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Cytotoxicity of hydrophobic substances - How to dissolve highly hydrophobic substances in aqueus growth medium? (May/05/2009 )


I am dealing with following problem. Recently I have recieved set of antituberculotic drugs which I am about to test for their cytotoxic effect. Unfortunately these substances are highly hydrophobic and in higher concentrations they are about to precipitate in growth medium (added in DMSO solution, final concetration of DMSO in growth medium 0,5%). Is there any way how to prevent it? I was thinking about some inert surfactant, but I am afraid that this would interfere with IC50 determination. As far as I know in such case drugs wouldn't be present in growth medium in a "free form" but encapsulated in micelles ...

Hope you understand my czech English :)



Your english is fine...

I would try a range of solvents other than just DMSO, Dimethyl Formamide will probably work quite well, but you will probably run into the problem with solubility that you mentioned. Unfortunately, I don't think there is a solution (no pun intended) to your problem, addition of surfactants will probably damage the cells, and make it hard to determine the efficacy of the drugs. It may be possible (check with the suppliers for such reagents) to use some micellar delivery systems such as Fugene (Roche) or lipofectamine (Invitrogen) to deliver the drug directly. These micellar systems are optimised for DNA/RNA delivery, but could work if you have the right charge on the drugs.


I wouldn’t worry too much about interfering with the IC50, anything you add to solubilise the compounds will ‘interfere’ but the results will still be better than a precipitate. It’s just one of the problems we have to live with when working in vitro.

I agree with Bob that Dimethyl Formamide is a good start point; and a couple of other things to try:
1)I’ve been told (but never tried it) that a 1:1 DMSO:EtOH works better than either solvent on its own.
2)See if serum will hold the compounds in suspension (think of serum as a natural surfactant)
3)Finally, try one of the cyclodextrin family. I use randomly methylated beta-cyclodextrin but others may be just as good.