Human Genome Sciences has turned down an unsolicited proposal from GlaxoSmithKline, its partner for the lupus drug Benlysta to acquire the firm for $13.00 per share in cash.

The HGS board says it has carefully reviewed and considered the GSK offer, which values the firm at around $2.60 billion. However, after consultation with financial and legal advisors, the firm's management believes the bid "does not reflect the value inherent in HGS".

The directors have now retained the services of Goldman Sachs and Credit Suisse to explore "strategic alternatives in the best interests of shareholders, including, but not limited to, a potential sale of the company". GSK, which has yet to comment on the bid,  "has been invited to participate in this process".

HGS noted that it has requested additional information regarding investigational products in GSK’s clinical pipeline to which it has "substantial financial rights". These include the late-stage cardiovascular drug darapladib and albiglutide, currently in Phase III for the treatment of type 2 diabetes.