I have been exposing B lymphoma cells to pharmaceuticals at different concentrations for a toxicological analysis. I used a couple of assays to get an overall picture of potential effects that the pharmaceuticals could cause. My results are however (at least to what I understand) a bit contradictory. 

At 66 h of exposure I see a 50% inhibition of proliferation in one of my assays (assessment of proliferation via radiolabeled 3H-thymidine). In this assay the cells are stimulated with the mitogen LPS. 

At 24 h of exposure following a wash and further 72 h of incubation in clean medium I see a stimulation of cells from the G0/G1 phase of the cell cycle into the S phase (cell cycle assay with PI only; percentage of cells in G0/G1 decreased significantly whereas the percentage of cells in the S phase increased). Of course, having only one stain does unfortunately not give me much information on the kinetics of the cell cycle, so this argument is unfortunately a bit limited.

Viability and apoptosis are unaffected.

Of course exposure times are not identical in the two different assays and the mitogen LPS is probably also a factor influencing differences... 

Most papers I found were talking about arrest of certain phases of the cell cycle. I could not find any that were observing this kind of stimulation (if it is one). I just wonder if there is something that I'm missing that makes my observations easier to explain in the subsequent publication. :)

I would appreciate your insight!

Thank you!