I'm trying to use GW2974 to run cytotoxicity assays on cancer cell lines. It is insoluble in water but soluble in DMSO. I've been trying to make solutions by dissolving in DMSO first and then adding culture media but the drug precipitates every time I try to do that and I can see crystals in the wells.

Anyone had experience with this drug before? Any advice on how to make solutions without precipitation would be appreciated.

Hi! I have not used this particular compound, but in general, the following outline protocol has worked well for me:
Dissolve a 100+x concentration of the drug in a minimal volume of DMSO (i.e. 100 or 200 or more fold concentrated than the highest conc. in your final concentration range).
Add either an equal vol, or 3xfold volume of 100% ethanol (conc will now be 50 or 25 x if you started with 100x).
Mix well.
Add media to make the conc ~10x immediately before use. Add this to your cell culture. Remember to have a vehicle control made with the same amts of DMSO:Ethanol:medium.

This staged protocol usually avoids the kind of precipitation you are seeing. If you still get to see pptn, try increasing the ethanol amts - thats much better tolerated by cells in culture, compared to DMSO.

Let us know how it goes!
-sam