Cancer is an insidious disease where one’s own cells reproduce uncontrollably. This article describes the treatment developed for leukemia, a cancer of the blood and bone marrow.

In the late 19th century, scientists first discovered enzymes as the agents which drive chemical reactions in cells (see Defining the Target). Further research showed that enzymes only act on specific chemicals, like a lock and key mechanism. Scientists realized that if they could supply a different chemical that could mimic the one an enzyme acted on, they could effectively ‘jam’ the enzyme and stop the chemical reaction (see Locks and Keys). A chemical group called sulfonamides was the first example of such a jamming agent; they blocked the chemical pathway for cell growth by mimicking an essential chemical (called a metabolite) (see Blocking the Production Line).

Chemotherapy, or treatment using chemicals, was a new field in the early part of the twentieth century. At that time, the high fatality rate of childhood leukemia encouraged some researchers to see if chemotherapy would work against cancer. Their jumping-off point was interference with the building blocks that make up DNA (see Early Chemotherapy). Research into the structure of DNA allowed scientists to design and synthesize the antimetabolites (the “jamming” molecules) based on the DNA bases. The drugs aminopterin and methotrexate were found to be effective in leukemia patients. Next came a highly successful antimetabolite, 6-mercaptopurine (6-MP) which controlled leukemia without undue toxicity (see A Leap of Faith). Doctors conducted clinical trials to determine the efficacy of treatments and realized that it was necessary to remove every last cancerous cell to prevent a relapse (see Systematic Medical Research). Antimetabolites have gone beyond treating leukemia and are now used to reduce the immune system’s rejection of transplanted organs and to treat gout as well as various herpes virus infections (see New Horizons).

This article is available in Japanese, and Spanish.