Induction of autophagy-dependent and caspase- and microtubule-acetylation-independent cell death by phytochemical-stabilized gold nanopolygons in colorectal adenocarcinoma cells.

Collective functionalization of the phytochemicals of medicinal herbs on nanoparticles is emerging as a potential cancer therapeutic strategy. This study presents the facile synthesis of surface-functionalized gold nanoparticles using Bacopa monnieri (Brahmi; Bm) phytochemicals and their therapeutically relevant mechanism of action in the colorectal cancer cell line, HT29. The nanoparticles were characterized using UV-visible spectroscopy, TEM-EDAX, zeta potential analysis, TGA, FTIR and 1H NMR spectroscopy, and HR-LC-MS. The particles (Bm-GNPs) were of polygonal shape and were stable against aggregation. They entered the target cells and inhibited the viability and clonogenicity of the cells with eight times more antiproliferative efficacy (25 ± 1.5 µg mL-1) than Bm extract (Bm-EX). In vitro studies revealed that Bm-GNPs bind tubulin (a protein crucial in cell division and a target of anticancer drugs) and disrupt its helical structure without grossly altering its tertiary conformation. Like other antitubulin agents, Bm-GNPs induced G2/M arrest and ultimately killed the cells, as confirmed using flow cytometry analyses. ZVAD-FMK-mediated global pan-caspase inhibition and the apparent absence of cleaved caspase-3 in treated cells indicated that the death did not involve the classic apoptosis pathway. Cellular ultrastructure analyses, western immunoblots, and in situ immunofluorescence visualization of cellular microtubules revealed microtubule-acetylation-independent induction of autophagy as the facilitator of cell death. Together, the data indicate strong antiproliferative efficacy and a possible mechanism of action for these designer nanoparticles. Bm-GNPs, therefore, merit further investigations, including preclinical evaluations, for their therapeutic potential as inducers of non-apoptotic cell death.

Exploring the efficacy of tryptone-stabilized silver nanoparticles against respiratory tract infection-causing bacteria: a study on planktonic and biofilm forms.

Respiratory tract infections (RTIs) are a common cause of mortality and morbidity in the human population. The overuse of antibiotics to overcome such infections has led to antibiotic resistance. The emergence of multidrug resistant bacteria is necessitating the development of novel therapeutic techniques in order to avoid a major global clinical threat. Our study aims to investigate the potential of tryptone stabilised silver nanoparticles (Ts-AgNPs) on planktonic and biofilms produced byKlebsiella pneumoniae(K. pneumoniae)and Pseudomonas aeruginosa(P. aeruginosa). The MIC50of Ts-AgNPs was found to be as low as 1.7 µg ml-1and 2.7 µg ml-1forK. pneumoniae and P.aeruginosarespectively. Ts-AgNPs ability to alter redox environment by producing intracellular ROS, time-kill curves showing substantial decrease in the bacterial growth and significantly reduced colony forming units further validate its antimicrobial effect. The biofilm inhibition and eradication ability of Ts-AgNPs was found to be as high as 93% and 97% in both the tested organisms. A significant decrease in the eDNA and EPS quantity in Ts-AgNPs treated cells proved its ability to successfully distort the matrix and matured biofilms. Interestingly Ts-AgNPs also attenuated QS-induced virulence factors production. This study paves way to develop Ts-AgNPs as novel antibiotics against RTIs causing bacterial biofilms.

Biochemical and in silico analysis of the binding mode of erastin with tubulin.

