The structure of cyclocreatine is fairly flat (planar), which aids in passive diffusion across membranes. It has been used with success in an animal study, where mice suffered from a SLC6A8 (creatine transporter at the blood brain barrier) deficiency, which is not responsive to standard creatine supplementation.  This study failed to report increases in creatine stores in the brain, but noted a reduction of mental retardation associated with increased cyclocreatine and phosphorylated cyclocreatine storages.  As demonstrated by this animal study and previous ones, cyclocreatine is bioactive after oral ingestion   and may merely be a creatine mimetic, able to phosphorylate ADP via the creatine kinase system. 
AD = Approval date.
MS = Myelosuppression.
D = Diarrhoea.
FR = Fluid retention.
As far as myelosuppression, diarrhoea and fluid retention goes: +++ means >70% of patients exhibit clinically significant myelosuppression. ++ means 30-70% of patients exhibit significant myelosuppression. + means 10-30% of patients exhibit significant myelosuppression. - means 0-10% of patients exhibit this side effect.
General references templates are given, which refer the reader to the respective drug database.
2-Methoxyestradiol exhibits the inhibitory activity of cellular proliferation in a breast carcinoma cell line MDA-MB-435 and an ovarian carcinoma cell line SK-OV-3 with IC50 of μM and μM, respectively. Furthermore, 2-Methoxyestradiol also inhibits cellular microtubule depolymerization in rat aortic smooth muscle A-10 cells with EC50 of μM.  2-Methoxyestradiol inhibits proliferation of MCF-7 and BM cells with IC50 of 52 μM and 8 μM.  In MDA-MB-231 cells, 2-Methoxyestradiol inhibits HIF-1-mediated transcriptional activation of target genes without affecting the transcription of HIF-1α itself.  A recent study shows that 2-Methoxyestradiol ( μM), blocks TGF-β3-induced expression of collagen (Col) type I(αI), Col III(αI), plasminogen activator inhibitor (PAI) 1, connective tissue growth factor (CTGF), and α-smooth muscle actin (α-SMA). Moreover, 2-Methoxyestradiol ameliorates TGF-β3-induced Smad2/3 phosphorylation and nuclear translocation, and inhibits TGF-β3-induced activation of the PI3K/Akt/mTOR pathway.