Oestrogen deprivation resistant MCF7 X cells differ in that they do not have up regulation of HER2. and indeed such growth factor receptors thoroughly only rarely increase in clinical endocrine relapse samples. It is thus probable that some dependence on the PI3K Akt pathway in MCF7 X cells coupled with only low HER2 activity cumulatively results in their prominent growth insensitivity to RAD001. Rapalogue insensitive acquired endocrine resistant cells retain sensitivity to mTOR kinase inhibition Given their substantial RAD001 growth insensitivity, TamR and MCF7 X cells could comprise useful models to under stand everolimus resistance in tamoxifen or oestrogen deprivation resistant patients and to determine improved treatments. In Inhibitors,Modulators,Libraries this regard, our findings suggest that inhib ition of both TORC2 Akt and TORC1 may be critical.

We have shown that growth of cancer cells unresponsive to an allosteric mTOR inhibitor can still be sensitive to mTOR kinase blockade, with AZD8055 substantially inhibiting samples and our additional results here are encour aging in that they show AZD8055 is also highly growth inhibitory Inhibitors,Modulators,Libraries in a further ER acquired endocrine resistant model, T47D tamR. Our TamR and MCF7 X signalling studies indicate that the difference in the mechanism of action of these drugs enables AZD8055 to target mTORC2 signalling in addition to mTORC1. thus, basal p Aktser 473 is rapidly and substantially inhibited by AZD8055 in both models but is unaffected by RAD001. Furthermore, inhibition of a negative feedback loop downstream of mTORC1 can result in induction of Akt activity in patients treated with everolimus.

This event may limit the effectiveness of mTORC1 targeting therapy since it can be associated with shortened time to progression in pa tients. However, in both Inhibitors,Modulators,Libraries TamR and MCF7 X cells, basal Akt ser473 inhibition by AZD8055 was sus tained with no up regulation over 24 hours treatment. A similar response to AZD8055 has been reported in fur ther breast cancer cell lines, while clinically a close analogue of AZD8055, AZD2014, also inhibits Inhibitors,Modulators,Libraries pAKT, pS6 and p4EBP 1 in some tumours. AZD8055 has previously been reported to induce cell death and autophagy in lung and leukaemia cancer cells, contrasting rapalogues that are often poor inducers of cell death. In the present study, some cell death was induced in TamR but not in MCF7 X cells by AZD8055. Since bcl 2 mRNA was detected basally in MCF7 X, but Inhibitors,Modulators,Libraries not in TamR cells, this anti apoptotic factor may contribute Lapatinib Ditosylate towards the somewhat reduced AZD8055 sensitivity in MCF7 X versus TamR cells. Interest ingly, rapamycin resistant tumours have previously been reported to express high levels of bcl 2.