Conjugated polymer-based real-time fluorescence caspase assays.

Area of Science:

• Biochemistry
• Analytical Chemistry
• Biotechnology

Background:

• Caspases are crucial proteases involved in apoptosis.
• Developing sensitive and specific assays for caspase activity is vital for research and drug discovery.
• Existing methods may have limitations in sensitivity, specificity, or throughput.

Purpose of the Study:

• To develop novel conjugated polyelectrolyte-based fluorescence turn-on assays for detecting caspase 3 and caspase 8 activity.
• To validate the sensitivity, specificity, and applicability of these new assays.
• To assess the potential of these assays for in vitro screening of caspase inhibitors.

Main Methods:

• Utilized a cationic polyphenylene ethynylene polymer (PPE4+) and a p-nitroaniline modified caspase peptide substrate.
• Designed a fluorescence turn-on mechanism based on the cleavage of the peptide substrate by caspases, releasing the quenching effect.
• Validated assay performance by determining kinetic parameters, sensitivity, specificity against other proteases, and IC50 values for a known inhibitor.

Main Results:

• Achieved high sensitivity with detection limits in pmol/L for caspase 3 and nmol/L for caspase 8.
• Demonstrated high specificity, with no significant signal observed from other proteases like caspase 8, papain, pepsin, and trypsin.
• Successfully determined the IC50 value for the caspase inhibitor Z-VAD-FMK, which closely matched literature values.

Conclusions:

• Developed a robust and sensitive fluorescence turn-on assay platform for caspase activity detection.
• The assay exhibits excellent specificity and sensitivity, suitable for various research applications.
• This assay design holds significant potential for high-throughput screening of small molecule inhibitors in drug discovery programs.