Using fluorescence resonance energy transfer (FRET), we performed a high-throughput screen (HTS) in a reconstituted membrane system, seeking compounds that reverse inhibition of sarcoplasmic reticulum Ca-ATPase (SERCA) by its cardiac regulator, phospholamban (PLB). Such compounds have long been sought to correct aberrant Ca2+ regulation in heart failure. Donor-SERCA was reconstituted in phospholipid membranes with or without acceptor-PLB, and FRET was measured in a steady-state fluorescence microplate reader. A 20 000-compound library was tested in duplicate. Compounds that decreased FRET by more than three standard deviations were considered hits. From 43 hits (0.2%), 31 (72%) were found to be false-positives upon more thorough FRET testing. The remaining 12 hits were tested in assays of Ca-ATPase activity, and six of these activated SERCA significantly, by as much as 60%, and several also enhanced cardiomyocyte contractility. These compounds directly activated SERCA from heart and other tissues. These results validate our FRET approach and set the stage for medicinal chemistry and preclinical testing. We were concerned about the high rate of false-positives, resulting from the low precision of steady-state fluorescence. Preliminary studies with a novel fluorescence lifetime plate reader show 20-fold higher precision. This instrument can dramatically increase the quality of future HTS.
Bibliographical noteFunding Information:
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by a grant to D.D.T. from the National Institutes of Health (GM27906), and by grant to D.D.T., R.L.C., D.J., and R.D. from Celladon Corporation. R.L.C., T.B., D.J., R.D., and D.D.T. were paid consultants for Celladon Corporation. K.M.Z. is president, director and CEO of Celladon Corporation. R.L.C., T.B., R.D., D.D.T., and K.M.Z. have been issued Celladon Corporation stock options. G.D.G. is president of Fluorescence Innovations, Inc.
- calcium pump
- calcium transport
- fluorescence lifetime
- reconstituted membrane