Figure 9.

NRF2 inhibition with bexarotene sensitises EGFR signalling pathway to HER1 inhibitors (a) lapatinib and (b) erlotinib. Immunoblot analysis showing bexarotene-dependent repression of EGFR signalling following its combination with lapatinib and erlotinib. Exponentially growing cells were either left untreated in media containing 1 nM heregulin (UT) or treated with the same media containing in the presence of 1 nM heregulin with lapatinib (Lap) alone or erlotinib (Erl) alone, each at 5 μM, or with cotreatment of 2.5 μM bexarotene (Lap + Bex) or (Erl + Bex) for 24 h before and processed for immunoblotting using relevant antibodies, and β-actin was used as loading control. (c) NRF2 knockdown and inhibition increase the chance of cytotoxicity of HER family-targeted agents, lapatinib and erlotinib in ovarian cancer cells. Exponentially growing cells were seeded in triplicates in 96-well plates for 24 h. Following this, cells were either left untreated in media containing 1 nM heregulin (H) or treated with same media containing in the presence of 1 nM HRG with 5 μM each of lapatinib (H + L) or erlotinib (H + E) or treated with combination 5 μM lapatinib and 2.5 μM bexarotene (H + L + BEX) or combination of 5 μM erlotinib and 2.5 μM bexarotene (H + E + BEX). Cell number was assessed indirectly by use of the cell titre glo assay. Data shown are means ± S.D. of triplicates, normalised to (H), expressed in fold change with statistical significance was calculated by one-way ANOVA followed by Tukey's post hoc test according to the scale: (^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, and ^∗∗∗∗p < 0.0001).