Skp2-IN-4 is an Skp2 inhibitor with an IC50 of 0.38 μM for Skp2-Cks1 binding. It enhances antitumor activity by targeting Skp2, inhibiting tumor proliferation, and inducing S phase cell arrest. Skp2-IN-4 also significantly boosts chemosensitivity to Cisplatin in the NCl-H1299 xenograft mouse model by inhibiting tumor cell stemness, presenting potential for lung and esophageal cancer research.

Skp2-IN-4 (Compound 10 h) is an effective inhibitor of tumor activity, demonstrating IC50 values of 11.24 μM against lung cancer cells NCl-H1299 and 10.32 μM against esophageal cancer cells KYSE-510. At a temperature range of 57-68 °C, Skp2-IN-4 (4 h) enhances the stability of the Skp2 protein and disrupts its interaction with Cks1 in KYSE-510 and NCl-H1299 cells. It inhibits cell colony formation and DNA synthesis in a dose-dependent manner at concentrations of 2.5-10 μM over 1-10 days in these cells. Skp2-IN-4 at 5-15 μM for 48 hours reduces Skp2 expression, induces accumulation of its substrates (p21 and p27) causing S phase cell cycle arrest, with more pronounced effects at 10 μM. Co-administration of Skp2-IN-4 (10 μM, 48 hours) with Cisplatin markedly suppresses sphere and colony formation in NCl-H1299 cells, induces G2/M phase arrest and apoptosis, and inhibits the protein levels of CD44, Nanog, OCT4, and SOX2 (cancer stem cell markers).

Skp2-IN-4 (Compound 10 h) administered orally at 25 mg/kg every other day for 20 days can enhance the chemosensitivity of NCl-H1299 cells to Cisplatin in an NCl-H1299 xenograft mouse model, effectively inhibiting tumor growth.