* Indian firm files "pre-grant opposition" to Sovaldi patent
* Natco filing argues Sovaldi not inventive - source
* Sovaldi's high cost under fire in U.S., developing world
(Adds details on Sovaldi and patent opposition grounds)
MUMBAI, April 10 (Reuters) - India's Natco Pharma Ltd has formally asked the Indian patent office to deny U.S. drugmaker Gilead Sciences Inc's new hepatitis C drug Sovaldi a patent in India, a source with direct knowledge of the matter said.
If successful, the move could clear the way for the Indian company to launch a cheap generic version of the drug.
Gilead, whose medicine has been hailed by doctors as a breakthrough in treating the liver-destroying disease, has come under fire over its product's $1,000 per pill price tag in the United States.
India's patent laws allow a third party to dispute the validity of a pending patent application. Natco has filed a so-called "pre-grant opposition" with the Controller General of Patents, Designs & Trademarks, said the source, who declined to be named because the information was not public yet.
It was not clear when Natco filed the opposition and Reuters could not immediately obtain a copy of the filing.
Natco Chief Executive Rajeev Nannapaneni declined to comment. Officials at Gilead and at the patent department in Mumbai were not immediately available for comment.
Natco has opposed the patent on the same grounds as New York-based Initiative for Medicines, Access & Knowledge (I-MAK), arguing that Sovaldi is not "inventive" enough, the source told Reuters.
I-MAK, a group of lawyers and scientists, filed an opposition in November 2013 to the grant of a patent in India on Sovaldi, chemically called sofosbuvir, saying the drug uses "old science".
Natco's opposition comes amid a growing clamour by healthcare campaigners and doctors to ensure that Sovaldi and other new hepatitis C pills are made affordable in developing countries.
In the United States, some healthcare providers have described the $84,000 price tag for a 12-week course of treatment as "outrageous".
"OLD SCIENCE" CLAIM
The medical charity Médecins Sans FrontiEeres (MSF) supported I-MAK's opposition and believes a 12-week course of treatment and diagnosis should cost no more than $500, saying a high cost would put the drug out of reach to most of the 90 percent of hepatitis C patients living in low-and middle-income countries.
The World Health Organisation estimates as many as 12 million people in India, a country of more than 1.2 billion people, have hepatitis C. Other experts put the figure even higher.
Egypt, where Gilead has agreed a voluntary deal to cut its drug price by 99 percent, has the world's highest prevalence of the liver-destroying virus.
Foster City, California-based Gilead is already in talks to license Sovaldi to three or four Indian generic manufacturers, and launch the drug in India at a price of $2,000 for 24 weeks of treatment, a company executive told Reuters on Tuesday.
Indian-made generics of the drug would be available in most of sub-Saharan Africa, selected Asian countries including India, Pakistan and Myanmar, and some smaller developing nations.
Sovaldi is the first among a bunch of new hepatitis C drugs that have been shown to raise cure rates and cut treatment duration without the side-effects of current injection-based treatment regimes.
(Additional reporting by Ben Hirschler in LONDON; Editing by Tony Munroe and Elaine Hardcastle)