Towards the mode of action of Strobilanthes crispus through integrated computational and experimental analyses
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Bioactive sub-fractions from the tropical herbal plant Strobilanthes crispus (S. crispus) has been shown to induce apoptosis of breast cancer cells in vitro and reduce tumor size in vivo by our earlier studies. We have recently isolated five major compounds from S. crispus sub-fraction, namely lutein, β-sitosterol, campesterol, stigmasterol and pheophytin a. In this study, we set out to investigate each compound’s protein targets and mechanism of action through prediction of protein targets via a ligand-based target prediction protocol, Prediction IncluDinG INactives, and radioligand binding assays. The three phytosterol molecules (β-sitosterol, campesterol, stigmasterol) showed enrichment of hormone signaling GO terms [average ratio (AR) <0.01], while the SMAD signaling pathway was associated with pheophytin a (AR < 0.01). GO terms associated with retinoic acid receptor (RAR) and retinoid X receptor (RXR) were distinctly represented by protein targets of lutein (AR < 0.01). All members of the RAR/RXR family of proteins were predicted to be targeted by lutein, a feature that was not present in the other four S. crispus-derived compounds. Radioligand binding assay in vitro validated that lutein showed higher binding affinity with RXRα (IC50: 5.74 µM; Ki: 4.55 µM) than RARα (IC50: 25.1 µM; Ki: 14 µM). Molecular docking analysis demonstrated that lutein could occupy a large hydrophobic cavity of the hRXRα-LBP crystal structure mainly through hydrophobic interactions with leucine and isoleucine residues, and also hydrogen bond between a hydroxyl group of lutein with Glu239. Our findings suggest that lutein-RXRα interaction might play a role in the anti-breast cancer effects rendered by S. crispus.
KeywordsStrobilanthes crispus PIDGIN Phytosterol Pheophytin a Lutein RAR/RXR
Prediction IncluDinG INactives
Retinoic acid receptor alpha
Retinoid X receptor alpha
This work was supported by Universiti Sains Malaysia research (1001/PPSP/853002) and travel grants (1001/JPNP/AUPRM006) awarded to NSY and KKW, respectively. LHM would like to thank BBSRC and AstraZeneca, and for their funding.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Atigadda VR et al (2003) Conformationally defined retinoic acid analogues. 5. Large-scale synthesis and mammary cancer chemopreventive activity for (2E,4E,6Z,8E)-8-(3′,4′-dihydro-1′(2′H)-naphthalen-1′-ylidene)-3,7-dimethyl-2,4,6- octatrienoic acid (9cUAB30). J Med Chem 46:3766–3769CrossRefPubMedGoogle Scholar
- ChemAxon Standardizer (2015) https://www.chemaxon.com/products/standardizer/. Accessed 7 Sep 2015
- Mohamad Zobir SZ, Mohd Fauzi F, Liggi S, Drakakis G, Fu X, Fan TP, Bender A (2016) Global mapping of traditional chinese medicine into bioactivity space and pathways annotation improves mechanistic understanding and discovers relationships between therapeutic action (Sub) classes. Evid Based Complement Alternat Med 2016:2106465CrossRefPubMedPubMedCentralGoogle Scholar
- Nurraihana H, Norfarizan-Hanoon NA (2013) Phytochemistry, pharmacology and toxicology properties of Strobilanthes crispus. Int Food Res J 20:2045–2056Google Scholar
- Pedregosa F et al (2011) Scikit-learn: machine learning in Python. J Mach Learn Res 12:2825–2830Google Scholar
- RDKit: Open-Source Cheminformatics Software (2015) http://www.rdkit.org. Accessed 7 September 2015
- Reynoso-Camacho R, Gonzalez-Jasso E, Ferriz-Martinez R, Villalon-Corona B, Loarca-Pina GF, Salgado LM, Ramos-Gomez M (2011) Dietary supplementation of lutein reduces colon carcinogenesis in DMH-treated rats by modulating K-ras, PKB, and beta-catenin proteins. Nutr Cancer 63:39–45PubMedGoogle Scholar
- Tanaka T, Suh KS, Lo AM, De Luca LM (2007) p21WAF1/CIP1 is a common transcriptional target of retinoid receptors: pleiotropic regulatory mechanism through retinoic acid receptor (RAR)/retinoid X receptor (RXR) heterodimer and RXR/RXR homodimer. J Biol Chem 282:29987–29997CrossRefPubMedGoogle Scholar
- Yaacob NS, Hamzah N, Nik Mohamed Kamal NN, Zainal Abidin SA, Lai CS, Navaratnam V, Norazmi MN (2010) Anticancer activity of a sub-fraction of dichloromethane extract of Strobilanthes crispus on human breast and prostate cancer cells in vitro. BMC Complement Altern Med 10:42CrossRefPubMedPubMedCentralGoogle Scholar