GSK's chronic hepatitis B drug helps one in five achieve functional cure in key studies

* GSK's drug helps 19% of patients achieve functional cure ​across ⁠two studies

* Drug is central to GSK's ​long-term ambition of over 40 billion pounds in revenues

* Regulatory decisions in US, Japan expected this year

LONDON, ‌May 28 (Reuters) - GSK said its experimental chronic hepatitis B drug helped nearly one in five patients achieve ⁠a functional cure in late-stage studies, raising hopes for ⁠a finite treatment course as ​an alternative to lifelong antiviral pills.

The British drugmaker presented detailed data from two studies of bepirovirsen on Thursday at a medical conference.

The drug is central to GSK's plans to achieve ​more than £40 billion ($54 ‌billion) in annual revenue by 2031. The company expects peak annual sales of more than £2 billion for the drug.

GSK said six months of treatment with bepirovirsen helped 19% of patients who started with surface antigen levels of 3,000 international units per millilitre (IU/ml) ​or below achieve a functional cure. That means patients were off treatment for at least six ‌months and had both hepatitis B virus DNA and surface antigen below detectable levels.

The response rate rose to 26% among ‌patients with surface antigen levels of 1,000 IU/ml or below.

Analysts had estimated a 15% to 20% response rate would be significant and could support broad adoption.

More than 250 million ​people globally live with chronic hepatitis B, and current standard-of-care treatments help only 1% to 4% of patients ‌clear the virus for a sustained period.

Nucleotide analogues, a widely used class of therapies, are often taken for life and suppress the virus but rarely eliminate it.

"To have six months ⁠of injections ⁠to achieve functional cure of this magnitude ... is, to me, ‌a great advance in the management of my patients," said Dr. Seng Gee Lim, lead investigator of the studies.

He ​added the drug ​was generally well tolerated, with most side effects limited to ‌mild injection-site reactions.

GSK has sought regulatory approval for bepirovirsen in the U.S., Japan, China and Europe. A decision from the U.S. regulator is expected by October 26.

Glaxosmithkline