Hsp90-Cdc37-IN-4 is a novel derivative of triptolide that inhibits the protein-protein interaction (PPI) between Hsp90 and Cdc37. It selectively inhibits casein kinase 2 (CK 2), reducing the phosphorylation of its substrate Cdc37 at the serine 13 site. Additionally, Hsp90-Cdc37-IN-4 induces cell cycle arrest in the G0/G1 phase and triggers apoptosis via the mitochondrial pathway. This compound exhibits significant anti-breast cancer activity.

Hsp90-Cdc37-IN-4 (Compound 11) exhibits antiproliferative effects on five human cancer cell lines, with IC50 values of 0.21 μM (MBGC-23), 0.27 μM (HOS), 0.33 μM (HCT-116), 0.43 μM (MCF-7), and 0.25 μM (MDA-MB-231) over a 48-hour period. At concentrations of 0.5-8.0 μM over 2 hours, it strongly inhibits CK2α1. When administered at 0.2-0.8 μM for 24 hours, Hsp90-Cdc37-IN-4 reduces levels of p-Cdc37 (Serine 13) and p-Akt (Serine 129) in MDA-MB-231 cells, indicating suppression of intracellular CK2 activity and concentration-dependent inhibition of Cdc37 phosphorylation. In addition, at 0.15-0.6 μM over 24 hours, it induces G0/G1 phase cell cycle arrest in MDA-MB-231 cells in a concentration-dependent manner. Lastly, at 0.2 μM for 24 hours, it induces apoptosis in MDA-MB-231 cells by inhibiting the Hsp90-Cdc37 cycle.

Hsp90-Cdc37-IN-4 (1 mg/kg, administered via intraperitoneal injection once daily for 21 days) demonstrates significant antitumor activity in the MDA-MB-231 xenograft mouse model.