Recently, I have performed MTT assay on my samples which were hexane-soluble extracts from a plant source on MCF-7 and MDA-MB-231 cell lines. Data from the assay showed horrible results and I found out what caused it. It was because my sample was not completely dissolved in 0.5% DMSO which is the commonly used solvent system in MTT assay. After communicating with my thesis adviser, she told me that I should try to dissolve in 5 mg/mL of PEG (polyethylene glycol, specifically PEG 8000 because that is what we only have in our lab). However, after several researches on solvent systems used in MTT assays, I have found out that 0.1% THF (tetrahydrofuran which is more non-polar as compared to DMSO) was also used as a solvent in several MTT assays. Now my question would be which among the two would be more recommended to be used for my assay given that I have limited amount of sample left and that I also have limited time left for my experimentation because I will be presenting my study in a month from now. If there are even better solvent system to be used rather than these two, what is this solvent and why is it much better? Any suggestions that is backed up by ones' experience or scientific studies would be of much help to me. Thank you and I love this scientific community.
Dear Zane Edward Haddrill, if I understand your question well, you are diluting a hexane-soluble extract with a solvent that contains 0.5% v/v DMSO and 99.5% v/v water (am I right?) and then you try to measure the toxic effects on two cell lines. As you yourself comment, it is common that when testing the cytotoxic effects of drugs or extracts DMSO is used as a solvent and that the final concentration of DMSO in the culture medium is 0.5% v/v. To avoid the problems of solubility of the components of your extract, I recommend preparing 200X solutions of your extract in pure DMSO and then adding 1 uL of this solution for every 199 uL of culture medium, in this way the DMSO will have a final concentration maximum of 0.5% v/v and the extract a concentration X.
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