Abstract 1847: Influence of growth factors on resistance to EGFR inhibitor treatment in HNSCC - Temsirolimus as a potential concept
Authors: Tepper Susanne R. , Zuo Zhixiang , Khattri Arun , Heitmann Jana , Heß Jochen , Seiwert Tanguy 
Published: May 2015

Abstract
Background
Epidermal growth factor receptor (EGFR) - targeted therapy is commonly used for treatment of advanced HNSCC due to numerous findings that describe overexpression and/or high activity of EGFR in the majority of HNSCC. But response rates are moderate and most patients develop resistance in course of treatment. Biomarkers predicting the response to anti-EGFR treatment are still lacking.
We investigated the influence of growth factors (GFs) secreted both autocrine and/or paracrine from cancer associated fibroblasts (CAFs) on resistance to EGFR inhibitors (EGFRIs). Temsirolimus which seems to have a positive therapeutic effect in clinic if combined with specific EGFRIs was tested for its potential of reducing GF and receptor tyrosine kinase (RTK) expression in fibroblasts (FBs).
Methods
A panel of HNSCC cell lines was treated with Gefitinib alone and in combination with recombinant GFs. SYTO® 60 red fluorescent nucleic acid stain was used to assess viability. AlamarBlue® Assays were performed to evaluate responsiveness to Gefitinib under co-treatment with single or combined GFs. Caspase-Glo® 3/7 Assay Systems were used to measure apoptotic activity in HNSCC cells under Gefitinib and GF treatment. FB cell lines were treated with Temsirolimus. GF expression was analyzed using qRT-PCR and RTK expression was studied by immunoblotting.
Results
In 5/5 tested HNSCC cell lines Gefitinib treatment reduced viability. Co-treatment with AREG, HGF, IGF1, FGF1 or FGF2 impaired response of tumor cells to Gefitinib. Only TGFb1 seemed to intensify the growth suppressing effect of Gefitinib in some cell lines. GF combinations are much more potent than single ligands. GFs do not just increase growth but also take influence on apoptosis by diminishing the apoptotic effect of Gefitinib or even down-regulating the basal level of apoptosis in tumor cells. GF expression of FBs treated with Temsirolimus wasn't definitely assessable as Temsirolimus seemed to change the expression both of endogenous control genes and target genes. In summary, there might be a tendency of increased GF expression in FBs under Temsirolimus treatment. RTK expression appeared to be upregulated too.
Conclusions
GFs have significant impact on growth and apoptotic behavior of HNSCC cell lines treated with Gefitinib in vitro. HNSCC are known to contain a mix of different GFs in vivo secreted both by tumor and stromal cells. Determining GF levels in patient biopsies could be a method to predict responsiveness to EGRFI treatment. Furthermore it might be important to investigate potentialities for reducing GF levels in HNSCC tumors. Temsirolimus - although showing positive effects in clinic - seems to upregulate GF and RTK expression in fibroblasts in vitro. An EGFR inhibitor combined with a drug reducing GF levels could be content of a new and more effective therapeutic approach for patients resistant to single EGFRI treatment.
Citation Format: Susanne R. Tepper, Zhixiang Zuo, Arun Khattri, Jana Heitmann, Jochen Heß, Tanguy Seiwert. Influence of growth factors on resistance to EGFR inhibitor treatment in HNSCC - Temsirolimus as a potential concept. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1847. doi:10.1158/1538-7445.AM2014-1847