The first small molecule CID system was developed in 1993 and used FK1012, a derivative of the drug tacrolimus (FK506), to induce homo-dimerization of FKBP. This system was used in vivo to induce binding between cell surface receptors which could not bind in the normal way because they lacked the transmembrane and extracellular domain. Addition of FK1012 to the cells caused signal transduction.