Synthesis of C8-linked pyrrolo[2,1-c][1,4]benzodiazepine–benzimidazole conjugates with remarkable DNA-binding affinity

Benzimidazole Scaffold as Anticancer Agent: Synthetic Approaches and Structure-Activity Relationship

Cancer, also known as malignant neoplasm, is a dreadful disease which involves abnormal cell growth having the potential to invade or spread to other parts of the body. Benzimidazole is an organic compound that is heterocyclic and aromatic in nature. It is a bicyclic compound formed by the fusion of the benzene and imidazole ring systems. It is an important pharmacophore and a privileged structure in medicinal chemistry. According to the World Health Organisation (2015 survey), one in six deaths is due to cancer around the globe, accounting for 8.8 million deaths of which 70% of the cases were from low- and middle-income countries. In the efforts to develop suitable anticancer drugs, medicinal chemists have focussed on benzimidazole derivatives. This review article covers the current development of benzimidazole-based anticancer agents along with the synthetic approaches and structure-activity relationships (SAR).

Synthesis and investigation of novel benzimidazole derivatives as antifungal agents

The rise and emergence of resistance to antifungal drugs by diverse pathogenic fungal strains have resulted in an increase in demand for new antifungal agents. Various heterocyclic scaffolds with different mechanisms of action against fungi have been investigated in the past. Herein, we report the synthesis and antifungal activities of 18 alkylated mono-, bis-, and trisbenzimidazole derivatives, their toxicities against mammalian cells, as well as their ability to induce reactive oxygen species (ROS) in yeast cells. Many of our bisbenzimidazole compounds exhibited moderate to excellent antifungal activities against all tested fungal strains, with MIC values ranging from 15.6 to 0.975μg/mL. The fungal activity profiles of our bisbenzimidazoles were found to be dependent on alkyl chain length. Our most potent compounds were found to display equal or superior antifungal activity when compared to the currently used agents amphotericin B, fluconazole, itraconazole, posaconazole, and voriconazole against many of the strains tested.

Diversity oriented synthesis of benzimidazole-based biheterocyclic molecules by combinatorial approach: a critical review

Because of the wide ranging bioactivities associated with the benzimidazole nucleus, this review highlights the advances made in the synthesis of benzimidazole-based biheterocyclic molecules by combinatorial approaches.

Rational approaches, design strategies, structure activity relationship and mechanistic insights for anticancer hybrids

A Hybrid drug which comprises the incorporation of two drug pharmacophores in one single molecule are basically designed to interact with multiple targets or to amplify its effect through action on another bio target as one single molecule or to counterbalance the known side effects associated with the other hybrid part(.) The present review article offers a detailed account of the design strategies employed for the synthesis of anticancer agents via molecular hybridization techniques. Over the years, the researchers have employed this technique to discover some promising chemical architectures displaying significant anticancer profiles. Molecular hybridization as a tool has been particularly utilized for targeting tubulin protein as exemplified through the number of research papers. The microtubule inhibitors such as taxol, colchicine, chalcones, combretasatin, phenstatins and vinca alkaloids have been utilized as one of the functionality of the hybrids and promising results have been obtained in most of the cases with some of the tubulin based hybrids exhibiting anticancer activity at nanomolar level. Linkage with steroids as biological carrier vector for anticancer drugs and the inclusion of pyrrolo [2,1-c] [1,4]benzodiazepines (PBDs), a family of DNA interactive antitumor antibiotics derived from Streptomyces species in hybrid structure based drug design has also emerged as a potential strategy. Various heteroaryl based hybrids in particular isatin and coumarins have also been designed and reported to posses' remarkable inhibitory potential. Apart from presenting the design strategies, the article also highlights the structure activity relationship along with mechanistic insights revealed during the biological evaluation of the hybrids.

Synthesis of new conjugated coumarin-benzimidazole hybrids and their anticancer activity

A series of novel coumarin-benzimidazole hybrids, 3-(1H-benzo[d]imidazol-2-yl)-7-(substituted amino)-2H-chromen-2-one derivatives of biological interest were synthesized. Six out of the newly synthesized compounds were screened for in vitro antitumor activity against preliminary 60 tumor cell lines panel assay. A significant inhibition for cancer cells was observed with compound 8 (more than 50% inhibition) compared with other compounds and active known drug 5-fluorouracil (in some cell lines) as positive control. Compound 8 displayed appreciable anticancer activities against leukemia, colon cancer and breast cancer cell lines.

The development of pyrrolobenzodiazepines as antitumour agents

INTRODUCTION

DNA interacting agents play a major role in cancer chemotherapy, either as single agents, in combination drug regimens, or as components of novel targeted therapies. The search for more selective and efficacious drugs that can deliver critical DNA damage with minimal side effects continues.

AREAS COVERED

The development of the pyrrolobenzodiazepines (PBDs) from their discovery as natural products in the 1960s, through synthetic PBD monomers, PBD hybrids and conjugates, and PBD dimers is described. The latter molecules are capable of forming sequence selective, non-distorting and potently cytotoxic DNA interstrand cross-links in the minor groove of DNA. In particular, the development of PBD dimer SJG-136 (SG2000), currently in Phase II clinical trials, is presented. Potential future cancer therapeutic applications of PBDs, including their use as components of targeting strategies, are also discussed.

EXPERT OPINION

The culmination of over four decades of study on structure-activity relationships of PBDs has led to a detailed understanding of how to introduce structural modification to enhance biological activity and potency. The challenge for the next phase in the development of the PBDs is to harness this activity and potency in a new generation of cancer therapeutics.

