WASHINGTON – Most biotech start-ups, even the most successful, will at some point hit a cash flow wall, where they need a large infusion of funding to get a product to the regulatory finish line. Recent economic trends have largely taken the initial public offering (IPO) option off the table, so for most companies the choice comes down to partnering or acquisition. At BIO 2011, Calistoga Pharmaceuticals Inc. CEO Carol Gallagher and Athersys Inc. CEO Gil Van Bokkelen discussed how they arrived at the decision to partner or sell.