Next-generation RNA sequencing reveals transcriptomic changes after brief exposure to preoperative nab-paclitaxel, bevacizumab, and trastuzumab.

Abstract

10508 Background: Identification of differentially expressed transcripts after brief exposure to preoperative therapy can help determine likely response markers. We quantify and compare differential gene and isoform expression using RNA-seq on patient samples with 10 day exposure to one dose of trastuzumab, bevacizumab or nab-paclitaxel. Methods: We sequenced transcriptomes of 23 pairs of core biopsy RNA from breast cancers pre/post 10 day exposure to therapy. Paired-end sequencing was done on the Illumina GAII platform using amplified total RNA with 74bp read length, yielding data on transcript abundance for a total of 22,160 genes and 34,449 transcripts. Differential expression of transcripts between pre/post samples was estimated assuming Poisson-distributed read-counts, followed by multiple testing correction and enrichment analysis of 185 KEGG pathways. Results: PAM50-based clustering showed individual samples cluster together, demonstrating that tumor subtypes do not change over the 10-day treatment (SABCS 2011). We identified genes that were significantly differentially expressed (p<0.05; FDR<0.1) in at least 60% of samples within each therapy arm: 780 genes in trastuzumab, 302 in bevacizumab, and 176 in nab-paclitaxel. Surprisingly, only THAP11 and TINF2 were common amongst them. THAP11 is involved in stem cell maintenance and TINF2 is important for regulation of telomere length. Immune system and metabolism-related pathways were commonly affected (p<0.05) across all arms. The bevacizumab arm showed significant down-regulation of angiogenesis-associated genes: ESM1 and VEGFR2 in > 80% of samples. The nab-paclitaxel arm exhibited changes in TGF-beta signaling, Nod-like receptor and Wnt signaling. The trastuzumab arm exhibited consistent alteration of ErbB2 and mTOR pathways, with SOX11 and TOP2B downregulated in every sample. Conclusions: This is the first study to compare gene expression with brief exposure across therapies using RNA-seq technology. The unique aspects of transcriptional response to each treatment underscore the need for specific markers of therapeutic response to nab-paclitaxel, bevacizumab and trastuzumab.