The mammalian target of rapamycin (mTOR) is centrally involved in cell growth, metabolism, and angiogenesis. While showing clinical efficacy in a subset of tumors, rapamycin and rapalogs are specific and allosteric inhibitors of mTOR complex 1 (mTORC1), but they do not directly inhibit mTOR complex 2 (mTORC2), an emerging player in cancer. Here, we report chemical structure and biological characterization of three pyrazolopyrimidine ATP-competitive mTOR inhibitors, WAY-600, WYE-687, and WYE-354 (IC 50 , 5-9 nmol/L), with significant selectivity over phosphatidylinositol 3-kinase (PI3K) isofoms (>100-fold). Unlike the rapalogs, these inhibitors acutely blocked substrate phosphorylation by mTORC1 and mTORC2 in vitro and in cells in response to growth factor, amino acids, and hyperactive PI3K/AKT. Unlike the inhibitors of PI3K or dual-pan PI3K/mTOR, cellular inhibition of P-S6K1(T389) and P-AKT(S473) by the pyrazolopyrimidines occurred at significantly lower inhibitor concentrations than those of P-AKT(T308) (PI3K-PDK1 readout), showing mTOR selectivity in cellular setting. mTOR kinase inhibitors reduced AKT downstream function and inhibited proliferation of diverse cancer cell lines. These effects correlated with a strong G 1 cell cycle arrest in both the rapamycin-sensitive and rapamycin-resistant cells, selective induction of apoptosis, repression of global protein synthesis, and down-regulation of angiogenic factors. When injected into tumor-bearing mice, WYE-354 inhibited mTORC1 and mTORC2 and displayed robust antitumor activity in PTENnull tumors. Together, our results highlight mechanistic differentiation between rapalogs and mTOR kinase inhibitors in targeting cancer cell growth and survival and provide support for clinical development of mTOR kinase inhibitors as new cancer therapy. [Cancer Res 2009;69(15):6232-40]

The mammalian target of rapamycin (mTOR) is a central regulator of G1 cell cycle protein synthesis that precedes commitment to normal cellular replication. We have studied the effect of cell cycle inhibitor-779 (CCI-779), a rapamycin ester that inhibits mTOR function, on the proliferation of a panel of breast cancer cell lines. Six of eight lines studied were sensitive (IC 50 ȅ 50 nM) and two lines were resistant (IC 50 >1. kip-1 levels. There was good correlation between activation of the Akt pathway and sensitivity to CCI-779. Amplification of mTOR-regulated p70S6 kinase, which is downstream of Akt, may also have conferred CCI-779 sensitivity to MCF-7 cells. Taken together, the data suggest that mTOR may be a good target for breast cancer therapy, especially in tumors with Akt activation resulting from either growth factor dependency or loss of PTEN function. Endocrine-Related Cancer (2001) 8 249-258

