Synopsis This article presents an overview of the PI3K/Akt/mTOR signaling pathway. As a central regulator of cell growth, protein translation, survival, and metabolism, activation of this signaling pathway contributes to the pathogenesis of many tumor types. Biochemical and genetic aberrations of this pathway observed in various cancer types will be explored. Lastly, pathway inhibitors both in development and already FDA-approved will be discussed.

We tested the antitumor efficacy of mTOR catalytic site inhibitor MLN0128 in models with intrinsic or acquired rapamycin-resistance. Cell lines that were intrinsically rapamycin-resistant as well as those that were intrinsically rapamycinsensitive were sensitive to MLN0128 in vitro. MLN0128 inhibited both mTORC1 and mTORC2 signaling, with more robust inhibition of downstream 4E-BP1 phosphorylation and cap-dependent translation compared to rapamycin in vitro. Rapamycin-sensitive BT474 cell line acquired rapamycin resistance (BT474 RR) with prolonged rapamycin treatment in vitro. This cell line acquired an mTOR mutation (S2035F) in the FKBP12-rapamycin binding domain; mTORC1 signaling was not inhibited by rapalogs but was inhibited by MLN0128. In BT474 RR cells, MLN0128 had significantly higher growth inhibition compared to rapamycin in vitro and in vivo. Our results demonstrate that MLN0128 may be effective in tumors with intrinsic as well as acquired rapalog resistance. mTOR mutations are a mechanism of acquired resistance in vitro; the clinical relevance of this observation needs to be further evaluated.

Background Society of University Surgeons (SUS) has an ongoing competitive funding program to support research training for residents. We sought to determine the career track of award recipients. Methods SUS resident awardees who completed awards from 1989-2007 were included in the study. Characteristics of awardees and their academic productivity were extracted from curriculum vitae provided by awardees (n=24), or from online sources (n=7). Results The awardees spent an average of 2.7 years (range 1-4) of dedicated research time during residency. Awardees averaged 9.8 publications (range 1-32) with 5.4 as first author (range 1-17) with their mentor within three years of award completion, with an average maximum impact factor of 5.7. Twenty-five residents (81%) pursued fellowships. At an average follow-up of 11.4 years (range 4-22) from end of the award, and 7.2 years (0-18) from end of their clinical training, the awardees had an h-index of 14.5 (2-48). At the time of the study, 26 awardees (84%) were in academic surgery. Of the 23 awardees that had completed surgical training three years earlier or more, 11 (48%) received independent research funding, of which 7 (30%) received R01 or equivalent funding. Conclusions The SUS resident research awardees had a very productive research experience. Although our retrospective study cannot determine causation, the SUS award mechanism delivers on its promise of supporting junior surgeon-scientists that pursue academic careers and establish independent research programs. Further studies are needed to determine how rates of subsequent independent research funding can be improved.

Introduction: The mammalian target of rapamycin (mTOR) pathway plays a central role in cancer biology. mTOR forms two multiprotein complexes, mTOR complex 1 and 2 (mTORC1 and mTORC2). Rapamycin and analogues are allosteric mTOR inhibitors that predominantly inhibit mTORC1. Rapamycin analogues have been FDA approved for several cancer types and are in clinical trials for treatment of many others. MLN0128 is a mTOR kinase inhibitor, that inhibit s both mTORC1 and mTORC2. We hypothesized that MLN0128 may have antitumor efficacy in cancer cell lines with intrinsic or acquired rapamycin-resistance. Methods: Twenty immortalized human cancer cell lines representing various cancer types and a range of rapamycin sensitivity were treated with Rapamycin, MLN0128 or vehicle. Sulforhodamine B assay was used to determine rapamycin and MLN0128 half maximal inhibitory concentrations (IC50), which were later confirmed with colony formation assay (CFA). Acquired resistance models were created in BT-474 and MCF-7 cell lines through culturing in progressively increasing doses of rapamycin until sustained growth at supratherapeutic (10uM) doses was achieved. Western blotting was used to characterize PI3K/mTOR signaling pathway expression. Flow cytometry and cell sorting (FACS) was used to detect and quantify apoptosis of Annexin-V-FLUOS stained cancer cell lines. Xenograft models of nu/nu mice were treated with MLN0128 and rapamycin or everolimus for 28 days. Results: Cell lines that were intrinsically rapamycin sensitive as well as those that were intrinsically rapamycin resistant were sensitive to MLN0128. MLN0128 induced cell cycle arrest; Induction of apoptosis or autophagy with MLN0128 was not detected with western blotting and annexin labeling in most cell lines tested. MLN0128 demonstrated greater inhibition of mTORC1 signaling, especially with a decrease in p4E-BP1 across all cell lines. In addition, MLN0128 demonstrated inhibition of mTORC2, with decline in pAKT473 and pAKT450. However a feedback-dependent phosphorylation of AKT S308 was observed. In cell lines with acquired rapamycin resistance, treatment with MLN0128 produced a significantly higher growth inhibition compared to rapamycin. Thus far, we have demonstrated that MLN0128 treatment resulted in increased tumor growth inhibition compared to rapamycin in xenograft models of BT474 cells with acquired rapamycin resistance. Conclusion: Cancer cell lines with intrinsic as well as acquired resistance to rapamycin are responsive to mTOR kinase inhibitor MLN0128. Further investigations are needed to study the efficacy of MLN0128 in clinical trials and to evaluate its potential as a treatment option in cases of resistance to rapalogs. Citation Format: Burhan Hassan, Argun Akcakanat, Takafumi Sangai, Farrell Adkins, Kurt Evans, Gordon B. Mills, Funda Meric-Bernstam. mTOR inhibitor MLN0128 Has antitumor efficacy in cell lines with intrinsic and acquired rapamycin resistance in vitro and in vivo. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2448. doi:10.1158/1538-7445.AM2013-2448

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