By Marshall A. Ledger
From Penn Medicine, Summer 2012
There’s “good” cholesterol and there’s “bad” cholesterol. Raise the good and lower the bad. What could be plainer, more direct? The words even carry moral authority. In a world where medical science is rarely definitive, here is an easy-to-follow health directive to reduce the risk of atherosclerosis and other heart diseases.
Then comes Penn Medicine’s Daniel J. Rader, M.D., prominent among his peers for his work on cholesterol metabolism and familiar to the media as one of their go-to experts for commentary when the topic makes news. He has helped muddy at least part of that tidy formula.
The bad stuff is still bad — the lower our LDL, the better — but its full story is still unfolding. “Honestly,” Rader says, “a decade ago we thought we pretty much understood most of what existed about the regulation of LDL levels,” but that complacency is gone.
His chief concern is with HDL, which is still good, but not as absolute as the term sounds. “It’s nuanced,” he says. “As we learn more and more, it’s not completely clear that all HDLs of any type are good. There may be more to it than that.”
Readers of the front page of The New York Times on May 17 saw the report of a new study that builds on the work Rader has been doing on HDL – and for which Rader was a co-author. According to the lead author of the study, Benjamin F. Voight, Ph.D., assistant professor of pharmacology at Penn, “Through our research, we have found that all roads that raise HDL do not always lead to the promised land of reduced risk of heart attack.”
In addition to a new hypothesis about HDL, Rader’s work has helped lead to the discovery of a new gene, the creation of an assay that is now widely used, and the application of a discarded drug to help a certain group of under-served patients.
He has been recognized for his achievements. He holds an endowed chair as the Edward S. Cooper, M.D./Norman Roosevelt and Elizabeth Meriwether McLure Professor of Medicine.
As a researcher, he has received coveted, long-term funding in grants that come with such labels as “Freedom to Discover,” “Distinguished Clinical Investigator Award,” “Networks of Excellence,” and “M.E.R.I.T,” i.e., “Method to Extend Research in Time.”
As a clinician, he has been recognized as a “top doc” in national listings as well as in Philadelphia Magazine, where he has appeared every year for more than a decade, and he has won teaching awards in the School of Medicine and his department.
He regularly delivers invited lectures at other universities, serves on committees of national organizations in his field, and engages in editorial and peer-review activities for general and specialized journals in medicine. He also co-founded and serves on the board of Vascular Strategies LLC, a company focused on treatments for cardiovascular disease.
Last year, he was one of 70 in the country elected to the Institute of Medicine “for excellence and professional achievement.”
“He certainly is a world leader in lipoprotein metabolism,” says one of his first mentors, Julian B. Marsh, M.D. ’47, “but he is still not at the apex of his career.”
Before cholesterol gained cachet
Rader was unwittingly introduced to his field as a student at the Medical College of Pennsylvania in the early 1980s, when he worked in Marsh’s laboratory there.
At that time, Marsh was professor and chair of physiology and biochemistry at M.C.P. (he had held a comparable position at Penn, in both the School of Medicine and the School of Dental Medicine). He is one of the deans of lipoprotein metabolism, and Rader was interested in gaining experience from a proven scientist, more so than in entering that specific field.
He stood out: “He was very enthusiastic, learned quickly, and had a very good mind. You could tell at that time he was going to do well,” says George H. Rothblat, Ph.D., then an M.C.P. biochemist who would later collaborate with Rader on some major projects.
Although Rader showed potential, the field promised less. “Cholesterol was still a backwater,” Rader recalls. There were no statins to lower cholesterol (the first would appear in 1987), and the best drugs available – niacin and bile acid sequestrants – had many side effects.
Even more, “we didn’t have any evidence that treating cholesterol actually lowered cardiovascular risk,” he says, “so the times were very different.”
Rader had just started his residency at Yale-New Haven Hospital in 1985 when Michael S. Brown, M.D. ’66 and Joseph L. Goldstein, M.D., won the Nobel Prize for their discoveries on how LDL works. Their work, says Rader, was “certainly inspiring to the field. It started to give some real molecular underpinnings to our understanding of why certain people have high cholesterol. But it was still a long way off from a vision of treatment of cholesterol as a way of reducing cardiovascular risk.”
