I want to down-regulate gene of interest in SCC cells but this cells are hard to transfect. I have tried using Xtreme gene as well but got 10-15% transfection.
I do not have any experience with this particular cell line but have you optimized DNA:transfection reagent ratio with Xtreme gene? Try 1:2, 1:3, 1:4 or 1:5 ratio. Otherwise, I have transfected difficult to transfect cells with turbofect and it seemed to work fine. Try the same conditions with Turbofect when optimizing.
We normally use SAINT-18 for hard to transfect cell ines. This compound was used by Cambrex/Lonza in there no longer commercial available Primefect Reagents.