An alkylating antineoplastic agent is an alkylating agent used in cancer treatment that attaches an alkyl group (CnH2n+1) to DNA. The alkyl group is attached to the guanine base of DNA, at the number 7 nitrogen atom of the purine ring. Since cancer cells, in general, proliferate faster and with less error-correcting than healthy cells, cancer cells are more sensitive to DNA damage—such as being alkylated. Alkylating agents are used to treat several cancers. However, they are also toxic to normal cells (cytotoxic), particularly cells that divide frequently, such as those in the gastrointestinal tract, bone marrow, testicles and ovaries, which can cause loss of fertility. Most of the alkylating agents are also carcinogenic. History Before their use in chemotherapy, alkylating agents were better known for their use as sulfur mustard, ("mustard gas") and related chemical weapons in World War I. The nitrogen mustards were the first alkylating agents used medically, as well as the first modern cancer chemotherapies. Goodman, Gilman, and others began studying nitrogen mustards at Yale in 1942, and, following the sometimes dramatic but highly variable responses of experimental tumors in mice to treatment, these agents were first tested in humans late that year. Use of methyl bis (B-chloroethyl)emine hydrochloride (mechlorethamine, mustine) and tris (B-chloroethy) amine hydrochloride for Hodgkin's disease lymphosarcoma, leukemia, and other malignancies resulted in striking but temporary dissolution of tumor masses. Because of secrecy surrounding the war gas program, these results were not published until 1946. These publications spurred rapid advancement in the previously non-existent field of cancer chemotherapy, and a wealth of new alkylating agents with therapeutic effect were discovered over the following two decades. A common myth holds that Goodman and Gilman were prompted to study nitrogen mustards as a potential treatment for cancer following a 1943 incident in Bari, Italy, where survivors exposed to mustard gas became leukopenic. In fact, animal and human trials had begun the previous year, Gilman makes no mention of such an episode in his recounting of the early trials of nitrogen mustards, and the marrow-suppressing effects of mustard gas had been known since the close of World War I. Agents acting nonspecifically Some alkylating agents are active under conditions present in cells; and the same mechanism that makes them toxic allows them to be used as anti-cancer drugs. They stop tumor growth by crosslinking guanine nucleobases in DNA double-helix strands, directly attacking DNA. This makes the