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 synthesis and SAR of a series of triazolopyrimidines as anticancer agents are described. Treatment of 5-chloro-6-(trifluorophenyl)-N-fluoroalkyl [1,2,4]triazolo[1,5-a]pyrimidin-7-amine with an alcohol, a thiol, or an alkylamine provided the corresponding final compounds. A clear SAR requirement has been established for optimal activity. A (1S)-2,2,2-trifluoro-1-methylethylamino group or an achiral 2,2,2-trifluoroethylamino group is required at the 5-position to achieve high potency. On the phenyl ring, both fluoro atoms, at the positions ortho to the triazolopyrimidine core, are needed for optimal activity. At the position para to the triazolopyrimidine core, on the phenyl ring, the best activity is achieved with an oxygen linkage followed by a three-methylene unit, and an alkylamino or a hydroxy group. The mechanism of action for this series of triazolopyrimidines was shown to be unique in that they promoted tubulin polymerization in vitro, but did not bind competitively with paclitaxel.1 Instead, they inhibit the binding of vincas to tubulin. Selected compounds were studied further, and it was shown that these compounds were able to overcome resistance attributed to several multidrug resistance transporter proteins. Lead compounds were shown to inhibit tumor growth in several nude mouse xenograft models, with high potency and efficacy, when dosed either orally or intravenously.

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.

Purpose: The aim of this study was to show preclinical efficacy and clinical development potential of PKI-587, a dual phosphoinositide 3-kinase (PI3K)/mTOR inhibitor.Experimental Design: In vitro class 1 PI3K enzyme and human tumor cell growth inhibition assays and in vivo five tumor xenograft models were used to show efficacy.

The PI3K/Akt signaling pathway is a key pathway in cell proliferation, growth, survival, protein synthesis, and glucose metabolism. It has been recognized recently that inhibiting this pathway might provide a viable therapy for cancer. A series of bis(morpholino-1,3,5-triazine) derivatives were prepared and optimized to provide the highly efficacious PI3K/mTOR inhibitor 1-(4-{[4-(dimethylamino)piperidin-1-yl]carbonyl}phenyl)-3-[4-(4,6-dimorpholin-4-yl-1,3,5-triazin-2-yl)phenyl]urea 26 (PKI-587). Compound 26 has shown excellent activity in vitro and in vivo, with antitumor efficacy in both subcutaneous and orthotopic xenograft tumor models when administered intravenously. The structure-activity relationships and the in vitro and in vivo activity of analogues in this series are described.

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.

Deregulated phosphatidylinositol 3-kinase (PI3K) signaling pathway is widely implicated in tumor growth and resistance to chemotherapy. While a strong rationale exists for pharmacological targeting of PI3K, only a few proof-of-principle in vivo efficacy studies are currently available. PWT-458, pegylated-17-hydroxywortmannin, is a novel and highly potent inhibitor of PI3K in animal models. Upon in vivo cleavage of its poly(ethyleneglycol) (PEG), PWT-458 releases its active moiety 17-hydroxywortmannin (17-HWT), the most potent inhibitor in its class. Here we show that a single intravenous injection of PWT-458 rapidly inhibited PI3K signaling, as measured by a complete loss of AKT (Ser-473) phosphorylation in xenograft tumors grown in nude mice. Following a daily X5 dosing regimen, PWT-458 demonstrated single-agent antitumor activity in nude mouse xenograft models of U87MG glioma, nonsmall cell lung cancer (NSCLC) A549, and renal cell carcinoma (RCC) A498. Efficacious doses ranged from 0.5 mg/kg to 10 mg/kg, achieving a superior therapeutic index over 17-HWT. PWT-458 augmented anticancer efficacy of a suboptimal dose of paclitaxel against A549 and U87MG tumors. Combination treatment of PWT-458 and an mTOR inhibitor, Pegylated-Rapamycin (Peg-Rapa), resulted in an enhanced antitumor efficacy in U87MG. Finally, PWT-458 in combination with interferon-alpha (Intron-A) caused a dramatic regression of RCC A498, which was not achieved by either agent alone. These studies identify PWT-458 as an effective anticancer agent and provide strong proof-of-principle for targeting the PI3K pathway as novel anticancer therapy.

propoxy]phenyl]-N -[(1S )-2,2,2-trifluoro-1-methylethyl]- [1,2,4]triazolo [1,5-a]pyrimidin-7-amine butanedioate (TTI-237) is a microtubule-active compound of novel structure and function. Structurally, it is one of a class of compounds, triazolo[1,5a]-pyrimidines, previously not known to bind to tubulin. Functionally, TTI-237 inhibited the binding of [ 3 H]vinblastine to tubulin, but it caused a marked increase in turbidity development that more closely resembled the effect observed with docetaxel than that observed with vincristine. The morphologic character of the presumptive polymer is unknown at present. When applied to cultured human tumor cells at concentrations near its IC 50 value for cytotoxicity (34 nmol/L), TTI-237 induced multiple spindle poles and multinuclear cells, as did paclitaxel, but not vincristine or colchicine. Flow cytometry experiments revealed that, at low concentrations (20-40 nmol/L), TTI-237 produced sub-G 1 nuclei and, at concentrations above 50 nmol/L, it caused a strong G 2 -M block. The compound was a weak substrate of multidrug resistance 1 (multidrug resistance transporter or P-glycoprotein). In a cell line expressing a high level of P-glycoprotein, the IC 50 of TTI-237 increased 25-fold whereas those of paclitaxel and vincristine increased 806-fold and 925-fold, respectively. TTI-237 was not recognized by the MRP or MXR transporters. TTI-237 was active in vivo in several nude mouse xenograft models of human cancer, including LoVo human colon carcinoma and U87-MG human glioblastoma, when dosed i.v. or p.o. Thus, TTI-237 has a set of properties that distinguish it from other classes of microtubule-active compounds.