SPEN-IN-1 (compound X1) is a selective inhibitor of the SPEN protein factor, with a dissociation constant (K d) of 47 nM. It specifically targets RepA, a 431-nucleotide domain within Xist (a non-coding RNA prototype), characterized by 8.5 repeats of a GC-rich motif instrumental in gene silencing [1].

SPEN-IN-1 (0-100 μM) inhibits RepA-PRC2 and RepA-SPEN with IC50 values of 30 μM and 48 μM, respectively, and inhibits RepA, PRC2, and SPEN with Kd values of 400 nM, 47 nM, and 420 nM, respectively [1]. SPEN-IN-1 selectively disrupts the interaction between Xist and homologous proteins both in vitro and in cells and markedly suppresses the accumulation of H3K27me3 and PRC2 [1].

SPEN-IN-1 reduces the in vivo interaction of RepA-SPEN [1].