Discovery of 8,9-seco- ent -Kaurane Diterpenoids as Potential Leads for the Treatment of Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is a lethal malignancy without safe and effective therapeutic drugs. In this study, the anti-TNBC bioassay-guided isolation of the medicinal plant Croton kongensis followed by the structural modification led to the construction of a small ent -kaurane diterpenoid library ( 1 - 25 ). With subsequent biological screening, 20 highly potent compounds (IC ₅₀ s < 3 μM) were identified. Among them, 8,9-seco- ent -kaurane 6 displayed comparable activity (IC ₅₀ s ∼ 80 nM) to doxorubicin but with better selectivity. The analysis of structure-activity relationships suggested that the cleavage of the C8-C9 bond and the presence of α,β-unsaturated ketone moiety were essential for the activity. The mechanistic study revealed that 6 induced apoptosis, autophagy, and metastasis suppression in TNBC cells via inhibition of Akt. In vivo , 6 significantly suppressed the TNBC tumor growth without causing side effects. All these results suggested that 6 may serve as a promising lead for the development of novel anti-TNBC agents in the future.