By Ben Hirschler
LONDON (Reuters) - GlaxoSmithKline and its partner Shionogi are progressing a new drug against HIV into final-stage clinical testing, ramping up competition in a class of AIDS drugs known as integrase inhibitors.
The two drugmakers said on Wednesday they would be progressing the experimental medicine, S/GSK1349572, into Phase III clinical trials later this year, following promising results from two Phase IIb studies.
The decision to advance the drug comes one day before the release of the keenly awaited mid-stage clinical trial results on the medicine at the International AIDS Conference in Vienna.
Industry analysts believe '572 could reach the market in 2013, assuming it performs well in the next phase of testing.
Integrase inhibitors like '572 are designed to block genetic information needed for the human immunodeficiency virus (HIV) to reproduce and are seen as an important new weapon in the fight against AIDS.
Merck & Co already has an established integrase inhibitor drug called Insentress, which sold $752 million last year, and Gilead has a rival product currently in Phase III testing called elvitegravir.
But industry analysts believe Glaxo's next-generation once-daily compound, which does not require a booster, may have an edge over rivals, with initial data suggesting it is highly potent and also has a superior resistance profile.
Success with '572 could signal the re-emergence of Glaxo as a significant player to rival Gilead in the HIV marketplace, according to Sanford Bernstein analyst Geoffrey Porges.
Glaxo was an early pioneer and long-time market leader in the HIV field but the British-based company has been overtaken in recent years by its smaller Californian rival, which has come to dominate the market due to its focus on convenient combination pills.
In a bid to fight back, Glaxo last year pooled its HIV assets with those of Pfizer to form a new joint company majority-owned by Glaxo, called ViiV Healthcare, with an eye on regaining market leadership.
The new compound '572 is the first of two similar integrase inhibitors being developed by ViiV.
For Gilead, it could represent a strong competitor for its new combination pills, including a four-in-one "Quad" tablet currently in Phase III that contains Gilead's own integrase inhibitor elvitegravir.
Meanwhile, Glaxo will have the option of combining '572 with various other AIDS drugs, including its established product Combivir.
Glaxo will report financial results for the second quarter at 1100 GMT. Gilead reported earnings on Tuesday.
(Editing by Karen Foster)