(Corrects April 28 story to remove reference to debt in paragraph 3. The error was repeated in previous versions of the story.) By Anirban Sen (Reuters) -Investment firm All Blue Capital has approached Zymeworks Inc, a developer of antibody therapies for cancer, with a $773 million acquisition offer. In a regulatory filing late on Thursday, All Blue said it had made a non-binding offer for $10.50 per share in cash, which represents a 116% premium to Wednesday’s closing price of $4.86. There is no certainty that Zymeworks will negotiate a deal, people familiar with the matter said. The company …