LL-K12-18 is a CDK12 kinase inhibitor and a dual-site molecular glue. LL-K12-18 inhibits human CDK12 with an IC50 value of 283.9 nM, and selectively degrades cyclin K via the ubiquitin-proteasome system by stabilizing the CDK12-DDB1 complex. LL-K12-18 downregulates DNA damage response genes, reduces the phosphorylation level of CTD Ser2 in RNA polymerase II, and modulates biomarkers such as ATM, RAD51, gamma-H2AX and cleaved PARP, thereby effectively inducing apoptosis and inhibiting proliferation of breast cancer cells. LL-K12-18 exhibits high target selectivity and serves as a research tool for studies on triple-negative breast cancer[1][2].