Preclinical evaluation of PARP inhibition as a treatment for endometrioid endometrial carcinomas.

Abstract

5065 Background: Loss of function of PTEN is the most common genetic defect in endometroid endometrial carcinomas (EEC). PTEN plays a pivotal role in the regulation of the AKT and mTOR signalling pathways and is reported to be inactivated in up to 80% of EECs. PTEN loss of function has recently been shown to cause genetic instability through defects in homologous recombination (HR) DNA repair of double strand breaks. Cancer cells with defective HR have an exquisite sensitivity to inhibitors of the poly(ADP) ribose polymerase (PARP) inhibitors. Recent data suggest PTEN deficiency may also lead to sensitivity to PARP inhibition. Methods: PTEN expression was tested in a panel of eight EEC cell lines by western blotting. Cells were tested for their ability to elicit phospho-γ-H2AX foci (a marker of induction of DNA damage) and RAD51 foci (a marker of competent HR DNA repair) when challenged with ionising radiation. The sensitivity of these cell lines to the PARP inhibitor KU0058948 was tested in vitro. PTEN was silenced and re-expressed in cell lines by generating stably transfected cell lines with either two short hairpin-RNAs against PTEN or with a pBABE retroviral PTEN expression vector, respectively. Results: Out of the 8 EEC cell lines, two cell lines expressed PTEN (Hec-1b, EFE-184). ECC cells lacking PTEN expression (Nou-1, Ishikawa, RL95-2, EN, AN3-CA, Hec-59) were unable to elicit HR DNA repair. PTEN deficient EEC cells showed a significantly greater sensitivity to KU0058948 than PTEN wild-type EEC cells (IC50 10−8M vs 10−4M, respectively). PTEN silencing in Hec-1b cells resulted in a reduced RAD51 foci formation and in increased sensitivity to PARP inhibition. PTEN re-expression in Ishikawa and Nou-1 cells resulted in enhanced RAD51 foci formation and in a lower sensitivity to KU0058948. Conclusions: Given that most EECs lack PTEN expression and that EEC cell lines lacking PTEN expression show an exquisite sensitivity to KU0058948, our results suggest that PARP inhibitors may constitute a novel therapeutic approach for the majority of EECs. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Merck Merck AstraZeneca, Pfizer AstraZeneca