a group of synthetic compounds containing alkyl groups that combine readily with other molecules. Their action seems to be chiefly on the DNA in the nucleus of the cell, so that they are cell cycle phase nonspecific. They cross-link the strands of DNA, preventing its replication and the transcription of RNA; the major site of action is on the base guanine. They are primarily used in
chemotherapy of cancer (see
antineoplastic therapy). However, they do not damage malignant cells selectively, but also have a toxic action on normal cells; all killing occurs primarily in rapidly proliferating tissue. Locally they cause blistering of the skin and damage to the eyes and respiratory tract. Systemic toxic effects are nausea and vomiting, reduction in both leukocytes and erythrocytes, hemorrhagic tendencies, amenorrhea or impaired spermatogenesis, damage to the intestinal mucosa, and alopecia. Among the agents of this group used in therapy are
busulfan,
cyclophosphamide,
ifosfamide, and
thiotepa; the
nitrogen mustardschlorambucil,
melphalan, and
mechlorethamine; and the
nitrosoureascarmustine,
lomustine, and
streptozocin. They may be carcinogenic in humans; some have been linked to bladder cancer and acute leukemia. However, the major benefits obtained in treating diseases such as lymphoma, Hodgkin's disease, breast cancer, and multiple myeloma far outweigh the risks of developing a second malignancy.