Impact of dual mTORC1/2 mTOR kinase inhibitor AZD8055 on acquired endocrine resistance in breast cancer in vitro

Abstract

IntroductionUpregulation of PI3K/Akt/mTOR signalling in endocrine-resistant breast cancer (BC) has identified mTOR as an attractive target alongside anti-hormones to control resistance. RAD001 (everolimus/Afinitor®), an allosteric mTOR inhibitor, is proving valuable in this setting; however, some patients are inherently refractory or relapse during treatment requiring alternative strategies. Here we evaluate the potential for novel dual mTORC1/2 mTOR kinase inhibitors, exemplified by AZD8055, by comparison with RAD001 in ER + endocrine resistant BC cells.MethodsIn vitro models of tamoxifen (TamR) or oestrogen deprivation resistance (MCF7-X) were treated with RAD001 or AZD8055 alone or combined with anti-hormone fulvestrant. Endpoints included growth, cell proliferation (Ki67), viability and migration, with PI3K/AKT/mTOR signalling impact monitored by Western blotting. Potential ER cross-talk was investigated by immunocytochemistry and RT-PCR.ResultsRAD001 was a poor growth inhibitor of MCF7-derived TamR and MCF7-X cells (IC50 ≥1 μM), rapidly inhibiting mTORC1 but not mTORC2/AKT signalling. In contrast AZD8055, which rapidly inhibited both mTORC1 and mTORC2/AKT activity, was a highly effective (P <0.001) growth inhibitor of TamR (IC50 18 nM) and MCF7-X (IC50 24 nM), and of a further T47D-derived tamoxifen resistant model T47D-tamR (IC50 19 nM). AZD8055 significantly (P <0.05) inhibited resistant cell proliferation, increased cell death and reduced migration. Furthermore, dual treatment of TamR or MCF7-X cells with AZD8055 plus fulvestrant provided superior control of resistant growth versus either agent alone (P <0.05). Co-treating with AZD8055 alongside tamoxifen (P <0.01) or oestrogen deprivation (P <0.05) also effectively inhibited endocrine responsive MCF-7 cells. Although AZD8055 inhibited oestrogen receptor (ER) ser167 phosphorylation in TamR and MCF7-X, it had no effect on ER ser118 activity or expression of several ER-regulated genes, suggesting the mTOR kinase inhibitor impact was largely ER-independent. The capacity of AZD8055 for ER-independent activity was further evidenced by growth inhibition (IC5018 and 20 nM) of two acquired fulvestrant resistant models lacking ER.ConclusionsThis is the first report demonstrating dual mTORC1/2 mTOR kinase inhibitors have potential to control acquired endocrine resistant BC, even under conditions where everolimus fails. Such inhibitors may prove of particular benefit when used alongside anti-hormonal treatment as second-line therapy in endocrine resistant disease, and also potentially alongside anti-hormones during the earlier endocrine responsive phase to hinder development of resistance.

Dual mTOR Kinase Inhibitor MLN0128 Sensitizes HR+/HER2+ Breast Cancer Patient-Derived Xenografts to Trastuzumab or Fulvestrant

“…Instead, MLN0128 targeting to both mTORC1 and mTORC2 was developed to treat HR þ as well as HER2 þ breast cancers in vitro and in vivo (15,20,41). In ER þ breast cancer, dual mTORC inhibitors (e.g., AZD8055 and AZD2014) combined with endocrine agents exhibited superior inhibition effects on in vitro culture system or cell-based xenografts compared to that of single-drug treatment (14,16). Additionally, MLN combined with and the dual tyrosine kinase inhibitor lapatinib has synergistic effects on HER2 þ cancer cell lines and PDXs, which are resistant to anti-HER2 drugs (15).…”

“…The protein kinase mTOR, which exists in two complexes (mTORC1 and mTORC2) and serves as the catalytic subunit, transduces proliferation cues to the signaling components of the PI3K/AKT/mTOR axis. While activation, PI3K and mTORC2 activate AKT, leading to upregulation of mTORC1 and the downstream S6K1 and 4EBP1 for promoting cell proliferation and survival (16)(17)(18)(19)(20). Due to the PI3K/AKT rebound effect, long-term treatment of mTORC1 inhibition has been known to alleviate AKT activation by mTORC2.…”

“…The PI3K/AKT/mTOR axis, as the downstream of the RTK cascade, is considered to be a promising therapeutic target in HR þ and HER2 þ breast cancers (14)(15)(16). The protein kinase mTOR, which exists in two complexes (mTORC1 and mTORC2) and serves as the catalytic subunit, transduces proliferation cues to the signaling components of the PI3K/AKT/mTOR axis.…”

“…In addition, activation of the PI3K/AKT/mTOR signaling has been reported in the establishment of endocrine resistance, leading to estrogen-independent ERa activation. In the clinic, the mTORC1 inhibitor everolimus has been prescribed with endocrine agents for advanced and AI-resistant HR þ breast cancers (11)(12)(13)(14)(15)(16).…”

Molecular Docking and Pharmacokinetic of Highly Specific Novel Pan-Mtor Inhibitors against Solid Tumors

“…AZD8055 inhibits the phosphorylation of S6K atSer235/236 and Akt at Ser473. AZD8055 was proved to be a better therapeutic agent than allosteric inhibitors for endocrine resistant breast cancers [42,43]. AZD2014 is 5 fold less effective than AZD8055 but has better pharmacokinetic profile [44].…”