The Emperor of All Maladies: A Biography of Cancer (67 page)

At MIT, in Boston
, another young virologist, David Baltimore, had also picked up the hint of an RNA
→
DNA conversion activity, although in a different retrovirus. Brilliant, brash, and single-minded, Baltimore had met and befriended Howard Temin in the 1940s at science summer camp in Maine, where Temin had been a teaching assistant and Baltimore a student. They had parted ways for nearly a decade, yet their intellectual paths had kept crisscrossing. As Temin was exploring reverse transcription in Rous sarcoma virus in Madison, Baltimore had begun to amass evidence that his retrovirus also possessed an enzyme that could convert RNA into DNA. He, too, was steps away from isolating the enzyme.

On the afternoon of May 27, 1970, a few weeks after he had found initial evidence for the RNA
→
DNA converting enzyme in his lab, Temin caught a flight to Houston to present his work at the Tenth International Cancer Congress. The next morning, he walked to the cavernous auditorium at the Houston Civic Center. Temin’s talk was entitled “The Role of DNA in the Replication of RNA Viruses,” a title left intentionally bland. It was a short, fifteen-minute session. The room was filled mainly with tumor virus specialists, many already dozing off to sleep.

But as Temin began to unfold his findings, the importance of his talk dawned on the audience. On the surface, as one researcher recalled, “
It was all very dry biochemistry
. . . . Temin spoke in his usual nasal, high-pitched monotone, giving no indication of excitement.” But the significance of the work crystallized out of the dry biochemical monotone. Temin was not
just talking about viruses. He was systematically dismantling one of the fundamental principles of biology. His listeners became restive, unnerved. By the time Temin reached the middle of the talk, there was an awestruck silence. Scientists in the audience were feverishly taking notes, filling page after page with harrowed scribbles. Once outside the conference room, Temin recalled, “You could see people on the telephone. . . . People called people in their laboratories.” Temin’s announcement that he had identified the long-sought-after enzyme activity in the virus-infected cells left little doubt about the theory. RNA could
generate
DNA. A cancer-causing virus’s genome could become a physical part of a cell’s genes.

Temin returned to Madison the next morning to find his laboratory inundated with phone messages. The most urgent of these was from David Baltimore, who had heard an inkling of Temin’s news from the meeting. Temin called him back.

“You know there is [an enzyme] in the virus particles,” Baltimore said.

“I know,” said Temin.

Baltimore, who had kept his own work very, very quiet, was stunned. “How do you know?”

“We found it.”

Baltimore had also found it. He, too, had identified the RNA
→
DNA enzymatic activity from the virus particles. Each laboratory, working apart, had converged on the same result. Temin and Baltimore both rushed their observations to publication. Their twin reports appeared back-to-back in
Nature
magazine in the summer of 1970.

In their respective papers
, Temin and Baltimore proposed a radical new theory about the life cycle of retroviruses. The genes of retroviruses, they postulated, exist as RNA outside cells. When these RNA viruses infect cells, they make a DNA copy of their genes and attach this copy to the cell’s genes. This DNA copy, called a provirus, makes RNA copies, and the virus is regenerated, phoenixlike, to form new viruses. The virus is thus constantly shuttling states, rising from the cellular genome and falling in again—RNA to DNA to RNA; RNA to DNA to RNA—ad infinitum.

It is surely a sign of the prevailing schizophrenia of the time that Temin’s work was instantly embraced as a possible mechanistic explanation for cancer by cancer scientists, but largely ignored by clinical oncologists. Temin’s presentation in Houston was part of a mammoth meeting on can
cer. Both Farber and Frei had flown in from Boston to attend. Yet, the conference epitomized the virtually insurmountable segregation between cancer therapy and cancer science. Chemotherapy and surgery were discussed in one room. Viral carcinogenesis was discussed in another. It was as if a sealed divider had been constructed through the middle of the world of cancer, with “cause” on one side and “cure” on the other. Few scientists or clinical oncologists crossed between the two isolated worlds. Frei and Farber returned to Boston with no significant change in the trajectories of their thoughts about curing cancer.

Yet for some scientists attending the conference, Temin’s work, pushed to its logical extreme, suggested a powerful mechanistic explanation for cancer, and thus a well-defined path toward a cure. Sol Spiegelman, a Columbia University virologist known for his incendiary enthusiasm and relentless energy, heard Temin’s talk and instantly built a monumental theory out of it—a theory so fiercely logical that Spiegelman could almost conjure it into reality. Temin had suggested that an RNA virus could enter a cell, make a DNA copy of its genes, and attach itself to a cell’s genome. Spiegelman was convinced that this process, through a yet unknown mechanism, could activate a viral gene. That activated viral gene must induce the infected cell to proliferate—unleashing pathological mitosis, cancer.

It was a tantalizingly attractive explanation. Rous’s viral theory of the origin of cancer would fuse with Boveri’s internal genetic theory. The virus, Temin had shown, could
become
an endogenous element attached to a cell’s genes, and thus both an internal aberration and an exogenous infection would be responsible for cancer. “Spiegelman’s conversion to the new religion [of cancer viruses] took only minutes,” Robert Weinberg, the MIT cancer biologist recalled. “The next day [after Temin’s conference] he was back in his lab at Columbia University in New York City, setting up a repeat of the work.”

Spiegelman raced off to prove
that retroviruses caused human cancers. “
It became his single-minded preoccupation
,” Weinberg recalled. The obsession bore fruit quickly. For Spiegelman’s schema to work, he would need to prove that human cancers had retrovirus genes hidden inside them. Working fast and hard, Spiegelman found traces of retroviruses in human leukemia, in breast cancer, lymphomas, sarcomas, brain tumors, melanomas—in nearly every human cancer that he examined. The Special Virus Cancer Program, launched in the 1950s to hunt for human cancer viruses, and moribund for two decades, was swiftly resuscitated: here, at
long last, were the thousands of cancer viruses that it had so long waited to discover. Money poured into Spiegelman’s lab from the SVCP’s coffers. It was a perfect folie à deux—endless funds fueling limitless enthusiasm and vice versa. The more Spiegelman looked for retroviruses in cancer cells, the more he found, and the more funds were sent his way.

