Synthesis and cytotoxic activity of madecassic acid–silybin conjugate compounds in liver cancer cells†

A series of 14 conjugates of 2α,3β,23-triacetyl-madecassic acid and silybin were designed and synthesized. The madecassic acid unit was linked to silybin either directly at position C-7 or C-3; or through an amino acid linker (glycine, β-alanine, or 11-aminoundecanoic acid) at position C-3. The conjugates were tested in vitro for their cytotoxic effect on HepG2 cells using the MTT assay. The results confirmed that the conjugated compounds demonstrated a stronger cytotoxic effect compared to the parent compounds. Of these compounds, the most promising conjugate, compound 8, was evaluated for cytotoxic activity in the additional Hep3B, Huh7, and Huh7R human hepatocellular carcinoma cell lines and also for cell cycle changes and induction of apoptosis in HepG2 cells. This compound caused a rapid and significant induction of caspase 3 activity and induced cell cycle arrest in the S phase – effects distinct from the activity of madecassic acid. This is the first study on the synthesis and cytotoxicity of madecassic acid–silybin conjugates, and of their testing against liver cancer cell lines and provides evidence for a distinct biological profile versus madecassic acid alone.