The PI3-K/AKT/mTOR pathway as a target for breast cancer therapy

Abstract

3511 Background: The PI3K/Akt/mTOR pathway is found dysregulated in multiple tumours, including breast cancer (BC). RAD001 is a recently developed drug which blocks mTOR. To study this compound’s anti-tumour effect and interactions with the aforementioned pathway, we set up a translational research program which integrates basic and clinical research data. Methods: The preclinal studies performed in BC cell lines and xenografts included the use of proliferation assays, western blot (WB), small interfering RNA and immunohistochemistry (IHC) analysis. The clinical studies consisted in a phase I study with escalating doses and collection of tumour biospies at different time points Results: Our first achievement was validating the antibodies used in WB and IHC and directed towards different components of the PI3K/Akt/mTOR pathway. We first reported that sensitivity to RAD001 correlated to basal levels of p-Akt. We then observed that RAD001 inhibits mTOR downstream, pS6 and eIF4G, but increases the levels of p-Akt, both in vitro and in patients’tumour biopsies. We demonstrated that knock down of the pS6 kinase mimics the effect of RAD001. Indeed, by combining the PI3K inhibitors and the genomic approch of p85 dominant negative vector, we demonstrated that RAD001 induced p-Akt is through PI3K. Besides the p-Akt induction we also found a RAD001 induction of IRS-1, the pivot mediator of the Insulin like Growth factor-1 Receptor (IGF-1R). We reported that RAD001 resulted in a prolonged activation of IRS-1 and in a sustained association with the p85 subunit of PI3K. Thus RAD001 disrupts an inhibitory mechanism impinging on the PI3K signalling, resulting in sustained activation of the IGF-1R pathway. Accordingly we demonstrated that combination of RAD001 with coumpounds directed against the IGF-1R, i.e. both IGF-1R tyrosine kinase inhibitors and monoclonal antibodies, prevented RAD001 induced p-Akt and resulted in a supradditive growth inhibitory effects both in vitro and in MCF-7 human BC derived xenografts.We are now conducting a phase I study with a monoclonal antibody directed at the IGF-1R that blocks IGF-1R signalling. Conclusions: Dual inhibition of mTOR and IGF-1R completely blocks the PI3K/Akt/mTOR pathway and provide a mechanistic-based combined approach. Clinical studies in BC patients are being planned. No significant financial relationships to disclose.