Shares in Vertex slipped yesterday as investors mulled over the mixed fortunes of two of its early-stage hepatitis C (HCV) candidates, with one showing promise while the other reached the end of the line.

The group's stock had slipped just over 4% in late afternoon trading, after the firm said it is pulling the plug on clinical development of ALS-2158 in HCV as it failed to show significant antiviral activity in early trials.

On the up side, experimental HCV drug ALS-2200 - which, like its less fortunate peer ALS-2158, is also a nucleotide polymerase inhibitor - will be moved into two Phase II clinical studies.

The decision comes on the back of new data from an additional cohort of an ongoing study evaluating ALS-2200 alongside ribavirin. 

This showed a significant reduction from baseline in HCV RNA after seven days of dosing patients with 200mg of the combination once daily. 

In addition, the therapy was found to be well tolerated, with no patients dropping out of the trial due to adverse events and no serious adverse events observed.

"Our goal is to develop all-oral regimens that are well-tolerated and provide a high rate of viral cure in a broad population of people with chronic hepatitis C," said Robert Kauffman, Senior Vice President and Chief Medical Officer at Vertex. 

Good progress

"We're making good progress and expect to begin all-oral Phase 2 combination studies by the end of this year," he said.

Under the plans, which remain subject to regulatory approval, one of the trials will examine ALS-2200 in combination with ribavirin, while the other will assess it in combo with Vertex' own HCV medicine Incivek (telaprevir).

Vertex is in a race with several other companies - such as Gilead and Abbott - to get approval for an HCV therapy that sidesteps the need for injectable interferon, which is associated with unpleasant side-effects that can interfere with adherence and therefore affect treatment outcomes.