Objective: Uterine carcinosarcoma (UCS) is an aggressive malignancy, making up less than 5% of uterine cancers. Pharmacologic inhibition of ATR kinase synergistically enhances the ability of cisplatin to kill carcinoma cells of many solid tumor types and is further enhanced in ATM low carcinoma cells. It is unknown whether ATR inhibition (ATRi) offers a therapeutic opportunity in UCS. The goal of this study was to evaluate ATM expression in UCS tumors and determine the response of an ATM low UCS model to ATRi + cisplatin combination.

Methods: ATM expression was evaluated in full tissue sections from 74 UCS tumors by immunohistochemistry (IHC) with an ATM specific monoclonal antibody (clone Y170, Abcam), and was categorized as negative vs any positive staining in the carcinomatous (C) vs sarcomatous (S) components. In vitro models of UCS: SK-UT-1, SK-UT-1B, KLE, and RL95-2 cell lines were treated with an ATRi (AZD6738), cisplatin, and ATRi + cisplatin. ATM low models were generated in RL95-2 cells using short hairpin RNA (shRNA) lentivirus targeting ATM and a non-target control. Cells were subjected to cisplatin and ATRi dose response analyses.

Results: Negative IHC expression of ATM protein was observed in 24% of the C vs 31% of the S components of the 74 UCS cases (Table 1). ATRi increased the sensitivity of uterine carcinosarcoma cell line models to cisplatin. Western blot confirmed a 57% knockdown in ATM in RL95-2 cells infected with shRNA for ATM and treatment with ATRi +cisplatin therapy showed ~20% increase in cell death in ATM low vs control cells lines, p=0.02.

Conclusions: IHC analyses of UCS tumors showed an average of ~27% of tumors have loss of ATM in C and S components. Preliminary evidence shows that ATRi increases the sensitivity of UCS cell models to cisplatin therapy, which is further increased in ATM low uterine carcinoma cells. These findings suggest a novel therapeutic opportunity for ATRi + cisplatin therapy in UCS patients with low ATM expressing tumors.

Immunohistochemistry-based quantification of ATM expression in uterine carcinosarcoma tumors

ATM  Uterine Carcinosarcoma 
Intensity Carcinomatous Component Sarcomatous component 
0-1 31 (41.9%) 33 (44.6%) 
 18 (24.3%) 23 (31.1%) 
 13 (17.6%) 10 (13.5%) 
2-3 43 (58.1%) 41 (55.4%) 
 11 (14.9%) 10 (13.5%) 
 32 (43.2%) 31 (41.9%) 
TOTAL 74 74 
ATM  Uterine Carcinosarcoma 
Intensity Carcinomatous Component Sarcomatous component 
0-1 31 (41.9%) 33 (44.6%) 
 18 (24.3%) 23 (31.1%) 
 13 (17.6%) 10 (13.5%) 
2-3 43 (58.1%) 41 (55.4%) 
 11 (14.9%) 10 (13.5%) 
 32 (43.2%) 31 (41.9%) 
TOTAL 74 74 

Citation Format: Emily R. Penick, Paulette Mhawech-Fauceglia, Nicholas Bateman, Kelly Conrads, Tracy Litzi, Chunqiao Tian, Chad A. Hamilton, Kathleen Darcy, George Maxwell, Thomas Conrads. Inhibition of the ATR kinase enhances therapeutic efficacy of cisplatin in ATM low uterine carcinosarcoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2359. doi:10.1158/1538-7445.AM2017-2359