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A New Way to Target Cancer Cells Compound Triggers Release of Nitric Oxide to Fight Leukemia and Tumors

April 14, 2003 — Researchers from the University of Utah and the National Cancer Institute developed an experimental drug that reacts with a substance inside cancer cells, releasing nitric oxide to kill the cells or slow their growth without harming healthy cells.

Tests showed the drug, called JS-K, induced the cell-suicide process in acute myeloid leukemia (AML) cells grown in culture and inhibited their growth in mice. AML is the most common and most deadly form of leukemia. In other tests on cell cultures, the drug also inhibited growth of AML cells and – to a lesser extent – prostate, colon and breast cancer cells. It also inhibited growth of prostate cancer cells in mice.

“If all goes well, this would be the first cancer chemotherapeutic agent based on selective delivery of nitric oxide to tumor cells and therefore would constitute a novel class of cancer drugs,” said physician Paul Shami, an associate professor of medical oncology at the University of Utah School of Medicine, member of the university’s Huntsman Cancer Institute and chief of hematology-oncology at the Salt Lake City Veterans Affairs Medical Center. “It looks promising in cell culture and mice, but much work needs to be done before we know if it can be used in humans for the treatment of cancer.”

Nitric oxide is distinct from nitrous oxide or “laughing gas,” which is used as a dental anesthetic. Nitric oxide in sufficiently large concentrations is toxic to cells, and it can cause dangerously low blood pressure. Yet it is found naturally in the body and helps control blood pressure. Nitric oxide also is released in response to sexual stimulation, triggering a series of chemical steps that increase blood flow to the penis and produce an erection. The anti-impotence drug Viagra works by enhancing nitric oxide’s effects, specifically by inhibiting activity of a substance that works against nitric oxide.

The new study was published in the April issue of the journal Molecular Cancer Therapeutics. It was conducted by 14 scientists, led by Shami and by Larry K. Keefer of the National Cancer Institute (NCI) in Frederick, Md. Lai Y. Wang, a senior lab specialist at the University of Utah, assisted Shami. Other coauthors are from various branches of the NCI and from the University of Pittsburgh and George Mason University in Fairfax, Va.

Shami, who treats leukemias and other cancers in adults, cautioned that even if all goes well, JS-K will not undergo initial safety and efficacy trials in human leukemia patients until at least 2005, and that “to get to where your community physician will be able to prescribe it is maybe five years away, assuming everything goes according to plan.”

He also said: “We have not done any formal animal toxicology studies, so we don’t know the full side effects. One thing of primary concern to us is the effect on blood pressure. At the doses we’ve used to treat cancer in mice, it did not induce low blood pressure, but if and when it gets into human trials, we’ll have to look at whether it induces low blood pressure. And we’ll look at what it does to normal bone marrow cells and other normal cells.”

The Study

Previous studies by Shami, Brice Weinberg at Duke University and colleagues showed nitric oxide inhibits growth and induces cell suicide among acute myeloid leukemia cells grown in culture. In the new study, the researchers tested compounds that would trigger the release of nitric oxide inside cancer cells.

Shami and Wang tested in cell culture and sometimes in mice some 50 compounds designed to trigger nitric oxide release, and found JS-K was the most active. The compounds were sent to them by the researchers at NCI, where JS-K was synthesized by study coauthor Joseph Saavedra. It is named for his initials and is letter K in a series of compounds he synthesized. JS-K’s chemical name is O2-(2,4-Dinitrophenyl) 1-[4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate.

In a key experiment, acute myeloid leukemia cells known as HL-60 cells were implanted under the skin of mice that had suppressed immune systems and could not naturally combat the cancer cells, which grew to produce tumors. After 16 days of treatment with JS-K, the volume of the tumors was less than half the tumor volume in untreated mice. The treated mice did not suffer significant low blood pressure.

When the AML cells were grown in culture flasks, three days of treatment with JS-K caused the rate of cell suicide (called apoptosis) to increase from 7 percent without treatment to 27 percent and 43 percent, respectively, with two different concentrations of JS-K.

“This is in the league of currently available chemotherapeutic agents for this and other cancers,” Shami said.

He said further experiments might find some other compound that works like JS-K but is more effective, more soluble or easier to use, so JS-K is considered a “lead compound” for further study and not necessarily a future chemotherapy drug.

How JS-K Works

JS-K is designed to react with natural enzymes called glutathione S-transferases, or GSTs, which help pump foreign substances out of certain cells. GSTs help the liver get rid of toxic substances in blood. But they also help cancer cells resist chemotherapy drugs. When GSTs in cancer cells interact with JS-K, there are two anticancer effects: GST activity is inhibited, making the cells less resistant to chemotherapy drugs, and nitric oxide is released.

“You have delivered nitric oxide inside your target cancer cell, and the nitric oxide will kill it,” Shami said. “Other cancer-killing mechanism also may be occurring, and more work is needed to define them.”

Much less GST is found in healthy cells compared with cancer cells, so researchers hope the reaction of GST with JS-K to release nitric oxide will occur to a much greater extent in cancer cells without harming healthy cells.

Funding and Commercialization

The new study was funded by the National Cancer Institute, the Leukemia & Lymphoma Society and the National Institute of Environmental Health Sciences.

JS-K’s potential has been recognized by the NCI. The institute accepted the compound into its Rapid Access to Intervention Development (RAID) program, which tries to speed development of new cancer therapies. Work done so far within the RAID program has shown JS-K is active against a broad spectrum of cancer cells.

“Dr. Shami is the first investigator in Utah to win a RAID grant,” says Eric Gosink, of the University of Utah’s Technology Transfer Office. “This grant allows him to coordinate work with a panel of National Institutes of Health scientists dedicated to testing the efficacy of the compound.”

The Technology Transfer Office is trying to commercialize development of the experimental cancer drug and is seeking patent protection for its action as an anticancer compound, while the NCI is seeking a patent on the entire family of compounds to which JS-K belongs, Shami and Gosink said

Acute Myeloid Leukemia

Acute myeloid or myelogenous leukemia (AML) is the most common and most deadly form of leukemia, with 10,600 new cases diagnosed in the United States in 2002, according to the Leukemia & Lymphoma Society booklet Facts 2002. Only 19 percent of patients overall – and 46 percent of childhood AML patients – survive five years or more, the group says. That illustrates the need for new drugs to treat AML.

In AML, bone marrow cells called myeloblasts become cancerous instead of developing normally into white blood cells called neutrophils and monocytes. The cancerous cells build up in the bone marrow, which then fails to make enough normal blood cells, causing weakness, shortness of breath, bleeding, fever, vulnerability to infection and other symptoms. The cancerous cells can spread to other organs. Death can come from infection or from bleeding due to lack of adequate platelets.