Epigenetic activation of HORMAD1 in basal-like breast cancer: role in Rucaparib sensitivity
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Xian Wang1,2,3,4,*, Ying Tan3,4,*, Xixi Cao3,4, Jin Ah Kim3,4, Tianmeng Chen1,2, Yiheng Hu1,2, Matthew Wexler1,2 and Xiaosong Wang1,2,3,4
1UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA 15232, USA
2Department of Pathology, University of Pittsburgh, PA 15232, USA
3Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, TX 77030, USA
4Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, TX 77030, USA
*These authors contributed equally to this work
Xiaosong Wang, email: email@example.com
Keywords: HORMAD1; PARP inhibitor; basal-like breast cancer; xenograft
Received: May 13, 2018 Accepted: June 22, 2018 Published: July 10, 2018
Basal-like breast cancer (BLBC) is an aggressive breast cancer subtype with features similar to the basal cells surrounding the mammary ducts. Treatment of patients with BLBC has been challenging due to the lack of well-defined molecular targets. Due to the clinical and pathological similarities of BLBC with BRCA-deficient breast cancers, the effectiveness of Poly (ADP-ribose) polymerase inhibitors (PARPi) has been tested in early phase clinical trials for patients with advanced BLBC, with limited clinical responses. Recently, it was reported that HORMAD1 overexpression sensitizes BLBC to HR-targeting agents by suppressing homologous recombination. Our independent analysis suggests that HORMAD1 is aberrantly overexpressed in about 80% of BLBC, and its expression in normal tissues is restricted to testis. Our experimental data suggests that HORMAD1 overexpression correlates with focal hypomethylation in BLBC. On the other hand, investigation of the Genomics of Drug Sensitivity in Cancer dataset revealed significantly reduced sensitivity of HORMAD1-overexpressing BLBC cell lines to Rucaparib, a commonly used PARPi. To further assess the role of HORMAD1 in PARPi sensitivity, we generated three HORMAD1-overexpressing xenograft models using the HORMAD1-low BLBC cell lines HCC1954, HCC1806, and BT20; we then subjected these xenograft models to Rucaparib treatment. Ectopic expression of HORMAD1 enhances tumor formations in two of these models, and significantly reduces sensitivity to Rucaparib in the HCC1954 model. Taken together, our data suggest that epigenetic activation of HORMAD1 by hypomethylation in BLBC may endow reduced sensitivity to Rucaparib treatment in some tumor models.
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