Shares in UK drug group ARK Therapeutics nosedived on Friday as investors shrank back on news that European advisors have adopted a negative opinion on its flagship brain therapy Cerepro.

The group’s stock had lost almost half its value at one point in the day after it emerged that the European Committee for Medicinal Products for Human Use has advised the European Medicines Agency to reject the gene-based therapy for operable malignant glioma at this time, on fears over treatment bias.

According to Ark, the Committee remains concerned that some patients given the drug in trials may, for some reason, have been made to wait longer before receiving re-intervention from doctors than those who were not, leaving them at a greater risk of their cancer progressing. “As time to re-intervention is the main efficacy measure in the primary endpoint, the assessors determined that they could not recommend approval based on the data presented by Ark so far,” the company explained.

The CHMP feels that ARK has failed to provide enough evidence to prove the therapy’s efficacy, but the company said it plans to file for re-assessment in the next few days as it believes it already has enough clinical data from the trial submitted to sufficiently address its concerns.

ARK is certainly standing firm in its belief in Cerepro’s potential, and seems to be taking the view that the CHMP’s ruling is more of a setback than death sentence for the therapy, particularly as all issues relating to the other aspects of the regulatory package, such as Chemistry and Manufacturing Controls, were considered approvable by the Committee.

While disappointed with the decision, ARK’s chief executive Nigel Parker said the firm is also “pleased that Ark's underlying adenovirus platform has cleared all other barriers to a full approval,” and stressed that this is “a major milestone both for Ark and the industry and gives us the confidence to progress development of our complete adenovirus portfolio”.

Also voicing his confidence in Cerepro’s future, Professor Seppo Ylä-Herttuala, Consultant Director of Molecular Medicine at Ark, claiming that it is only a matter of time until the product gains approval. Cerepro has “produced good safety and efficacy data in a difficult to treat disease where new treatments are much needed,” he said, stressing that it has “the potential to be the first gene-based medicine to be approved and, as such, is navigating uncharted waters from a regulatory perspective”.