Nuisance compounds in cellular assays.

Compounds that exhibit assay interference or undesirable mechanisms of bioactivity ("nuisance compounds") are routinely encountered in cellular assays, including phenotypic and high-content screening assays. Much is known regarding compound-dependent assay interferences in cell-free assays. However, despite the essential role of cellular assays in chemical biology and drug discovery, there is considerably less known about nuisance compounds in more complex cell-based assays. In our view, a major obstacle to realizing the full potential of chemical biology will not just be difficult-to-drug targets or even the sheer number of targets, but rather nuisance compounds, due to their ability to waste significant resources and erode scientific trust. In this review, we summarize our collective academic, government, and industry experiences regarding cellular nuisance compounds. We describe assay design strategies to mitigate the impact of nuisance compounds and suggest best practices to efficiently address these compounds in complex biological settings.

Quantitative optimization of reverse transfection conditions for 384-well siRNA library screening.

A necessary step in all small interfering RNA (siRNA) library screens is introduction of the siRNA into cells. We describe the use of a commercially available glyceraldehyde 3-phosphate dehydrogenase enzymatic assay that is capable of simultaneously assessing the efficiency of siRNA delivery into cells and the lipid toxicity. This assay has been modified to work in 384-well plates using reverse transfection. The assay is fast, inexpensive, and quantitative. Conditions identified as optimal using this technique have been employed successfully in library screens.

IkappaBalpha kinase inhibitor IKI-1 conferred tumor necrosis factor alpha sensitivity to pancreatic cancer cells and a xenograft tumor model.

Tumor necrosis factor alpha (TNFalpha) has been used to treat patients with certain tumor types. However, its antitumor activity has been undermined by the activation of IkappaBalpha kinase (IKK), which in turn activates nuclear factor-kappaB (NF-kappaB) to help cancer cells survive. Therefore, inhibition of TNFalpha-induced IKK activity with specific IKK inhibitor represents an attractive strategy to treat cancer patients. This study reveals IKI-1 as a potent small molecule inhibitor of IKKalpha and IKKbeta, which effectively blocked TNFalpha-mediated IKK activation and subsequent NF-kappaB activity. Using gene profiling analysis, we show that IKI-1 blocked most of the TNFalpha-mediated mRNA expression, including many genes that play important roles in cell survival. We further show that in vitro and in vivo combination of TNFalpha with IKI-1 had superior potency than either agent alone. This increased potency was due primarily to the increased apoptosis in the presence of both TNFalpha and IKI-1. Additionally, IKKbeta small interfering RNA transfected cells were more sensitive to the treatment of TNFalpha. The study suggests that the limited efficacy of TNFalpha in cancer treatment was due in part to the activation of NF-kappaB, allowing tumor cells to escape apoptosis. Therefore, the combination of IKI-1 with TNFalpha may improve the efficacy of TNFalpha for certain tumor types.

Impact of image segmentation on high-content screening data quality for SK-BR-3 cells.

BACKGROUND: High content screening (HCS) is a powerful method for the exploration of cellular signalling and morphology that is rapidly being adopted in cancer research. HCS uses automated microscopy to collect images of cultured cells. The images are subjected to segmentation algorithms to identify cellular structures and quantitate their morphology, for hundreds to millions of individual cells. However, image analysis may be imperfect, especially for "HCS-unfriendly" cell lines whose morphology is not well handled by current image segmentation algorithms. We asked if segmentation errors were common for a clinically relevant cell line, if such errors had measurable effects on the data, and if HCS data could be improved by automated identification of well-segmented cells. RESULTS: Cases of poor cell body segmentation occurred frequently for the SK-BR-3 cell line. We trained classifiers to identify SK-BR-3 cells that were well segmented. On an independent test set created by human review of cell images, our optimal support-vector machine classifier identified well-segmented cells with 81% accuracy. The dose responses of morphological features were measurably different in well- and poorly-segmented populations. Elimination of the poorly-segmented cell population increased the purity of DNA content distributions, while appropriately retaining biological heterogeneity, and simultaneously increasing our ability to resolve specific morphological changes in perturbed cells. CONCLUSION: Image segmentation has a measurable impact on HCS data. The application of a multivariate shape-based filter to identify well-segmented cells improved HCS data quality for an HCS-unfriendly cell line, and could be a valuable post-processing step for some HCS datasets.

Discovery of novel inhibitors of the ZipA/FtsZ complex by NMR fragment screening coupled with structure-based design.

ZipA is a membrane anchored protein in Escherichia coli that interacts with FtsZ, a homolog of eukaryotic tubulins, forming a septal ring structure that mediates bacterial cell division. Thus, the ZipA/FtsZ protein-protein interaction is a potential target for an antibacterial agent. We report here an NMR-based fragment screening approach which identified several hits that bind to the C-terminal region of ZipA. The screen was performed by 1H-15N HSQC experiments on a library of 825 fragments that are small, lead-like, and highly soluble. Seven hits were identified, and the binding mode of the best one was revealed in the X-ray crystal structure. Similar to the ZipA/FtsZ contacts, the driving force in the binding of the small molecule ligands to ZipA is achieved through hydrophobic interactions. Analogs of this hit were also evaluated by NMR and X-ray crystal structures of these analogs with ZipA were obtained, providing structural information to help guide the medicinal chemistry efforts.