220 | wileyonlinelibrary.com/journal/cbdd Chem Biol Drug Des. 2018;91:220–14. © 2017 John Wiley & Sons A/S. Received: 23 November 2016 | Revised: 21 March 2017 | Accepted: 8 July 2017 DOI: 10.1111/cbdd.13073 RESEARCH ARTICLE Novel menadione hybrids: Synthesis, anticancer activity, and cell-based studies Chakka Vara Prasad 1 | Vadithe Lakshma Nayak 2 | Sistla Ramakrishna 2 | Uppuluri Venkata Mallavadhani 1 1 Natural Products Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad, India 2 Department of Medicinal Chemistry and Pharmacology, CSIR-Indian Institute of Chemical Technology, Hyderabad, India Correspondence Uppuluri Venkata Mallavadhani, Natural Products Chemistry Division, CSIR- Indian Institute of Chemical Technology, Hyderabad, India. Email: uvmavadani@yahoo.com Funding information Fellowship A series of novel menadione-based triazole hybrids were designed and synthesized by employing copper-catalyzed azide-alkyne cycloaddition (CuAAC). All the syn- thesized hybrids were characterized by their spectral data ( 1 H NMR, 13 C NMR, IR, and HRMS). The synthesized compounds were evaluated for their anticancer activity against five selected cancer cell lines including lung (A549), prostate (DU-145), cer- vical (Hela), breast (MCF-7), and mouse melanoma (B-16) using MTT assay. The screening results showed that majority of the synthesized compounds displayed sig- nificant anticancer activity. Among the tested compounds, the triazoles 5 and 6 ex- hibited potent activity against all cell lines. In particular, compound 6 showed higher potency than the standard tamoxifen and parent menadione against MCF-7 cell line. Flow cytometric analysis revealed that compound 6 arrested cell cycle at G0/G1 phase and induced apoptotic cell death which was further confirmed by Hoechst staining, measurement of mitochondrial membrane potential (ΔΨm) and Annexin- V-FITC assay. Thus, compound 6 can be considered as lead molecule for further development as potent anticancer therapeutic agent. KEYWORDS 1,2,3-triazole, 1,4-naphthoquinone, apoptosis, cell cycle arrest, cytotoxicity, menadione 1 | INTRODUCTION Quinones are widely distributed in nature as secondary me- tabolites. Both natural quinones and their synthetic analogues possess broad spectrum of biological activities, including antifungal, antibacterial, antimalarial, antiviral, and antican- cer activity. [1–3] Moreover, the quinone scaffold is present in many clinically useful cancer drugs such as daunorubi- cin, doxorubicin, saintopin, mitomycin, and mitoxantrone (Figure 1). The most important chemical class in the qui- none family is the 1,4-naphthoquinones. Recently, naturally occurring 1,4-naphthoquinones such as menadione (vitamin K3), juglone, and plumbagin have grabbed attention for their significant anticancer activity against various cancer cell lines as well as in vivo in animal models. [4–6] Particularly, menadione has been reported to exhibit in vitro anticancer activity against mammary, breast, hepatic, blood, bladder, and oral cancer cell lines. [7,8] Menadione was effective even against multidrug-resistant leukemia cell lines and parental leukemia cell lines. [9,10] The main mechanism of the cyto- toxicity of menadione in cancer cells involves the oxidative stress via redox cycling of quinone to produce reactive ox- ygen species (ROS), which leads to DNA damage and cell death. [11] A phase I clinical study showed that menadione is reasonably well tolerated, and menadione showed synergistic cytotoxicity effect with other anticancer drugs such as 5-FU, bleomycin, mitomycin C, and vitamin C. [12] Due to its re- markable bioactivities, much more effort has been devoted in synthesizing novel analogues of menadione with newer and enhanced cytotoxic activities. The triazole ring system is a very well-recognized phar- macophore. This five-membered heterocycle is a prominent