Fig. 2

Sensitive and resistant SKBR3-derived cell lines retained their HER2 and EGFR expression levels. Assessment of mRNA levels in SKBR3-derived cell lines showed no differences in the mRNA levels of HER2 (a) and EGFR (b) in trastuzumab-resistant cell lines (RT₁, RT₂, RV₁, RV₂) compared to sensitive age-matched control cell lines (SV₁, SV₂). All mRNA levels were normalised to 18S rRNA and values expressed as −ΔC_T (n = 3 ± SD). The protein level of HER2 (c) and EGFR (d) were analysed in all SKBR3-derived cell lines and representative immunoblots are shown in (c i) and d i). All protein levels were normalised to β-actin protein expression, parental SKBR3 cells were used to assess changes in protein levels through continuous culture, MDA-MB-231 cells were used as a HER2-negative control (c) and MDA-MB-468 as an EGFR positive control (d). HER2 (c ii) and EGFR (d ii) protein expression was normalised to the SKBR3 parental cell line in biological replicates (n = 3 ± SD). Sensitive and resistant SKBR3-derived cell lines showed similar levels of EGFR and HER2 protein expression. Statistical analyses were performed using one-way ANOVA with Bonferroni post-tests (p > 0.05)