Xenome starts Phase I trial of pain drug

Unlisted Brisbane biotech Xenome has initiated a Phase I clinical trial of its lead candidate for treating neuropathic pain, Xen2174.

Adelaide clinical trials specialist CMAX, a division of the Institute of Drug Technology Australia (ASX:IDT), will evaluate the safety and tolerability of Xen2174 by administering it to 20 healthy male volunteers.

Previous trials of the drug in an animal model of pain associated with nerve damage have indicated that Xen2174, a peptide derived from the venom of an Australian cone shell, is a more potent and longer-acting suppressor of chronic neuropathic pain than morphine.

The Adelaide trial will be a randomised, placebo-controlled, double-blind, dose-ranging study.

Xenome's head of drug development, Dr Michael Thurn, said the trial would provide more data on the pharmacokinetics -- the activity and persistence of the drug in the body -- and its inhibitory effect on the pain-perception pathways in the brain and spinal cord.

Like most conotoxins, Xen2174 must be administered intrathecally -- by direct injection into the cerebrospinal fluid bathing the spinal cord.

Peptide drugs cannot be delivered orally, because they do not survive transit through the digestive tract, and are rapidly degraded by peptidase enzymes when injected intravenously.

The only commercially available conotoxin, Élan Pharmaceuticals' Ziconotide, is administered intrathecally because it causes a sharp drop in blood pressure when injected into the bloodstream.

But Thurn said the company considered intrathecal administration an advantage, because it delivers the drug directly to its pharmacological target, reducing the risk of side-effects.

Xen2174 inhibits transport of the norepinephrine by binding to the norepinephrine transporter (NET), a protein molecule that normally removes the neurotransmitter from nerve synapses. The accumulation of norepinephrine in synapses prolongs its ability to prevent pain signals from injured nerves reaching the brain's pain-perception centres.

Animal studies indicate that the pain-killing activity of Xen2174 lasts for between 24-48 hours, but Thurn said it would be desirable to extend the drug's activity to avoid the inconvenience of repeated intrathecal injections.

If clinical trials confirm the peptide's promise, Thurn said, the company would investigate the possibility of developing a slow-release spinal cord implant that would deliver the drug for up to three months at a time.

Thurn said one of the interesting features of the NET molecule was that it is also the target for tricyclic anti-depressants, commonly used to treat chronic depression.

Patients treated with other NET-inhibitors for chronic pain have reported relief from their depressive symptoms, so Xen2174 may also have potential as a novel treatment for depression.