Oncology drug discovery applications using the FMAT 8100 HTS system

Mammalian cell-based sensor system

Use of living cells or cellular components in biosensors is receiving increased attention and opens a whole new area of functional diagnostics. The term "mammalian cell-based biosensor" is designated to biosensors utilizing mammalian cells as the biorecognition element. Cell-based assays, such as high-throughput screening (HTS) or cytotoxicity testing, have already emerged as dependable and promising approaches to measure the functionality or toxicity of a compound (in case of HTS); or to probe the presence of pathogenic or toxigenic entities in clinical, environmental, or food samples. External stimuli or changes in cellular microenvironment sometimes perturb the "normal" physiological activities of mammalian cells, thus allowing CBBs to screen, monitor, and measure the analyte-induced changes. The advantage of CBBs is that they can report the presence or absence of active components, such as live pathogens or active toxins. In some cases, mammalian cells or plasma membranes are used as electrical capacitors and cell-cell and cell-substrate contact is measured via conductivity or electrical impedance. In addition, cytopathogenicity or cytotoxicity induced by pathogens or toxins resulting in apoptosis or necrosis could be measured via optical devices using fluorescence or luminescence. This chapter focuses mainly on the type and applications of different mammalian cell-based sensor systems.

Fluorescent detection of apoptotic cells by using zinc coordination complexes with a selective affinity for membrane surfaces enriched with phosphatidylserine

The appearance of phosphatidylserine on the membrane surface of apoptotic cells (Jurkat, CHO, HeLa) is monitored by using a family of bis(Zn2+-2,2'-dipicolylamine) coordination compounds with appended fluorescein or biotin groups as reporter elements. The phosphatidylserine affinity group is also conjugated directly to a CdSe/CdS quantum dot to produce a probe suitable for prolonged observation without photobleaching. Apoptosis can be detected under a wide variety of conditions, including variations in temperature, incubation time, and binding media. Binding of each probe appears to be restricted to the cell membrane exterior, because no staining of organelles or internal membranes is observed.

Development of Peptidomimetics Targeting IAPs

Inhibitor of apoptosis proteins (IAPs) such as XIAP subvert apoptosis by binding and inhibiting caspases. Because occupation of the XIAP BIR3 peptide binding pocket by Smac abolishes the XIAP–caspase 9 interaction, it is a proapoptotic event of great therapeutic interest. An assay for pocket binding was developed based on the displacement of Smac 7-mer from BIR3. Through the physical and biochemical analysis of a variety of peptides, we have determined the minimum sequence required for inhibition of the Smac–BIR3 interaction and detailed the dimensions and topology of the BIR3 peptide binding pocket. This work describes the structure–activity relationship (SAR) for peptide inhibitors of Smac-IAP binding.

Development of fluorescence-linked immunosorbent assay for high throughput screening of interferon-gamma

BACKGROUND

Human interferon-gamma (hIFN-gamma) is produced by lymphocytes and has a variety of biological properties. Measurement of hIFN-gamma is widely used for various immunological responses for allergic or autoimmune diseases. Enzyme-linked immunosorbent assay (ELISA) is an established immunoassay used to quantify cellular metabolites or cytokines. ELISA requires many incubation and wash steps and is not practically suitable for screening large numbers of samples.

METHODS

We have developed a fluorescence-linked immunosorbent assay (FLISA) method for the detection of hIFN-gamma. We measured the 50% inhibitory concentration (IC50) value of the hIFN-gamma production by interleukin (IL)-18 binding protein and anti-IL-18 monoclonal antibody. The IC50 described by FLISA was compared with that by ELISA.

RESULTS

We developed a new system for measuring hIFN-gamma using Allophycocyanine (APC) fluorescent protein and compared it with the previous method using Cy5.5. The proposed FLISA had a smaller coefficient of variation than ELISA, and the means of coefficient of variation using the same samples measured by ELISA and FLISA were, respectively, 11.1% and 3.8%, suggesting that the edge effect often giving non-specific results may be smaller in FLISA than in ELISA.

CONCLUSIONS

The improved FLISA system proposed is ideally suited for efficient measurements of hIFN-gamma. This homogeneous and multiplex method will be a powerful tool for high throughput screening for drug discovery research.

Continuous perfusion microfluidic cell culture array for high-throughput cell-based assays

We present for the first time a microfluidic cell culture array for long-term cellular monitoring. The 10 x 10 array could potentially assay 100 different cell-based experiments in parallel. The device was designed to integrate the processes used in typical cell culture experiments on a single self-contained microfluidic system. Major functions include repeated cell growth/passage cycles, reagent introduction, and real-time optical analysis. The single unit of the array consists of a circular microfluidic chamber, multiple narrow perfusion channels surrounding the main chamber, and four ports for fluidic access. Human carcinoma (HeLa) cells were cultured inside the device with continuous perfusion of medium at 37 degrees C. The observed doubling time was 1.4 +/- 0.1 days with a peak cell density of approximately 2.5*10(5) cells/cm(2). Cell assay was demonstrated by monitoring the fluorescence localization of calcein AM from 1 min to 10 days after reagent introduction. Confluent cell cultures were passaged within the microfluidic chambers using trypsin and successfully regrown, suggesting a stable culture environment suitable for continuous operation. The cell culture array could offer a platform for a wide range of assays with applications in drug screening, bioinformatics, and quantitative cell biology.

Small-molecule antagonists of the oncogenic Tcf/beta-catenin protein complex

Key molecular lesions in colorectal and other cancers cause beta-catenin-dependent transactivation of T cell factor (Tcf)-dependent genes. Disruption of this signal represents an opportunity for rational cancer therapy. To identify compounds that inhibit association between Tcf4 and beta-catenin, we screened libraries of natural compounds in a high-throughput assay for immunoenzymatic detection of the protein-protein interaction. Selected compounds disrupt Tcf/beta-catenin complexes in several independent in vitro assays and potently antagonize cellular effects of beta-catenin-dependent activities, including reporter gene activation, c-myc or cyclin D1 expression, cell proliferation, and duplication of the Xenopus embryonic dorsal axis. These compounds thus meet predicted criteria for disrupting Tcf/beta-catenin complexes and define a general standard to establish mechanism-based activity of small molecule inhibitors of this pathogenic protein-protein interaction.

A "Mix and Read" Assay for Insulin Using Fluorometric Microvolume Assay Technology

We describe a novel, "mix and read" immunoassay for insulin in biological samples using FMAT. Current commercial assays for insulin require multiple washing steps and can be expensive. The insulin assay described is a simple two-step, time-saving assay and amenable to robotics. The linear response for the fluorometric signal is comparable to that observed using classical ELISA and RIA. A series of mouse plasma samples were tested for insulin levels and yielded results comparable to that measured using a commercial ELISA for insulin.