Design, synthesis, and evaluation of phosphorylated rhein derivatives with enhanced antiproliferative activity.

Rhein, a natural anthraquinone, possesses anticancer properties but is hampered by modest potency and poor bioavailability. To overcome these limitations, we synthesized a series of novel phosphonate derivatives of rhein and evaluated their antiproliferative activity across several cancer cell lines. The derivative C9 emerged as the most potent compound against human hepatocellular carcinoma (HepG2) cells, with an IC50 value of 11.88 ± 0.93 μM, representing a 6.5-fold enhancement over the parent compound while maintaining a favorable selectivity index (SI = 8.0) against normal hepatocytes. Mechanistic studies in HepG2 cells showed that C9 inhibited cell migration, induced apoptosis, and arrested the cell cycle at the G2/M phase. To provide a molecular-level rationale for these observations, we employed a dual computational approach. Firstly, molecular dynamics simulations suggested a potential mechanism for enhanced cellular uptake, as C9 appeared to penetrate a model DPPC lipid bilayer more deeply than rhein. Secondly, molecular docking and subsequent ELISA validation supported CDK1, a key G2/M regulator, as a direct intracellular target. C9 treatment led to a significant downregulation of CDK1 protein levels in HepG2 cells. In conclusion, this work presents a successful dual-purpose modification of rhein, where phosphorylation appears to improve its predicted membrane permeability and enhance its inhibitory activity against CDK1, making C9 a promising lead compound for further development as a novel antiproliferative agent.