The relentless drama in the boardroom at US biotech ImClone Systems entered a new phase yesterday as two directors, including chairman David Kies, resigned from the board.

The development brings billionaire Carl Icahn a step closer to seizing control of the company. Icahn had asked shareholders in the company to oust Kies, interim chief executive Joe Fischer and four other board members, and elect one of his associates to boot.

With Kies and another director, William Crouse, now out of the picture, Icahn has moved closer to gaining a majority position on the 10-member board. He has said he wants to bring in an experienced biotech CEO to accelerate the development and sales of ImClone’s only marketed product, cancer drug Erbitux (cetuximab) – although analysts have suggested that he wants ImClone to put itself up for sale once again.

ImClone said it was looking for a buyer for the business earlier this year, but abandoned the plan in August after failing to receive a suitable offer. Since then, the need for strong management at the firm has become acute, as Erbitux is now facing competition in the USA from Amgen’s Vectibix (panitumumab), which was cleared by the US Food and Drug Administration late last month.

Meanwhile, one company rumoured to be looking at ImClone, France’s Sanofi-Aventis, definitively ruled itself out of any bid. ImClone had said last week that it had received a $36-per-share offer but claimed Icahn had stymied the deal. There has been widespread speculation that Sanofi was the suitor.

Shares in ImClone rose 4% in premarket trading on the Nasdaq after the resignations were announced.