['The brain isoform of creatine kinase (CKBB), an enzyme involved in energy metabolism, has been implicated in cellular transformation process. Cyclocreatine (CCr), a creatine kinase (CK) substrate analogue, was shown to inhibit the growth of a broad spectrum of solid tumors expressing high levels of CK. Cyclocreatine phosphate (CCrP) generated by CK, was proposed to be the active form responsible for growth inhibition.', 'We synthesized CCrP and tested its cellular uptake and anti tumor activity in stem cell assays and in athymic mouse models.', 'CCrP seems to be taken up by cells and inhibits the growth of solid tumors with high levels of CK. CCr and CCrP have similar specificity and potency.'] Does the synthetic phosphagen cyclocreatine phosphate inhibit the growth of a broad spectrum of solid tumors?