Exploring Derivatives of Quinolizidine Alkaloid Sophoridine in the Design and Biological Mechanistic Evaluation of Histone Deacetylase Inhibitors against Triple‐Negative Breast Cancer

As a critical epigenetic modulator of gene expression, histone deacetylases (HDACs) have been involved in the pathogenesis and therapeutic investigation of cancer. Quinolizidine alkaloid sophoridine is known to have anticancer efficacy but with limited indication. By incorporating the pharmacophore of the HDAC inhibitor into the ring‐opened sophoridine core, a new series of sophoridine hydroxamic acid derivatives were synthesized. After structure‐activity studies, a selected compound was found to exert significant cytotoxicity in triple‐negative breast cancer CAL‐51 cells (IC50 1.17 μM), and demonstrated low nanomolar inhibitory potency toward HDAC1/3/6. Cellular functional assays indicated that this compound was able to induce apoptosis and cause accumulation of cells in the S phase of the cell cycle. Western blot analysis revealed it to decrease the expression of DNMT1, DNMT3a and DNMT3b by down‐regulating phosphor‐ERK1/2. Furthermore, treatment with this compound proved to block the PI3K/AKT/mTOR signaling in the PI3KCA and PTEN‐mutant CAL‐51 cells. Collectively, this work provides a novel lead compound for the development of potential therapeutics against triple‐negative breast cancers, possibly mesenchymal‐like subtype. By incorporating the pharmacophore of an HDAC inhibitor into the ring‐opened core of sophoridine, a new series of sophoridine hydroxamates were synthesized. Compound 11 g was found to exert significant cytotoxicity in triple‐negative breast cancer CAL‐51 cells (IC50 1.17 μM), and demonstrated low nanomolar IC50 values toward HDAC1/3/6. This work provides a novel lead for the development of potential therapeutics against triple‐negative breast cancers.