Science / Medicine : Poison Tested on Cancer

Scientists said they have injected one of the most poisonous substances known into four humans in an attempt to see if the chemicals may be used to kill cancer cells without killing normal cells.

The human tests, conducted at the National Institutes of Health, will show whether a deadly poison derived from the common bacteria known as Pseudomonas aeruginosa, has been rendered safe by genetic engineering.

Ira Pastan, chief of the molecular biology laboratory at the National Cancer Institute, said researchers took the bacterial gene responsible for production of a deadly toxin, and modified it by deleting an essential part that allows the poison to attach to cells.

Based on work with laboratory animals, the scientists believe that once the poison had been modified by deleting the attachment part and combining it with the antibody or growth factor it would be nontoxic until it actually got inside cancer cells.

But the only way to be sure was to test it in very tiny doses in humans. Pastan said four cancer patients, who had not responded to other treatments, volunteered to take the “oncotoxins” or cancer poisons.

Tiny doses were used, he said, to be sure that the treatment did not have side effects, and were likely too small to kill the cancer cells.

Eventually, patients will get larger doses, and Pastan believes that these will be much more specific for cancer cells than are chemicals currently used to treat cancer. He said certain receptors for the designer oncotoxins are much more abundant on cancer cells than on normal cells.

The unmodified toxin is so poisonous that an amount weighing no more than a grain of salt could kill a human, Pastan said.