Mifepristone is indeed recognized as a leading progesterone receptor blocker. For further information on selective progesterone receptor modulators, the following publications may provide useful references:
1. Climacteric. 2018 Aug;21(4):375-379. doi: 10.1080/13697137.2017.1386650. Epub 2018 Jan 17. Titled "Selective progesterone receptor modulators: current applications and perspectives" PMID: 29338440
2. Curr Opin Investig Drugs. 2006 Oct;7(10):882-90. Titled "Progesterone receptor antagonists" PMID: 17086932
While our lab has not tested this compound on chondrocytes, a publication on the use of mifepristone on chondrocytes may be of interest:
Growth Horm IGF Res. 2008 Dec;18(6):497-505. doi: 10.1016/j.ghir.2008.04.004. Epub 2008 Jun 2. Titled "IGF-I and not IGF-II expression is regulated by glucocorticoids in human fetal epiphyseal chondrocytes" PMID: 18515166