One out of the three compounds from this screen (compound 48) reduced MAPK activation in a dose dependent manner independent of RKIP, suggesting off target effects.
The variable levels of effects of epigenetic inhibitors on COX-2 mRNA/protein expression and PGE2 production despite similar effects on methylation status at the COX-2 promoter may also suggest off-target effects of the inhibitors on genes that may have control of COX-2 expression and function.
These and other evidences such as inhibition of tumor cell production of cytokines, anti-angiogenesis, induction of apoptosis and others, suggest off targets effects for PIs, and hints to the concept of a new class of drugs against cancer with multiple anti-cancer effects.
Previous work using MK2 inhibitors in WS cells was inconclusive because the inhibitors resulted in cessation of cellular growth that appeared to be unrelated to the ability of the inhibitors to inhibit MK2 [11], suggesting off-target issues (or cellular toxicity) that are a known problem with MK2 inhibitors [7].
When the concentration of TAM was elevated to 100 μM, there was no obvious difference in cell survival, suggesting off-target effects of TAM at high concentrations.
Since cleaved Notch levels were not decreased at 2 h post PF-03084014 treatment may suggest that off target effects were responsible for cleavage of caspase 3 and PARP.
The mismatches at the 5′ end reduced cleavage, suggesting that the off target effects can be abolished in vivo by selecting target sites with unique sequences at 3′ end.
These data suggest that off-target effects of the siRNAs targeting Pink1 are responsible for their protective effects against TNF-necroptosis.
Thus, while other factors could contribute to the lack of overlap between screens (e.g. differences in RNAi protocol, knockdown efficiency, cell type), our results suggest that off-targets are an important factor.
These studies also suggest that off-target cleavage, or its aberrant repair, may be greater in cell lines than in animals, so the program allows the user to select the stringency of the algorithm employed.
Together, the K 1 and K' 1 results suggest that off-target effects are favored when the cycle 1 phosphatase reaction tends toward inefficiency and the cycle 1 kinase reaction tends towards efficiency.
