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Friday, January 16, 2009

The New Virus Killer

Scientists try to turn HIV’s greatest strength—mutation—against itself

Death by Mutation: A scientist isolates virus samples from an AIDS patient. Hank Morgan/Getty Images

At first it sounds like a terrible plan, the kind that results in zombies ruling the Earth. Imagine a killer virus, a bug that mutates so often that it inevitably finds a way to resist every drug. Now, rather than fight its ability to evolve, you enhance it. You speed up the mutation rate, forcing such dramatic genetic change that the virus crashes completely. In the movies, this technique, known as lethal mutagenesis, would create a supergerm, but in real life it’s spawning a powerful new class of antiviral drugs. “It’s a fundamentally different strategy,” says University of Washington biologist Robert Smith. “Death by mutation.”

Few Options: A clinic in India admits 60 HIV patients a day as the worldwide total hits 33 million. M. Lakshiman/AP Photo
Several university labs are investigating this tactic for combating viruses such as hepatitis C and West Nile. But the research that’s furthest along, and that a few pharmaceutical companies are backing, targets HIV, a virus that is rapidly out-evolving the medications on which 33 million infected people depend. Seattle-based Koronis Pharmaceuticals is leading the way with the first HIV mutation booster to advance to human trials.
Known as KP-1461, the drug employs a counterintuitive attack. When an HIV particle invades a cell, it transforms its genetic information into double-stranded DNA. The cell, mistaking the infected DNA for its own, replicates it and churns out more HIV particles. Most drugs disrupt this process, but HIV evolves around them. KP-1461 lets the replication run so wild that the virus self-destructs.

The trick is disguising the drug’s molecules as the building blocks of HIV. When the virus replicates, it inserts the KP-1461 imposters throughout its genetic code, creating so many mistakes that it no longer has enough viable DNA to sustain its basic functions, let alone take over a host cell. As a result, the virus dies.

KP-1461: KP-1461 molecules [yellow] kill a virus by disrupting DNA [blue] replication. Koronis Pharmaceuticals
Though promising, the basic premise has raised concerns about cultivating that Hollywood-caliber supergerm. Louis Mansky, a virologist at the University of Minnesota, says that risk is minimal. In nature, he points out, the vast majority of mutations are either harmful or neutral to organisms, and a virus must replicate 10, 20 or even 100 times for drug resistance to evolve. Crippling the bug before that stage is key, he says.

But nailing that cutoff remains a sticking point. Mansky is lab-testing a drug cocktail that kills nearly the entire population of HIV cells after just one round of replication, but human tests are a few years away. Koronis’s clinical trials of KP-1461 last summer weren’t as effective as lab tests. Jeff Parkins, the vice president of clinical development, says researchers are honing the dosing strategy for trials planned for later this year.
Harnessing lethal mutagenesis may soon become easier, following a new mathematical formula by bioengineer Michael Deem of Rice University that could help researchers fine-tune compounds earlier in the process. Given a few key variables, such as how often viral genes shuffle inside cells, his equations can provide the minimum mutation rate to safely kill a virus. At this pace the virus won’t have time to correct errors or absorb drug-evading changes, and it will crash. “It’s not going to come back and cause problems,” Deem assures.

Coupled with work like Deem’s, lethal mutagenesis could lead to a penicillin-like drug that knocks out numerous viruses—influenza, SARS and more. Parkins maintains hope that his company’s drug could eradicate HIV, or at least offer an alternative to current treatements. And that, researchers say, is what makes the mutation tactic attractive. “Even if it just leads to a different antiviral,” says virologist Satish Pillai of the University of California at San Francisco, “it would still be great for patients who have very few options left.”