Functionalization of carboxylated multiwall nanotubes with imidazole derivatives and their toxicity investigations

Imidazoles and their derivatives are compounds with chemotherapeutic applications. In this study, we investigated the chemical functionalization of carboxylated multiwalled carbon nanotubes (MWNT-COOH) by 1,2-phenylendiamine. Multiwalled nanotube (MWNT)-benzimidazole was obtained by an MWNT-amide reaction with POCl(3) after 72 hours, which was confirmed by Fourier transform infrared, scanning electron microscopy, thermal gravimetric analysis, and elemental analysis. These functionalizations were chosen due to -NH(2) and NHCO active sites in MWNT-amide for future application. Toxicity assays with fibroblast cells and MTT test for measurement of viable cell numbers were also performed. Cellular results did not show any toxicity change in modified samples from that of the reference samples.

Solution structure of a covalently bound pyrrolo[2,1-c][1,4]benzodiazepine-benzimidazole hybrid to a 10mer DNA duplex

A pyrrolo[2,1-c][1,4]benzodiazepine-benzimidazole hybrid (PBD-BIMZ) derived from the tricyclic anticancer PBD antibiotics can covalently bind to a guanine base at its exocyclic 2-amino group in double-helical DNA. Through the formation of stable DNA adducts, these hybrids have previously been shown to have significant anticancer activity in a number of cell lines. Here, the three-dimensional solution structure of the complex formed between the self-complementary DNA decamer 5'-AACAATTGTT-3' and PBD-BIMZ has been investigated by two-dimensional NMR spectroscopy and NOE distance restraint molecular dynamics simulations. Refinements using an explicit solvation model yielded a complex structure that is in good agreement with the NMR structural data. Successful convergence is indicated by an average mutual root-mean-square deviation of <1 A for three final representative structures selected by clustering methods from the molecular dynamics trajectories at 300 K. The ligand binds in an (11S,11aS) configuration to one of the two symmetrically located guanine bases of the duplex and is oriented with its benzimidazole moiety toward the 5'-end of the modified guanine. It is accommodated within the minor groove covering the centrally located 6 bp. Conformational and helical parameters of the DNA adduct are typical of a B-like duplex, and more significant helical distortions by the covalent binding of PBD-BIMZ are mostly confined to the covalent binding site and the junction between complexed and noncomplexed DNA segments. In contrast to the overall well-determined conformation of the bound hybrid, its terminal N-methylpiperazine ring appears to adopt various conformations associated with increased flexibility.

Spectroscopic and calorimetric studies on the DNA recognition of pyrrolo[2,1-c][1,4]benzodiazepine hybrids

DNA binding of two hybrid ligands composed of an alkylating pyrrolo[2,1-c][1,4]benzodiazepine (PBD) moiety tethered to either a naphthalimide or a phenyl benzimidazole chromophore was studied by DNA melting experiments, UV and fluorescence titrations, CD spectroscopy and isothermal titration calorimetry (ITC). Binding of both hybrids results in a remarkable thermal stabilization with an increase of DNA melting temperatures by up to 40 degrees C for duplexes that allow for a covalent attachment of the PBD moiety to guanine bases in their minor groove. CD spectroscopic measurements suggest that the naphthalimide moiety of the drug interacts through intercalation. In contrast, the PBD-benzimidazole hybrid binds in the DNA minor groove with a preference for (A,T)(4)G sequences. Whereas the binding of both ligands is enthalpy-driven and associated with a negative entropy, the benzimidazole hybrid exhibits a less favourable binding enthalpy that is counterbalanced by a more favourable entropic term when compared to the naphthalimide hybrid.

Development of pyrrolo[2,1-c][1,4]benzodiazepine beta-galactoside prodrugs for selective therapy of cancer by ADEPT and PMT

The pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a class of well-studied DNA-interactive agents with a potential for use in the treatment of cancer. The clinical utility of these molecules is limited because of the lack of selectivity for tumor tissues, high reactivity of the pharmacophoric imine functionality, low water solubility, and stability. To address the shortcomings, especially the lack of selectivity, associated with the molecules, two new beta-galactoside prodrugs of PBDs have been synthesized and evaluated for their potential use in selective therapy of solid tumors by ADEPT and PMT protocols. The preliminary studies reveal the prodrugs to be much less toxic compared to the parent moieties. These prodrugs are activated by E. coli beta-galactosidase (EC 3.2.1.23) to form the active cytotoxic moiety signifying their utility in ADEPT of cancer. One of the significant outcomes of the present study is the toxification of the prodrug 1 a by the endogenous beta-galactosidase of human liver cancer cells (Hep G2) to form the cytotoxic moiety, enabling selective therapy of hepatocellular carcinoma. Another important property of these molecules is their enhanced water solubility and stability, which are essential for a molecule to be an effective drug.

Fluorogenic label for biomolecular imaging

Traditional small-molecule fluorophores are always fluorescent. This attribute can obscure valuable information in biological experiments. Here, we report on a versatile "latent" fluorophore that overcomes this limitation. At the core of the latent fluorophore is a derivative of rhodamine in which one nitrogen is modified as a urea. That modification enables rhodamine to retain half of its fluorescence while facilitating conjugation to a target molecule. The other nitrogen of rhodamine is modified with a "trimethyl lock", which enables fluorescence to be unmasked fully by a single user-designated chemical reaction. An esterase-reactive latent fluorophore was synthesized in high yield and attached covalently to a cationic protein. The resulting conjugate was not fluorescent in the absence of esterases. The enzymatic activity of esterases in endocytic vesicles and the cytosol educed fluorescence, enabling the time-lapse imaging of endocytosis into live human cells and thus providing unprecedented spatiotemporal resolution of this process. The modular design of this "fluorogenic label" enables the facile synthesis of an ensemble of small-molecule probes for the illumination of numerous biochemical and cell biological processes.