Poster Presentation 27th Lorne Cancer Conference 2015

Overcoming Resistance of Targeted EGFR/panHER Monotherapy by Inhibition of STAT3 Escape Pathway in Sarcoma (#304)

Xiaochun Wang 1 2 , Philip Crowe 2 , David Goldstein 3 , Jia-Lin Yang 1 2
  1. Sarcoma and Nano-oncology Group, Adult Cancer Program, Lowy Cancer Research Centre, Prince of Wales Hospital, Universtiy of New South Wales, Sydney, NSW, Australia
  2. Department of Surgery, Prince of Wales Hospital, Universtity of New South Wales, Sydney, NSW, Australia
  3. Department of Medical oncology, Prince of Wales Hospital, University of New South Wales, Sydney, NSW, Australia

Sarcoma is a lethal disease with 5-year survival of 16% at metastatic stage (1). We have proven that phosphorylated EGFR (pEGFR) was an independent predictor of overall survival in sarcoma (2). This study aimed to investigate the therapeutic potential and resistance mechanisms of targeting EGFR/panHER and identify new strategies to improve the effectiveness of biological therapies in sarcoma.
Methods: Crystal-violet colorimetric and clonogenic assays were used to measure drug effects. The expression and phosphorylation of HER family and its signal transducers was investigated by Western blot. Combination data were analysed using Chou & Talalay method and CalcuSyn software. Balb/c/nude mice bearing with orthotopic human fibrosarcoma xenografts were investigated for combination therapy in vivo.
Results: Thirteen sarcoma cell lines showed resistance to EGFR inhibitor gefitinib (IC50>10µM) and panHER inhibitor dacomitinib (IC50>0.2µM) monotherapy, although gefitinib/dacomitinib dramatically blocked pEGFR, pHER2, pAKT and pERK. However, gefitinib/dacomitinib failed to decrease the ratio of pSTAT3/pSTAT1 in the JAK/STAT pathway, suggesting relative STAT3 abundance and activation may be involved in the drug resistance. STAT3 inhibitor S3I-201 plus gefitinib achieved synergism (CI=0.15-0.62) at IC50 level in 3/3 sarcoma cell lines, through perturbing pSTAT3/pSTAT1. The supra-addition was achieved for dacomitinib-plus-S3I-201 in 7/9 cell lines. Moreover, S3I-201-plus-gefitinib in vivo showed a consistent result, whereby the tumours from combination group (418mm3) were significantly (p<0.05) smaller than those from untreated (1032mm3) or single drug group (912 and 798mm3).
Conclusion: We have identified that activation of the STAT3 escape pathway is associated with the process of targeting EGFR/panHER. Additionally, we report for the first time that adding a STAT3 inhibitor can enhance the sarcoma growth inhibitory effect of gefitinib or dacomitinib. Our findings may have clinical implications on overcoming the resistance to EGFR inhibition and thereby optimizing EGFR/panHER targeted therapy in sarcoma.

  1. Ando, K. Heymann, M.F. Stresing, V. Mori, K. Redini, F. & Heymann, D. (2013) Cancers. 5, 591-616.
  2. Yang, J.L. Gupta, R.D. Dawes, I.W. & Crowe, P.J. (2006) Proc Amer Assoc Cancer Res. 47, 1234