The master growth regulator downstream of Akt–a validated drug target in multiple cancers.
mTORC1 integrates signals from growth factors (via PI3K/Akt), amino acids, and energy status (via AMPK) to control protein synthesis through S6K and 4E-BP1. Active mTORC1 promotes cell growth and proliferation.
mTORC2 is less understood but phosphorylates Akt at S473, contributing to full Akt activationLoading.... This creates a feedback relationship: Akt activates mTORC1, while mTORC2 activates Akt.
The Master Regulator: mTOR integrates signals about nutrients, energy, and growth factors. It controls whether cells grow and divide (mTORC1) and affects cell survival and metabolism (mTORC2).
In Cancer: mTOR is often overactive due to upstream PI3K/Akt activation, PTEN loss, or direct pathway alterations.
Rapamycin analogs (rapalogs) inhibit mTORC1:
Temsirolimus: First-line for poor-prognosis RCC.
Everolimus: Approved for RCC, breast cancerLoading... (with exemestane), neuroendocrine tumors, TSC-associated tumors.
Rapalogs have cytostatic rather than cytotoxic effects, and resistance develops through feedback activation of Akt/PI3K. Newer ATP-competitive mTOR inhibitors target both complexes.
Approved Drugs: Everolimus and temsirolimus are approved for kidney cancer, breast cancer (with hormone therapy), and certain other tumors.
Limitations: Response varies. Resistance develops. Not all patients with "activated" pathway benefit.
mTOR activity reflects upstream pathway status. Tumors with PTENLoading... loss or PIK3CA mutations show high mTOR activation. FRET measurement of Akt activation provides integrated information about the pathway feeding into mTOR.
The Akt activationLoading... studies in breast cancer and ccRCC are directly relevant to mTOR inhibitor selection–high Akt activation indicates pathway dependence that mTOR inhibition could address.
Downstream of Akt: mTOR activation often reflects upstream Akt activation. The validated Akt assay provides functional insight into this pathway axis.
Integration: Functional measurement of multiple pathway nodes could provide more complete picture of pathway activity than any single marker.
