November 27, 2013
There’s just a “thin wall of protection against a total collapse in malaria chemotherapy,” warned a team of scientists led by Michael Riscoe, Ph.D., in a research paper five years ago.
It was one of many such alerts from Dr. Riscoe and other infectious disease experts who cautioned that the drugs we all depend on to fight malaria were rapidly losing their effectiveness. The mosquito-borne parasite that causes the most severe and frequently fatal form of the disease was developing a resistance to them – and increasingly penetrating that protective drug wall.
But this latest alert came as Dr. Riscoe, director of the Experimental Chemotherapy Laboratory at the Portland Veterans Affairs Medical Center and professor of molecular microbiology and immunology at OHSU, and his team were closing in on an answer.
Because of ELQ-300, a drug Dr. Riscoe and his colleagues designed and synthesized, scientists may be on the doorstep not only of rolling back a scourge that has plagued mankind for thousands of years but of conquering it. The Riscoe lab, in collaboration with an international consortium of scientists, disclosed in May that ELQ-300 could not only shore up the wall of protection but, more than that, potentially treat, prevent and ultimately eradicate human malaria.
If ELQ-300 proves itself in human clinical trials, it would come none too soon. The need is urgent for new, safe and inexpensive drugs for treating a disease that every year seriously incapacitates 100 to 200 million people and kills one to three million, many of them pregnant women and children younger than six.
“A clever beast”
The human toll has subsided somewhat recently, in part, because of mosquito-control programs in malaria-endemic countries. But it’s a lull before the storm, many scientists say, because of the tenacity of the parasite that causes the deadliest form of the disease.
Plasmodium falciparum is a “clever beast,” Dominican University pharmacologist Roland Cooper says. It has developed resistance to each new drug thrown against it, sometimes with astonishing speed. In Southeast Asian countries, it’s starting to foil artemisinin derivatives, the key drug in a cocktail that now is the first-line treatment.
The hope is that ELQ-300 will be the game changer in this life-and-death struggle. Studies by Akhil Vaidya, Ph.D., director of the Center for Molecular Parasitology at Drexel University, have shown that the parasite has not been able to develop a resistance to it.
“It ticks a number of boxes necessary in a next-generation antimalarial,” said Timothy Wells, chief scientific officer for Medicines for Malaria Venture (MMV), a Switzerland-based nonprofit coordinating and helping fund the project along with the U.S. Department of Veterans Affairs, National Institutes of Health and OHSU. “It has potential to become part of a combination therapy that could cure patients, prevent infection and block the transmission of malaria – all at low doses – which means fewer and smaller pills for patients at a lower cost.”
Into the lost-and-found
The trail Dr. Riscoe and his band of sleuths followed to produce ELQ-300 has taken some twists and turns. The University of Kansas graduate earned his Ph.D. in biochemistry and biophysics at Oregon State University, went on to a postdoctoral fellowship at OHSU and launched a career focused on cancer research. But in 1992 his father-in-law gave him a book that spurred him to look deeper into “the mother of fevers” as the disease has been called. The book, The Malaria Capers by Robert S. Desowitz, is an impassioned narrative about the long battle against malaria and is required reading for the summer students Dr. Riscoe brings into his lab each year.
That book is where the quest for an effective antimalarial began for Dr. Riscoe. But the roots of ELQ-300 stretch back more than 60 years to the work of Johann “Hans” Andersag, Ph.D., at the Bayer pharmaceutical labs in Germany. Dr. Andersag had developed chloroquine, which by the 1950s, was the principal drug for treating the disease. By the late 1940s, Dr. Andersag had come upon something he thought was even better, the quinolone family of compounds, of which endochin is one.
Malaria was a disease of birds and reptiles before the dawn of civilization, so Dr. Andersag tested endochin on canaries, finches and turkeys – and it not only treated the infection but worked as a prophylactic to prevent it. It meant endochin was active not only against the early blood stage of the infection but also against the tissue and liver stages even before disease symptoms begin. But, alas, it failed in experiments with mice and nonhuman primates, and endochin was consigned to the dustbin.
The Riscoe lab quest began with xanthones, a naturally occurring chemical class of compounds made up of three interconnected rings of atoms. That led them to acridones, another tricylic compound which they sought to optimize by reducing it to a two-ring molecule, a quinolone. (Shrinking the size of a molecule diminishes the likelihood of adverse side effects.) “That was when we fell onto Dr. Andersag’s work,” said Dr. Riscoe, “and found ourselves retracing his steps. We went into the antimalarial lost-and-found and rediscovered endochin.”
