SY-5609 (CDK7-IN-3) is a selective non-covalent CDK7 inhibitor (Kd value is 0.07 nM), with weak inhibitory activity against CDK2, CDK9 and CDK12 with IC50 values ​​of 5.5, 1.9 and 1.7 μM, respectively, and has anti-tumor activity and inhibits cell apoptosis.

CDK12:870 nM (Ki), CDK7:0.065 nM (Kd), CDK9:960 nM (Ki), CDK2:2600 nM (Ki)

METHODS: HCC70 cells were treated with SY-5609 （CDK7-IN-3） (25, 50, 100, 250, 500 nM), and protein samples were collected at 6, 24 and 48 h after treatment. Immunoblotting was used to detect the protein levels of Phospho-CDK2 T160, total CDK2, c-MYC, MCL1, cyclinB1, RNAPII Ser5 phosphorylation and total RNAPII; HCC70, MDA-MB-468, CAOV3, OVCAR3 and HDF cells were treated with SY-5609 （CDK7-IN-3） (100, 250, 500 nM) for 48 and 72 h, and Annexin V-FITC and propidium iodide (PI) were used to detect cell apoptosis.
RESULTS Treatment of HCC70 cells with SY-5609 （CDK7-IN-3） for 24 and 48 hours inhibited phosphorylation of CDK2 at Thr160 by loss of CAK function; inhibition of CDK7 in TFIIH resulted in reduced phosphorylation of Ser5 in the C-terminal heptad repeat of RNA polymerase II and decreased cMyc levels; SY-5609 （CDK7-IN-3） treatment resulted in a mild reduction in MCL1 protein only at 48 h; SY-5609 （CDK7-IN-3） induced apoptosis and cell cycle arrest at G2/M in multiple cancer cell lines at 48 and 72 h, as detected by Annexin V/PI staining, but not in primary fibroblast cell lines. [1]

METHODS: SY-5609 (CDK7-IN-3) (2 mg/kg, orally, once daily, for 21 days) was administered to HCC70 cell line-derived xenograft models, and tumor volume and body weight were measured twice weekly. One-tailed t test was used to evaluate the significance of the anti-tumor effect of SY-5609 (CDK7-IN-3).
RESULTS The plasma exposure in mice treated with SY-5609 (CDK7-IN-3) was 261.28 ng h/mL, Cmax was 50.67 ng/mL (103 nM), and the elimination half-life was 3.33 h. During the 21-day dosing period, the tumor regressed and was well tolerated, with no tumor regrowth on day 28. [1]