Effect of BMS-345541 on inhibition of IκB and p65 phosphorylation in vivo. MT-2, C8166, and CEM cells were treated with BMS-345541 at 0.1, 0.5, 1, and 5 μM for 48 hr. Total cell extracts were collected and subjected to Western blot analysis using anti-IκB, phospho IκB (ser 32), p65, phospho p65 (ser 536), p50, p52, Tax and actin. Twenty five microgram of each extract was used to separate on a 4–20% SDS/PAGE. Levels of total IκB and p65 did not change between cell types, however there was a dramatic increase of phosphor-IκB and phosphor-p65 in HTLV-1 infected cells and their suppression by BMS-345541 which inhibits IKKβ activity in vivo.