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Alnylam Eyes RNAi for Highly Pathogenic Flu; Doesn t Formally Add It to Pipeline

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Alnylam Pharmaceuticals said this week that it is investigating the use of RNAi to treat and prevent highly pathogenic influenza.

The project, however, is not an effort the company categorizes as a formal development program at this point. Currently, Alnylam considers only its age-related macular degeneration and respiratory syncytial virus projects as likely to enter human testing in the near term. The company has said, however, that it plans to announce the third main development program before the end of the year.

Alnylam announced that it has formed a collaboration with researchers from the University of Georgia to "discover and develop a directly administered RNAi-based drug for the prevention and treatment of respiratory infection from newly emerging, highly pathogenic strains of influenza virus."

According to Alnylam President and CEO John Maraganore, the company decided to pursue this portion of the influenza market because it believes "the greatest unmet need at this time is for novel treatment strategies, such as RNAi, to address the potential outbreak of a flu pandemic. Based on this clear need, we are very focused on pandemic flu at this time," he said in an e-mail to RNAi News.

Maraganore declined to comment on whether competition played a role in Alnylam's decision not to immediately target more common strains of influenza in its RNAi program, but there certainly is no dearth of players in the flu therapy market.

Tamiflu has become a big moneymaker for Roche, with the drug raking in roughly $357 million in the first quarter alone. Meanwhile, GlaxoSmithKline just this week filed for US approval of a flu vaccine, Fluarix, and start-up Galenea has projected that it will file an investigational new drug application for its RNAi-based flu drug in 2007.

Ralph Tripp, professor in the department of infectious diseases at the University of Georgia, said that the need for new flu treatments is pressing with the emergence of resistant and aggressive strains of the virus such as avian subtype H5N1, which has begun to infect humans in Vietnam, Thailand, and Cambodia.

"The emerging viral infections that are occurring out in Southeast Asia, particularly the H5N1 strain, has been [found] to have resistance against two of the most common antiviral agents: rimantadine and amantadine," Tripp told RNAi News this week. He added that there are also indications that the virus has some level of resistance to Tamiflu, which the World Health Organization currently recommends for the treatment of suspected H5N1 infections.

"The evidence for viral resistance to antiviral agents indicates that at least one more drug is going to be necessary to combat flu — clearly to enhance the effectiveness of the current antivirals, as well as prevent viral resistance to the existing drugs," Tripp said.

Tripp said that he expects an RNAi-based flu treatment would be effective as a monotherapy, citing data showing that siRNAs directed against highly conserved regions of the nucleoprotein or acidic polymerase were able to inhibit influenza A virus replication in vivo. These data were published in the Proceedings of the National Academy of Sciences last year by Stephen Mark Tompkins from the US Food and Drug Administration.

However, an RNAi drug would also offer benefits when used in conjunction with existing therapies, in part by helping to prevent drug resistance, he noted. Tripp said that it is unclear whether flu viruses would be less likely to develop resistance to RNAi drugs than other antivirals, primarily because the technology is too new.

He pointed out that drug resistance has not been detected in his work developing RNAi treatments for RSV — which he said is also being done with Alnylam — but noted that this program "is in its infancy still in relative terms."

It is hoped, however, that by targeting multiple viral genes at once, an RNAi drug will have an edge against the development of drug-resistant strains of influenza. Tripp said that in the University of Georgia's work with Alnylam "there will be several RNAi candidates for, say, two or three genes on the virus that are most conserved amongst all the known strains."

— Doug Macron ([email protected])

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