Canaani wanted to see if the RNA made by this gene was different from the RNA made by the normal abl proto-oncogene that existed in normal, non-CML cells. Was the instruction encoded by abl in healthy people different from the instruction encoded by the version of abl present in people with CML?
It was. The RNA in the CML cells that Canaani was investigating was not present in normal human cells, those that lacked the Philadelphia chromosome translocation. In CML cells, the RNA was present in copious amounts. Here was the third piece of crucial evidence that abl was directly involved in the development of CML.
Suddenly, the story had taken on a life of its own, as if it had somehow amassed enough material to have a gravitational pull. Facts began coming together in rapid succession. In 1984, Witte and his group reported that the CML protein, the strangely large one that had been so quickly engulfed by the antibody with which his student had been experimenting, was a mutant form of the Abl kinase. They weighed the mutant protein and found out that it was much heavier than the normal Abl kinase, suggesting that something had been added to it.
The discovery mirrored exactly what Witte had found in mice infected with the Abelson virus. When he had extracted a protein with the Gag antibody from mice infected with the Abelson virus, he’d found that the Gag protein had something else attached to it. That something else had been named Abl, the product of the abl oncogene. Gag and Abl had fused together to form the supersized protein Witte had called Gag/Abl. Now, he discovered that the Abl protein, a tyrosine kinase, in CML cells had also fused to another protein, just as it had done in the mice. What that other protein was he didn’t know.
plate 9
At nearly the same moment, Heisterkamp and Groffen completed their map of chromosome 9. They knew a piece of the abl gene was broken off and moved to chromosome 22. And they had isolated the exact region on chromosome 22 where that break occurred, within a gene subsequently named bcr. Now they showed that the broken-off piece of bcr from chromosome 22 was next to what remained of the abl gene back on chromosome 9. In CML cells that had the Philadelphia chromosome, abl was fused to bcr. The two previously distinct genetic sequences had melded together, to become bcr/abl.
This change, they knew, had to be responsible for the cancer-causing tendencies of abl. The only difference between normal cells and CML cells was that in the former, bcr and abl were separate and that in the latter, bcr and abl were fused. And that fusion turned the once-harmless abl into an oncogene. Instead of the normal Abl kinase of healthy cells, bcr/abl expressed an abnormal kinase that induced CML. That fusion protein had to be the cause of CML.
There was one final question that no one had yet answered. How did Bcr/Abl cause cancer? Everyone knew it was a tyrosine kinase. They knew, from years of research at the Cohen lab in Dundee and elsewhere, that kinases set events—such as the production of blood cells—in motion by taking phosphates from ATP and placing them on proteins sitting at the top of the pathways responsible for those events. Adding Bcr/Abl to other research, tyrosine kinases appeared to be involved in many cancers, leading many researchers to suspect them as a general mechanism by which cancer operated. But what was the difference between normal tyrosine kinases and those involved in cancer?
A rapid succession of research spelled out exactly what was happening. The main clue came from a leukemia cell line known as K562. These cells were derived from a CML patient in blast crisis, intentionally created for laboratory research. In 1984, Witte and his lab reported that a kinase in those cells was continually active. That is, instead of transporting phosphates to proteins only intermittently, the kinase was doing it all the time. Two years later, the Baltimore lab made the connection that the kinase in that cell line was the same one encoded by the bcr/abl gene in human CML. That link sealed the conclusion: The Bcr/Abl tyrosine kinase caused CML because it was deregulated. It never stopped powering up the protein responsible for launching the pathway leading to white blood cell production. The kinase was, in scientific terms, constitutively active. In more accessible language: The Bcr/Abl tyrosine kinase was out of control.
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“THAT WORD IS ONCOGENES”
The story was now clear. Finally, the work done by Nowell, Hungerford, Abelson, Rowley, Erikson, Hunter, Rosenberg, Witte, Goff, Heisterkamp, Groffen, Grosveld, Canaani, and a score of others during those twenty-five years had come together. Many of these people knew of each other over the years, but just as often they were strangers separated by years, geography, and the unawareness that their pursuits were connected. None of them envisioned how their strands of research would finally weave together.
