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Abstract 2642: Antisense oligonucleotide-based induction of dominant-negative variants of STAT3 and EGFR in breast and lung cancer cells

The signal transducer and activator of transcription 3 (STAT3) is linked to multiple cancers, including breast and lung adenocarcinomas, where it is known to activate multiple oncogenic pathways and serve as a bypass mechanism in drug resistance. For example, STAT3 is known to be a driver in some basal-like Triple-negative breast cancers (TNBC) and a resistance mechanism to EGFR inhibitors in non-small cell lung cancer (NSCLC). Thus STAT3 has become an attractive target in cancer therapeutics. A naturally occurring alternative splicing variant, STAT3-beta, is truncated and lacks the C-terminal trans-activation domain. Stat3-beta can act in a dominant negative fashion. We recently demonstrated that splice-switching oligonucleotides (SSOs) can be used to induce a shift in endogenous expression from the abundant, oncogenic STAT3-alpha to the truncated dominant-negative STAT3-beta isoform. This leads to decreased cell viability in triple-negative breast cancer cells and to tumor regression in mice, as compared to full STAT3 knock-down or controls. Our aim was to test a panel of next-generation SSOs in order to evaluate their efficacy in basal-like breast cancer cells, which are typically refractory to tyrosine kinase inhibitors. Based on our previous studies, we generated a panel of optimized SSOs targeting STAT3, and assayed the extent of the STAT3 alpha-to-beta switch, at the RNA and protein level, and at their efficacy at eliciting cell apoptosis in MDA-MB-468 TNBC cells, and identified one which show a 5-10 fold improvement of activity in vitro, compared to our previous leading published compound. The optimized STAT3 SSO sequence was also tested in RTK inhibitor-resistant H1975 non-small cell lung cancer cells and was found to be effective in killing the cancer cells as compared to Stat3 knockdown. We also used a similar antisense approach to induce the expression of a dominant-negative variant of the EGFR and tested in combination with our STAT3 SSO. While both the SSO-induced dominant negative variants of EGFR or STAT3 were able to effectively kill lung cancer cells individually, we observed a marked synergistic increase in inhibition when the two compounds where used in combination. Citation Format: Prasad Subramaniam, Luca Cartegni. Antisense oligonucleotide-based induction of dominant-negative variants of STAT3 and EGFR in breast and lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2642.