Tonabersat is first of an exciting new selective class of drugs called neuronal gap junction blockers, which are the focus of considerable interest from clinicians and pharmaceutical researchers.

Worldwide development and marketing rights to tonabersat were acquired from GlaxoSmithKline initially for indications in the prevention and treatment of migraine and, more recently, the rights have been extended to include epilepsy, pain and other neurological conditions.

Tonabersat’s mode of action is understood to be its ability to influence the interactions between nerve cells and between nerve and glial cells. Abnormalities in these interactions are increasingly thought to underlie many neurological conditions, hence giving tonabersat considerable potential utility. Minster has initiated collaborative studies at the University of California, Los Angeles, and the Missouri State University to gain further insights into tonabersat’s mode of action.

Tonabersat completed a phase IIa clinical trial in prophylaxis (prevention) of migraine in 2007. Positive data from this study include a significant increase in subjects classed as ‘responders’ – defined as a 50% or greater reduction in migraine attacks at the end of the three-months of treatment – on tonabersat compared with those on placebo. The figures were 62% for tonabersat compared with 45% for placebo (p< 0.05).

At the same time there was a clinically and statistically significant decrease in use of ‘rescue medication’ – Imigran, painkillers etc – in subjects taking tonabersat. In the third month of the study the number of days when such medication was needed was reduced by 60% in the tonabersat group compared with 34% for placebo (p<0.02).

Tonabersat was consistently superior to placebo across a range of further outcome measures though these differences did not achieve statistical significance in this trial. The data suggest that the benefits of tonabersat relative to placebo continued to increase in the final month of the study.  There were few significant adverse events and tonabersat was well tolerated. Based on experience gained in the previous study the Company is currently undertaking a phase IIb study in 500 patients in the US and Canada. This study includes evaluation of higher daily doses of tonabersat and longer periods of dosing.

A further phase II trial in migraine with aura is underway under the auspices of Professor Jes Olesen at the Danish Headache Centre, Copenhagen.

The market for the prevention of migraine has been radically changed following the approval in mid 2004 of the Johnson & Johnson product Topamax, which had sales that exceeded $1bn in 2007 for migraine prophylaxis. The level of sales of the product gives an indication of the demand for preventive treatment of migraine.