The Philadelphia chromosome was a translocation that brought together a piece of bcr and a piece of abl. This fusion gene created a fusion protein. Normally, abl encoded a tyrosine kinase. The fusion protein was a tyrosine kinase with heightened activity. A bit of Bcr put the Abl kinase into a perpetual “on” setting. In that abnormal mode, Abl would not stop phosphorylating proteins. In a never-ending loop, the kinase plucked phosphates and stuck them onto the tyrosine key hooks on proteins inside white blood cells. This continuous phosphorylation triggered a signaling pathway that resulted in the excess production of these cells. That addition of just a portion of the bcr gene—a tiny scrap of DNA sequence—turned the Abl kinase into a killing machine.
The unfolding of events was uncanny. Herb Abelson’s experiments had led to the discovery of a spontaneously arising virus. If the thymus-annihilating experiments were repeated today, the virus wouldn’t necessarily appear. (“In later years we talked about repeating the whole experiment, but never got around to it,” Abelson said. “Biology is testy and fickle.”) At MIT, the Baltimore lab discovered that the virus had engulfed a proto-oncogene that, once integrated into the viral genome, became a leukemia-causing oncogene in mice. That understanding had been made possible by work on the opposite coast when Bishop and Varmus identified the cellular origin of the src oncogene. Their work, derived from decades of research on a virus extracted from a chicken by Peyton Rous in 1912, had directly informed the study of the cancer-causing Abelson virus. Then Witte identified the cancer-inducing protein encoded by abl as a tyrosine kinase, a fact that was the scientific descendant of Ray Erikson and Marc Collett’s discovery that src encoded a kinase and of Tony Hunter’s revelation that this kinase phosphorylated a previously ignored amino acid called tyrosine.
The fact that the culprit gene in the Abelson virus was the culprit gene in this human leukemia came as a shock even to the most seasoned researchers behind the work. That the fusion gene and fusion protein Witte isolated in Abelson-infected mouse cells would have an exact parallel in the fusion gene and protein isolated in human CML cells was completely unforeseen. And then to find, as Heisterkamp and Groffen had, that the human version of abl was on chromosome 9 and moved to chromosome 22 in the Philadelphia abnormality—the story was almost too good to believe.
The pursuit of the src oncogene’s origin and that of its protein product had begun as distinct efforts to unravel the mechanism behind virally caused cancer. These strands of research had been completely separate from the Philadelphia chromosome and from the Abelson virus. Gradually, unknowingly, they had become inextricably woven together.
Recombinant DNA and chromosome banding techniques had come along at just the right time. Herb Abelson ended up just upstairs from the Baltimore lab. Witte, Rosenberg, and Goff brought the right skills to the right place at the right time. And the research had all been careful and airtight.
The way the Philadelphia chromosome led to CML was a story that unfolded like a hundred painters applying brushes to a canvas at some time or another over twenty-five years, driven only by curiosity and, sometimes, a vague hope that their work might eventually be relevant to human cancer. There’d been no final picture in mind and no awareness that they were even painting something together. And yet there it was. A scientific masterpiece.
IN AUGUST 1984, Nick Lydon, the res
earcher who’d been so captivated by kinases at the University of Dundee, was enjoying a warm summer in Dardilly, a small town in southern France just outside Lyons. He’d left Dundee for Paris in 1982 to work for the pharmaceutical company Schering-Plough, which had just opened a new lab in the quiet countryside. On a lunch break, he picked up that month’s issue of Scientific American and began to read an article by Tony Hunter, “The Proteins of Oncogenes.” In it, Hunter, the scientist who’d found the first tyrosine-aimed kinase, described all that had been discovered about kinases. Again and again, proto-oncogenes were found to encode kinases, and as the gene transformed from normal to mutant, so did the kinase move from healthy to cancer inducing. A shift in the gene transformed the kinase into its haywire state, continually phosphorylating proteins and thus continually sending the signal for the cell to reproduce. It was, as Witte and others had suspected, a widespread mechanism for cancer transformation.
