Abstract PD09-09: The Akt inhibitor MK-2206 is an effective radio-sensitizer of p53 deficient triple negative breast cancer (TNBC) cells.

Abstract

Abstract Purpose: Triple negative breast cancer (TNBC) is an aggressive tumor with a higher locoregional recurrence compared to estrogen receptor (ER) positive breast cancer. Mutations in the PI3K/Akt/mTOR pathway leading to up-regulation of Akt occur with high frequency in TNBC. Hyperactive Akt is associated with increase radiation resistance, mediated through inhibition of apoptosis and up-regulation of DNA damage-induced G2 arrest. p53 plays a key role in mediating G1 cell cycle arrest following genotoxic stress such as radiation; p53-deficient cells however must rely on alternate mechanisms for cell cycle arrest in S- and G2-phases. Inhibition of Akt therefore would be expected to act in a synthetic lethal fashion to radiosensitize p53 deficient TNBC cells by decreasing their ability to arrest in G2. Given that p53 mutations occur in 44% of TNBC this may be an effective strategy for radiosensitizing TNBC. Methods: Experiments were conducted using MDA-MB-468, MDA-MB-231 and SUM 149 cells, all well established models for p53-deficient TNBC. Cells were treated with MK-2206, a potent allosteric Akt inhibitor, alone or in combination with increasing doses of radiation from 0–8 Gy. In vitro studies preformed included; cell survival assays, MTT assay, immunoblot analysis of key proteins, FACS analysis for cell cycle, apoptosis, and gH2AX staining. Results: We found that the combination of IR and Akt inhibition by MK-2206 is synergistic. MK-2206 inhibited both endogenous and radiation-induced Akt activation and phosphorylation of its down-stream targets. Decreased clonogenic survival was seen after 2 or 24 hours pretreatment with MK-2206 as well as decreased viability by MTT assay. Cell cycle analysis demonstrates MK-2206 decreases the proportion of cells in G2/M arrest following irradiation, as well as induced a greater proportion of apoptosis. Evaluation of the DNA damage response pathway demonstrated decreased levels of total DNA-PK, as well as a delayed DNA damage response. Conclusions: These studies demonstrate that targeted inhibition of Akt effectively radiosensitizes p53 deficient TNBC cells lines, possibly through a synthetic lethal effect on the DNA damage response. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD09-09.