LONDON (Reuters) - An experimental once-daily AIDS drug from GlaxoSmithKline and its Japanese partner Shionogi proved better than Gilead's market-leading Atripla in a late-stage clinical trial, increasing hopes for the product.
Dolutegravir, which could reach the market late next year, belongs to a novel class of drugs known as integrase inhibitors that fight HIV/AIDS by blocking the virus causing the disease from entering cells.
It should help British group GSK rejuvenate its HIV/AIDS business - an area it used to dominate but where it has fallen behind rivals, notably U.S.-based Gilead.
The stakes are high with Atripla, the leading HIV/AIDS treatment in the United States, raking in sales of $3.2 billion last year.
Dolutegravir's impressive result may also make a spin-off of GSK's HIV/AIDS business ViiV Healthcare more likely, analysts said. ViiV is currently run as a joint venture with Pfizer, with Britain's biggest drugmaker holding an 85 percent stake.
Dolutegravir's success against Atripla, taken as a single tablet, may impress clinicians as Gilead's own new Quad pill, which also contains an integrase inhibitor, only matched Atripla.
In the latest Phase III study, 88 percent of patients taking a regimen of dolutegravir plus two older drugs for 48 weeks had their virus suppressed against 81 percent for those on Atripla, GSK and Shionogi said on Wednesday.
The superior efficacy was driven by the fact that more patients taking Atripla dropped out of treatment, with 10 percent of those on the Gilead drug stopping due to side effects against 2 percent in the dolutegravir arm.
The result was the second positive final-stage clinical read-out for dolutegravir, following encouraging results against U.S. company Merck & Co's rival Isentress in April.
Two further Phase III trials are expected to report results by the end of the year and dolutegravir could potentially be filed for approval with regulators before the end of 2012, a company spokesman said.
That means the medicine may reach the market before the end of 2013, ramping up competition in the HIV/AIDS market.
GSK shares were up 0.7 percent by 1150 GMT, while Gilead was down 2 percent in pre-market Nasdaq trading.
Dolutegravir is viewed by analysts as a potential multibillion-dollar-a-year seller, as its once-daily dosing is likely to be attractive to patients. However, the financial gain to GSK will be diluted by its deals with Shionogi and Pfizer.
Income from the medicine will be shared 50:50 between ViiV and Shionogi, so GSK will receive only just over 40 percent after taking account of Pfizer's minority stake in ViiV.
The creation of ViiV in 2009 marked an unusual drug industry collaboration because of the way in which it pooled GSK and Pfizer's HIV/AIDS operations into a new business. There have been doubts, however, as to whether the joint venture would have a viable future, given uncertainty about its new drug pipeline.
The impressive results with dolutegravir will lay some of those worries to rest.
Mark Schoenebaum, an analyst at ISI Group, said the latest data was "a bit better than expected", although it might not be enough to drive big shifts away from Gilead's drugs.
Citi analysts also noted that concerns remained about the cardiovascular safety of Epzicom, one of the older drugs used with dolutegravir.
Still, the findings are clearly an overall plus for GSK's HIV unit and could help make it a viable standalone business.
"Today's news may prompt further market discussion of a possible spin-off of ViiV as dolutegravir is much the most important pipeline product for this venture," Deutsche Bank analysts said in a note.
GSK Chief Executive Andrew Witty said last year he had no immediate plans to spin off ViiV but was "open-minded" about the unit's long-term future.
Merck's Isentress, which had sales of $1.4 billion last year, is currently the only integrase inhibitor approved by regulators, although Gilead's Quad pill containing its integrase inhibitor elvitegravir was recommended by a U.S. expert panel in May.
Editing by Jon Loades-Carter