BALTIMORE, May 13 (UPI) -- The discovery of an enzyme that can shut off tumor growth could lead to new treatments for cancer, Johns Hopkins University scientists report in the latest Proceedings of the National Academy of Sciences.
"When we turn this enzyme off, the tumor cells cannot grow ... anymore," Chi Dang, director of the division of hematology and principal investigator of the study, told United Press International on Monday.
Dang, also a professor of medicine, cell biology, pathology and oncology, believes the enzyme is a good target for cancer drugs but said he is not aware of any currently available drugs that block it.
The enzyme, called PRDX3, is found in the mitochondria -- tiny, ancient structures within cells that produce energy. Its function is to neutralize free radicals or toxins called peroxides.
Dang and his colleagues determined PRDX3 is turned on by a gene called c-MYC known to play a role in causing many types of cancer. So they set out to determine if manipulating PRDX3 would alter cancer cells.
They turned off the enzyme in a mouse model of fibrosarcoma, a type of bone cancer, and found tumor cells could no longer grow in the mice.
Furthermore, when PRDX3 was overexpressed or produced in excess, the tumors doubled in size, providing more evidence the enzyme was linked to cancer.
"When a cell is malignant, the mitochondria (are) basically in a turbocharged mode and (need) this enzyme to destroy any toxins made when (they get) really revved up," Dang explained.
By turning PRDX3 off, toxins build up and kill the cancer cells. But "inhibition of PRDX3 (with drugs) may not have untoward effects" on healthy cells "because there are other mechanisms to get rid of these toxins" and PRDX3 appears only to be necessary to cancer cells, Dang said.
He said his team will be "extending these studies into human cell lines."
The role of PRDX3 in cancer is a new concept so it is not yet known in which types of cancers the enzyme may be involved. One strong candidate, however, is breast cancer because research shows PRDX3 "is elevated in more than 70 percent of cases," Dang said.
Additional experiments in test tubes have shown turning off the enzyme in human breast cancer cells "inhibits the tumor quite dramatically," he noted.
Dang expects his findings to spur researchers to begin looking for other specific cancers where PRDX3 levels are elevated.
Deborah Johnson, professor in biochemistry and molecular biology at the University of Southern California's Keck school of medicine, said the findings are "essential" to improve understanding and treatment of cancer.
Different people respond better to different cancer drugs and this information will help us understand that, said Johnson, who is also a member of the Norris Comprehensive Cancer Center at USC.
(Reported by UPI Medicine and Health Correspondent Steve Mitchell in Washington)