Erastin (ERN) is a small molecule that induces different forms of cell death. For example, it has been reported to induce ferroptosis by disrupting tubulin subunits that maintain the voltage-dependent anion channels (VDACs) of mitochondria. Although its possible binding to tubulin has been suggested, the fine details of the interaction between ERN and tubulin are poorly understood. Using a combination of biochemical, cell-model and in silico approaches, we elucidate the interactions of ERN with tubulin and their biological manifestations. After confirming ERN's antiproliferative efficacy (IC50, 20 ± 3.2 M) and induction of cell death in the breast cancer cell line MDA-MB-231, the binding interactions of ERN with tubulin were examined. ERN bound to tubulin in a concentration-dependent manner, disorganizing the structural integrity of the protein, as substantiated via the tryptophan-quenching assay and the aniline-naphthalene sulfonate binding assay, respectively. In silico studies based on molecular docking revealed a docking score of -5.863 kcal/mol, suggesting strong binding interactions of ERN with tubulin. Additionally, molecular dynamics simulation and Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) analyses evinced the binding free energy (ΔGbinding) of -31.235 kcal/mol, substantiating strong binding affinity of ERN with tubulin. Ligplot analysis showed hydrogen bonding with specific amino acids (Asn A226, Thr A223, Gln B247 and Val B355). QikProp-based ADME (absorption, distribution, metabolism and excretion) assessment showed considerable therapeutic potential for ERN.Communicated by Ramaswamy H. Sarma.

Therapeutic and diagnostic applications of carbon nanotubes in cancer: recent advances and challenges.

Carbon nanotubes (CNTs) are allotropes of carbon, composed of carbon atoms forming a tube-like structure. Their high surface area, chemical stability, and rich electronic polyaromatic structure facilitate their drug-carrying capacity. Therefore, CNTs have been intensively explored for several biomedical applications, including as a potential treatment option for cancer. By incorporating smart fabrication strategies, CNTs can be designed to specifically target cancer cells. This targeted drug delivery approach not only maximizes the therapeutic utility of CNTs but also minimizes any potential side effects of free drug molecules. CNTs can also be utilised for photothermal therapy (PTT) which uses photosensitizers to generate reactive oxygen species (ROS) to kill cancer cells, and in immunotherapeutic applications. Regarding the latter, for example, CNT-based formulations can preferentially target intra-tumoural regulatory T-cells. CNTs also act as efficient antigen presenters. With their capabilities for photoacoustic, fluorescent and Raman imaging, CNTs are excellent diagnostic tools as well. Further, metallic nanoparticles, such as gold or silver nanoparticles, are combined with CNTs to create nanobiosensors to measure biological reactions. This review focuses on current knowledge about the theranostic potential of CNT, challenges associated with their large-scale production, their possible side effects and important parameters to consider when exploring their clinical usage.

Smart Delivery Systems Responsive to Cathepsin B Activity for Cancer Treatment.

Cathepsin B is a lysosomal cysteine protease, contributing to vital cellular homeostatic processes including protein turnover, macroautophagy of damaged organelles, antigen presentation, and in the extracellular space, it takes part in tissue remodeling, prohormone processing, and activation. However, aberrant overexpression of cathepsin B and its enzymatic activity is associated with different pathological conditions, including cancer. Cathepsin B overexpression in tumor tissues makes this enzyme an important target for smart delivery systems, responsive to the activity of this enzyme. The generation of technologies which therapeutic effect is activated as a result of cathepsin B cleavage provides an opportunity for tumor-targeted therapy and controlled drug release. In this review, we summarized different technologies designed to improve current cancer treatments responsive to the activity of this enzyme that were shown to play a key role in disease progression and response to the treatment.

Nano-ayurvedic medicine and its potential in cancer treatment.

Nano-ayurvedic medicine is an emerging field in which nanoparticles are functionalized with active principles of potent ayurvedic herbs to enhance their efficacy and target-specific delivery. Scientific advances in the past couple of decades have revealed the molecular mechanisms behind the anticancer potential of several ayurvedic herbs, attributed chiefly to their secondary metabolites including polyphenols and other active substances. With the advancement of nanotechnology, it has been established that size-, shape-, and surface-chemistry-optimized nanoparticles can be utilized as synergizing carriers for these phytochemicals. Nano-ayurvedic medicine utilizes herbs that are commonly used in Ayurveda to functionalize different nanoparticles and thereby enhance their potency and target specificity. Studies have shown that the active phytochemicals of such herbs can be coated onto the nanoparticles of different metals, such as gold, and that they work more efficiently than the free herbal extract, for example, in inhibiting cancer cell proliferation. Recently, an Ayurveda, Yoga & Naturopathy, Unani, Siddha and Homeopathy (AYUSH)-based clinical trial in humans indicated the anticancer potential of such formulations. Nano-ayurvedic medicine is emerging as a potential treatment option for hyperproliferative diseases.

