(Adds detail on drug's other uses, Sanofi investor day)

Nov 11 (Reuters) - An experimental biotech drug for moderate to severe asthma from France's Sanofi and its U.S. partner Regeneron has produced good results in clinical tests, suggesting that its dual-action mechanism may be highly effective.

The encouraging data allows the companies to begin final-stage Phase III asthma trials on the medicine, which is also being developed for atopic dermatitis and chronic sinusitis with nasal polyps.

Dupilumab is one of the new medicines Sanofi is expected discuss at an investor day on Nov. 20 - an event that will be overshadowed by uncertainties about the company's future after the summary dismissal of its chief executive.

Dupilumab is a latecomer among a new class of antibody drugs for people whose asthma does not respond adequately to inhalers, but unlike rivals such as GlaxoSmithKline's mepolizumab it hits two targets at once.

In a mid-stage Phase IIb clinical study, dupilumab cut serious asthma attacks, known as exacerbations, by 64 to 75 percent. The Sanofi drug works by blocking two key inflammatory chemicals that drive asthma, called IL-4 and IL-13.

Analysts believe that Sanofi's product could be launched in 2019, putting it well behind GSK's drug, which is leading the pack and has already filed for regulatory approval.

Nevertheless, Berenberg Bank analyst Alistair Campbell said that dupilumab could still be a commercial success, with potential annual sales of $1.5 billion by 2025, if the strong data in current tests were replicated in final-stage Phase III studies.

Other companies working on similar biotech asthma drugs include AstraZeneca, Roche and Teva.

(Reporting by Ben Hirschler; Editing by David Goodman)