“I wonder if . . .”
After his residency, Rader went directly to work in the laboratory of H. Bryan Brewer Jr., M.D., at the National Institutes of Health. The move was a bit atypical, because Rader had no subspecialty training in cardiology or endocrinology. But he learned a lot of basic science and treated patients — “what we now call translational research,” he says — and he knew he wanted to pursue a career that included both bench investigations and patients.
In Brewer’s lab, Rader began strands of research that he would continue at Penn. He studied the metabolism of HDL in humans — why some people have especially high or low levels of HDL — and helped define some genetic mutations that affected the metabolism and thus HDL levels.
He also worked on a subclass of lipoprotein abbreviated as LP(a). Although discovered in 1963, it did not interest scientists for decades, so little was known about it. Rader was part of the Brewer team that published studies on the metabolism and regulation of LP(a) levels, contributions to the field that are still cited.
Now, he says, interest in LP(a) is “through the roof.” LP(a) turns out to be an unusual lipoprotein because it ranges from almost undetectable levels to nearly 1,000 mg/dL (milligrams of glucose per deciliter of blood, but the unit tags for cholesterol levels are rarely used in ordinary conversation). As Rader puts it, that is “a huge range, almost all genetic, and it’s an independent risk factor for heart disease.”
The Brewer group was also looking for the gene that underlies a rare disease of essentially zero LDL, abetalipoproteinemia. Rader followed many of the N.I.H.’s patients with this disorder, and one day he attended a talk by a colleague describing his new discovery, a protein in the liver of cows.
Afterward, Rader chatted with the speaker and wondered aloud if the protein could be the defect compound in abetalipoproteinemia. The two scientists and others joined in a collaboration that ultimately showed that the gene MTP was mutated in patients with this disease.
Building a lab
After nearly six years at the N.I.H., Rader decided to move to a more traditional academic environment with medical students and patients in a regular hospital setting. He knew that Philadelphia (“surprisingly”) did not have a major presence in the cholesterol field, so he inquired at Penn. (“A lot of recruitment is very serendipitous,” he observes.)
At Penn, Rader would be close to Lancaster, Pa., where he grew up, and he’d be able to start a lipid clinic and an HDL research program. In addition, Penn was getting into gene therapy, which he thought might prove beneficial for the LDL-receptor deficiency that Brown and Goldstein had identified and that causes the disease of excessively high LDL, known as familial hypercholesterolemia.
In 1994, when Rader arrived at Penn, the foremost HDL hypothesis was that raising HDL levels would reduce cardiovascular risk. “That’s what the epidemiology taught us, and that’s what the animal models taught us,” he says. Others – individuals and companies – were interested in developing drugs, but gene therapy seemed promising. “Frankly,” he says, “there was a lot we didn’t understand about what fundamentally regulated HDL levels and why some were high and some were low.”
Rader thought he and his team could learn from patients with unusually high numbers (80 for a man and 90 for a woman would put the individual in the top 5th percentile). Today Penn has the largest population of these patients in the world, which helps Rader’s lab sort out both the genes that cause high HDL and its effect on cardiovascular risk.
Rader’s team includes three former colleagues from the Medical College of Pennsylvania who now are Penn research professors of pediatrics based at The Children’s Hospital of Philadelphia: Sissel Lund-Katz, Ph.D.; Michael C. Phillips, Ph.D., D.Sc.; and Rothblat. (A fourth, the late Jane M. Glick, Ph.D., had taught Rader in medical school and come to Penn about when he did; she helped him set up the lab.)
Asked what Rader adds to a research project, Rothblat says: “He’s extremely bright, he has a fantastic memory and knowledge of the field, he can synthesize hypotheses and design appropriate experiments to test the hypotheses. He’s a really fine investigator.”
His mentor Julian Marsh puts it this way: “If you had to use one word to describe Dan, it would have to be brilliant.” He adds: “No matter how bright and how much the top scientists achieve, it’s very, very difficult for them to succeed at very high levels unless they are very good at interpersonal relationships — and that’s another area where Dan is a standout.”
