Synthesis of novel derivatives from machilin C/D as antiproliferative agents against triple negative breast cancer

Abstract

Lignans are small polyphenolic compounds that play an active role in plant defense against pathogens and predators. Recently, lignan machilin D was reported to be effective as an anti-tumorigenic agent in triple negative breast cancer (TNBC) tumor-bearing mice. Previous studies have relied on plant-extracted material limiting scalability and diversification of the natural scaffold. Herein, we describe a generalizable one-pot synthesis of machilin D and its derivatives via an iron chloride-induced dimerization of isoeugenol. Employing this synthetic methodology allowed for a robust diversification campaign to access seven (7) new lignan derivatives of the machilin D family with superior anti-proliferative properties in 2D and 3D TNBC models. Overall, this work enables lignan natural product-based drug discovery as a platform to identify new probes to elucidate lignan targets in biology and therapeutics for aggressive cancers such as TNBC.

Keywords: Antiproliferatives; Dehydrodiisoeugenol; Iron chloride; Isoeugenol; Licarin A; Lignans; Machilin C; Machilin D; Machilus thunbergii; Natural products; Saururus chinensis; Traditional Chinese medicine; Triple negative breast cancer.

Fig. 1.

(A) Structures of machilin C&D. May also present as [R,S] and [R,R], respectively. (B) Photographs of common machilin C&D sources: Saururus chinensis (left) [36] and Machilus thunbergii (right) [37].

Fig. 2.. Synthesis of lignan derivatives of machilin C/D.

(A) Synthetic scheme for dimerization of isoeugenol to produce compounds 1–8. (B) Functional groups specific to compounds 1–8, labeled as such.

Fig. 3.. Cell viability of machilin C/D derivatives.

(A) IC₅₀ (±SEM) values as calculated by MTT assay in three TNBC cell lines. Cisplatin used at positive control. (B) Comparison chart of IC₅₀ values for compounds 1–8 and positive control cisplatin. (C) Comparison of IC₅₀ values for compounds 7A and 7B in three TNBC cell lines (***P = 0.003, ****P < 0.0001). (D) Selectivity study of compound 7A in TNBC cell lines and normal cell line (HEK293).

Fig. 4.

(A) Clonogenic assay images in triplicate. (B) Select mammosphere images taken over period of 6 days. (C) Summary of Cell Cycle Assay using compound 7A at 22 μm (16, 24, 48 h). (D) Representative apoptosis charts of control and treated sample (7A at 22 μm) at 24 h. Full chart summary in supporting information. (E) Summary of Apoptosis Assay results using compound 7A at 22 μm (24 h).

Scheme 1.

Mechanism of iron(III) chloride dimerization of isoeugenol. Top route leads to recognized product dehydrodiisoeugenol (licarin A). Bottom route is proposed mechanism for formation of machilin C&D. Image created in ChemDraw.