Contraction and relaxation of smooth muscle cells and fibroblasts within the bronchial airways dramatically affects airflow, and being able to modulate these processes is critical for treating asthma and allergic responses. Citing that the traditional assay for monitoring cellular contraction is neither accurate nor reproducible and is laborious, requiring “multiple manual steps and extended experimental time (often several days),” Jianyong Wang and colleagues at Genentech have just described a groundbreaking replacement assay using the xCELLigence RTCA technology. Providing real-time data and requiring just a few hours to complete, this automated approach yields substantial gains in sensitivity and reproducibility along with a dramatically simplified workflow. Collectively, these improvements are expected to accelerate the discovery and optimization of new asthma therapies.
Affecting roughly 8% of the US population and costing more than $50 billion per year, Asthma is characterized by chronic inflammation of the bronchial airways. This causes bronchial smooth muscle cells (BSMCs) and lung fibroblasts to become hyper-contractile, leading to reduced airflow. As a means of studying the contractility of smooth muscle cells and fibroblasts, these cells have traditionally been embedded in a 3D matrix of polymerized collagen in the bottom of a microtiter plate well. Upon treatment with a contraction agonist, the embedded cells shrink in size and thereby cause a reduction in the diameter/surface area of the gelatinous disc, which can then be quantified manually with a ruler or with image analysis software. Besides being labor intensive and requiring large numbers of cells, this gel contraction assay is fraught with technical challenges that make results unreliable. Wang and colleagues surmised that the biosensor arrays of the xCELLigence RTCA instrument might provide an easier and simpler means of monitoring cellular contraction. This is indeed the case. As described in the newest issue of the Journal of Pharmacological and Toxicological Methods, after seeding either BSMCs or lung fibroblasts in the specialized xCELLigence microtiter plates, the biosensors recorded distinct attachment and proliferation phases. Upon addition of contraction agonists, the biosensor signal displayed a rapid decrease in signal which returned to baseline after about two hours. Importantly, microscopy demonstrated that this dynamic biosensor signal correlates perfectly with the contraction and subsequent relaxation of these cells.
Using the above xCELLigence RTCA assay, the scientists were able to generate highly reproducible dose-response curves to determine the effective concentration of multiple contraction agonists and antagonists. Moreover, the real-time nature of the xCELLigence RTCA data made it possible to accurately quantify the kinetics of contraction and relaxation, data that would be very difficult to obtain using traditional methods. The authors concluded that beyond basic research applications this novel contraction assay should be a boon for high throughput functional screening in the pharmaceutical industry.