Purity >98%. O6 -Methylguanine-DNA methyltransferase (MGMT) is a DNA repair protein which removes an alkyl group from the O6 position on guanine in an autoinactivating reaction. Although important in normal DNA repair, this reaction confers resistance to treatments that use O6 -alkylating agents to produce cytotoxicity, e.g., in cancer. Lomeguatrib is a modified quanine base which acts as a pseudosubstrate inactivator of MGMT (IC50 = ~3 nM). A non-toxic compound, lomeguatrib completely inactivates MGMT in human prostate and colorectal tumors when given as a single 120 mg oral dose and in primary central nervous system cancers at 160 mg.