One final proof remained to confirm without a doubt that the mutated Bcr/Abl kinase—and that alone—was sufficient to cause CML. That step was necessary in order to consider the link an established fact. Even with all of the work that had been accomplished, the connection between Bcr/Abl and CML could still only be called an association. Someone had to demonstrate that this abnormal protein alone was responsible for the cancer. When that happened, the abnormal kinase could be called the cause of CML.
But for Lydon, that last proof was a formality that would come when he was well on his way toward his new goal. By 1984, the weight of the work already done was enough to convince him of the wayward kinase’s involvement in CML. Adding all that up with Hunter’s magazine summary solidified Lydon’s view that the kinase, as a general mechanism, was a driving factor in the development and progression of cancer. This enzyme—the one that had so piqued his curiosity during his postdoc years, the protein product of the first oncogene ever identified, the substance connected to nearly every oncogene identified to date—compelled Lydon toward a singular mission: creating a drug that would block the kinase and thereby stop the growth of cancer.
At around that same time, Brian Druker was having, as he puts it, his “plastics moment,” referring to the famous scene of The Graduate when a family friend tells Dustin Hoffman’s character that his future lay in plastics. Having finished medical school near the top of his class, he’d gone to Washington University for a residency in internal medicine at Barnes Hospital, one of the most rigorous training programs in the country. These were still the years before limits were put on resident shifts, and Druker was working 100-hour weeks, on call for multiple nights each week. It was another proving ground, one in which the number of admissions handled was a badge of honor, and asking for help was a sign of weakness. Spare time was nonexistent; he and his friends (a group that included Lawrence Piro, who would later become famous as Farrah Fawcett’s oncologist, and Brian Kobilka, who won the 2012 Nobel Prize in Chemistry) would frequently scrape together pennies for after-work pizzas, because there’d been time to stop at a bank.
But Druker had an advantage: his inexplicable interest in cancer. He’d already pushed himself to handle particularly difficult rotations during medical school, putting him at relatively greater ease with his new environment. “I was comfortable taking care of the sickest of the sick,” he recalled later. And he flourished, becoming the go-to person for questions, taking on extra hours. “I loved taking care of patients,” he said.
It was during this time that Druker had his first exposure to bone marrow transplants, a dangerous procedure that for many years was the only hope for curing CML. At the time, high doses of chemotherapy, followed by a bone marrow transplant, was a treatment option for colon cancer, melanoma, breast cancer—basically any metastatic, terminal cancer. “In those days, it was essentially a one-way ticket out,” said Druker. “The issue was: Do you torture somebody before they die, or do you just resign to the fact that they are going to die?” Bone marrow would be removed from the patient, who then received drugs followed by a reinfusion of their marrow. But patients frequently ended up in the intensive care unit before the marrow could recover. “Almost nobody made it out of the [ICU],” says Druker. “It was just this incredibly frustrating experience.”
If that horror did anything for Druker’s medical career, it was to strengthen it. He would sit by patients’ bedsides long after his shift had ended, and he would administer treatments himself rather than hand a distressed patient over to someone unfamiliar. He was there for the first patient at Barnes to ever be given human insulin, a landmark breakthrough in the treatment of diabetes, especially for people who were allergic to pork or beef insulin, the only prior options. That was the first time he witnessed a man being brought back to life from the brink of death.
But at the end of those three years, it was time for Druker to finally settle on a specialty, a decision he’d been resisting for more than ten years. Unable to deny his wish to focus on cancer any longer, he finally mustered the courage to speak it out loud.
“I think I want to do cancer,” he told David Kipnis, the chair of medicine at Washington University at the time.