All of those qualities, and his achievements, have brought Rader impressive funding: for instance, a National Institutes of Health M.E.R.I.T. Award; an award of nearly $15 million under the American Recovery and Reinvestment Act of 2009 for the Complex Genetics Initiative (Rader is the principal investigator); a $9-million N.I.H. grant for stem cell research with Penn’s Edward Morrisey, Ph.D., professor of medicine and of cell and developmental biology, and Stephen A. Duncan, Ph.D., at the Medical College of Wisconsin; and a 5-year, $6-million grant from the Paris-based Fondation Leducq.
These awards have helped drive his laboratory, which takes up the 11th floor of the Translational Research Center, some 45,000 square feet of offices and lab space with some 25 investigators and others. As we walk through, he calls out “So, did it work?” to a pair of researchers hunched over some equipment at a workstation.
They look up in surprise and laugh. “We’re about to find out,” one of them says. “Just took a protein reading.”
Rader extends a thumbs-up sign, says, “All right, all right!” and we move on.
The Translational Research Center, with seven floors of labs in all, is adjacent to the Perelman Center for Advanced Medicine, a clinical building. (For more on “translational,” see the sidebar.) “Part of the idea,” says Rader, “is to encourage interactions between clinicians and scientists and among scientists of different disciplines, so that we can have these serendipitous kinds of conversations that lead to new discoveries.”
One of the Rader team’s major pursuits is what he calls the “nuanced” sense of HDL. As he explains the metabolic process, the liver makes cholesterol, and LDL transports it to blood vessels, which take it up. One of HDL’s main functions, goes the hypothesis, is to interact with the plaque in the blood vessels, extracting the cholesterol and returning it to the liver, where the body excretes it.
The process is formally known as “reverse cholesterol transport,” but Rader calls it “efflux.” “It’s an elegant, overly simplistic concept,” he says, “but it’s part of what we think HDL does to make HDL protective.”
As the basic scientists extracted cholesterol from cells and Rader contributed the animal models and patients, the team developed a novel method to measure efflux. They took cells from mice and inserted a cholesterol “tracer” that can be followed as it moves in the body. Then they injected the cells back into the mice in order to trace the movement of the cholesterol from the cells’ macrophage to the liver and out into the feces. The procedure, in use for some six years now in more than two dozen labs around the world, is often referred to as the Rader Assay.
It has also helped confirm the efflux hypothesis — just when some new drugs that raised HDL proved to be failures in reducing the risk of heart disease. The New England Journal of Medicine published the Rader group’s results in 2011. They are now developing and evaluating the effect of new therapeutic approaches that will promote HDL efflux.
“New therapies to bolster the good cholesterol and allow the body to naturally cleanse itself of the bad cholesterol are the new frontier,” observes Richard P. Shannon, M.D., the Frank Wister Thomas Professor of Medicine and chair of the Department of Medicine, where Rader is based. “Dan is the foremost figure in the translational approach to HDL as a therapeutic target.”
One route could be gene therapy, for which Rader and his team, along with the late Michael Jaye, Ph.D., then at the pharmaceutical firm Rhone-Poulenc Rorer, took the crucial first step. They found a gene — an enzyme called endothelial lipase — that is important in regulating HDL metabolism and HDL levels; they confirmed the gene’s functions in mice and subsequently in patients with high HDL.
They went on to find a variant that occurs in about one percent of the population; the mutation inactivates the gene and raises HDL. Next, they joined in a collaborative study of more than 100,000 people and verified the finding.
Because these people had high HDL, Rader reasoned, they should have had a lower risk of heart disease — but that’s not what the investigators found. “It was somewhat disappointing,” he says, “but it circles back a bit to what I said: Maybe it’s not just the HDL level, we also need efflux.
“So in that vein, we continue to use human genetics – that is, sequencing other genes and even whole-genome approaches – to look for genes that impact on HDL levels. Our goal is to find some genes that actually raise HDL levels and seem to protect against heart disease, and our hypothesis is that they’ll also promote the efflux. This is work in progress.”
A new role for academe in drug development
Meanwhile, Rader has resumed another strand of work that dated from his arrival at Penn. In the mid-’90s, he started to explore gene therapy to treat patients with familial hypercholesterolemia, or FH, which causes excessively high LDL — over 500. Two of his five patients had modest LDL reductions, but he stopped the work because the results were inconsistent.
