A few years ago, Stanford pharmacogenomic expert Gary Peltz, MD, PhD, collaborating with researchers in Japan, developed a line of bioengineered mice whose livers were largely replaced with human liver cells that recapitulate the architecture and function of a human liver. Now, in a recent study published in PLoS Medicine, Peltz's team has shown that routine use of this altered lab mouse in standard toxicology tests preceding clinical trials would save human lives.
Among the liver's numerous other job responsibilities, one of the most important is chemically modifying drugs in various ways to make them easier for the body to get rid of. But some of those chemical products, or metabolites, can themselves be quite toxic if they reach high levels before they've been excreted.
The Food and Drug Administration requires that prior to human testing, a drug's toxicological potential be assessed in at least two mammalian species. But we humans metabolize things differently from other mammals, because our livers are different. That can make for nasty surprises. All too often, drugs showing tremendous promise in preclinical animal assessments fail in human trials due to unforeseen liver toxicity, said Peltz, a former pharmaceutical executive who is intimately familiar with established preclinical testing procedures in the industry.
That's what happened in 1993 when, after a short safety trial of a drug called FIAU concluded without incident, the comp0und was placed in a phase-2 clinical trial of a drug for hepatitis B. FIAU belongs to a class of drugs that can interfere with viral replication, so it was considered a great candidate for treating virally induced infections such as hepatitis B.
As I wrote in my release about the new study:
"FIAU was supposed to be a revolutionary drug," Peltz said. "It looked very promising in preclinical tests. In phase 1, when the drug was administered to subjects for a short period of time, the human subjects seemed to do fairly well." But the phase-2 trial was stopped after 13 weeks, when it became clear that FIAU was destroying patients' livers.
In fact, nearly half the patients treated with FIAU in that trial died from complications of liver damage. Yet, before advancing to clinical trials FIAU had been tested for as long as six months in mice, rats, dogs and monkeys without any trace of toxicity. An investigation conducted by the National Academy of Sciences later determined that the drug had shown no signs of being dangerous during those rigorous preclinical toxicology tests.
In Peltz's new study, though, FIAU caused unmistakable early signs of severe liver toxicity in the bioengineered mice with human livers. This observation would have served as a bright red stop signal that would have prevented the drug from being administered to people.
Bonus item: Using bioengineered mice with human livers instead of mice with murine ones would no doubt result in the clinical and commercial success of some drugs that never got to the human-testing stage because they caused liver toxicity in mice.
Previously: Fortune teller: Mice with 'humanized' livers predict HCV drug candidate's behavior in humans, Alchemy: From liposuction fluid to new liver cells and Immunology escapes from the mouse trap
Photo by erjkprunczyk