“‘I’m going to tell you one word. Are you listening?’” Druker recalled Kipnis replying, a memory colored by The Graduate’s famous dialogue. “‘That word is oncogenes.’”
Aside from the cloistered world of his residency, Druker knew nothing about what was happening in the world of cancer research. He had never heard of the Philadelphia chromosome. He knew nothing about the Abelson virus, the Bcr/Abl tyrosine kinase, or any of the work that had been going on during the past two-plus decades. “All I knew was that I was sleep deprived and trying to take good care of patients,” Druker said later. But he listened to Kipnis. “He understood where the future of cancer research was going. This is going to be where the discoveries will happen, and I needed to pay attention to that,” Druker said. “And he was absolutely right.”
Despite the intensity of his residency, Druker never forgot about his interest in lab research. So when it came time to decide exactly how to pursue his finally declared interest in cancer, and now armed with the forcefully delivered insights from Kipnis, Druker knew where he wanted to go: Dana-Farber Cancer Institute. For someone who wanted to research cancer in the lab without losing touch with patient care, Dana-Farber was the perfect match. His fellowship training began there in 1984. He arrived in Boston at virtually the same time that Lydon was reading Tony Hunter’s Scientific American declaration about the role of kinases in cancer and just a few years before the two would meet.
PART II
Rational Design
1983–1998
• • •
Although logic and evidence had become the pillars of modern medicine, cancer treatments were mostly the desperate products of trial and error. Drugs were not made to target the cause of a malignancy, and no methods existed for creating medications that would do so.
Following the discovery of the Philadelphia chromosome, blood from every patient diagnosed with CML was tested for the genetic abnormality as a matter of routine. But the information was meaningless to the care and survival of people with CML. No one knew why almost every patient with CML had the Philadelphia chromosome. Even when the connection between the genetic mutation and the cancer was understood, the science was irrelevant to the patients harboring the abnormality.
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BECOMING A DOCTOR, AND THEN A SCIENTIST
By the time he joined Dana-Farber in 1983, Brian Druker had already been thrown around and tossed ashore by the rough waves of medical training. He had obtained his medical license and had come out the other side of a rigorous training in internal medicine. As he looked back, he saw how those years had been stamped with his low-key ways. He’d always been a successful student, but his mellow mannerism didn’t attract the attention that the type-A students had always seemed to garner, sitting at the front of the classroom and raising their hands, and he’d never been good at p
laying the game. (When a med school interviewer had asked him what scientific prizes he dreamed of winning, he answered with the names of actual prizes; the thought of replying, “Just doing the work is enough for me” hadn’t even occurred to him.) Those traits, combined with his reticence about pursuing medicine in the first place, left him under the radar.
With each step, he’d had to find his footing and figure out where he stood in the pecking order. Would he be among the top students at medical school? Would he be among the best doctors at Barnes Hospital? He’d never minded the fact that his ambitions and interests seemed to run counter to those of his colleagues. But he knew he was smart, and a part of him craved recognition for that fact, a legacy of an upbringing where academic success was prized above all by his parents. By the end of his residency years, he’d clearly proved himself to be an excellent physician. He was the one always willing to take on the most difficult patients. He’d excelled in his medical knowledge, and his understated personality made him a calm and reassuring presence at a hospital bedside. But now here he was at Dana-Farber with doctors who’d been in the Harvard system since their freshman year in college. The old insecurities came flooding back.
He was assigned about eighty patients during his first fellowship year, now with no senior resident looking over his shoulder, as there had been at Barnes. Though he’d cared for some cancer patients in those years, he still had only very little official training in oncology. By his own admission, he was basically clueless about how to treat cancer. But the stigma against asking for help was pervasive in medical training, and he was loath to show signs of weakness. “How much am I willing to admit that I don’t know versus the fact that I’m practically drowning?” Druker said, recalling his state of mind that first year.
The Philadelphia Chromosome Page 10