Quick identification of apoptosis inducer from Isodon eriocalyx by a drug discovery platform composed of analytical high-speed counter-current chromatography and the fluorescence-based caspase-3 biosensor detection

Analytical high-speed counter-current chromatography (HSCCC), a unique liquid-to-liquid separation technology, has an inherent capability to provide perfect fractionation for tracking active ingredients of medicinal herbs, in a quick, efficient, and high-recovery manner. A high throughput screening (HTS) method which utilizes a novel biosensor that selectively detects apoptosis based on the fluorescence resonance energy transfer (FRET) technique, was newly established and proved to be very sensitive in detecting apoptosis induced by various known anticancer drugs. The first combination of both advanced techniques formed an efficient platform for drug discovery and succeeded in quickly identifying the most potent apoptotic constituent of a Chinese herb namely Isodon eriocalyx. The system of n-hexane/ethyl acetate/methanol/water was used as the separation solvent. The solvent ratio was first set at 3:5:3:5 to check the water-soluble part of the crude extract, and then 1:1:1:1 was used to isolate the target compounds. The active fraction was tracked and purified continuously using HSCCC which was guided by the apoptosis detection at gradually decreased drug concentrations. As a result, the most potent apoptosis inducer in this herb was discovered by analytical HSCCC equipped with a 16 ml mini-coil column, using less than 50 ml diphase solvent, from about 50 mg active fraction. It was identified as eriocalyxin B, a well-known antitumor natural product, by NMR analysis of the HSCCC purified fraction.