Abstract 6500: Synergistic suppression of hepatocellular carcinoma cancer stem cells by combined curcumin and PLK1 inhibition

Abstract Background: Hepatocellular carcinoma (HCC) is highly aggressive due to frequent recurrence, chemoresistance, and the persistence of cancer stem cells (CSCs). CSCs exhibit strong self-renewal, tumor-initiating capacity, and resistance to standard therapies, making them key therapeutic targets. Curcumin, a bioactive compound from Curcuma longa, has antitumor effects but limited potency. Polo-like kinase 1 (PLK1), a critical mitotic regulator often overexpressed in HCC, supports CSC survival. PLK1 inhibition (PLK1i) has emerged as a promising strategy to disrupt CSC maintenance. This study evaluates the synergistic effects of combining curcumin with a PLK1 inhibitor to target HCC CSCs. Methods: CSCs derived from HepG2, Hep3B, and Huh7 cells were enriched through serum-free sphere culture and validated by elevated stemness markers and enhanced tumorigenicity in limiting-dilution xenograft assays. CSC spheres were treated with curcumin, the selective PLK1 inhibitor volasertib, or the combination. Sphere formation, CSC-related gene expression, cell-cycle status, DNA damage, and apoptosis were assessed. Combination treatment was further tested in vivo on tumors derived from HepG2 and Huh7 CSCs. Results: Curcumin alone moderately reduced CSC properties, consistent with its known tumor-suppressive but limited effects. PLK1 inhibition more strongly impaired CSC viability and self-renewal, yet the curcumin-PLK1i combination produced a pronounced synergistic reduction in CSC activity. The combined treatment markedly downregulated stemness factors Oct4, Sox2, Nanog, and the CSC marker CD133, and it suppressed spheroid formation more effectively than either monotherapy. Mechanistically, the combination induced robust G2/M arrest, surpassing individual treatments, and led to substantial DNA-damage accumulation, evidenced by increased gH2AX foci and protein levels. Co-treatment also elicited stronger activation of intrinsic apoptotic pathways, including caspase-9/3/7 and PARP cleavage. By impairing mitotic progression and exacerbating genomic instability, the combination heightened apoptosis and reduced CSC survival. In vivo, PLK1i-curcumin produced far greater tumor regression than either agent alone, accompanied by decreased Ki67 and increased gH2AX and cleaved caspase-3 in immunohistochemistry. Conclusion: The combined use of curcumin and PLK1i exerts a powerful synergistic effect in suppressing hepatocellular carcinoma CSCs in vitro and in vivo. These findings support a promising therapeutic strategy integrating a traditional medicine-derived compound with a targeted inhibitor and warrant further preclinical and clinical development. Citation Format: Yue Wang. Synergistic suppression of hepatocellular carcinoma cancer stem cells by combined curcumin and PLK1 inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6500.