Current cancer drugs were discovered through drug-screening programs that measured the drugs' effects on prolonging the survival of leukemic mice.
More recently, the NCI in the U.S. has sought to improve specificity and reduce costs by first developing a profile measuring how actively a drug kills tumor cells of a particular type growing in laboratory cultures. This profile is compared to the profile of established drugs. If the new drug seems promising, its effects against tumors in animals are studied, including human cancers transplanted into mice.
Many of the new generation of compounds are designed by computers to attack certain biochemical targets known to be more common in cancer cells than in normal cells. But most compounds continue to be introduced because of knowledge acquired through the study of older drugs already proven effective against some cancers and through the application of new concepts.
Preclinical Testing Drugs that appear promising in the laboratory undergo preclinical testing. At this stage, they are characterized according to their stability and purity and their toxicity in animals. This testing ends with the development of a pure and stable preparation for administration to humans.
Phase I This is when clinical study begins. A starting dose level (based on the drug's effects on mice) is given to groups of cancer patients who volunteer for a clinical trial because their standard treatments have not been effective. This dose is then increased in groups of similar patients by increments initially of 10 times the dose previously shown to be safe, and by lesser increments as toxicity is noted.
