Abstract 6074: Resistance to MK-0752 alters Notch activity and expression of stemness markers in uterine leiomyosarcoma cell lines
Authors: Abedin Yasmin , Alpert Emily , Rego Erica , Larios Karla , Cheung Emma , Gabrilovich Sofia , Zhao Qingshi , Einstein Mark H. , Douglas Nataki 
Published: June 2022

Abstract
Introduction: Uterine leiomyosarcoma (uLMS) is a rare tumor with poor survival and few therapeutic options. The Notch pathway is evolutionarily conserved, is active in uterine processes, has oncogenic properties in many cancers, but has not been well studied in uLMS. Cancer stem cells (CSC) are subpopulations of cancer cells that are treatment resistant. In certain tumors, activation of canonical Notch signaling, via gamma secretase, supports CSC survival and the acquisition of chemoresistance. Our objective is to identify and characterize the subpopulation of uLMS cells that are viable after treatment with the half maximal inhibitory concentration (IC50) of MK-0752, a gamma secretase inhibitor (GSI) in phase I trials. We will determine Notch signaling activity and expression of markers associated with stem-like potential in GSI resistant uLMS cells.
Methods: MTT assays were performed on SK-LMS-1 and SK-UT-1B, two uLMS cell lines, to identify the IC50 for MK-0752. Cells were exposed to MK-0752 at the IC50 or DMSO (control) for 24 hours and viable cells were collected. First, expression of stemness markers, CD133, cMYC and SOX2, in uLMS cells was compared to human uterine smooth muscle cells (hUT-SMC) at baseline. After treatment with MK-0752, the remaining subpopulations of resistant uLMS cells were evaluated for Notch signaling activity by expression of HES1. Stemness marker expression was also assessed. Gene expression was measured with qRT-PCR. Mean fold change (FC) gene expression was determined by FC experimental divided by FC control, relative to expression of 18S rRNA. P≤0.05 was considered significant.
Results: In untreated uLMS cells, expression of CD133 and c-MYC was significantly higher in SK-LMS-1 (fibroblast morphology) vs hUT-SMC, while expression of CD133 and SOX2 was significantly higher in SK-UT-1B (epithelial morphology) vs hUT-SMC. After treatment with MK-0752 at IC50 (427.4 µM for SK-LMS-1 or 128.4µM for SK-UT-1B) expression of HES1 was decreased in SK-LMS-1 (0.35x, p≤0.05) and increased in SK-UT-1B (2.38x, p≤0.01) in treatment resistant, viable cells as compared to untreated cells. Expression of c-MYC was decreased (0.38x, p≤0.01) and CD133 was similar (1.64x, p&gt;0.05) in GSI resistant SK-LMS-1 cells, while expression of CD133 and SOX2 was similar (1.43x and 1.30x, respectively, p&gt;0.05) in GSI resistant SK-UT-1B cells compared to untreated cells.
Conclusions: Cellular morphology, Notch signaling activity and expression of stemness markers differs in GSI resistant SK-LMS-1 compared to GSI resistant SK-UT-1B cells. The subpopulation of MK-0752 resistant SK-LMS-1 cells have reduced Notch activity and reduced expression of stemness marker, c-MYC, while the resistant SK-UT-1B cells have increased Notch activity. Further studies are required to identify additional factors associated with uLMS resistance to GSIs and the importance of this heterogeneity of uLMS in vivo.
Citation Format: Yasmin Abedin, Emily Alpert, Erica Rego, Karla Larios, Emma Cheung, Sofia Gabrilovich, Qingshi Zhao, Mark H. Einstein, Nataki Douglas. Resistance to MK-0752 alters Notch activity and expression of stemness markers in uterine leiomyosarcoma cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6074.