Macroautophagy is a key stress-response pathway that can suppress or promote tumorigenesis depending on the cellular context. Notably, Kirsten rat sarcoma (KRAS)-driven tumors have been reported to rely on macroautophagy for growth and survival, suggesting a potential therapeutic approach of using autophagy inhibitors based on genetic stratification. In this study, we evaluated whether KRAS mutation status can predict the efficacy to macroautophagy inhibition. By profiling 47 cell lines with pharmacological and genetic lossof-function tools, we were unable to confirm that KRAS-driven tumor lines require macroautophagy for growth. Deletion of autophagyrelated 7 (ATG7) by genome editing completely blocked macroautophagy in several tumor lines with oncogenic mutations in KRAS but did not inhibit cell proliferation in vitro or tumorigenesis in vivo. Furthermore, ATG7 knockout did not sensitize cells to irradiation or to several anticancer agents tested. Interestingly, ATG7-deficient and -proficient cells were equally sensitive to the antiproliferative effect of chloroquine, a lysosomotropic agent often used as a pharmacological tool to evaluate the response to macroautophagy inhibition. Moreover, both cell types manifested synergistic growth inhibition when treated with chloroquine plus the tyrosine kinase inhibitors erlotinib or sunitinib, suggesting that the antiproliferative effects of chloroquine are independent of its suppressive actions on autophagy.M acroautophagy is a catabolic pathway that shuttles cytoplasmic components via double-membrane vesicles (autophagosomes) into lysosomes for degradation and recycling. Autophagosome formation and elongation are facilitated by ubiquitin-like molecules such as MAP1LC3A/B (herein referred to as "LC3") and its homologs which are directly conjugated to phosphatidylethanolamine (PE), a reaction which requires the ubiquitin E1-like activity of autophagy-related 7 (ATG7), the E2-like activity of ATG3, and the E3-like activity of the ATG5-ATG12-ATG16L1 complex (1). Autophagy cargo receptors such as p62/ SQSTM1 bind both LC3 and ubiquitinated cargo, enabling cargo recruitment into autophagosomes and delivery to lysosomes (2, 3).Basal levels of macroautophagy control cellular homeostasis by clearing misfolded proteins or damaged organelles (4, 5). Upon starvation, macroautophagy can be induced above basal levels to supply the cell with nutrients (6, 7). This prosurvival function of macroautophagy is also used by cancer cells under conditions of metabolic stress (8). However, the role of autophagy in cancer is complex and context dependent, because the pathway has been reported to have tumor-suppressing as well as tumor-promoting properties (9-11). Liver-specific deletion of ATG7 results in increased formation of liver tumors through the activation of the Nrf2 pathway (12). Furthermore, the essential autophagy component beclin-1 inhibits tumorigenesis of breast carcinoma cells, and monoallelic deletion of beclin-1 is associated with an enhanced risk of breast cancer (13-15). I...

The mammalian target of rapamycin (mTOR) regulates growth via promoting translation and transcription. Here, employing an mTOR active-site inhibitor WYE-125132 (WYE-132), we have performed quantitative phospho-proteomics and identified a Ser-75-containing phosphopeptide from Maf1, a known repressor of RNA polymerase III (Pol III) transcription. Treatment of cancer cells with WYE-132 or the rapamycin analog CCI-779 led to a rapid loss of the phosphorylation at Ser-75, whereas this effect was not seen in cells treated with cytotoxic agents or unrelated inhibitors. WYE-132-induced Maf1 dephosphorylation correlated with its accumulation in the nucleus and a marked decline in the cellular levels of pre-tRNAs. Depletion of cellular Maf1 via small interfering RNA increased basal pre-tRNA and rendered tRNA synthesis refractory to mTOR inhibitors. Maf1 mutant proteins carrying S75A alone or with S60A, T64A, and S68A (Maf1-S75A, Maf1-4A) progressively enhanced basal repression of tRNA in actively proliferating cells and attenuated amino acid-induced tRNA transcription. Gene alignment revealed conservation of all four Ser/Thr sites in high eukaryotes, further supporting a critical role of these residues in Maf1 function. Interestingly, mTOR inhibition led to an increase in the occupancy of Maf1 on a set of Pol III-dependent genes, with concomitant reduction in the binding of Pol III and Brf1. Unexpectedly, mTORC1 itself was also enriched at the same set of Pol III templates, but this association was not influenced by mTOR inhibitor treatment. Our results highlight a new and unique mode of regulation of Pol III transcription by mTOR and suggest that normalization of Pol III activity may contribute to the therapeutic efficacy of mTOR inhibitors. The mammalian target of rapamycin (mTOR)3 is a central metabolic sensor that coordinates cell growth and proliferation with the availability of growth factors, nutrients, and energy sufficiency. mTOR exists in two multiprotein complexes: mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) (1-3). Under conditions of rapid growth and proliferation, mTOR stimulates several anabolic processes, including mRNA translation, transcription, and lipid biosynthesis. The mTORC1 is well known to enhance cap-dependent translation initiation through the direct phosphorylation of S6K1 and 4E-BP1 in response to mitogen and nutrient stimulation (4). The more recently discovered mTORC2 can directly phosphorylate AKT and conventional protein kinase C and is involved in maintenance of actin cytoskeleton in a yet to be defined mechanism. mTOR is a major signaling component of the phosphatidylinositol 3-kinase/AKT pathway that is most frequently dysregulated in cancer (3, 5-7).In addition to the direct control of translational apparatus by mTORC1, several reports have implicated the mTOR signaling in the molecular events occurring the nucleus, such as RNA polymerase (Pol) I transcription, essential for the ribosomal biogenesis and accumulation of cell mass (8 -10). The genetic and biochemical studies in bu...

