Magazine article Science News

Look What's Hidden in the Pawpaw

Magazine article Science News

Look What's Hidden in the Pawpaw

Article excerpt

During World War II, when bananas were scarce, Jerry L. McLaughlin's dad gave him some "Indiana bananas" -- the custard-like fruit of Asimina triloba, better known as the pawpaw tree. Though only about 4 years old at the time, McLaughlin recalls, "I threw up and never forgot them."

A pharmacognosist at Purdue University in West Lafayette, Ind., McLaughlin now searches for plants possessing natural medicinal properties. Based on his unforgettable encounter with the Indiana banana, he focused a few years ago on the pawpaw. After all, he notes, "parmacology is simply toxicology at a lower dose." The result: He reports finding a family of biologically active compounds -- acetogenins -- "that's very good against cancer, and also terrific at killing insects."

A crude extract of pawpaw twigs killed brine shrimp at a concentration of just 0.04 parts per million (ppm)--well below the 70 ppm concentration of strychnine needed to elicit the same effect. One novel acetogenin his team isolated from the pawpaw extract -- asimicin -- also proved lethal to blowfly larvae, two-spotted spider mites, Mexican bean beetles, mosquito larvae, melon aphids, striped cucumber beetles and a nematode. McLaughlin expects that natural asimicin-based pesticides, for which he holds a patent, may be marketed within four or five years.

McLaughlin also subjected brine shrimp to extracts from the pawpaw's relatives. He hit a lode with Annona bullata, a Cuban native closely related to the "custard apple." From this plant he extracted two acetogenins with anticancer prospects. In tests conducted by a major pharmaceutical company, one of those acetogenins -- bullatacin -- proved 1 million times more potent than the common anticancer drug cisplatin in inhibiting the growth of human ovarian tumors transplanted into mice. …

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