Development of a scintillation proximity assay for human insulin-like growth factor-binding protein 4 compatible with inhibitor high-throughput screening

Scintillation proximity assay in lead discovery

BACKGROUND

Scintillation proximity assay (SPA) is a homogeneous scintillant bead-based platform for the measurement of biological processes and plays an important role in the identification of active chemical entities in drug discovery.

OBJECTIVE

The design and development of solid-phase SPA approaches are examined and compared with alternative non-radiometric fluorescence-based technologies.

METHODS

This review provides background on the principle of SPA and its application to biomolecular interactions from a variety of biological sources.

CONCLUSION

The SPA approach is well suited to the demands of commercial high volume automation and assay miniaturization for target-based high-throughput screening campaigns on synthetic and natural product libraries as well as for benchtop characterization and confirmation studies. In the near future, innovations in the way SPA and fluorescence-based screening strategies are multiplexed will improve our comprehensive understanding of cellular system biology and dramatically advance the lead discovery process for the treatment of complex target-related disorders.

Real-time, high-throughput measurements of peptide-MHC-I dissociation using a scintillation proximity assay

Efficient presentation of peptide-MHC class I complexes to immune T cells depends upon stable peptide-MHC class I interactions. Theoretically, determining the rate of dissociation of a peptide-MHC class I complexes is straightforward; in practical terms, however, generating the accurate and closely timed data needed to determine the rate of dissociation is not simple. Ideally, one should use a homogenous assay involving an inexhaustible and label-free assay principle. Here, we present a homogenous, high-throughput peptide-MHC class I dissociation assay, which by and large fulfill these ideal requirements. To avoid labeling of the highly variable peptide, we labeled the invariant β2m and monitored its dissociation by a scintillation proximity assay, which has no separation steps and allows for real-time quantitative measurement of dissociation. Validating this work-around to create a virtually label-free assay, we showed that rates of peptide-MHC class I dissociation measured in this assay correlated well with rates of dissociation rates measured conventionally with labeled peptides. This assay can be used to measure the stability of any peptide-MHC class I combination, it is reproducible and it is well suited for high-throughput screening. To exemplify this, we screened a panel of 384 high-affinity peptides binding to the MHC class I molecule, HLA-A*02:01, and observed the rates of dissociation that ranged from 0.1h to 46h depending on the peptide used.

Scintillation proximity assay for total p53 protein as an alternative to ELISA

Measurement of the level of a specific protein can be an important parameter to discern as that can change and reflect disease status. A number of methods have been developed to quantitate the level of a protein, some amenable to high throughput screening. A method is described to measure the total level of the tumor suppressor p53 using scintillation proximity assay (SPA) beads and radiolabeled streptavidin. Three different cell extracts were used, with one used to develop the standard curve for the amount of p53. This method allows the specific detection of p53 in the range of 50 to 300 pg in 10 microl of an extract. While this detection is less than what can be detected by commercially available enzyme linked immunosorbent assay (ELISA) kits, the SPA compares favorably on time required and cost. This new assay also has the potential to be coupled with measurements for p53 DNA binding, a unique aspect of this approach.