Why hadn’t endochin worked for Dr. Andersag in mammals? Dennis R. Koop, Ph.D., professor of physiology and pharmacology, found that it was because the drug is metabolized, or destroyed, by protective human liver enzymes. That didn’t occur in birds, which metabolize drugs differently. “That was our ‘ah-ha’ moment,” said Dr. Riscoe. “Now we knew our challenge was to chemically modify endochin so it would not get broken down that way.”
There was another problem. Other labs were working on quinolones, too, and none could get any response to the drug, or in vivo activity, in a mouse model. That was the critical next step, and without it, the project would have been aborted. But Rolf Winter, Ph.D., a senior scientist and synthetic chemist who started as a postdoc with Dr. Riscoe and has been with him since, found a way to pull it off.
Endochin is about as soluble as sawdust in water, so Dr. Winter, working with Aaron Nilsen, Ph.D., a research scientist at the Portland VA Medical Center, devised a way to manipulate the molecule to make it a bit more soluble without negating its potency. It worked: the mouse livers didn’t metabolize the drug and in vivo activity resulted. That was in 2008.
MMV agreed to commit funds to the project and help set up a research and development consortium involving Monash University in Australia, University of South Florida and GlaxoSmithKline’s research facility in Tres Cantos, Spain.
From then on, said Dr. Riscoe, “it was a lot of iterative chemistry, designing and making compounds and testing them in our in vitro assay.” (See sidebar about the OHSU origins of this assay.) The lab has created some 500 variants of ELQ for endochin-like quinolone and tested them in 96-well plates – the workhorse device used in drug discovery labs – for activity against the parasite.
What’s ahead for ELQ-300
Now that MMV has anointed it a preclinical candidate, the next steps, said Dr. Riscoe, are to fine-tune the formulation of ELQ-300 and move it toward human clinical trials. That work, it is hoped, will occur over the next couple of years, much of it through MMV. The goal is to produce one, low-cost, 50- to 100-milligram pill, which can be administered once as part of a drug cocktail and which protects an individual up to a month while preventing disease transmission.
Even as they push the work ahead, this research team and American scientists everywhere are grappling with increasingly constrained resources. It’s tough for academic labs to maintain funding levels needed to underwrite a drug discovery effort, Dr. Riscoe said, because of the decades-long decline in NIH funding. “All I know is that this team is ready and anxious to move on our ideas for improved drugs for malaria and other neglected diseases,” he said.
One of the secrets of the lab’s success is, of course, Dr. Riscoe himself. “He’s probably the most enthusiastic person I’ve ever met,” said Allison Stickles, an M.D./Ph.D. student who has worked in the lab for three years. “Someone has an idea, and you’re testing it a few days later. The lesson I take from that is if you have someone who’s really excited about it, like Mike, ideas will take off.”
Written by Harry Lenhart, photos by Aaron Bieleck
Hope dyed green
The story of the Malaria SYBR®Green assay
In 2002, Martin Smilkstein, M.D., an emergency medicine physician at OHSU, took leave to work in a Médecins Sans Frontières hospital in Kailahun, Sierra Leone, where more than 65 percent of pediatric hospitalizations and over half of all outpatient visits were due to malaria. “The needs were overwhelming, the population desperate, death very common,” he said. When he returned to Portland he sought out Dr. Riscoe. “I decided to see if there was a way to make a more effective and more affordable antimalarial treatment and make it available in places like Sierra Leone.”
Dr. Smilkstein, now an affiliate associate professor of emergency medicine at OHSU, went to work in the Riscoe lab, and in 2004, he developed a fluorescence-based assay for testing antimalarial drugs. It was an innovation using SYBR®Green dye that proved to be “transformative,” said Dr. Riscoe, not only for his lab but for the entire antimalarial drug discovery enterprise. It lowered the cost of testing antimalarial compounds against the parasite to pennies, permitting assays of many more drugs than was ever possible in the past.
“In a nod to Médecins Sans Frontières,” said Dr. Smilkstein, “we named it the Malaria SYBR-Green Fluorescence or MSF assay, which is now used in labs worldwide.” Working in the Riscoe lab, he said, has been “tremendously satisfying and, one hopes, will mean that the misery, suffering and death that malaria brings, will end soon.”