(Bloomberg) -- Bill Ackman was used to the question: how could he stick with a loser like Valeant?

But here it was again, this time over lunch with investors and bankers in London on Feb. 28. And there was Ackman, defending a signature investment that, on paper, had cost his clients billions. Yes, Valeant's share price had cratered. But he insisted to attendees that the drug company's turnaround prospects were bright, according to people with knowledge of the meeting.

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