Proximity ligation assays for isoform-specific Akt activation in breast cancer identify activated Akt1 as a driver of progression.

The PI3K/Akt signal transduction pathway plays an important role in cancer progression and cell survival. Akt activation is associated with poor outcome in endocrine-treated breast cancer, whereas high levels of cytoplasmic Akt2 are associated with an improved overall survival. Proximity ligation assays (PLAs) were used to determine quantitative expression levels of isoform-specific activation (phosphorylation) of Akt1 and Akt2 in formalin-fixed, paraffin-embedded cell lines and breast cancer tumour tissues in situ. PLAs demonstrated a range of expression in breast cancer samples for total pAkt1 and pAkt2. High levels of pAkt1 were associated with reduced DRFS (HR: 1.45, 95% CI 1.14-1.83, p = 0.002) and OS (HR: 1.42, 95% CI 1.10-1.83, p = 0.007). When PLA results were combined, patients that had high levels of pAkt1 only had a significantly decreased DRFS (HR: 1.92, 95% CI 1.34-2.76, p = 0.005) and OS (HR: 1.94, 95% CI 1.32-2.86, p = 0.008) compared to other patients. Using PLAs to discriminate activation of Akt1 versus Akt2 suggests that Akt1 drives progression in early breast cancers. In cases where both Akt1/Akt2 are activated, Akt2 may act to reverse this effect. Using PLAs, we have measured activation of Akt1 and Akt2 proteins separately in situ in FFPE breast cancer samples.