Poster Presentation 27th Lorne Cancer Conference 2015

Targeting the PI3K/PTEN/Akt/mTOR Pathway in Sarcoma Cell Lines (#199)

Hui Jun Lim 1 , Xiaochun Wang 1 , David Goldstein 1 , Phil Crowe 1 , Jia-Lin Yang 1
  1. Sarcoma and Nano-oncology Group, Adult Cancer Program of Lowy Cancer Research Centre, and Department of Surgery of Prince of Wales Clinical School, Faculty of Medicine, University of New South Wales, Sydney, NSW, Australia

Sarcoma carries a poor prognosis prompting the need for targeted therapies aimed at deregulated signalling pathways.1,2,3,4 These include PI3K/Akt/mTOR pathway commonly upregulated in malignancies attributed to loss of PTEN expression.5,6 However, PTEN status and activation state of PI3K/Akt/mTOR pathway have not been comprehensively studied in sarcoma. Furthermore, mTOR inhibition is a potential approach to impede PI3K/Akt/mTOR signalling.

Aims

The aims of this study are to characterise PTEN genomic and protein expression, in conjunction with total Akt (tAkt) and phosphorylated Akt (pAkt) expression, in a panel of 10 sarcoma cell lines. Additionally, mTOR inhibition using ridaforolimus will be assessed in comparison with monotherapy controls, gefitinib (upstream inhibitor) and S3I-201 (parallel pathway inhibitor). Combination treatment with gefitinib and S3I-201 will also be evaluated.

Methods

PTEN genomic expression was analysed using Sanger sequencing. PTEN protein, tAkt and pAkt expression were quantified with western blot analysis. Antiproliferative effects of treatment regimens were designed using Chou & Talalay’s isobologram7, determined with crystal violet assay and analysed with CalcuSyn software.

Results

Nine cell lines have wild-type PTEN (exons 2 to 8), with normal protein expression. The GCT cell line had a missense mutation in exon 6 (C>T), associated with loss of PTEN protein expression. Increased pAkt expression was found in untreated cell lines, indicating wild-type PTEN in nine cell lines are unable to inhibit activated PI3K/Akt/mTOR signalling. Nonetheless, all cell lines demonstrated sensitivity to ridaforolimus within clinically relevant dose range (IC50:0.5-10nM). Although cell lines displayed limited sensitivity to gefitinib (IC50:13.9-29.0µM) and S3I-201 (IC50:15.1-139.3µM), their combined use achieved synergistic growth inhibition (CI:0.03-0.98) and drug-dose reductions (DRI:3.6-335.6) to clinically acceptable dose range in several cell lines.

Conclusion

PTEN mutation is rare in sarcoma cell lines and constitutive activation of PI3K/Akt/mTOR is independent of PTEN status. Targeted inhibition with ridaforolimus monotherapy and combination treatment using gefitinib and S3I-201 are promising avenues to further investigate in sarcoma treatment.  

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