* Drug fights most common muscle wasting disease in over 50s
* Currently no approved medicines to treat rare condition
* BYM338 blocks pathway that regulates muscle growth
* Concern it may be used for doping by athletes
By Caroline Copley
BASEL, Dec 6 (Reuters) - Fifteen years ago Ian Parkhill was diagnosed with a rare muscle-wasting disease that gradually robbed him of the strength in his thighs.
Now, he struggles to walk. The waning muscle in his arms will soon hinder his ability to pull himself out of a chair, he fears, and simple tasks such as holding a pen are increasingly difficult as the dexterity in his fingers declines.
"The only sort of grip I have is between the thumb and the palm," said 81-year-old Parkhill, a former electrical engineer, who lives in Droitwich, England. "If I put a pencil on a flat surface, I can't pick it up. I've got to use both hands."
Parkhill's rare condition has, to date, gained little attention from drugmakers - but that is starting to change.
Big Pharma is focusing a lot more these days on drugs for rare diseases like Parkhill's - and the sky-high prices they can command - and some are also eying the potential of addressing related muscle problems behind a range of more common diseases.
Sporadic Inclusion Body Myositis (sIBM) is the most common muscle-wasting disease in the over 50s, yet its exact cause remains unknown and there are no approved drugs to treat it.
Although sIBM affects no more than 71 people per million, Swiss drugmaker Novartis is developing a treatment that stimulates muscle growth in sufferers.
It is betting that the drug, known as bimagrumab or BYM338 and developed with German biotech company MorphoSys, might help combat muscle loss associated with conditions like cancer and chronic lung disease that affect millions of people.
It could even be beneficial for patients recovering from injury or an operation, and the drugmaker is currently conducting a Phase II trial for hip fracture recovery.
Novartis is not the only pharmaceutical firm working on muscle-building treatments. But it is heading the field in sIBM with BYM338, which was granted breakthrough therapy status from U.S. health regulators in August and is entering late-stage trials. It expects to file for approval in 2016.
Eli Lily is coming up close behind with two mid-stage studies for its drug LY2495655 as a treatment for muscle weakness and muscular atrophy.
Meanwhile, Regeneron and Sanofi have a drug in early stage development as a treatment for sarcopenia, the muscle loss associated with aging.
Still, developing medicines for muscle disorders is not without risk. In August GTx's experimental drug to treat muscle-wasting in cancer patients failed in key trials.
DOPING DRUG FOR ATHLETES?
Novartis recently completed a proof of concept study for BYM338, which found that eight weeks after a single infusion of the medicine, patients' muscle volume increased by 5 percent - the kind of muscle growth normally seen after two months of intensive exercise.
While those statistics offer hope for patients suffering from sIBM, the drug - which is named after Bhima, a character in the Hindu epic Mahabharata renowned for his strength - has rung alarm bells at the World Anti Doping Agency (WADA).
WADA's list of banned substances includes all agents that modify the function of myostatin - a protein regulating muscle growth.
Novartis global head of development Tim Wright played down the risk that unscrupulous athletes might use the drug as a quick way to bulk up.
"We've already developed a very, very sensitive assay for this and we've been in communication with the World Health Organisation and WADA, so we don't anticipate any significant issue with this," he told Reuters in an interview at Novartis' Basel headquarters.
Because the drug is a biologic medicine with a long half life, it should be possible to detect if it has been used in recent months, he said.
Phil Watson, a lecturer in sports nutrition at the University of Loughborough, said Novartis' drug could be attractive for athletes that may have lost muscle mass due to injury or a long period of inactivity. But he noted that bigger muscles do not always improve athletic performance.
"It would seem this type of treatment would be most attractive to strength and power athletes, but there does become a trade off at some point," he said. "There is a point at which carrying too much muscle can become detrimental."
The drug, which is administered intravenously, works by targeting a pathway known as Activin RIIb that regulates muscle growth. By blocking the pathway, the drug allows the muscle cell to respond to other stimuli such as exercise, and grow.
Novartis believes it is too early to speculate on the potential market size for BYM338, but analysts at Jefferies estimate peak sales for the drug of $300 million in sIBM.
Pedro Machado, a senior clinical research associate at the MRC Centre for Neuromuscular Diseases at University College London (UCL) described Novartis' approach as promising.
But he said it needed to be determined whether increasing muscle volumes will actually translate into improved muscle strength and performance, as well as whether there are any long-term side effects.