Tryptone-stabilized silver nanoparticles' potential to mitigate planktonic and biofilm growth forms of Serratia marcescens.

Several microbial pathogens are capable of forming biofilms. These microbial communities pose a serious challenge to the healthcare sector as they are quite difficult to combat. Given the challenges associated with the antibiotic-based management of biofilms, the research focus has now been shifted towards finding alternate treatment strategies that can replace or complement the antibacterial properties of antibiotics. The field of nanotechnology offers several novel and revolutionary approaches to eradicate biofilm-forming microbes. In this study, we evaluated the antibacterial and antibiofilm efficacy of in-house synthesized, tryptone-stabilized silver nanoparticles (Ts-AgNPs) against the superbug Serratia marcescens. The nanoparticles were of spherical morphology with an average hydrodynamic diameter of 170 nm and considerable colloidal stability with a Zeta potential of - 24 ± 6.15 mV. Ts-AgNPs showed strong antibacterial activities with a minimum inhibitory concentration (MIC50) of 2.5 µg/mL and minimum bactericidal concentration (MBC) of 12.5 µg/mL against S. marcescens. The nanoparticles altered the cell surface hydrophobicity and inhibited biofilm formation. The Ts-AgNPs were also effective in distorting pre-existing biofilms by degrading the extracellular DNA (eDNA) component of the extracellular polymeric substance (EPS) layer. Furthermore, reduction in quorum-sensing (QS)-induced virulence factors produced by S. marcescens indicated that Ts-AgNPs attenuated the QS pathway. Together, these findings suggest that Ts-AgNPs are an important anti-planktonic and antibiofilm agent that can be explored for both the prevention and treatment of infections caused by S. marcescens.

In vitro characterization and molecular dynamic simulation of shikonin as a tubulin-targeted anticancer agent.

Shikonin (SK), a naphthoquinone compound from the purple gromwell, Lithospermum erythrorhizon, possesses a considerable antiproliferative potential. By using a combination of biophysical techniques, cellular assays, immunofluorescence imaging, and molecular dynamic simulation, we identified a possible mechanism of action of SK. SK inhibited the viability of the triple negative breast cancer cells MDA-MB-231 (IC50 of 1 ± 0.1 µM), and its inhibitory effect was irreversible. It strongly suppressed the clonogenic and migratory potential of the cells. Although SK did not show any phase-specific inhibition of cell cycle progression, it induced apoptosis as confirmed by annexin-V-based flow cytometry and Western immunoblotting of PARP1. Probing further into its mechanism using a tryptophan-quenching assay, it was found that SK binds the microtubule-building protein tubulin with a dissociation constant (Kd) of 8 ± 2.7 µM, without grossly damaging the tertiary structure of the protein. The drug-bound tubulin could not assemble microtubules properly in vitro as confirmed by polymer mass analysis, turbidimetry analysis, and transmission electron microscopy, and in cells, as visualized by immunofluorescence imaging. In cells, SK also suppressed the dynamicity of microtubules as indicated by considerable acetylation of the cellular microtubules. The fine details of tubulin-SK interactions were then elucidated using molecular docking and molecular dynamic simulation. The free energy change of the interaction (ΔGbind,pred) was found to be -14.60 kcal/mol and the binding involved both the intermolecular van der Waals (ΔEvdw) and the electrostatic (ΔEele) interactions. Taken together, our data provide evidence for a possible mechanism of action of SK as a tubulin-targeted anticancer agent.

Proteomic and metabolomic profiling combined with in vitro studies reveal the antiproliferative mechanism of silver nanoparticles in MDA-MB-231 breast carcinoma cells.

