After studies in primates showed high levels of toxicity from GDNF, Amgen halted further human trials.
Many people with Parkinson's were crushed by Amgen's decision to stop the GDNF trial.
The first group received six injections of the special virus called lenti-GDNF to boost nutrients in their brain.
But at least two researchers still working on GDNF say Amgen's problem was the way the drug was delivered.
In 2004 biotech firm Amgen began trials of a Parkinson's drug called glial cell line-derived neurotrophic factor, or GDNF.
Amgen may not have examined why GDNF failed, but Pfizer has been learning from its failed clinical trials for decades.
Grove has funded several researchers trying to inject GDNF into the brain.
They developed the condition but this was reversed once they received lenti-GDNF.
In 2004 biotech firm Amgen (nasdaq: AMGN - news - people ) began trials of a Parkinson's drug called glial cell line-derived neurotrophic factor, or GDNF.
Steven Gill, the British neurosurgeon who ran that first GDNF infusion trial, believes the cause of the toxicity was the improper infusion of the drug into the monkeys' brains.
Amgen may not have examined why GDNF failed, but Pfizer (nyse: PFE - news - people ) has been learning from its failed clinical trials for decades.
In late November Grove began trying to persuade a large medical company with which he has no affiliation to license the GDNF program from Amgen, in order to revive it.
In an earlier trial five patients in the U.K. had undergone a surgery in which a tiny catheter implanted in their brains continuously delivered GDNF from a pump inserted in the stomach (the pump is refilled with a needle through the skin).
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