Synthesis, antiproliferative activity, and biological profiling of C-19 trityl and silyl ether andrographolide analogs in colon cancer and breast cancer cells

Andrographolide, a labdane diterpenoid isolated from Andrographis paniculata, putatively functions through covalent inhibition of NF-κB, a transcription factor that modulates tumor survival and metastasis. Previous studies have found that functionalization of the C-19 hydroxyl alters the primary mode of action from inhibition of NF-κB to the modulation of the Wnt1/β-catenin signaling pathway. Here, we synthesized a series of twelve C-19 trityl and silyl ether analogs, including three novel substituted trityl analogs and four novel substituted silyl analogs of andrographolide. MTT assays revealed cell line selectivity between colorectal and breast cancer cells, which is consistent with known mechanisms of β-catenin-driven cell proliferation in colorectal cancer cell lines. Most compounds exhibited cell line specific antiproliferative activity in HCT-116 and HT-29 colorectal cancer cell lines. Specifically, within 24 h, C-19 analogs of andrographolide exhibit far more limited antiproliferative activity in MCF-7 breast cancer cells compared to HCT-116, HT-29, and MDA-MB-231 cells. Through in vitro TNF-α-dependent NF-κB reporter and Wnt1-dependent luciferase reporter assays, we observed that several analogs generally exhibit greater inhibitory activity compared to andrographolide. Fluorescence imaging demonstrated that cells treated with andrographolide and its C-19 analogs retained similar distributions of active β-catenin, but notable differences in antiproliferative potency upon co-delivery with GSK-3β inhibitor CHIR99021 indicate that several lead compounds exhibit attenuated biological activity selectively in HT-29 cells. Collectively, this work indicates that modest structural modifications at C-19 of andrographolide can have profound implications for its biological activity in mechanisms connected to its anticancer activity.