The next stage of testing further winnows the list of contestants. Only one in ten of the extracts that kill tumor cells in a petri dish actually shrinks tumors in mice. They test the chemicals on 60 different tumor cell lines. The successful extracts kill a few types of cancers and leave alone the rest. Scientists reason that the toxins that cut down all types of tumor cells will probably also blaze through a patient's normal cells.
Some scientists try to be even more selective in their tests on the extracts.
For example, Kenneth Bair, a medicinal chemist at Navartos Pharmaceuticals Corporation, and coworkers want to know whether the toxins can cripple particular proteins that are mutated or overexpressed in cancer cells. The team isolates these cellular components responsible for transforming normal cells into cancerous ones and then tests how well the sponge extracts disrupt the protein's functions. The researchers hope to find extracts that kill cancer cells harboring these protein defects but that leave alone normal cells.