Figure 6A shows an increase of prosurvival Mcl-1 in spheroids as compared to monolayers. The expression of Bid, Bak and Bax was not changed in spheroids whereas the expression of Bcl-xL was modestly increased in spheroids. The expression of Bcl-2 was not detectable in either spheroids or monolayers. The increased expression of Mcl-1 may play a role in the inhibition of immunotoxin-induced apoptosis in spheroids. A previous study indicated that high expression of Mcl-1 in 3D lung cancer spheroids based on the H1299 cell line caused its drug resistance [22]. Here, BID is linked to lung cancer.