ONE of the body鈥檚 greatest blunders in the fight against cancer is to repair
tumour cells that would otherwise succumb to chemotherapy. Now chemists in
Virginia have discovered plant extracts that could deliver a killer blow to
wounded cancer cells by blocking such repairs.
Sidney Hecht and his colleagues in the departments of chemistry and biology
at the University of Virginia in Charlottesville screened extracts from several
plants to see if they could block the action of DNA polymerase. This is the main
enzyme that repairs damage inflicted on cancer cells鈥� DNA by bleomycin,
cisplatin and neocarzinostatin, chemotherapy鈥檚 鈥渉eavy guns鈥�.
Hecht discovered five substances in the roots of a rare Californian plant,
Schoepfia californica, that are capable of blocking the action of DNA
polymerase. The most potent inhibitor was anacardic acid, a compound related to
salicylic acid, the active component in aspirin (Chemical
Communications, p 2769). When these were combined with bleomycin, the
mixture killed cultures of cells twice as effectively as bleomycin alone.
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鈥淚t鈥檚 the first proof of concept,鈥� says Hecht. 鈥淲e鈥檝e done extensive cell
culture studies, and we鈥檝e found that the compounds at all sorts of levels
enhance the toxicity of anticancer agents.鈥� The team now plans to test mixtures
containing modified versions of the plant extracts.
Alan McGowan, head of drug development at the British Cancer Research
Campaign鈥檚 Patterson Institute for Cancer Research in Manchester, says that the
enzyme blocker has potential, provided there are no adverse effects. Many normal
cells, particularly those in the gut and bone marrow, are damaged by
chemotherapy, for example. Patients could suffer if the extracts block the
repair of these noncancerous cells, says McGowan.
Hecht admits this could be a problem, but stresses that the drugs would be
given for short periods only, and that toxicity tests have shown the extracts
themselves are harmless.