FORT LAUDERDALE, Fla--Interest in neurotoxins derived from marine
cone snails has led to development of a calcium-channel blocking
agent that could potentially be used as an alternative to opioid
analgesics for patients with cancer pain. Early clinical studies
with the agent (SNX-111, being developed by Neurex Corporation,
Menlo Park, Calif) have found it to be more potent than morphine
and free of opioid side effects, Richard W. Tsien, DPhil, said
at a conference on gene technology organized by the University
Biochemistry & Molecular Biology Foundation, Inc. and Bio/Technology
Dr. Tsien, professor of molecular and cellular physiology, Stanford
University, spoke at a session on calcium channel research sponsored
by Boehringer Mannheim.
Among the more than 1 million patients who suffer from cancer
pain, a significant proportion, about 100,000 in the US alone,
experience severe intractable symptoms of neuropathic origin,
Paul Goddard, PhD, chairman and CEO of Neurex, said in an interview.
While no selective treatments for neuropathic pain are currently
available, Dr. Goddard said, SNX-111 appears to block both neuropathic
and nociceptive pain (see box below) and to have analgesic effects
100 to 1,000 times more potent than those of morphine.
In initial results from phase I/II studies among terminally ill
cancer patients with severe, morphine-resistant pain, 8 of 9 evaluable
patients responded to therapy with SNX-111 infused intrathecally
(1 to 100 ng/kg/hr). Of these patients, 5 received up to 10 months
of therapy and experienced continued relief.
The drug appears to be safe and well-tolerated, Dr. Goddard said.
The majority of patients experienced partial or complete pain
relief without common opioid side effects. "Most terminally
ill patients want both pain relief and lucidity," Dr. Goddard
said. Importantly, he added, tolerance to SNX-111 has not developed
in preclinical studies.
Continuing expanded trials with 30 patients are showing similar
benefits to those seen in the first patients, he said.