Activating mTOR Mutations in a Patient with an Extraordinary Response on a Phase I Trial of Everolimus and Pazopanib

Cancer Discovery (Impact Factor: 19.45). 03/2014; 4(5). DOI: 10.1158/2159-8290.CD-13-0353
Source: PubMed


Understanding the genetic mechanisms of sensitivity to targeted anticancer therapies may improve patient selection, response to therapy, and rational treatment designs. One approach to increase this understanding involves detailed studies of exceptional responders: rare patients with unexpected exquisite sensitivity or durable responses to therapy. We identified an exceptional responder in a phase I study of pazopanib and everolimus in advanced solid tumors. Whole-exome sequencing of a patient with a 14-month complete response on this trial revealed two concurrent mutations in mTOR, the target of everolimus. In vitro experiments demonstrate that both mutations are activating, suggesting a biologic mechanism for exquisite sensitivity to everolimus in this patient. The use of precision (or "personalized") medicine approaches to screen patients with cancer for alterations in the mTOR pathway may help to identify subsets of patients who may benefit from targeted therapies directed against mTOR.

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    ABSTRACT: Genes encoding components of the PI3K–AKT–mTOR signaling axis are frequently mutated in cancer, but few mutations have been characterized in MTOR, the gene encoding the mTOR kinase. Using publicly available tumor genome sequencing data, we generated a comprehensive catalog of mTOR pathway mutations in cancer, identifying 33 MTOR mutations that confer pathway hyperactivation. The mutations cluster in six distinct regions in the C-terminal half of mTOR and occur in multiple cancer types, with one cluster particularly prominent in kidney cancer. The activating mutations do not affect mTOR complex assembly, but a subset reduces binding to the mTOR inhibitor DEPTOR. mTOR complex 1 (mTORC1) signaling in cells expressing various activating mutations remains sensitive to pharmacologic mTOR inhibition, but is partially resistant to nutrient deprivation. Finally, cancer cell lines with hyperactivating MTOR mutations display heightened sensitivity to rapamycin both in culture and in vivo xenografts, suggesting that such mutations confer mTOR pathway dependency. Significance: We report that a diverse set of cancer-associated MTOR mutations confer increased mTORC1/2 pathway activity and that cells harboring these mutations are highly sensitive to rapamycin in culture and in vivo. These findings are clinically relevant as the MTOR mutations characterized herein may serve as biomarkers for predicting tumor responses to mTOR inhibitors.
    Full-text · Article · Mar 2014 · Cancer Discovery
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    ABSTRACT: The identification of activating mutations in mTOR that explain an exceptional response in a patient with bladder cancer is the latest example of mechanistic insights that can be gleaned from analyzing exceptional responders in otherwise failed trials. The NCI plans to sequence 100 such exceptional responders to help identify other cancer-related mutations that could predict drug response.
    No preview · Article · Mar 2014 · Science-Business eXchange

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