A few years later, he resumed it. Several of his former colleagues, who had moved from government and academe to Bristol-Myers Squibb, were trying to develop a drug that targeted the protein whose mutations made LDL abnormally low; such a drug, they surmised, would help people with high LDL.
Rader led a proof-of-concept study and showed that the drug lowered LDL from 190 to about 70. But the drug gave some patients gastrointestinal side effects such as diarrhea, and it raised the fat in the liver, so the pharmaceutical firm stopped the program.
But Rader considered the situation of his patients with FH: They get heart disease as children and generally die of cardiovascular problems before the age of 30. With those dire prospects, he figured the side effects could be managed, so he applied for the rights to the drug.
“There was a fair amount of discussion,” he says, “but at the end, to their credit, Bristol-Myers Squibb transferred the intellectual property of the drug to Penn to further develop.”
With a Doris Duke Charitable Foundation grant to pursue his idea, and with six patients, Rader showed that the drug reduced LDL by fifty percent — “which in this disease is pretty much unheard of.”
FH qualifies as an “orphan disease,” meaning that there are fewer than 200,000 patients with the condition in the United States. Drug companies generally aren’t interested in disorders with small markets, so the Food and Drug Administration sometimes steps in with funding, which Rader received. Such diseases follow a different path to approval than that used for mass-market medicines. He and his team filed a new drug application in February and hope to hear of approval by the end of the year.
Rader has mitigated the drug’s GI side effects by starting the dose low and titrating it over time, and by counseling on diet. Experiments suggest that higher liver fat might not be problematic. After rising, it plateaus, and “might even start to come down a bit,” he says, “so it won’t be a problem for these patients at least.”
Then he muses: “It’s an interesting rescue of an abandoned drug.” He explains that there is growing interest in drugs that fail because of safety, tolerability, or efficacy but that may be repurposed for specific groups of patients who would otherwise get no treatment at all. Rader notes that Francis S. Collins, M.D., the head of the National Institutes of Health, has declared an interest in this area.
Indeed, since Rader and his group completed their work, the Perelman School of Medicine has established the Penn Center for Orphan Disease Research and Therapy (see Penn Medicine, Fall 2011). It offers the prospect of finding therapies for orphan diseases on a large scale, and Rader is optimistic.
“It’s a fantastic role for academe in drug development,” he says. “We don’t do certain things that the drug industry does very well — make the molecules, for instance. But we have the patients, we understand these rare diseases very well, we understand what is needed to approach them, and we have the motivation to look for drugs that might be useful for particular rare-disease application and get them to these patients.”
Optimism about gene therapy
Meanwhile, Rader continues to seek new and better ways to target the liver for gene therapy, collaborating with James M. Wilson, M.D., Ph.D., professor of pathology and laboratory medicine, and using techniques Wilson has pioneered. As part of an N.I.H.-funded initiative, Rader and others have shown that vectors, or delivery systems, using the adeno-associated virus can be used against FH.
In March, Rader was the “sponsor” of a group that presented a protocol to the Recombinant DNA Advisory Committee at the N.I.H. (The “sponsor” has the regulatory role of overseeing the principal investigator and making sure the research is carried out properly.)
Eventually, Rader feels, FH patients will receive the gene therapy, which will lower their cholesterol but not normalize it, and receive the drug that targets MTP, the gene Rader had studied earlier, which will reduce cholesterol further. “The combination of those two, I think, will convert this disease that is almost invariably fatal by the age of 30 to a chronic manageable disease.”
Genetics is likely to play an even greater role in finding new pathways that regulate cholesterol metabolism. Rader and his group are involved in the global effort to use “genome-wide association studies,” which scan the entire human genome for common variants that might be related to a particular disease. As he says, “It’s an open-ended, unbiased way of asking, ‘What other genes are out there that we don’t know about yet that impact on my disease of interest?’”
Two years ago, he was part of a team that published a piece in Nature identifying 95 different areas of the genome associated with LDL and HDL, most previously not known. To Rader, that’s a start toward understanding the biology of how the genes work on cholesterol.
One new finding was the gene Sort1, which encodes the protein sortilin. Investigators at Penn (including Rader) and elsewhere figured out how it regulates LDL. It is, he says, “a whole new pathway. That might be a target for new drug development, we don’t know – but it’s certainly new biology.”
