Question 1

What does AKT1 do in cancer?

Accepted Answer

AKT1 promotes cell survival and proliferation by phosphorylating substrates that inhibit apoptosis (BAD, FOXO3a), stimulate protein synthesis (mTORC1 via TSC2), and drive cell cycle entry (MDM2 activation, GSK3β inhibition). It is the central hub of the PI3K pathway — the most frequently activated oncogenic pathway in human cancer.

Question 2

What is the AKT E17K mutation?

Accepted Answer

The AKT1 E17K substitution in the pleckstrin homology domain promotes constitutive membrane association and AKT activation independent of PIP3 levels. It occurs in ~5% of HR+ breast cancers and is a predictive biomarker for AKT inhibitors. Capivasertib combined with fulvestrant received FDA approval for AKT1/PIK3CA/PTEN-altered breast cancer in 2023.

Question 3

What is the difference between AKT1, AKT2, and AKT3?

Accepted Answer

The three AKT isoforms share high structural homology but differ in tissue expression and substrate preferences. AKT1 is ubiquitous and primarily linked to cell survival; AKT2 is enriched in insulin-responsive tissues and metabolic regulation; AKT3 is brain-enriched and implicated in neurological cancers. AKT1 is the most commonly mutated isoform in solid tumours.

Question 4

What is the AKT1 E17K mutation and how does it differ mechanistically from PIK3CA mutations?

Accepted Answer

AKT1 E17K substitutes a positively charged lysine for glutamate at position 17 in the pleckstrin homology (PH) domain. This charge reversal increases PH domain affinity for negatively charged phosphoinositides including PI(3,4)P2 and even PI(4,5)P2, enabling AKT1 membrane recruitment and activation independent of PIP3 levels. Unlike PIK3CA mutations that increase upstream PIP3 production to activate all downstream PH-domain-containing proteins, AKT1 E17K acts specifically and constitutively on AKT1 itself, making it a more targeted molecular event. The E17K mutation occurs in ~5% of HR+ breast cancers and is a predictive biomarker for AKT inhibitor response, independent of PIK3CA mutation status.

Question 5

How does capivasertib work and in which patients is it approved?

Accepted Answer

Capivasertib is an oral, pan-AKT allosteric inhibitor that binds the PH domain of AKT when AKT is in its inactive conformation, preventing membrane recruitment and activation. Because it targets the regulatory PH domain rather than the catalytic kinase domain, it can inhibit both wild-type and E17K mutant AKT. Capivasertib combined with fulvestrant received FDA approval in November 2023 for HR+/HER2− advanced breast cancer with AKT1, PIK3CA, or PTEN pathway alterations who progressed on aromatase inhibitor ± CDK4/6 inhibitor. CAPItello-291 demonstrated a median PFS of 7.3 months versus 3.1 months (HR 0.60) in the biomarker-selected population — a 4.2-month improvement. Key toxicities include hyperglycaemia, rash, and diarrhoea from on-target PI3K pathway inhibition in normal tissues.

Question 6

What is the relationship between AKT and mTOR, and why is it therapeutically relevant?

Accepted Answer

AKT activates mTORC1 by phosphorylating and inactivating the TSC1/TSC2 GAP complex, allowing RHEB-GTP to accumulate and activate mTORC1 at the lysosomal surface. mTORC2 (a separate mTOR complex) reciprocally phosphorylates AKT Ser473 for full AKT activation, creating a positive feedback loop between the two kinases. This bidirectional relationship has a critical therapeutic implication: when mTORC1 is inhibited (by everolimus or rapamycin analogues), the S6K1-driven negative feedback on PI3K is relieved, causing AKT Thr308 hyperphosphorylation. mTORC2 remains active under rapalog treatment, maintaining AKT Ser473 phosphorylation. The net result is that mTORC1 inhibition paradoxically activates AKT, limiting the therapeutic effect — the primary rationale for developing dual PI3K/mTOR inhibitors and AKT inhibitors.

AKT1 Gene Function

Overview

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