Silver nanoparticles, shaped and stabilized by various means, are known to alter biological systems and promote cytotoxicity. However, the precise mechanism by which they induce toxic outcomes in cancer cells is poorly understood. Using a combination of cellular and biophysical assays and proteomic and metabolomic analyses, we report the cytotoxic mechanism of action of tryptone-stabilized silver nanoparticles (T-AgNPs). After their facile synthesis and characterization using an assortment of spectroscopic techniques and transmission electron microscopy, the mechanism of action of the particles was elucidated using MDA-MB-231 breast cancer cells as the cell model. The nanoparticles inhibited the proliferative (IC50:100 ± 3 µg mL-1) and clonogenic potential of the cells. Flow cytometry analyses revealed an absence of phase-specific cell cycle arrest but extensive cell death in the treated cells. The mechanism of action of the particles consisted of their direct binding to the microtubule-building protein tubulin and the disruption of its helical integrity, as confirmed via fluorometric analysis and far-UV spectropolarimetry, respectively. The binding hampered the assembly of microtubules, as confirmed via polymer mass analysis of in vitro assembled, purified tubulin and immunofluorescence imaging of cellular microtubules. Proteomic and metabolomic analyses revealed the downregulation of lipid metabolism to be a synergistic contributor to cell death. Taken together, we report a novel antiproliferative mechanism of action of T-AgNPs that involves tubulin disruption and the downregulation of lipid metabolism.

Targeting disorders in unstructured and structured proteins in various diseases.

Intrinsically disordered proteins (IDPs) and intrinsically disordered protein regions (IDPRs) are proteins and protein segments that usually do not acquire well-defined folded structures even under physiological conditions. They are abundantly present and challenge the "one sequence-one structure-one function" theory due to a lack of stable secondary and/or tertiary structure. Due to conformational flexibility, IDPs/IDPRs can bind with multiple interacting partners with high-specificity and low-affinity and perform essential biological functions associated with signalling, recognition and regulation. Mis-functioning and mis-regulation of IDPs and IDPRs causes disorder in disordered proteins and disordered protein segments which results in numerous human diseases, such as cancer, Parkinson's disease (PD), Alzheimer's disease (AD), diabetes, metabolic disorders, systemic disorders and so on. Due to the strong connection of IDPs/IDPRs with human diseases they are considered potentential targets for drug therapy. Since they disobey the "one sequence-one structure-one function" concept, IDPs/IDPRs are complex systems for drug targeting. This review summarises various protein disorder diseases and different methods for therapeutic targeting of disordered proteins/segments. Targeting IDPs/IDPRs for diseases will open up a new era of rational drug design and drug discovery.

The spontaneous remission of cancer: Current insights and therapeutic significance.

Many diseases heal spontaneously. The common cold, for example, remedies itself within a few days in people with an uncompromised immune system. If a disease with a poor prognosis heals in the absence of a targeted therapeutic, many even call it a miracle cure. Such is the case with the spontaneous regression (SR) of malignant neoplasms, a rare but well-documented phenomenon that finds its first mention in the Ebers Papyrus of 1550 BCE. Given the challenges associated with current cancer treatment modalities such as rapidly evolving drug resistance mechanisms, dose-limiting side effects, and a failure to completely eliminate cancer cells, knowledge of how a tumour heals itself would be immensely helpful in developing more effective therapeutic modalities. Although the intricate mechanisms of SR have yet to be fully elucidated, it has been shown that infection-mediated immune system activation, biopsy procedures, and disruptions of the tumour microenvironment play pivotal roles in the self-healing of many tumours. Bacterial and viral infections are especially well-documented in instances of SR. Insights from these findings are paving the way for novel therapeutic strategies. Inspired by bacteria-mediated SR, Bacillus Calmette-Guérin (BCG) has been used as an approved treatment option for non-muscle-invasive bladder cancer (NMIBC). Similarly, Talimogene laherparepvec (T-VEC), the first engineered oncolytic herpes simplex virus (HSV), has been approved by the United States Food and Drug Administration for the treatment of some forms of advanced melanoma. Here we describe the current understanding of SR, explore its therapeutic significance, and offer perspectives on its future.

