Arena Pharmaceuticals and partner Eisai are hopeful regulators will look kindly on its obesity drug lorcaserin after responding to a rejection issued by the US Food and Drug Administration in October 2010.

Arena has submitted its reply to the complete response letter from the FDA which cited a number of reasons for its decision, notably concerns about tumours found in animal studies. The response includes data and analyses that were not incorporated in the original New Drug Application, including the results of the Phase III BLOOM-DM trial, which evaluated lorcaserin for weight loss in patients with type 2 diabetes.

The new information also includes data and analyses from activities intended to address tumors observed in a two-year lorcaserin rat carcinogenicity study, "cell culture experiments intended to further refine serotonin subtype 2 receptor activity and rat studies designed to further assess abuse potential". However, it was stressed that the FDA "may analyse or weigh the data differently than Arena and Eisai".

Arena chief executive Jack Lief said "we have worked diligently with Eisai to prepare this submission that we believe will address the issues raised in the CRL". He added that the results of the recently-completed rat mechanistic studies "provide additional data supporting lorcaserin's benefit-risk profile".

Arena is in a race with two other firms to get their weight loss pills approved. Vivus and Orexigen Therapeutics were also turned down by the FDA, and the former resubmitted Qnexa (phentermine/topiramate) in October. In September, Orexigen and partner Takeda said they had identified "a clear and feasible path to approval" with the FDA for Contrave (naltrexone/bupropion), which will involve a cardiovascular outcomes trial.