Abstract 3957: Analyzing the effects of radiotherapy on the metastatic phenotype: a role for combined therapeutic approaches incorporating Src and PI3K targeting

Abstract

Abstract Background: Radiotherapy is used in the treatment of over 50% of cancer patients. Although seen as a positive intervention, there are reports of radiation enhancing the metastatic characteristics of cells. We have previously observed that radiotherapy activates a number of pathways associated with tumour metastases and aggressive phenotype including Src and phosphoinositide 3-kinase (PI3K). Here we wished to relate pathway activation to cellular phenotype and to investigate the impact of pharmacological inhibition on radiation response and metastases. Methods: The effects of radiotherapy alone, and combined with Src (AZD0530) and/or PI3K (GDC-0941) inhibition, on cell adhesion, migration and clonogenic survival were assessed in vitro using well-characterised assays. Initial in vivo studies, using FTC133 xenografts, evaluated the effects of radiation treatment on the Src and PI3K pathways and inhibition thereof using pAKT (Ser473) and pFAK (Tyr861) as biomarkers. The effect of single versus combined pathway inhibition with radiation therapy (5x2Gy fractions) on primary tumour growth and lung metastasis (via ex vivo clonogenic assay) was then evaluated. Results: In vitro, radiation combined with Src and/or PI3K inhibition resulted in a reduction in cell adhesion, cell spreading and cell migration compared to radiation alone, with the combined effects greater than either inhibitor alone. Radiation both in vivo and in vitro enhanced activity of the PI3K/AKT and the Src/FAK axis. In vivo, radiation combined with Src or PI3K inhibition showed little effect on tumour growth but did reduce metastatic lung colonisation, compared to radiation alone, with Src inhibition proving more efficacious. When radiation was combined with inhibition of both pathways a significant reduction in both primary tumour growth and metastatic lung colonisation was observed. Conclusion: Radiation enhances multiple pathways, two predominant ones being PI3K and Src, and by using rationale drug combinations we saw improved local control and reduced metastatic spread. From these data we can suggest that the PI3K and Src pathways are involved in the radiation enhancement in metastatic phenotype and this provides potential for application of these therapies in the clinic. Citation Format: Emily J. Rowling, Brian Telfer, Paul Elvin, Kaye J. Williams. Analyzing the effects of radiotherapy on the metastatic phenotype: a role for combined therapeutic approaches incorporating Src and PI3K targeting. [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 3957. doi:10.1158/1538-7445.AM2014-3957