PI3K/Akt pathway regulates essential cellular processes and is involved in pathogenesis of several human cancers.
The aim of this study was to evaluate the dysregulation of the PI3K/Akt pathway in breast cancer to clarify its role in cancer cell sensitivity to chemotherapy and in prognosis of node-negative breast cancer patients.
The involvement of the PI3K/Akt pathway in breast cancer cell response to chemotherapy was investigated in MDA-MB-435S and MCF-7 breast cancer cell lines with a different p53 gene status. Drug treatments were associated with a decrease in cell viability and apoptosis induction. Notably, p53mut MDA-MB-435S cells were more sensitive to Gemcitabine, Paclitaxel, and Epirubicin-induced apoptosis than p53wt MCF-7 cells.
Drug treatments induced a strong and significant Akt activation. The appearance of the apoptotic phenotype was associated with a decrease in the expression of phosphorylated and active Akt (pAkt), whereas high pAkt levels were kept in resistant cells, which showed a recovery of their proliferative activity after the release in a drug-free medium.
To assess whether the inhibition of the PI3K/Akt pathway could increase the efficacy of chemotherapy in breast cancer cells, cells were treated with the chemotherapeutic drugs in association with the PI3K inhibitor LY294002 and/or the mTOR inhibitor Rapamycin. LY294002 effectively inhibited the PI3K/Akt pathway, but seemed to antagonize Epirubicin, Gemcitabine, and Paclitaxel efficacy. On the other hand, Rapamycin has been shown to sensitize to chemotherapy the apoptosis resistant MCF-7 cells. These data show that Akt kinase plays a key role in the breast cancer cell resistance to chemotherapy and that Rapamycin in association with the conventional chemotherapy could increase the sensitivity of resistant breast cancer cells, whereas LY294002 could undermine the success of the therapy with drugs showing a cell cycle phase-specificity.
As to the second part of this research project, the prognostic value of the PI3K/Akt pathway was evaluated in a series of 72 node-negative breast cancer patients with a mean follow-up of 10 years. The expression of pAkt and PTEN was investigated by immunohistochemistry and the results were correlated with the main clinico-pathological and biological markers and with the disease free survival (DFS).
No statistical association was found between pAkt or PTEN and the main clinico-pathological and biological markers, although PTEN expression was significantly associated with the absence of disease recurrence, supporting an important role of PTEN tumor suppressor gene in breast cancer progression. Moreover, a statistically significant correlation was found between pAkt or PTEN expression and their downstream targets cyclin D1 and/or p27Kip1 that are involved in cell proliferation control.
Survival analysis showed a highly significant correlation between a decreased DFS and the dysregulated expression of pAkt, PTEN, p27Kip1, and the tumor proliferation assessed by Ki67 expression. Moreover, multivariate analysis using the Cox proportional-hazards regression model showed that PTEN and Ki67 are independent predictor factor of disease recurrence in node-negative breast cancer patients and that the simultaneous deregulation of both Ki67 and PTEN risk factors strongly increases the risk of disease recurrence. These results show that the dysregulation of key components of the PI3K/Akt pathway, as well as the high Ki67 proliferation index, indicate a more aggressive tumor behaviour and are significantly associated with a decrease in survival and a higher risk of disease recurrence in node-negative breast cancer patients.
In conclusion, the evaluation of the PI3K/Akt pathway status may be considered as a useful tool to identify the patients with a greater potential for the Akt/mTOR inhibition and the high-risk node-negative breast cancer patients who would benefit from adjuvant therapy.