So much discovered, so much to discover
What does Rader see when he places his HDL research into the field’s historical picture? “We are with HDL where we were with LDL a few decades back: a lot of interesting information, epidemiology, basic science, but complete uncertainty about whether targeting HDL from a therapeutic standpoint is actually going to reduce cardiovascular risk.”
So, yes, he’s amazed at the amassed knowledge, “but it’s a different kind of amazement, that we haven’t made more progress. We’ve learned a lot, but we have a long way to go.”
He mentions the hard-won certainty that lowering LDL reduces cardiovascular risk. “Believe me, in the mid-’80s, that was nowhere near a tenet of faith” despite the 1985 Nobel Prize in the field, he says. “Even in areas of science that we think we understand, there are new things to be discovered.”
Richard Shannon, the chair of medicine, agrees: “The discoveries that have been made in this era of genetics and genomics and molecular biology have opened entirely new opportunities to target new molecules in cells that contribute to disease — and there are thousands of these targets. Investigators working in teams to target these abnormalities through new kinds of therapeutics — that’s the real opportunity.”
And that’s an important concept for medicine at large, Rader adds. “It’s common, particularly among young trainees, to feel that most of the important things have already been discovered. Nothing could be further from the truth. There’s so much we have yet to learn. The cholesterol field is a microcosm for that.”
If you look up Daniel J. Rader on Penn’s Web site, you find, among summaries of his research initiatives, a daunting list of administrative appointments. I hand him a copy of the list as a way of asking how he fits these into his life. He immediately notices a few omissions — the list is outdated, it should name even more. But it has a general thrust fully harmonized with his work in his lab and clinics: translational medicine.
Translational medicine is a bridge between lab discoveries in biomedical science and the development of new therapies for patients. Its hub at Penn Medicine is the Institute for Translational Medicine and Therapeutics, an intellectual home to more than 800 investigators from Penn and surrounding institutions.
ITMAT is also the “world’s first such institute, in the sense that we gave form to a disciple that was in evolution and has now proliferated to every academic medical institution in the country and many in the world,” says its director, Garret A. FitzGerald, M.D., professor of medicine and pharmacology, chair of pharmacology, and the McNeil Professor in Translational Medicine and Therapeutics.
To illustrate how a translational researcher works, FitzGerald notes how Rader has elucidated the functional significance of genes associated with cholesterol. “That’s a model,” he explains, “because, up to now, the people involved in gene discovery have been a different tribe of people from the people interested in gene function. What Dan has done provides the translational glue between those two tribes.”
In his administrative roles, Rader often serves as a strategist. His key appointment is associate director of Penn’s Institute for Translational Medicine and Therapeutics; he is chief of a comparable division in the Department of Medicine. And he is leading the development of a comprehensive biobank at Penn Medicine.
He is also the liaison between his cardiovascular labs, on the 11th floor of the Translational Research Center, and a diabetes research unit on the floor above. He reaches for my sheet of interview questions. Turning it over for blank space, he draws two overlapping circles, one for cardiovascular research, the other for diabetes research. The overlap represents vascular disease, which, he notes, is a major problem for patients with diabetes. He heads the effort that seeks opportunities for the areas to interact.
A useful concept
Has the emergence of the term translational medicine, first used in 1993, furthered the goal?
“It’s become a bit of a buzz word,” Rader acknowledges, “but I think it’s helpful, especially for junior people. They need to have a sense of a viable career path.”
For instance, they know they can have careers as bench scientists, or do clinical trials as part of a clinical career in academe, or enter epidemiology, engaging in longitudinal projects such as the Framingham Heart Study.
“But translational medicine — where you do detailed, mechanistic studies in humans, often linked to laboratory-related research in service to that — had never been a defined career path before, so there’s an advantage in defining it .
“First, if you’ve defined it, people know what you’re talking about — it’s a useful term. Second, it defines a career path for younger people. They can point to it and see steps they can follow to get into it and the training they’ll need, and realize they could be an investigator who sits on this cusp between the bench and patient care, doing studies on humans to try to advance our understanding of disease. That’s really the major utility of it.”