Induction of microtubule hyper stabilization and robust G2 /M arrest by N-4-CN in human breast carcinoma MDA-MB-231 cells.

AIM: Elucidation of the antiproliferative efficacy and mechanism of action of a design-optimized noscapine analog, N-4-CN. METHODS: Cell viability was studied using an MTT assay. The drug-tubulin interactions were investigated using spectrofluorometry. The architectural defects, hyper stabilization, and recovery competence of cellular microtubules were studied using immunofluorescence microscopy. DCF-DH and rhodamine 123 were used as probes to to examine the levels of reactive oxygen species and the loss of mitochondrial membrane potential, respectively. Flow cytometry revealed the cell cycle progression pattern of the drug-treated cells. KEY FINDINGS: Among the cell lines tested, N-4-CN showed the strongest inhibition of the viability of the triple-negative breast cancer (TNBC) cell line MDA-MB-231(IC50 , 2.7 ± 0.1 µmol/L) and weakest inhibition of the noncancerous epithelial cell line, VERO (IC50 , 60.2 ± 3 µmol/L). It perturbed tertiary structure of tubulin and stabilized colchicine binding to the protein. In cells, N-4-CN hyperstabilized the microtubules, and prevented the recovery of cold-depolymerized microtubules. Its multitude of effects on tubulin and microtubules facilitated cell cycle arrest and subsequent cell death that were complemented by elevated levels of reactive oxygen species (ROS). SIGNIFICANCE: Owing to its ability to perturb a well-defined cancer drug target, tubulin, and to promote ROS-facilitated apoptosis, N-4-CN could be investigated further as a potential therapeutic against many neoplasms, including TNBC.

Mechanistic insights into encapsulation and release of drugs in colloidal niosomal systems: biophysical aspects.

Vesicular systems such as niosomes provide an alternative to improve drug delivery systems. The efficiency of a drug delivery vehicle is strongly dependent on its components which decide its interaction with partitioned drug(s) and locus of site of partitioning. A quantitative understanding of the physical chemistry underlying partitioning of drugs in complex systems of self-assemblies such as niosomes is scarcely available. In order to obtain quantitative mechanistic insights into partitioning and release of drugs [mitoxantrone (MTX) and ketoprofen (KTP)] in systems of niosomes, we have employed ultrasensitive calorimetry, spectroscopy and microscopy to establish correlations between functionality and energetics which could provide guidance towards rational drug design and choice of suitable non-ionic surfactant-based drug delivery vehicles. Electron microscopy and dynamic light scattering (DLS) methods were used for characterization and assessing the morphology of niosomes. We present here a calorimetry-based approach in assessing the partitioning of the anticancer drugs mitoxantrone and ketoprofen in niosomes and their release to human serum albumin (HSA) employing isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC) and comparison with equilibrium dialysis. The thermodynamic signatures and kinetics of release were analyzed to obtain insights into the role of the functional groups on the drugs in the partitioning process. The assessment of thermal and conformational stability of proteins during drug binding and the effect of drug delivery vehicles on proteins is also crucial. To assess these effects, DSC studies on HSA in the presence and absence of drugs and niosomes were also performed. Finally, the efficacy of the system to impact the cell viability of the MDA-MB-231 triple-negative breast carcinoma cell line was analysed using MTT assay.

9-PAN promotes tubulin- and ROS-mediated cell death in human triple-negative breast cancer cells.