The mammalian target of rapamycin (mTOR) is a major component of the phosphoinositide 3-kinase (PI3K)/ AKT signaling pathway that is dysregulated in 50% of all human malignancies. Rapamycin and its analogues (rapalogs) partially inhibit mTOR through allosteric binding to mTOR complex 1 (mTORC1) but not mTOR complex 2 (mTORC2), an emerging player in cancer. Here, we report WYE-125132 (WYE-132), a highly potent, ATP-competitive, and specific mTOR kinase inhibitor (IC 50 : 0.19 ± 0.07 nmol/L; >5,000-fold selective versus PI3Ks). WYE-132 inhibited mTORC1 and mTORC2 in diverse cancer models in vitro and in vivo. Importantly, consistent with genetic ablation of mTORC2, WYE-132 targeted P-AKT(S473) and AKT function without significantly reducing the steady-state level of the PI3K/PDK1 activity biomarker P-AKT(T308), highlighting a prominent and direct regulation of AKT by mTORC2 in cancer cells. Compared with the rapalog temsirolimus/CCI-779, WYE-132 elicited a substantially stronger inhibition of cancer cell growth and survival, protein synthesis, cell size, bioenergetic metabolism, and adaptation to hypoxia. Oral administration of WYE-132 to tumor-bearing mice showed potent single-agent antitumor activity against MDA361 breast, U87MG glioma, A549 and H1975 lung, as well as A498 and 786-O renal tumors. An optimal dose of WYE-132 achieved a substantial regression of MDA361 and A549 large tumors and caused complete regression of A498 large tumors when coadministered with bevacizumab. Our results further validate mTOR as a critical driver for tumor growth, establish WYE-132 as a potent and profound anticancer agent, and provide a strong rationale for clinical development of specific mTOR kinase inhibitors as new cancer therapy. Cancer Res; 70(2); 621-31. ©2010 AACR.

T cell-invigorating cancer immunotherapies have near-curative potential. However, their clinical benefit is currently limited, as only a fraction of patients respond, suggesting that these regimens may benefit from combination with tumor-targeting treatments. As oncogenic progression is accompanied by alterations in metabolic pathways, tumors often become heavily reliant on antioxidant machinery and may be susceptible to increases in oxidative stress. The cystine–glutamate antiporter xCT is frequently overexpressed in cancer and fuels the production of the antioxidant glutathione; thus, tumors prone to redox stress may be selectively vulnerable to xCT disruption. However, systemic inhibition of xCT may compromise antitumor immunity, as xCT is implicated in supporting antigen-induced T cell proliferation. Therefore, we utilized immune-competent murine tumor models to investigate whether cancer cell expression of xCT was required for tumor growth in vivo and if deletion of host xCT impacted antitumor immune responses. Deletion of xCT in tumor cells led to defective cystine uptake, accumulation of reactive oxygen species, and impaired tumor growth, supporting a cancer cell-autonomous role for xCT. In contrast, we observed that, although T cell proliferation in culture was exquisitely dependent on xCT expression, xCT was dispensable for T cell proliferation in vivo and for the generation of primary and memory immune responses to tumors. These findings prompted the combination of tumor cell xCT deletion with the immunotherapeutic agent anti–CTLA-4, which dramatically increased the frequency and durability of antitumor responses. Together, these results identify a metabolic vulnerability specific to tumors and demonstrate that xCT disruption can expand the efficacy of anticancer immunotherapies.

The mammalian target of rapamycin (mTOR) inhibitor

Dramatic improvements in mTOR-targeting selectivity were achieved by replacing morpholine in pyrazolopyrimidine inhibitors with bridged morpholines. Analogues with subnanomolar mTOR IC(50) values and up to 26000-fold selectivity versus PI3Kalpha were prepared. Chiral morpholines gave inhibitors whose enantiomers had different selectivity and potency profiles. Molecular modeling suggests that a single amino acid difference between PI3K and mTOR (Phe961Leu) accounts for the profound selectivity seen by creating a deeper pocket in mTOR that can accommodate bridged morpholines.