Potential mechanism of action of Mifepristone as antitumor treatment in Uveal melanoma

Abstract

Purpose : Mifepristone is an antiglucocorticoid and antiprogesterone drug that has emerged as a promising anti-cancer therapeutic agent. Our laboratory has previously shown mifepristone as a potent growth inhibitor of uveal melanoma (UM) cell lines. However, the mechanism of how mifepristone works on UM cells is still unclear. This work aimed to investigate the receptors possibly responsible for the observed actions of MF on UM.

Methods : Human MP41, MEL270 and OMM2.5 UM cell lines were used to analyze the mRNA expression of progesterone receptor (PR), progestin and adipoQ receptor family member 8 (PAQR8), membrane-associated progesterone receptor component 1 (PGRMC1) and component 2 (PGRMC2), as well as the glucocorticoid receptor, receptor subfamily 3 group C member 1 (NR3C1). β-Actin was used as a reference gene. Gene expression was quantified using SybrGreen-based Real Time PCR. UM cells were exposed to vehicle (DMSO) and IC₅₀ of mifepristone for 72 H. IC₅₀ was detected by the CCK8 assay. RNA was extracted using the RNeasy Plus Micro kit. cDNA was synthetized using iScript. A breast cancer cell line (MCF7) was used as a positive control.

Results : According to gene expression analysis by qPCR, primary MP41 and MEL270 as well as metastatic OMM2.5 cells express the glucocorticoid receptor (NR3C1). UM cells also express the non-classical progesterone receptors: PAQR8, PGRMC1, PGRMC2, while classical nuclear PR appears to be absent. To evaluate the expression of the receptors in the absence and presence of mifepristone, the expression of receptors was quantified after cells were exposed to either vehicle or IC₅₀ concentration of mifepristone (20 uM). We found the expression of NR3C1, PAQR8, PGRMC1, PGRMC2 receptors to be downregulated compared to control conditions. The mRNA levels were normalized using β-Actin.

Conclusions : While non-classical progesterone receptors (PAQR8, PGRMC1 and PGRMC2) and a glucocorticoid receptor (NR3C1) were detected, classical nuclear PR was not found by qPCR in UM cells. Given the lack of PR in UM, the antiproliferative action of mifepristone on UM appears to be independent of classical nuclear PR expression. The cytostatic effect of mifepristone may be through an agonist action of NR3C1 and/or membrane PR such as PGRMC1 and C2. A better understanding of the mechanism of action of mifepristone in UM will help determine its therapeutic potential.

This is a 2021 ARVO Annual Meeting abstract.