Activating mTOR mutations in a patient with an extraordinary response on a phase I trial of everolimus and pazopanib

Abstract

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.

Figure 1. A 70 year-old man with metastatic urothelial carcinoma with a 14-month complete response to everolimus and pazopanib

Prior to the start of treatment, axial (a) and coronal (b) CT images without intravenous contrast demonstrate retroperitoneal adenopathy in left paraaortic and retrocaval stations (white arrows). Follow-up non-contrast axial (c) and coronal (d) CT images obtained two months after the start of therapy demonstrate resolution of the pathologically enlarged retroperitoneal lymph nodes (yellow arrows).

Figure 2. Identification of two activating mTOR mutations in a patient with a complete response to everolimus and pazopanib

(a–b) Representative genome images from the Integrated Genome Viewer (IGV) for two alterations in MTOR found in found in a patient with urothelial cancer who had a complete response to everolimus and pazopanib. The number of reads for the reference allele and the variant allele are shown for each alteration. (c) Effect of overexpression of mutant mTOR on phosphorylation of the downstream target S6K1. Constructs expressing mTOR^E2014K, mTOR^E2419K, mTOR^{E2014K/E2419K}, or wildtype mTOR were co-expressed in HEK-293T cells with HA-GST-tagged S6K1. The levels of both endogenous and exogenously expressed phosphorylated and total S6K1 as well as Flag-tagged-mTOR and GAPDH are shown for HEK-293T cells expressing the MTOR mutations after a 6-hour incubation at 0 μM, 0.1 μM, or 1.0 μM rapacycin as indicated.

Figure 3. Structural model of mTOR^E2014K and mTOR^E2419K

Cartoon representation of the mTORΔN-mLST8-rapamycin-FKBP12 model with color-coded domains. mTor residues E2014 and E2419 are indicated in magenta, with side chains shown as spheres. The model was created by superposing the FRB domains of the FRB-rapamycin-FKBP12(24) and the mTORΔN-mLST8 structures(14). mLST8 is a requisite component of mTOR complex 1 and 2.