Storing conditioned media - (May/07/2009 )
I'm working on conditioning media from prostate cancer cell lines (DU145 and PC3). After 24 hours of incubation, we want to remove the media and store it (frozen?) since there are many tests we want do (invasion assays, migration assays, VEGF/SDF-1/HIF-1 levels to name a few). So far I have conditioned DU145 cells, have collected and aliquoted the samples (4 x 1ml) and stored them at -20C.
Today when I looked at the samples, many were not frozen, some were frozen, and a few were frozen but there was a clear separation of water and media (large white portion with a small pink layer). In anyone's experience, would it be best to flash freeze the samples before storing at -20C? Should they be stored at -80C?
Many of the secreted compounds are quite unstable, you are best to store at -80, flash freezing would be good too, but shouldn't be too much of a problem.
We used to have a similar problem (things not freezing properly) in one of our -20C freezers. Turned out it was a frost-free freezer. As soon as we moved everything to a non-frost free, it stopped happening.
We might have solved the problem - since we saw the same thing happening in another freezer that wasn't frost-free. The samples were being stored in a box, and with the lid on, the cold air wasn't able to circulate, which probably resulted in the uneven freezing. So from now on, we'll freeze without a top on the boxes first