Icagen, which recently announced a drug development partnership that could be worth up to $1 billion with Pfizer, has closed on the sale of $5 million in stock to Pfizer.

Icagen (Nasdaq: ICGN) has the option to sell Pfizer another $10 million in stock as part of the deal. Pfizer paid $1.86 per share.

Icagen shares closed down 7 cents at $1.92 on Monday.