Fig. 4: c-Myc drives HER2 antibody resistance in HER2+ breast cancer in vitro.

a mRNA levels of c-Myc and its target genes induced in HR6 cells compared with BT474T cells (n = 2). b, c RT-qPCR (b) and immunoblot (c) analyses of ZMYND8 and c-Myc in BT474T, HR6, ZMYND8 KO1 HR6, and ZMYND8 KO2 HR6 cells (n = 3). d Immunoblot analysis of ZMYND8 and c-Myc in BT474T cells expressing EV or c-Myc (n = 3). e, f Clonogenic growth of EV and c-Myc overexpressed BT474T cells treated with vehicle or trastuzumab (Tras.) for 6 days. Representative colony images (e) and quantification (f, n = 3). g Immunoblot analysis of ZMYND8 and c-Myc in parental and c-Myc KO1 or KO2 HR6 cells (n = 3). h, i Clonogenic growth of parental and c-Myc KO1 or KO2 HR6 cells treated with vehicle or trastuzumab for 6 days. Representative colony images (h) and quantification (i, n = 3). j, k Clonogenic growth of HR6 cells treated with vehicle, MYCi361, trastuzumab, or MYCi361+trastuzumab for 6 days. Representative colony images (j) and quantification (k, n = 3). l–o Growth of tumor organoids treated with vehicle, trastuzumab, MYCi361, or trastuzumab+MYCi361 for 9 days. Representative organoid images (l, n) and organoid viability quantification (m, o, n = 3). p–s Growth of tumor organoids treated with vehicle, trastuzumab, MYCi361, trastuzumab+pertuzumab, trastuzumab+MYCi361, or trastuzumab+pertuzumab+MYCi361 for 9 days. Representative organoid images (p, r) and organoid viability quantification (q, s, n = 3). Data from biological replicates represent mean ± SEM. P-value was determined by bioinformatics with edgeR (a), one-way ANOVA with Dunnett’s test (b) or Tukey’s test (q, s), or two-way ANOVA with Tukey’s test (f, i, k, m, and o). Scale bar, 200 μm. Source data are provided as a Source Data file.