Gregor Zlokarnik

Cell-permeant caged InsP3 ester shows that Ca2+ spike frequency can optimize gene expression.

Inositol 1,4,5-trisphosphate (InsP3) releases calcium from intracellular stores and triggers complex waves and oscillations in levels of cytosolic free calcium,. To determine which longer-term responses are controlled by oscillations in InsP3 and cytosolic free calcium, it would be useful to deliver exogenous InsP3, under spatial and temporal control, into populations of unpermeabilized cells. Here we report the 15-step synthesis of a membrane-permeant, caged InsP3 derivative from myo-inositol. This derivative diffused into intact cells and was hydrolysed to produce a caged, metabolically stable InsP3 derivative. This latter derivative accumulated in the cytosol at concentrations of hundreds of micromolar, without activating the InsP3 receptor. Ultraviolet illumination uncaged an InsP3 analogue nearly as potent as real InsP3, and generated spikes of cytosolic free calcium, and stimulated gene expression via the nuclear factor of activated T cells,. The same total amount of InsP3 analogue elicited much more gene expression when released by repetitive flashes at 1-minute intervals than when released at 0.5- or ⩾2-minute intervals, as a single pulse, or as a slow sustained plateau. Thus, oscillations in cytosolic free calcium levels at roughly physiological rates maximize gene expression for a given amount of InsP3.

High throughput P450 inhibition screens in early drug discovery.

This review of high throughput (HT) P450 inhibition technologies and their impact on early drug discovery finds the field at a mature stage. The relationship between P450 inhibition and drug-drug interactions is well understood. A wide variety of P450 inhibition detection technologies are readily available off-the-shelf, but what seems still to be missing is a general agreement on how much weight one should give to the various types of early discovery HT P450 inhibition data. Method-dependent potency differences are a cause of concern, and to resolve this issue the authors advocate calibration of the HT methods with a large set of marketed drugs.

A genome-wide functional assay of signal transduction in living mammalian cells.

We describe a genome-wide functional assay for rapid isolation of cell clones and genetic elements responsive to specific stimuli. A promoterless β-lactamase reporter gene was transfected into a human T-cell line to generate a living library of reporter-tagged clones. When loaded with a cell-permeable fluorogenic substrate, the cell library simultaneously reports the expression of a large number of endogenous genes. Flow cytometry was used to recover individual clones whose reporter-tagged genes were either induced or repressed following T-cell activation. Responsive clones were expanded and analyzed pharmacologically to identify patterns of regulation associated with specific genes. Although demonstrated using T cells, the genomic assay could be applied to map downstream transcriptional consequences for any propagating cell line in response to any stimulus of interest.

In silico prediction of drug safety: despite progress there is abundant room for improvement

Predictive models for drug safety are crucial for helping to avoid costly late-stage failures. We review recent work on models for genotoxicity, liver toxicity, CYP450 inhibition and cardiotoxicity. These models have improved somewhat in recent years, and research has expanded into new frontiers, such as the prediction of liver toxicity. However, much more needs to be done.:

Detection of β-lactamase reporter gene expression by flow cytometry

Flow cytometry of gene expression in living cells requires accurate, sensitive, nontoxic fluorescent indicators capable of detecting transcription of specific genes. This is typically achieved by using genes that encode fluorescent proteins or enzymes coupled to promoters of interest. The most commonly used reporters are green fluorescent protein and β‐galactosidase (lacZ). In this study, we characterized the performance of a cell‐permeant, ratiometric, β‐lactamase substrate, coumarin cephalosporin fluorescein (CCF2/AM). We compared its characteristics with that of the β‐galactosidase/fluorescein di‐β‐D‐galactopyranoside reporter system.