CCNK and cancer: Similarly, dCeMM2/3/4 connected CDK12 and CDK13 to the CRL4B E3 ligase complex, resulting in the ubiquitination and degradation of Cyclin K. Unfortunately, as impressive as these molecular glues were in impeding cancer cell proliferation in vitro, neither HQ461 nor NCT02 was metabolically stable in vivo, which restricted the use of these drugs in animals.