Abstract 3763: Treatment of soft tissue sarcoma cells by EGFR and/or STAT3 inhibitors

Abstract

Abstract Background: We previously found Epidermal Growth Factor Receptor (EGFR) inhibitor can block liposarcoma cell EGFR (HER1) survival signalling. However, it did not interfere with HER2 regulated Janus Kinases (JAK), and Signal Transducer and Activator of Transcription (STAT) signal transduction. Our research suggested JAK/STAT may be one mechanism for EGFR inhibitor resistance. Targeting both EGFR and STAT3, which has never been tested in sarcoma may overcome this problem. The principal aim of this preliminary study was to investigate the effect and mechanism of both STAT3 inhibitor alone and in combination with EGFR inhibitor in the treatment of soft tissue sarcoma (STS) cell lines. Methods: STAT3 inhibitor (S3I-201) mono-therapy or in combination with EGFR inhibitor Gefitinib was investigated in 7 STS cell lines (449b, 778, SW872, SW684, SW982, GCT and HT1080). Crystal-violet colorimetric and clonogenic assays were used to measure drug effects. For assessing a potential role of treatment, we investigated expression and activity of STAT and EGFR by Western blot and immunohistochemistry staining before and after treatment. Data were analysed using Chou & Talalay method and CalcuSyn software. Results: All 7 STS cell lines expressed phosphorylated/total STAT3 and EGFR. Anti-proliferative and anti-clonogenic effects of S3I-201 monotherapy on STS were dose- and time-dependent. Sensitive cells to S3I-201 (IC50 Δ50μM) were HT1080, SW684, GCT and SW982 (90% HT1080 were inhibited at day 3 post-administration of 25μM drug), partially sensitive cells were 449B and 778, and non-sensitive cells (IC50 ≤ 200μM) were SW872 (only 29% SW872 were inhibited at day 5 with 200μM S3I-201). Western blot analysis of whole-cell lysates from HT1080 showed phosphorylated STAT3 (pSTAT3) levels were significantly diminished after S3I-201 treatment, whereas pSTAT3 were not down-regulated in resistant cells SW872. IC50 of Gefitinib monotherapy on STS were 20 - 40μM, and 778 had minor effect (33% cells were inhibited after 5 days treatment). Combination therapy with Gefitinib and S3I-201 achieved synergistic antiproliferative effect (mean CIs < 0.90) in 6/7 STS cell lines (CI: 449b (0.3-1), 778 (0.1-0.2), SW872 (0.6-0.7), SW684 (0.2-0.5), GCT (0.3-0.4) and HT1080 (0.5-0.6)), except SW982 (1-1.2). For the most synergistic 778 cells, the drug reduction index for Gefitinib and S3I-201 was 5.9 and 12.7. Although treatment with Gefitinib alone inhibited pSTAT3 expression on serum-starved 778, EGF stimulation reversed the inhibition function. However in combination therapy, STAT3 phosphorylation was not induced by EGF stimulation. Conclusion: Combination therapy targeting both EGFR and STAT3 is a worthwhile treatment to pursue in anti-sarcoma therapy. Further studies will focus on potential mechanisms as well as the anti-sarcoma effect in the animal models. These results will have a clinical implication in treatment of STS in the future. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3763. doi:1538-7445.AM2012-3763