There's a headline I've never written before, for sure. A new paper in PNAS describes an assay in nematodes to look for compounds that have an effect on nerve regeneration. That means that you have to damage neurons first, naturally, and doing that on something as small (and as active) as a nematode is not trivial.
The authors (a team from MIT) used microfluidic chips to direct single nematodes into a small chamber where they're held down briefly by a membrane. Then an operator picks out one of its neurons on an imagining screen, whereupon a laser beam cuts it. The nematode is then released into a culture well, where it's exposed to some small molecule to see what effect that has on the neuron's regrowth. It takes about 20 seconds to process a single C. elegans, in case you're wondering, and I can imagine that after a while you'd wish that they weren't streaming along quite so relentlessly.
The group tried about 100 bioactive molecules, targeting a range of known pathways, to see what might speed up or slow down nerve regeneration. As it happens, the highest hit rates were among the kinase inhibitors and compounds targeting cytoskeletal processes. (By contrast, nothing affecting vesicle trafficking or histone deacetylase activity showed any effect). The most significant hit was an old friend to kinase researchers, staurosporine. Interestingly, this effect was only seen on particular subtypes of neurons, suggesting that they weren't picking up some sort of broad-spectrum regeneration pathway.
The paper acknowledges that staurosporine has a number of different activities, but treats it largely as a PKC inhibitor. I'm not sure that that's a good idea, personally - I'd be suspicious of pinning any specific activity to that compound without an awful lot of follow-up, because it's a real Claymore mine when it comes to kinases. The MIT group did check to see if caspases (and apoptotic pathways in general) were involved, since those are well-known effects of staurosporine treatment, and they seem to have ruled those out. And they also followed up with some other PKC inhibitors, chelerythrine and Gö 6983, and these showed similar effects.
So they may be right about this being a PKC pathway, but that's a tough one to nail down. (And even if you do, there are plenty of PKC isoforms doing different things, but there aren't enough selective ligands known to unravel all those yet). Chelerythrine inhibits alanine aminotransferase, has had some doubts expressed about it before in PKC work, and also binds to DNA, which may be responsible for some of its activity in cells. Gö 6983 seems to be a better tool, but it's is in the same broad chemical class as staurosporine itself, so as a medicinal chemist I still find myself giving it the fishy eye.
This is very interesting work, nonetheless, and it's the sort of thing that no one's been able to do before. I'm a big fan of using the most complex systems you can to assay compounds, and living nematodes are a good spot to be in. I'd be quite interested in a broader screen of small molecules, but 20 seconds per nematode surgery is still too slow for the sort of thing a medicinal chemist like me would like to run - a diversity set of, say, ten or twenty thousand compounds, for starters. And there's always the problem we were talking about here the other day, about how easy it is to get compounds into nematodes at all. I wonder if there were some false negatives in this screen just because the critters had no exposure?