" an acquistion by another company generally wipes out the tax loss"
That's close to right if the company does not have much in the way of assets other than its NOL. If there is an ownership change, the losses after the change can generally only be used to the extent of a published tax-exempt rate (4.5% in October) multiplied by the equity value of the company. So if the market cap were, say, $100 million, the NOL could be used each year to the extent of $4.5 million. The tax savings from that would be, say, $1.8 million; so the value of the NOL is the present value of $1.8 million per year in this example. GTOP's NOL would expire after a while, mostly unused, in that example.
On the other hand, if the company had an approved drug and was worth, say, $500 million, the NOL could be used to a much greater extent.