bind at N7 of guanine. Nonclassical Certain alkylating agents are sometimes described as "nonclassical". There is not a perfect consensus on which items are included in this category, but, in general, they include: Procarbazine Altretamine Some sources explicitly exclude the triazenes (dacarbazine, mitozolomide, temozolomide) from the nonclassical category. However, other sources list dacarbazine as nonclassical, and some include temozolomide. The platinum agents are also sometimes described as nonclassical. Limitations Alkylating antineoplastic agents have limitations. Their functionality has been found to be limited when in the presence of the DNA-repair enzyme O-6-methylguanine-DNA methyltransferase (MGMT). Cross-linking of double-stranded DNA by alkylating agents is inhibited by the cellular DNA-repair mechanism, MGMT. If the MGMT promoter region is methylated, the cells no longer produce MGMT, and are therefore more responsive to alkylating agents. Methylation of the MGMT promoter in gliomas is a useful predictor of the responsiveness of tumors to alkylating agents. See also List of hormonal cytostatic antineoplastic agents References External links University of Nebraska page on alkylating agent drugs Cancer Management Handbook: Principles of Oncologic Pharmacotherapy Alkylating antineoplastic agents Alkylating agents