A major change in the strategy by which the National Cancer Institute (NCI) searches for new anticancer drugs was recently announced. The NCI traditionally relied on mice, in which leukemia had been induced, to screen around I0,000 chemical substances a year. But it has been admitted that such an approach has not identified new drug candidates with particularly promising activity against any of the major cancers, including lung, colorectal, breast and prostate.(12) In the new system, the animals have been replaced by test tube studies with human cancer cells, at least in preliminary tests:13 drugs successful at this stage still proceed to further animal experiments. Other researchers argue this could be misleading and believe only human cancer tissue should be used to test the effectiveness of new drugs. Dr Sydney 'Salmon of the University of Arizona argues that the best means of assessing drugs successful in human tissue tests is not to carry out potentially misleading experiments on animals ("... inactivity in the mouse would not mean that a drug would be inactive in man") but to submit them for clinical trial in cancer patients.(14) Although the NCl's initiative is to be welcomed, it was over 30 years ago, in 1956, that Eagle and Foley first showed that human cancer cells could be used to test new anticancer drugs.(15)
Apart from searching for new drugs, human cancer tissue can also be used to identify which combination of existing remedies is most effective for individual patients. To do this, cancer cells are taken from patients and their sensitivity to drugs and radiation tested in vitro. The technique ensures that patients are less likely to be exposed to treatments that do not work.
Because AIDS is a uniquely human disease, scientists have been forced to rely on human cell tests to identify new treatments. Clinical observation of AIDS patients has shown how the HIV virus works, enabling a simple in vitro test to be developed.
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