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August 11, 2009
Dealing With Hedgehog Screening Results
I was looking over a paper in PNAS, where a group at Stanford describes finding several small molecules that inhibit Hedgehog signaling. That's a very interesting (and ferociously complex) area, and the more tools that are available to study it, the better.
But let me throw something out to those who have read (or will read) the paper. (Here's the PDF, which is open access). The researchers seem to have done a screen against about 125,000 compounds, and come up with four single-digit micromolar hits. Characterizing these against a list of downstream assays showed that each of these acts in a somewhat different manner on the Hedgehog pathway.
And that's fine - the original screen would have picked up a variety of mechanisms, and there certainly are a variety out there to be picked up. I can believe that a list of compounds would differentiate on closer inspection. What I keep looking for, though, is (first) a mention that these compounds were run through some sort of general screening panel for other enzyme and/or receptor activities. They did look for three different kinase activities that had been shown to interfere (and didn't see them), but I'd feel much better about using some new structures as probes if I'd run them through a big panel of secondary assays first.
Second, I've been looking for some indication that there might have been some structure-activity relationships observed. I assume that each of these compounds might well have been part of a series - so how did the related structures fare? Having a one-off compound doesn't negate the data, naturally, although it certainly does make it harder to build anything from the hit you've found. But SAR is another factor that I'd immediately look for after a screen, and it seems strange to me that I can't find any mention of it.
Have I missed these things, or are they just not there? If they aren't, is that a big deal, or not? Thoughts?
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