretinal deposits in both SFD and age-related macular degeneration have been shown to be rich in tissue inhibitor of metalloproteinase-3 (TIMP-3) (7,8). A serious complication of SFD is the invasion of the thickened Bruch's membrane by newly formed, thin-walled vessels derived from the choriocapillaris. These vessels grow into the subretinal space causing exudative detachment of the RPE and loss of photoreceptors (5). SFD has been linked with mutations in the TIMP-3 gene (10 -12) with five different missense mutations and a splice site mutation having been identi...

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