OBJECTIVES: To examine the antiproliferative effect of a rationally designed, novel noscapine analogue, 9-((perfluorophenyl)methylene) aminonoscapine, '9-PAN') on MDA-MB-231 breast cancer cell line, and to elucidate the underlying mechanism of action. METHODS: The rationally designed Schiff base-containing compound, 9-PAN, was characterized using IR, NMR and mass spectra analysis. The effect of the compound on cell viability was studied using an MTT assay. Cell cycle and cell death analyses were performed using flow cytometry. Binding interactions of 9-PAN with tubulin were studied using spectrofluorometry. Reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) were investigated using the probes, DCFDA and rhodamine-123, respectively. Immunofluorescence imaging was used to visualize cellular microtubules. KEY FINDINGS: 9-PAN inhibited cell proliferation (IC50 of 20 ± 0.3 µm) and colony formation (IC50 , 6.2 ± 0.3 µm) by arresting the cells at G2 /M phase of the cell cycle. It bound to tubulin in a concentration-dependent manner without considerably altering the tertiary conformation of the protein or the polymer mass of the microtubules in vitro. The noscapinoid substantially damaged cellular microtubule network and induced cell death, facilitated by elevated levels of ROS. CONCLUSIONS: 9-PAN exerts its antiproliferative effect by targeting tubulin and elevating ROS level in the cells.

Tubulin- and ROS-dependent antiproliferative mechanism of a potent analogue of noscapine, N-propargyl noscapine.

AIM: To rationally-design, synthesize, characterize, biologically evaluate, and to elucidate the anticancer mechanism of action of a novel analogue of noscapine, N-propargyl noscapine (NPN), as a potential drug candidate against triple-negative breast cancer (TNBC). MATERIALS AND METHODS: After the synthesis and IR, 1H, 13C NMR and mass spectral characterization of NPN, its antiproliferative efficacy against different cancer cell lines was investigated using Sulforhodamine B assay. Cell cycle progression was analysed using flow cytometry. The drug-tubulin interactions were studied using tryptophan-quenching assay, ANS-binding assay, and colchicine-binding assay. Immunofluorescence imaging was used to examine the effect of NPN on cellular microtubules. Levels of reactive oxygen species (ROS), loss of mitochondrial membrane potential (MMP), and cell death were studied by staining the cells with DCFDA, Rhodamine 123, and acridine orange/ethidium bromide, respectively. KEY FINDINGS: NPN strongly inhibited the viability (IC50, 1.35 ± 0.2 µM) and clonogenicity (IC50, 0.56 ± 0.06 µM) of the TNBC cell line, MDA-MB-231, with robust G2/M arrest. In vitro, the drug bound to tubulin and disrupted the latter's structural integrity and promoted colchicine binding to tubulin. NPN triggered an unusual form of microtubule disruption in cells, repressed recovery of cold-depolymerized cellular microtubules and suppressed their dynamicity. These effects on microtubules were facilitated by elevated levels of ROS and loss of MMP. SIGNIFICANCE: NPN can be explored further as a chemotherapeutic agent against TNBC.

Cell death mechanisms in eukaryotes.

Like the organism they constitute, the cells also die in different ways. The death can be predetermined, programmed, and cleanly executed, as in the case of apoptosis, or it can be traumatic, inflammatory, and sudden as many types of necrosis exemplify. Nevertheless, there are a number of cell deaths-some of them bearing a resemblance to apoptosis and/or necrosis, and many, distinct from each-that serve a multitude of roles in either supporting or disrupting the homoeostasis. Apoptosis is coordinated by death ligands, caspases, b-cell lymphoma-2 (Bcl-2) family proteins, and their downstream effectors. Events that can lead to apoptosis include mitotic catastrophe and anoikis. Necrosis, although it has been considered an abrupt and uncoordinated cell death, has many molecular events associated with it. There are cell death mechanisms that share some standard features with necrosis. These include methuosis, necroptosis, NETosis, pyronecrosis, and pyroptosis. Autophagy, generally a catabolic pathway that operates to ensure cell survival, can also kill the cell through mechanisms such as autosis. Other cell-death mechanisms include entosis, ferroptosis, lysosome-dependent cell death, and parthanatos.

Tryptone-stabilized gold nanoparticles induce unipolar clustering of supernumerary centrosomes and G1 arrest in triple-negative breast cancer cells.

