Triphala polyphenols-functionalized gold nanoparticles impair cancer cell survival through induction of tubulin dysfunction

Highlights

• Trl-GNPs were synthesized, characterized, and evaluated on MDA-MB-231 breast cancer cells.

• They effectively inhibited the cell viability.

• The mechanism of action of Trl-GNPs involved perturbation of tubulin function and consequent cell cycle arrest.

Abstract

Green-nanotechnology has enabled the development of several potential nanomedicines against diseases such as cancer. Triphala is an ayurvedic formulation with anticancer activities. The aim of the study was to synthesize, characterize, and biologically evaluate Trl-polyphenol-coated gold nanoparticles (Trl-GNPs) and to elucidate the mechanism of action of this formulation. Trl-GNPs were synthesized using the lyophilized powder of Trl extract and gold chloride trihydrate, and characterized by an assortment of spectroscopy techniques (UV–visible spectroscopy, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, size- and zeta potential-analysis, and one-dimensional proton nuclear magnetic resonance spectroscopy) and transmission electron microscopy. Cell viability analyses of the triple-negative breast cancer cell line, MDA-MB-231, were carried out using (3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) MTT assay. The nature of interactions of the Trl-GNPs with the purified tubulin was studied using spectrofluorimetry and circular dichroism. Microtubule architectural defects were investigated using immunofluorescence microscopy. Trl-GNPs were found to be inhibitory to the proliferative potential of the cells. The antiproliferative mechanism of action of Trl-GNPs involved perturbation of the structural the integrity of the mitotic-spindle-building protein, tubulin, at the secondary and tertiary levels. These disruptions of tubulin manifested as disrupted microtubule network in cells facilitating cell cycle arrest. Our data suggest a potential method for enhancing the delivery of Trl polyphenols to cancer cells, and elucidate the antiproliferative mechanism of action of these particles.

Introduction

Gold nanoparticles (GNPs) can be synthesized in desired shapes, sizes, and surface coating and such particles produce a variety of effects in biological systems [1,2]. GNPs coated with drug molecules, natural products, and formulations have been explored for improving drug delivery and for their potential synergistic impact on the target system [3,4]. For example, GNPs synthesized with Cannabis sativa inhibits bacterial biofilm formation [5] and many “green-synthesized” GNPs possess excellent wound-healing property [6]. In cancer chemotherapeutics research, paclitaxel-functionalized GNPs are emerging as potential theranostics [7,8]. Compared to other metal nanoparticles, GNPs hold superior efficacy in drug delivery [9]. Target-specific gold nanoparticles, such as 198AuNP-EGCg have shown considerable efficacy in treating prostate cancer [10].

Phytochemicals form a potent class of anticancer agents. Several phytochemicals are known for their chemopreventive and anticancer potential. Phytochemicals in tea, for example, can act as excellent building blocks for producing biocompatible gold nanoparticles [11]. Among the phytochemicals, polyphenols are shown to possess several anticancer properties. Tea polyphenols [12], and artichoke polyphenols [13], for examples, have anticancer efficacy against colorectal and breast cancer, respectively. Further, polyphenols of olive oil extract works against bladder cancers [14] and several other natural polyphenols have been investigated for their efficacy against multiple myeloma [15]. In addition to their ability to directly inhibit cancer cell viability, many polyphenols have been found to be useful in clinical settings to sensitize tumour cells to conventional therapeutics [13]. Negligible toxicity of these polyphenols to normal cells and their favourable pharmacokinetic properties add to their therapeutic value. Pioneering work of Katti et al. in the field of green nanotechnology and nano-Ayurvedic medicine have shed light on the cancer-treatment potential of nano ayurvedic medicines in preclinical evaluations and in pilot human clinical investigations [16].

Triphala (Trl) is an ayurvedic formulation of the dried powders of three fruits, Terminalia chebula (Haritaki), Terminalia bellirica (Bibhitaki), and Emblica officinalis (Amalaki or the Indian gooseberry). Trl has been in use in Ayurvedic medicinal practice for the treatment of a variety of diseases including digestive disorders, asthma, anaemia, and jaundice [17]. Several studies in the past have documented the antiproliferative efficacy and mechanism of action of Trl in cancer cells [18,19]. The antiproliferative activity of Trl has been attributed mostly to polyphenols [19]. However, one key challenge associated with the development of polyphenol-based therapeutics is the lack of potential means to bring these biomolecules to the site of the tumour. Given the ability of gold nanoparticles to selectively reach and retain at the site of tumours [20], polyphenol-coated gold nanoparticles could be an effective design to enhance the target-specific delivery of these molecules [21]. For example, gold nanoparticles that are functionalized with resveratrol polyphenols are found to possess antitumor efficacy against breast, pancreatic and prostate cancers [22]. To gain a deeper insight into the therapeutic potential of this approach, it is necessary to first elucidate the mechanistic details of such formulation in cancer cells. Here, we report the synthesis, biophysical and microscopical characterization, biological evaluation, and elucidation of the underlying mechanism of action of Trl-polyphenol functionalized GNPs (Trl-GNPs) against the triple-negative breast cancer cell line, MDA-MB-231.