oa Editorial [Hot topic: Using Bioluminescent Assays as Quantitative Cell-Based and Biochemical Biosensors (Guest Editor: John Watson)]

A fundamental challenge in bioscience research is to quantify changes in the concentration of key signaling molecules within the context of biologically relevant cellular model systems. Cell-based assays represent a useful midpoint between whole animals and purified molecules for understanding complex biological processes in a statistically valid way. In particular, they enable a reductionist approach to understanding biochemical interactions within the context of the native cytoplasmic milieu. The inverse is not always true however, in that cell based assays do not necessarily describe the native tissue based environment behavior of cells in a whole organism. While a number of technologies have been developed to quantify biochemical changes within cells, bioluminescent methods have evolved as a dominant technique for monitoring changes in cellular bioanalytes. The physics of bioluminescence provides inherent advantages for cell based assays because the photonic excitation energy is generated by a chemical reaction. In fluorescent methods the excitation energy is derived from an excitation photon that can overlap with the the emission spectra or cause off target fluorescence from cellular components or the exogenously added small molecule being studied. The chemistry of the luciferase based bioluminescence reaction has been exploited to quantify small molecules such as cellular ATP, the enzymatic activity of proteins such as Caspase-3, or cell signaling pathways with transcriptional endpoints such as NF-kappaB (Fig. 2). Recently, a circularly permuted luciferase has been developed that allows for real time monitoring of changes in intracellular cAMP concentrations (Fig. 3). The combination of this platform of bioluminescent chemistries with add-and-read Glo methodologies provides highly accurate tools for quantifying cellular changes due to pharmacological, developmental, oncological, or immunological perturbations. This issue of Combinatorial Chemistry and High Throughput Screening is designed to provide a partial survey of methods that have proved useful in describing different biological processes. Miraglia et al., present an overview of luminescent reporter assays and technical issues that impact assay robustness; Larson et al., leverage liquid handling instrumentation to multiplex bioluminescent ADMETox assays; Takagi et al., used biochemical luminescent assays to compare radioactive assays with bioluminescent methods for screening kinase inhibitors; Simmons reviews the use of luminescent genetic reporters as toxicity biomarkers; and Kokatam et al., used a creative reporter gene design to help understand the complex angiogenic signaling pathway....