Busulfan is a bifunctional alkylating agent that weakly binds to DNA; however, it has the ability to cross-linking. Busulfan selectively alkylates position N7 of guanine, and also alkylates the sulfhydryl group of glutathione and cysteine. Unlike other alkylating agents, it has little effect on lymphocytes and exhibits much less immunosuppressive ability. It has strong cytotoxic properties and the ability to kill stem cells. It can be taken orally. It is generally used for chronic myelogenic leukemia and polycythemia. Unlike other alkylating agents, it does not increase cases of secondary leukemia. Synonyms of this drug are cyto-sulfan, leukosulfan, myelosan, mytostan, and others.
The next group of antineoplastic drugs used in medicine is made up of nitrosoureas (lomustine, carbustine, streptozocin). There are also other drugs of this group (nimustine, semustine, and others), and they differ only in the presence of a different R group, which is shown in the scheme below. It is believed that in the body, nitrosoureas break down to /¡-chloroethanol and alkylisocyanate. The resulting /¡-chloroethanol is a highly reactive alkylating agent, and the alkylisocyanates are carbamoylating agents for proteins, which also exhibit certain cytotoxic activity.
The probable scheme of decomposition of nitrosourea in the body into active components is shown below.
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