Insulin Degrading Enzyme's Turn in the Spotlight Email This

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Well, you have to go back to the early days of this blog to find it, but I wrote here about insulin degrading enzyme. The name tells you some of what you need to know about it, for sure - it degrades insulin, so if you could stop that, insulin would probably hang around longer in the bloodstream. There's more to it - it's also been thought to be a way that insulin might be broken up inside cells as well, for one thing - but that's the elevator pitch for it.

And it has indeed been a diabetes target through the years. No one's come up with any really good inhibitors of it, although in vitro studies have been done with things like bacitracin and thioesters. Now a large multicenter academic team, led by the Mayo people from Florida, report some compounds that seem quite potent. (It's worth noting that these inhibitors are somewhat old news if you follow the patent literature).

The structures are not lovely, but there are a lot worse compounds in the protease inhibitor world. One thing that every experienced medicinal chemist will quickly notice about these is that they're hydroxamic acids. Those are compounds with a very spotty past in the business (although there is vorinostat (SAHA) out there on the market). Hydroxamates can be very potent inhibitors of metalloenzymes, and every time you target one they're always out there as a temptation, but the ugly clinical failures in that structural class tend to give people pause. Or was it just the targets (chiefly matrix metalloproteases) that the hydroxamates were aimed it? Have they been unfairly maligned? The arguments continue, and these compounds are unlikely to settle them.

Unless, of course, they go to the clinic and make a big success. I wonder if that's going to happen, though - the "go to the clinic" part, that is. This new paper is an interesting piece of work, and has a lot to say about the strange workings of IDE (which go a ways to explaining why there hasn't been much success targeting it - I was once involved briefly in the area myself). But it has nothing to say about whether these compounds have any exposure in any sort of animal, and that's the beginning of the really tricky part. These new compounds, in addition to be hydroxamic acids, are retro-inverso peptides. That's an old trick in the protease inhibitor world where you flip a natural sequence around and use the unnatural (D) amino acids to build it as well. Off the top of my head, I don't know of any retro-inverso compounds that have actually made it to market, although I'd be glad to be corrected on this.

The other complication will be IDE itself. One reason that no company has made a massive push on the target is that the enzyme is known to be multifunctional, as in "doing totally unrelated things all over the darn place", which makes one nervous about an inhibitor. Foremost among the off-target effects would be the beta-amyloid story (which is what led me to write about the enzyme back in 2003). IDE looks as if it could be one clearance mechanism for beta-amyloid (and perhaps for other easily-aggregating peptides), which has prompted people to think of actually trying to enhance its activity as an Alzheimer's therapy. One group that's tried this is, in fact, the same team that's now reporting the inhibitors (see this paper from 2009).

So I think these compounds will prove useful to figure out what IDE is doing, and that's a worthwhile goal. But I don't see them as drugs, no matter what the press release might say.