Celltrion Inc,. which scored a big win last year with the world's first officially approved biosimilar monoclonal antibody – Remsima, a biosimilar version of autoimmune blockbuster Remicade (infliximab, Johnson & Johnson) – has halted a late-stage trial testing a Rituxan/MabThera (rituximab) biosimilar.

The Korean company has not disclosed the reason for the trial's termination, and neither Celltrion nor partner Hospira Inc., of Lake Forest, Ill., could be reached for comment.

The EU Clinical Trials Register merely described the study, which was comparing Celltrion's CT-P10 to MabThera in patients with advanced follicular lymphoma at European trial sites, as "prematurely ended."

Shares of Celltrion (KOSDAQ:06827), which had gained in recent days on reports that the firm's founder, Seo Jung-jin, said he planned to sell his controlling interest in Celltrion, sank Thursday to close at 36,850 won, down 14.6 percent.

Celltrion has said that Phase III studies of CT-P10 are set to begin later this year, as previously planned, though the halted study left analysts and investors wondering.

"It is unclear whether the potential issues leading to the European trial termination could impact timelines or the molecule's future development," RBC Capital Markets analyst Shibani Malhotra wrote in a research report.

The news also adds to the growing fear that biosimilar drug development will prove trickier – and, perhaps costlier – than previously envisioned. In the last year, for instance, some much-lauded big pharma biosimilar deals came to abrupt ends, such as Pfizer Inc.'s deal with Indian generics maker Biocon Ltd. for biosimilar insulin products, and Merck & Co. Inc.'s agreement with Korea's Hanwha Chemical for a biosimilar version of Enbrel (etanercept, Amgen Inc.). (See BioWorld Today, Feb. 21, 2012.)

"If the [recent Celltrion CT-P10] trial was terminated due to complications, it would validate our view that developing biosimilars is very difficult and complex, and may not lead to scientific, regulatory or commercial success," Malhotra noted.

CT-P10 is one of eight programs included in the 2009 collaboration between Celltrion and Hospira.

That alliance led to the approval of Remsima in Korea last year, and a marketing authorization application is under review for the Remicade biosimilar in Europe, where it is expected to be launched as Infectra, according to GlobalData. (See BioWorld Today, Aug. 9, 2012.)

Applications have yet to be filed in the U.S., where biosimilar development is moving more slowly. Only a few weeks ago the FDA released draft guidance to help biosimilar sponsors request and be better prepared for formal meetings, and the agency said it will seek comments until May 31.

Celltrion is hardly the only firm working on a biosimilar version of Rituxan, a monoclonal antibody that binds to CD20 for treating hematological malignancies such as chronic lymphocytic leukemia (CLL). The product pulled in about $7 billion in sales in 2012, and developer Roche AG, of Basel, Switzerland, has been working to offset biosimilar threats by working on a subcutaneous formulation of Rituxan and creating a new compound, GA101, a glycol-engineered CD20 antibody that demonstrated promising early data in a Phase III CLL study. (See BioWorld Today, Feb. 1, 2013.)

According to the newest BioWorld Data report, The Biosimilars Game: A Scorecard for Opportunities, Threats and Critical Strategies, at least 27 companies had been identified with rituximab biosimilars in their pipelines. Among the other players include Novartis AG, Boehringer Ingelheim, Samsung Biologics and Teva Pharmaceuticals Industries Ltd.

Editor's note: For a copy of BioWorld's new biosimilars report, please contact the BioWorld Data account managers for exclusive introductory pricing at (800) 477-6307.