Compound X21 (CYP19A1/CYP11B2-IN-1) is a potent dual inhibitor of aromatase (CYP19A1) and aldosterone synthase (CYP11B2), with IC50 values of 2.3 nM and 29 nM, respectively. It exhibits strong antiproliferative and pro-apoptotic effects on cancer cells. Compound X21 is suitable for breast cancer research purposes [1].

CYP19A1/CYP11B2-IN-1 (Compound X21) exhibits time- and concentration-dependent inhibitory effects on the proliferation of MCF-7 and MDA-MB-231 cells when administered at concentrations ranging from 0.001 to 100 μM over a 24-hour period [1]. At a concentration of 700 nM for 24 hours, the compound significantly inhibits phosphorylation of mTOR in MCF-7 cells, negatively regulating the PI3K/Akt/mTOR axis [1]. It does not significantly inhibit hERG and Nav1.5 at concentrations of 20-30 μM, indicating a lack of cardiotoxicity [1]. In cell proliferation assays, the IC50 values were determined as 0.26±0.03 μM for MCF-7 cells and 27.10 ± 5.15 μM for MDA-MB-231 cells, confirming no toxicity to normal cells [1]. Apoptosis analysis revealed an increase in DNA fragmentation in both cell lines at concentrations of 0.35-1 μM and 10-50 μM after 24 hours of treatment, with higher concentrations (>40 μM) enhancing apoptotic signaling in MDA-MB-231 cells [1].