CKB and colorectal cancer: Similarly, in an in vivo experimental model of metastasis in mice, disseminated human colorectal cancer cells were found to secrete the protein creatine kinase brain-type (CKB) in the liver, where it catalyses the conversion of extracellular ATP and hepatic creatine into phosphocreatine, which is incorporated into metastatic cells via the creatine transporter, SLC6A8.