Gold nanoparticles of different sizes, shapes, and decorations exert a variety of effects on biological systems. We report a novel mechanism of action of chemically modified, tryptone-stabilized gold nanoparticles (T-GNPs) in the triple-negative breast cancer (TNBC) cell line, MDA-MB-231. The T-GNPs, synthesized using HAuCl4.3H2O and tryptone and characterized by an assortment of spectroscopy techniques combined with high-resolution electron microscopy, demonstrated strong antiproliferative and anti-clonogenic potential against MDA-MB-231 cells, arresting them at the G1 phase of the cell cycle and promoting apoptosis. The molecular mechanism of action of these particles involved induction of unipolar clustering and hyper amplification of the supernumerary centrosomes (a distinctive feature of many tumour cells, including TNBC cells). The clustering was facilitated by microtubules with suppressed dynamicity. Mass spectrometry-assisted proteomic analysis revealed that the T-GNP-induced G1 arrest was facilitated, at least in part, by downregulation of ribosome biogenesis pathways. Due to the presence of supernumerary centrosomes in many types of tumour cells, we propose chemical induction of their unipolar clustering as a potential therapeutic strategy.

Perturbation of tubulin structure by stellate gold nanoparticles retards MDA-MB-231 breast cancer cell viability.

Gold nanoparticles (GNPs) of different sizes and shapes have been investigated extensively for their therapeutic potential against several diseases including cancer. However, the mechanisms with which they affect the cells are yet to be fully comprehended. In this study, we report the strong antiproliferative potential of novel, star-shaped ("stellate") GNPs that target tubulin-the building-block protein of the cytoskeletal filaments called microtubules-and disrupt microtubule network integrity. The stellate GNPs ("sGNPs") were synthesized from tryptone-stabilized GNPs ("tGNPs") and characterized by various spectroscopy methods combined with high-resolution transmission electron microscopy. Among a panel of cancer cell lines tested, they showed strong antiproliferative and anti-clonogenic efficacy against MDA-MB-231 cells. The antiproliferative mechanism of the sGNPs involves perturbation of the secondary and tertiary conformation of tubulin as evidenced by far-UV circular dichroism and anilinonaphthalene sulphate-binding assays. The structural perturbation of tubulin retarded its assembly competence as evidenced by polymer mass analysis and electron microscopy imaging of tubulin assembled in vitro and by immunofluorescence visualization of the cellular microtubules. The treated cells also induced cell cycle arrest at G1 phase. Taken together, our data suggest that sGNPs are potent, tubulin-targeted antiproliferative particles that can be evaluated further for their anticancer potential.

Insights into the structure and tubulin-targeted anticancer potential of N-(3-bromobenzyl) noscapine.

BACKGROUND: Noscapine is a non-narcotic, antitussive alkaloid isolated from plants of Papaveraceae family. This benzylisoquinoline alkaloid and its synthetic derivatives, called noscapinoids, are being evaluated for their anticancer potential. METHODS: The structure of a novel analogue, N-(3-bromobenzyl) noscapine (N-BBN) was elucidated by X-ray crystallography. Effect of N-BBN on cancer cell proliferation and cellular microtubules were studied by sulphorhodamine B assay and immunofluorescence, respectively. Binding interactions of the alkaloid with tubulin was studied using spectrofluorimetry. RESULTS: N-BBN, synthesized by introducing modification at site B ('N' in isoquinoline unit) and a bromo group at the 9th position of the parent compound noscapine, was found to be superior to many of the past-generation noscapinoids in inhibiting cancer cell viability and it showed a strong inhibition of the clonogenic potential of an aggressively metastatic breast tumour cell line, MDA-MB-231. The compound perturbed the tertiary structure of purified tubulin as indicated by an anilinonaphthalene sulfonic acid-binding assay. However, substantiating the common feature of noscapinoids, it did not alter microtubule polymer mass considerably. In cells, the drug-treatment showed a peculiar type of disruption of normal microtubule architecture. CONCLUSION: N-BBN may be considered for further investigations as a potent antiproliferative agent.