into active drugs in the bloodstream; others transformed backward from active drugs to inactive molecules. Some were excreted in the urine; others condensed in the bile or fell apart immediately in the blood. One molecule might survive for days in an animal, but its chemical cousin—a variant by just a few critical atoms—might vanish from the body in minutes.
On April 19, 1910, at the densely packed216 Congress for Internal Medicine in Wiesbaden, Ehrlich announced that he had discovered yet another molecule with “specific affinity”—this one a blockbuster. The new drug, cryptically called compound 606, was active against a notorious microbe, Treponema pallidum, which caused syphilis. In Ehrlich’s era, syphilis—the “secret malady”217 of eighteenth-century Europe—was a sensational illness, a tabloid pestilence. Ehrlich218 knew that an antisyphilitic drug would be an instant sensation and he was prepared. Compound 606 had secretly been tested in patients in the hospital wards of St. Petersburg, then retested in patients with neurosyphilis at the Magdeburg Hospital—each time with remarkable success. A gigantic factory, funded by Hoechst Chemical Works, was already being built to manufacture it for commercial use.
Ehrlich’s successes with Trypan Red and compound 606 (which he named Salvarsan, from the word salvation) proved that diseases were just pathological locks waiting to be picked by the right molecules. The line of potentially curable illnesses now stretched endlessly before him. Ehrlich called his drugs “magic bullets”—bullets for their capacity to kill and magic for their specificity. It was a phrase with an ancient, alchemic ring that would sound insistently through the future of oncology.
Ehrlich’s magic bullets had one last target to fell: cancer. Syphilis and trypanosomiasis are microbial diseases. Ehrlich was slowly inching toward his ultimate goal: the malignant human cell. Between 1904 and 1908, he rigged several elaborate schemes to find an anticancer drug using his vast arsenal of chemicals. He tried amides, anilines, sulfa derivatives, arsenics, bromides, and alcohols to kill cancer cells. None of them worked. What was poison to cancer cells, he found, was inevitably poison to normal cells as well. Discouraged, he tried even more fantastical strategies. He thought of starving sarcoma cells of metabolites, or tricking them into death by using decoy molecules (a strategy that would presage Subbarao’s antifolate derivatives by nearly fifty years). But the search for the ultimate, discriminating anticancer drug proved fruitless. His pharmacological bullets, far from magical, were either too indiscriminate or too weak.
In 1908, soon after Ehrlich won the Nobel Prize for his discovery of the principle of specific affinity, Kaiser Wilhelm of Germany invited him to a private audience in his palace. The Kaiser was seeking counsel: a noted hypochondriac afflicted by various real and imagined ailments, he wanted to know whether Ehrlich had an anticancer drug within reach.
Ehrlich hedged. The cancer cell, he explained, was a fundamentally different target from a bacterial cell. Specific affinity relied, paradoxically, not on “affinity,” but on its opposite—on difference. Ehrlich’s chemicals had successfully targeted bacteria because bacterial enzymes were so radically dissimilar to human enzymes. With cancer, it was the similarity of the cancer cell to the normal human cell that made it nearly impossible to target.
Ehrlich went on in this vein, almost musing to himself. He was circling around something profound, an idea in its infancy: to target the abnormal cell, one would need to decipher the biology of the normal cell. He had returned, decades after his first encounter with aniline, to specificity again, to the bar codes of biology hidden inside every living cell.
Ehrlich’s thinking was lost on the Kaiser. Having little interest in this cheerless disquisition with no obvious end, he cut the audience short.
In 1915, Ehrlich fell ill with tuberculosis, a disease that he had likely acquired from his days in Koch’s laboratory. He went to recuperate in Bad Homburg, a spa town famous for its healing carbonic-salt baths. From his room, overlooking the distant plains below, he watched bitterly as his country pitched itself into the First World War. The dye factories that had once supplied his therapeutic chemicals—Bayer and Hoechst among them—were converted to massive producers of chemicals that would be turned into precursors for war gases. One particularly toxic gas was a colorless, blistering liquid produced by reacting the solvent thiodiglycol (a dye intermediate) with boiling hydrochloric acid. The gas’s smell was unmistakable, described alternatively as reminiscent of mustard, burnt garlic, or horseradishes ground on a fire. It came to be known as mustard gas.
On the foggy night of July 12, 1917, two years after Ehrlich’s death, a volley of artillery shells marked with small, yellow crosses rained down on British troops stationed near the small Belgian town of Ypres. The liquid in the bombs quickly vaporized, a “thick, yellowish green cloud219 veiling the sky,” as a soldier recalled, then diffused through the cool night air. The men in their barracks and trenches, asleep for the night, awoke to a nauseatingly sharp smell that they would remember for decades to come: the acrid whiff of horseradishes spreading through the chalk fields. Within seconds, soldiers ran for cover, coughing and sneezing in the mud, the blind scrambling among the dead. Mustard gas diffused through leather and rubber, and soaked through layers of cloth. It hung like a toxic mist over the battlefield for days until the dead smelled of mustard. On that night alone, mustard gas injured or killed two thousand soldiers. In a single year, it left thousands dead in its wake.
The acute, short-term effects of nitrogen mustard—the respiratory complications, the burnt skin, the blisters, the blindness—were so amply monstrous that its long-term effects were overlooked. In 1919, a pair of American pathologists220, Edward and Helen Krumbhaar, analyzed the effects of the Ypres bombing on the few men who had survived it. They found that the survivors had an unusual condition of the bone marrow. The normal blood-forming cells had dried up; the bone marrow, in a bizarre mimicry of the scorched and blasted battlefield, was markedly depleted. The men were anemic and needed transfusions of blood, often up to once a month. They were prone to infections. Their white cell counts often hovered persistently below normal.
In a world less preoccupied with other horrors, this news might have caused a small sensation among cancer doctors. Although evidently poisonous, this chemical had, after all, targeted the bone marrow and wiped out only certain populations of cells—a chemical with specific affinity. But Europe was full of horror stories in 1919, and this seemed no more remarkable than any other. The Krumbhaars published their paper in a second-tier medical journal and it was quickly forgotten in the amnesia of war.
The wartime chemists went back to their labs to devise new chemicals for other battles, and the inheritors of Ehrlich’s legacy went hunting elsewhere for his specific chemicals. They were looking for a magic bullet that would rid the body of cancer, not a toxic gas that would leave its victims half-dead, blind, blistered, and permanently anemic. That their bullet would eventually appear out of that very chemical weapon seemed like a perversion of specific affinity, a ghoulish distortion of Ehrlich’s dream.
What if this mixture do not work at all? . . .221
What if it be a poison . . . ?
—Romeo and Juliet
We shall so poison the atmosphere222
