Potential interplay between mTOR blockade using AZD8055 and ER signalling was further investigated by following website PCR examination of the ER regulated gene pS2 as well as several ER regulated genes more closely related to also inhibited growth by 60% in an ER nega tive acquired fulvestrant resistant cell line derived Inhibitors,Modulators,Libraries from MCF7 cells. This observation was also supported by AZD8055 growth studies in a T47D derived ER acquired fulvestrant resistant line with an IC50 of 18 nM. AZD8055 and fulvestrant in combination enhance growth inhibition in TamR and MCF7 X Inhibitors,Modulators,Libraries cells When ER positive breast tumours acquire resistance to an anti hormone, an alternative anti endocrine therapy can often be used successfully second line, although resistance invariably emerges.

In keeping with this, we have previously shown that the pure anti oestrogen Inhibitors,Modulators,Libraries fulvestrant is growth inhibitory in TamR or MCF7 X cells in vitro, but growth inhibition is only partial, with the cells subsequently acquiring resistance to ful vestrant. We have investigated whether co treating with a further anti hormonal measure alongside an mTOR kinase inhibitor could offer an improved second line treatment for endocrine resistant cells ver sus either strategy alone. This was also important to evaluate since AZD8055 appears to be inhibitory inde pendently of any substantial impact on ER regulated events in our acquired endocrine resistant models. Inhibitors,Modulators,Libraries When TamR cells were treated for seven days with 25 nM AZD8055 in combination with fulvestrant there was a further 60% decrease in growth above that caused by fulvestrant and a 50% enhancement of growth inhibition compared to AZD8055 alone.

A similar improved anti tumour effect was also observed in MCF 7X cells co treated with AZD8055 and fulvestrant in which 25 nM Inhibitors,Modulators,Libraries AZD8055 caused a further 60% decrease in growth above fulvestrant or AZD8055 alone. These results suggest that an mTOR kinase inhibitor plus anti oestrogen fulvestrant combination could have potential as a superior second line treatment for endocrine resistant breast cancers that do not respond well to the rapalogue everolimus. Finally, while seven day treatment with AZD8055 was also a good inhibitor of growth in anti oestrogen sensitive MCF 7 parental cells with an IC50 of 12 nM, a superior growth inhibition could again be obtained by co treatment with AZD8055 and either 4 OH tamoxifen or severe oestrogen deprivation.

The anti tumour effect was increased by 66% and 56%, respectively, by combination with 10 nM AZD8055 versus the our site anti hormone treatment alone. These findings suggest that in combination with anti hormone therapy, mTOR kinase blockade could also provide a first line treatment strategy to inhibit endo crine responsive disease more effectively and thereby hinder acquisition of resistance in breast cancer.