Research on a small but versatile compound shows potential for battling cancer and diminishing chemotherapy's side effects.
Sanjay Awasthi is a biochemistry research professor at The University of Texas at Arlington. He’s also an oncologist/hematologist at Texas Cancer Center in Arlington. And in his spare time, he’s in the transportation business.
That is, he studies the membranes of cancer cells and normal cells to identify transporter proteins that remove poisons (like chemotherapy drugs), their byproducts and other toxic chemicals generated from cellular metabolism.
Think of him as a long-haul trucker with a microscopic load.
Among the tiny treasures is a glutathione-conjugate transport protein that helps cells defend themselves against poisons. Its purpose was known long before it was proven to exist. Even now, all of its uses aren’t fully realized.
The story behind the powerful little protein called RLIP76 doesn’t begin with Sanjay Awasthi. But he and his colleagues gave the story life.
“This is just very basic chemical research,” he says.
Which, of course, depends mightily on your definition of “basic.”
Fanning the fight against cancer
RLIP76 protects cells from radiation poisoning. That’s great most of the time, but it’s deadly for cancer patients relying on radiation treatments for survival.
Here’s how the protein works. When glutathione or other chemicals naturally present in the body react with poisonous chemicals from outside the body or with poisons generated within cells exposed to stress (UV light, heat, radiation, oxidants), what’s produced is potentially toxic and must be removed.
If it’s not, a stereotyped death response called apoptosis ensues in the cell. That’s where RLIP76 comes in. The protein transports out this poison.
RLIP76 is, in Awasthi’s words, an “exhaust fan” for the cell, and cancer cells are much more dependent on it for survival than are normal cells. Blocking it selectively triggers apoptosis in cancer cells.
Conversely, supplying normal cells with an excess of RLIP76 protects them from ultraviolet light, X-radiation, heat, oxidant chemicals and chemotherapy drugs by removing the stressors’ poisonous byproducts.
Because the “motor” of this exhaust fan converts chemical energy into mechanical energy, the cell also uses it for other functions like cell division and endocytosis, a process in which the cell internalizes a piece of its membrane to terminate certain signals, like those initiated by insulin and growth factors.
Thus, RLIP76 plays a central role in defending cells from stress and in canceling the effects of signals from outside the cell. The clinical and physiological implications extend to diverse processes, including stress resistance, chemotherapy drug resistance, radiation resistance, oxidative stress-induced disease and even insulin resistance.
But it’s the search for RLIP76 that was really exhaustive.
“We assumed it existed, but no one could find it,” Awasthi said. “We and others have been looking for this protein for more than 25 years.”
For Awasthi, the quest dates to age 14, when he became interested in his father’s research (Yogesh Awasthi is a professor of biological chemistry and genetics at The University of Texas Medical Branch at Galveston and an expert in glutathione biochemistry). The younger Awasthi tackled the topic in 1985.
A major break came eight years ago when he and his research team discovered RLIP76, cloned it and showed that it was, in fact, the elusive protein they sought.
They created laboratory mice in which the protein was genetically removed. These “knockout” mice developed a sensitivity to oxidative stress and appeared to age faster.
More importantly, they became more vulnerable to radiation poisoning.
“Right now, if you get radiation poisoning with doses of radiation above a certain threshold, no available medical intervention can save you,” Awasthi said. “We can give genetically created RLIP76 to mice to protect them from lethal radiation. As the levels of this protein increase in cells, the cells resist death caused by most stressors, even the most powerful stressor—radiation.”
That’s why Awasthi believes RLIP76 has potential as an anti-cancer treatment. While the protein would not fight the cancer directly, removing RLIP76 from cancerous cells, as done in the mice, would leave the cells defenseless against chemotherapy, in effect opening them up for treatment. Additionally, increasing RLIP76 in healthy cells—especially in the vulnerable membranes lining the mouth, stomach and intestines, hair follicles and bone marrow—would shelter them from chemotherapy’s adverse side effects.
The Awasthi team has killed lung cancer in laboratory cultures by inhibiting the “exhaust fan” protein. The researchers also developed a technique to deliver RLIP76 to healthy cells by attaching them to liposomes, which deliver drugs to the body.
From mice to men
Two members of the research team recently received grants from the North Texas Cancer Research Foundation of Arlington.
Biochemistry Research Associate Professor Sharad Singhal said the research definitively links RLIP76 to chemotherapy resistance. Sushma Yadav, a postdoctoral fellow in biochemistry who’s assisting on the project, said manipulating RLIP76 can help cancer patients wage war on diseased cells.
While generating positive results in lab rats is not the same as showing it in humans, Awasthi said the leap from mice to men isn’t insurmountable.
“We could certainly do it now by preparing large enough quantities of RLIP76 through recombinant engineering,” he said. “Technically, it’s not that big a jump. But significant industrial or pharmaceutical collaboration and investment is necessary.”
RLIP76 treatment would require three or four years of clinical trials for approval. And though grants have supported Awasthi’s research since 1993, it’s not enough funding to get RLIP76 to the clinical phase.
“Taking a discovery like this and translating it to the clinic requires a larger number of grants and larger number of people working on it over time,” he said. “I’m a practicing oncologist, too, so I have somewhat of a limited schedule to pursue some of the research issues.”
So some of Awasthi’s colleagues picked up where he has left off. The Cleveland Clinic, one of the United States’ premier hospitals and a noted cancer research center, is studying RLIP76. Researchers in California, Arkansas, Virginia and Texas are also involved.
“The more people working on it, the more likely it is to take off and develop faster,” Awasthi said. “Eventually we have to take this to the clinic. It seems to be headed in that direction.”
Awasthi is helping spread the word. He has published more than 100 papers on his research, and his work is garnering international attention. Last fall, the Awasthi team graced the cover of the International Journal of Cancer. Earlier this year, the prestigious journal Cancer Research published his RLIP76 findings and the protein’s role in chemotherapy drug resistance in lung cancer. A recent issue of Cancer Research presents his findings on radiation resistance.
All this attention for some “basic” research.
“It’s not one of the sexy things people do with clinical trials and a variety of other things that are much more eye-catching,” Awasthi said. “This is grunt work. These are very basic biochemical mechanisms that just hadn’t been worked out.”
— Danny Woodward