Cell-based target validation, secondary screening, lead optimization, and structure-activity relationships have been recast with the advent of HCS. Prior to HCS, a computational approach to the characterization of the functions of specific target proteins and other cellular constituents, along with whole-cell functions employing fluorescence cell-based assays and microscopy, required extensive interaction among the researcher, instrumentation, and software tools. Early HCS platforms were instrument-centric and addressed the need to interface fully automated fluorescence microscopy, plate-handling automation, and seamless image analysis. HCS has since evolved into an integrated solution for accelerated drug discovery by encompassing the workflow components of assay and reagent design, robust instrumentation for automated fixed-end-point and live cell kinetic analysis, generalized and specific BioApplication software (Cellomics, Pittsburgh, PA) modules that produce information on drug responses from cell image data, and informatics/bioinformatics solutions that build knowledge from this information while providing a means to globalize HCS throughout an entire organization. This review communicates how these recent advances are incorporated into the drug discovery workflow by presenting a real-world use case.

The clinical usefulness of chemotherapeutic agents containing the platinum moiety is often limited by their nephrotoxicity. To investigate the mechanism of nephrotoxicity, and to assess the effects of platinum analogs on specific organelles and basal protein synthesis, biochemical and ultrastructural analyses were performed in rat renal proximal tubule cells (RPTCs). Neutral red (NR) uptake was used to measure lysosomal function, and conversion of MTT to formazan used to assess mitochondrial function. Despite their differential toxicity, cisplatin, carboplatin and CI-973 caused similar progressive inhibition of specific functions, suggesting they may share a common mechanism of nephrotoxicity. Protein synthesis was the earliest indicator of toxicity, followed by NR uptake and MTT conversion. Fluorescent probes for lysosomes (acridine orange) and mitochondria (rhodamine 123) confirmed that cisplatin's toxicity to RPTCs was delayed and cumulative. Condensation of nucleolar components and fragmentation of RER were observed in RPTCs treated for as little as two hours. Since the nucleolus is the site of ribosome biogenesis, the early inhibition of protein synthesis by cisplatin may arise from disruption of this region. In contrast, mitochondrial dysfunction and swelling were late-stage events, and are therefore unlikely to be the primary targets of nephrotoxic platinum compounds.

Thiazolidinediones (TZDs) are effective for the treatment of adult-onset insulin-resistant diabetes. Unfortunately, TZDs are associated with sporadic hepatic dysfunction that is not predictable from experimental animal studies. We investigated the response of isolated rat and human hepatocytes to various TZDs using biochemical assays, coherent multiprobe fluorescence microscopy and flow cytometric analyses. The results identified direct effects of TZD on mitochondria from live human and rodent hepatocytes. The multiprobe fluorescence assays showed disruption of mitochondrial activity as an initiating event followed by increased membrane permeability, calcium influx and nuclear condensation. Other TZD-related cellular effects were increased hepatic enzyme leakage, decreased reductive metabolism and cytoplasmic adenosine triphosphate depletion. Mitochondrial effects were similar in cryopreserved hepatocytes from diabetic or non-diabetic donors. Peripheral blood mononuclear cells (PBMCs) had baseline mitochondrial energetics and metabolism comparable with isolated hepatocytes. Mitochondrial effects in isolated hepatocytes were found in human PBMCs exposed to the TZDs. The relative potency of TZDs for causing hepatocyte and PBMC effects was troglitazone > pioglitazone > rosiglitazone. These studies clearly demonstrated that hepatic alterations in vitro are characteristic of TZDs, with only quantitative differences in subcellular organelle dysfunction. Monitoring mitochondrial function in isolated PBMCs may be beneficial in diabetics undergoing TZD therapy.

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