A-ring analogs of Andrographolide inhibit wnt1 signaling and exhibit potent anticancer activity in breast and colorectal cancer models

The natural product andrographolide, a labdane diterpenoid extracted from the plant Andrographis paniculata, has been extensively studied as an anticancer therapeutic, and is putatively known to function through covalent inhibition of NF-kB: a transcription factor at the crossroad of a myriad of cell signaling pathways that modulate tumor survival and metastasis. Functionalization of the C-19 hydroxyl has been shown to alter the primary mode of action from inhibition of NF-kB to modulation of the Wnt/beta-catenin signaling pathway. With a systematic series of 12 silyl and trityl ether analogs of Andrographolide, we evaluated their antiproliferative activity in MDA-MB-231 (triple-negative breast cancer), MCF-7 (metastatic breast adenocarcinoma), HCT-116 (human colorectal carcinoma), and HT-29 (colorectal adenocarcinoma) cell lines. These compounds displayed greater potency than the parent compound, andrographolide. We observe unique potency in HCT-116 with the chloro butyl analog (IC 50 = 0.32μM; 24 hr), and the chloro trityl analog (IC50 = 7.32μM; 24 hr). In MDA-MB-231, the chloro butyl analog exhibits an IC50 of 10.11 μM, and chloro trityl exhibits an IC50 of 2.88 μM. Trityl ether analogs in an NF-kB SEAP reporter cell experiment show inhibition of SEAP expression in a dose dependent fashion. Additionally, upon administration of trityl ether analogs, in a Wnt/beta-catenin reporter cell assay, we observe decreased luciferase expression at 10 μM. After investigating the activities of this series of compounds in connection to NF-κB and beta-catenin inhibition, two putative mechanisms of action previously reported as the cellular targets of andrographolide or its analogs, we find that subtle modifications to C-19 functionalization can greatly affect the in vitro biological profile of these compounds. Notably, the trityl analog displayed significant inhibition of SEAP-coupled NF-κB activity, and diminished antiproliferative activity with coadministration of CHIR99021 compared to the TPS (triphenylsilyl) analog with the only difference being the single substitution of a carbon to a silicon atom. This study underscores the potentially complex polypharmacology of andrographolide and its analogs and highlights the importance of further examination of the lead compounds from this work in other analogous in vitro and in vivo cancer cell models.