Everolimus induces Met inactivation by disrupting the FKBP12/Met complex

Abstract

Inhibition of the mechanistic target of rapamycin (mTOR) is a promising treatment strategy for several cancer types. Rapamycin derivatives such as everolimus are allosteric mTOR inhibitors acting through interaction with the intracellular immunophilin FKBP12, a prolyl isomerase with different cellular functions. Although mTOR inhibitors have significantly improved survival of different cancer patients, resistance and lack of predictive factors of response remain unsolved issues. To elucidate the mechanisms of resistance to everolimus, we evaluated Met activation in everolimus-sensitive/resistant human cancer cells, in vitro and in vivo. Biochemical and computational analyses were performed. Everolimus-resistant cells were xenografted into mice (10/group) and studied for their response to everolimus and Met inhibitors. The statistical significance of the in vitro results was evaluated by Student's t test.Everolimus reduced Met phosphorylation in everolimus-sensitive cells. This event was mediated by the formation of a Met-FKBP12 complex, which in turn is disrupted by everolimus. Aberrant Met activation in everolimus-resistant cells and overexpression of wild-type/mutant Met caused everolimus resistance. Pharmacological inhibition and RNA silencing of Met are effective in condition of everolimus resistance (P<0.01). In mice xenografted with everolimus-resistant cells, the combination of everolimus with the Met inhibitor PHA665752 reduced tumor growth and induced a statistically significant survival advantage (combination vs control P=0.0005).FKBP12 binding is required for full Met activation and everolimus can inhibit Met. Persistent Met activation might sustain everolimus resistance. These results identify a novel everolimus mechanism of action and suggest the development of clinical strategies based on Met inhibitors in everolimus-resistant cancers.

Impact on Autophagy and Ultraviolet B Induced Responses of Treatment with the MTOR Inhibitors Rapamycin, Everolimus, Torin 1, and pp242 in Human Keratinocytes

“…Collectively, these data demonstrated that only Rapamycin exhibited the effect of inducing autophagy among the four MTOR inhibitors tested in our study, although the crucial autophagy modulator, MTOR signaling, was inhibited in keratinocytes. The treatment doses of Rapamycin, everolimus, Torin 1, and pp242 were chosen according to those of previous studies [34, 43–45] and have been validated in the above work presented in Figure 1.…”

Targeting PI3K/Akt/mTOR in AML: Rationale and Clinical Evidence

“…Everolimus was granted FDA approval for progressive, well-differentiated non-functional, neuroendocrine tumors of gastrointestinal or lung origin with unresectable, locally advanced, or metastatic disease [182]. Everolimus interacts with FKBP12, affecting downstream effectors of mTORC1 and ultimately inhibiting cell proliferation [240,241]. However, rapamycin-induced targeting of mTORC1 has not been effective inhibiting PI3K/Akt/mTOR activity, which may relate to a negative feedback loop promoting paradoxical hyperactivation of Akt, insensitivity to rapamycin, and IGF-1-mediated feedback loops [242,243].…”

Molecular Approaches to Treating Pediatric Leukemias

“…Upon mutation, this pathway becomes constitutively active in several malignancies, including ALL and AML (106). In some solid malignancies such as breast cancer and renal cell carcinoma, mTOR inhibitors are already firmly established in therapeutic regimens (107).…”