Examination of SMARCA2 re-expression in small cell carcinoma of the ovary, hypercalcemic type with cardiac glycoside treatment
Small-Cell Carcinoma of the Ovary, Hypercalcemic Type (SCCOHT) is a rare and highly aggressive ovarian cancer with a median age of 24 years. SCCOHT is driven by germline or somatic mutation of SMARCA4 and epigenetic loss of expression of SMARCA2, which are two mutually exclusive ATPases of the SWI/SNF complex, and function as tumor suppressor genes (TSGs). Treatment options for this cancer, which include surgical debulking followed by multiagent chemotherapy, remain ineffective, as fewer than 50% of SCCOHT patients will survive to five years. In an effort to identify novel therapeutics in SCCOHT, high-throughput drug screening performed at TGen identified cardiac glycosides as top hits. Previous work has shown that cardiac glycosides target calcium signaling pathways, which results in reactivation of TSGs in cancer through changes in epigenetic regulation at their promoters. We sought to determine whether cardiac glycoside treatment reduces SCCOHT viability through the re-expression of SMARCA2, which is epigenetically silenced in SCCOHT. In addition, we aimed to test MeCP2 cellular relocalization, which was proposed by Raynal et al. as the mechanism for TSG reactivation by cardiac glycosides. To test this hypothesis, BIN67 and HT-1, two SCCOHT cell lines, were treated with two cardiac glycosides: digoxin (clinically approved for heart failure) and proscillaridin A (test compound in vitro). SMARCA2 expression in these cells was examined by reverse transcription and qRT-PCR and Western blot. Our results did not show that SMARCA2 is re-expressed in SCCOHT after a 48 hour treatment. There is still potential for cardiac glycosides to be an effective therapy for SCCOHT patients, although the mechanism still needs to be elucidated.