In Vitro: Used in a competition assay, CNX-500 detects free, uninhibited Btk and is excluded from interaction with Btk previously bonded by CC-292. In Ramos cells exposed to a range of CC-292 concentrations, the amount of Btk captured by the probe is compared with untreated samples and the extent of Btk bonded is demonstrated to be proportional to CC-292 drug concentration.