A week before the deadline it has set for potential buyers to come from, Human Genome Sciences says regulators in the US are again reviewing raxibacumab, its previously-rejected anthrax treatment.

The US Food and Drug Administration has acknowledged receipt of the resubmission of the Biologics License Application for raxibacumab and given it a Prescription Drug User Fee Act (PDUFA) action date of December 15. The agency has deemed the refiling a complete response to the letter it sewn out in November 2009 which requested further analyses of existing data as well as additional information.

HGS says the BLA resubmission contains additional evaluation of histopathology of survivors and non-survivors in animal studies, evaluation of potential added benefit of using raxibacumab with antibiotics versus antibiotics alone "and additional validation to confirm previous data".

Raxibacumab is a human monoclonal antibody "that represents a novel way to address the anthrax threat", the company says, noting that while antibiotics can kill the anthrax bacteria, "they are not effective against the deadly toxins that the bacteria produce".

The drug is being developed under a contract signed in 2006 with the US government and in 2009, HGS delivered the first 20,000 doses of raxibacumab to the national stockpile and the government exercised its option to purchase 45,000 additional doses for emergency use in treating inhalation anthrax.

Meantime, reports have been circulating that Celgene may be planning a bid for HGS as the latter's deadline for bids looms (July 16). However, most observers believe that the only offer will be GlaxoSmithKline's $2.60 billion which has been repeatedly rejected by the HGS board.