Alternate cell line not giving same results as first - (Jan/27/2016 )

I found an interesting result in protein expression when I treated my 184A1 immortalized human mammary epithelial cells with a certain compound.  These results were replicable multiple times in my 184A1 line.  My PI said I should try to replicate my results in another HMEC cell line, namely the MCF-10A.  However, I now notice that I am not getting any changes in protein expression in this cell line (I have done this twice).  This has me confused and concerned, especially since the only other cell lines I can use to check my results are 184B5 (which has the same genetic background as 184A1) and Hs578Bst (which does not grow very well).  Our cell-culture core does not carry hTERT-HME1 cells.  What are the chances my results are the artifact of the genetic background, and what would be the best way of checking this out?  I've already wasted enough time trying to grow the MCF-10A cells, then verify results.

You could check for target gene expression and some down-stream (maybe upstream as well) genes to see if the pathway is intact.