In the end, though, Spiegelman’s effort turned out to be systematically flawed. In his frenzied hunt for human cancer retroviruses, Spiegelman had pushed the virus-detection test so hard that he saw viruses or traces of viruses that did not exist. When other labs around the nation tried to replicate the work in the mid-1970s, Spiegelman’s viruses were nowhere to be found. Only one human cancer, it turned out, was caused by a human retrovirus—a rare leukemia endemic in some parts of the Caribbean. “
The hoped-for human virus
slipped quietly away into the night,” Weinberg wrote. “The hundreds of millions of dollars spent by the SVCP . . . could not make it happen. The rocket never left its launching pad.”

Spiegelman’s conjecture about human retroviruses was half-right and half-wrong: he was looking for the right kind of virus but in the wrong kind of cell. Retroviruses would turn out to be the cause of a different disease—not cancer. Spiegelman died in 1983 of pancreatic cancer, having heard of a strange illness erupting among gay men and blood-transfusion recipients in New York and San Francisco. One year after Sol Spiegelman’s death in New York, the cause of that disease was finally identified. It was a human retrovirus called HIV.

*
Other cancer-causing viruses, such as SV40 and human papillomavirus (HPV), would eventually be discovered in 1960 and 1983, respectively.

*
Temin’s statement was speculative, but it bore his unerring biological instinct. Formal proof of the structural attachment of RSV genes into the cellular genome would only come years later.

*
The term
retrovirus
was coined later by virologists.

For the Snark
was
a Boojum, you see.

—Lewis Carroll

Sol Spiegelman had got hopelessly lost hunting for cancer-causing retroviruses in humans. His predicament was symptomatic: cancer biology, the NCI, and the targeted Special Virus Cancer Program had all banked so ardently on the existence of human cancer retroviruses in the early 1970s that when the viruses failed to materialize, it was as if some essential part of their identity or imagination had been amputated. If human cancer retroviruses did not exist, then human cancers must be caused by some other mysterious mechanism. The pendulum, having swung sharply toward an infectious viral cause of cancer, swung just as sharply away.

Temin, too, had dismissed retroviruses as the causal agents for human cancer by the mid-1970s. His discovery of reverse transcription had certainly overturned the dogma of cellular biology, but it had not pushed the understanding of human
carcinogenesis
far. Viral genes could attach themselves to cellular genes, Temin knew, but this could not explain how viruses caused cancer.

Faced with yet another discrepancy between theory and data, Temin proposed another bold conjecture—again, standing on the thinnest foundation of evidence. Spiegelman and the retrovirus hunters, Temin argued, had conflated analogy with fact, confused messenger with message. Rous sarcoma virus could cause cancer by inserting a viral gene into cells. This proved that genetic alterations could cause cancer. But the genetic alteration, Temin proposed, need not originate in a virus. The virus had merely brought a message into a cell. To understand the genesis of cancer, it was that culprit
message
—not the messenger—that needed to be identified. Cancer virus hunters needed to return to their lamplit virus again, but this time with new questions: What was the viral gene that had unleashed
pathological mitosis in cells? And how was that gene related to an internal mutation in the cell?

In the 1970s, several laboratories began to home in on that gene. Fortuitously, RSV possesses only four genes in its genome. In California, by then the hotbed of cancer virus research, the virologists Steve Martin, Peter Vogt, and Peter Duesberg made mutants of the Rous virus that replicated normally, but could no longer create tumors—suggesting that the tumor-causing gene had been disrupted.
By analyzing the genes altered in these mutant viruses
, these groups finally pinpointed RSV’s cancer-causing ability to a single gene in the virus. The gene was called
src
(pronounced “sarc”), a diminutive of
sarcoma.

Src
, then, was the answer to Temin’s puzzle, the cancer-causing “message” borne by Rous sarcoma virus. Vogt and Duesberg removed or inactivated
src
from the virus and demonstrated that the
src
-less virus could neither induce cell proliferation nor cause transformation.
Src
, they speculated, was some sort of malformed gene acquired by RSV during its evolution and introduced into normal cells. It was termed an oncogene,
^*
a gene capable of causing cancer.

A chance discovery in Ray Erikson’s laboratory
at the University of Colorado further elucidated
src
’s function. Erikson had been a graduate student in Madison in the early 1960s when Temin had found retroviruses. Erikson had followed the discovery of the
src
gene in California and had been haunted by the function of
src
ever since. In 1977, working with Mark Collett and Joan Brugge, Erikson set out to decipher the function of
src
.
Src
, Erikson discovered, was an unusual gene. It encoded a protein whose most prominent function was to modify other proteins by attaching a small chemical, a phosphate group, to these proteins—in essence, playing an elaborate game of molecular tag.
^†
Indeed, scientists had found a number of similar proteins in normal cells—enzymes that attached phosphate groups to other proteins. These enzymes were called the “kinases,” and they were soon found to behave as molecular master switches within a cell. The attachment of the phosphate group to a protein acted like an “on” switch—activating the protein’s function. Often, a kinase turned “on” another kinase, which turned “on” another kinase, and so forth. The signal
was amplified at each step of the chain reaction, until many such molecular switches were thrown into their “on” positions. The confluence of many such activated switches produced a powerful internal signal to a cell to change its “state”—moving, for instance, from a nondividing to a dividing state.