br Competing interests br Acknowledgments This work was supp

Competing interests
Acknowledgments This work was supported by grants from Fujian Fujian Provincial Natural Science Foundation (2016J01612).
Introduction Cancer is still one of the most serious diseases in the world. According to the World Health Organization (WHO), cancer is the second most important cause of deaths worldwide that had reached 8.8 million in 2015. The number of new cases per year is projected to increase from 14.1 billion in 2012 to 21.6 billion in 2030. The epidermal growth factor receptor (EGFR) belongs to ErbB family of receptor tyrosine kinases. It is upregulated in many cancers such as breast cancer and head and neck squamous cell carcinoma. Moreover, in more than half of the patients with non-small cell lung cancer (NSCLC), EGFR is overexpressed [1,2]. Therefore, EGFR is an attractive target for anticancer therapy and a larger number of EGFR tyrosine kinase inhibitors (TKIs) have been developed [[3], [4], [5], [6], [7]]. They exert their action through competitive inhibition for MRT68921 binding in the tyrosine kinase domain. Benzimidazoles have various activities and have versatile use in medicinal chemistry. Various studies reported that a third generation EGFR inhibitor nazartinib [8], which has benzimidazole structure and the core structure of numerous biologically active compounds, always possess a wide range of bioactivities including antimicrobial [9], antiparasitic [10], antihistaminic [11], antiallergic [12], anticancer [[13], [14], [15], [16]] and antioxidant [[17], [18], [19]]. Other third generation EGFR TKIs, avitinib [20] and osimertinib [21], that bear indolopirimidine and indol rings, respectively, are bioisosteres to benzimidazole (Fig. 1) and are indicated for EGFR-mutated NSCLC (see Fig. 2). In this study, a series of benzimidazoles with thiosemicarbazide side chain or triazole and thiadiazole rings were designed and synthesized. Next, their inhibitory potencies of EGFR kinase activity were compared to erlotinib in vitro.
Results and discussion
Conclusion A series of benzimidazole derivatives bearing thiosemicarbazide side chain or triazole and thiadiazole rings were synthesized. Their EGFR kinase inhibitory efficiency was determined by comparing them with a known kinase inhibitor erlotinib in vitro and most of the compounds exhibited significant activities. Cell culture studies were also carried out for selected compounds (12b, 12c, 13c, 14c, 15c, 16 and 16c) which exhibited EGFR kinase inhibitory activities over ≥30%) against MCF7 cell and 12b was found to be the most active compound. This situation also supported by docking study that compound 12b indicated two-hydrogen bonding interactions with residues of LYS721 and THR830 at the binding pocket while other compounds show only one interaction with LYS721 side chain.
Experimental
Acknowledgement This study is partially funded by Ankara University-BAP 17H0237002 and TÜBITAK 214S574. The authors acknowledge Hitit University-Scientific Research Unit (BAP) with project number FEF19004.17.001 and the Aksaray University Science and Technology Application and Research Center, Aksaray, Turkey, for the use of the Bruker SMART BREEZE CCD diffractometer (purchased under grant No. 2010K120480 of the State of Planning Organization).
Introduction The epidermal growth factor receptor (EGFR or Her1/ErbB1), a vital member of the human epidermal receptor (HER) family, plays an important role in the growth and differentiation of normal epidermal cells [1]. EGFR, as a receptor tyrosine kinase (RTK), contains a glycosylated extracellular domain, a single hydrophobic transmembrane segment, an intracellular portion with a juxtamembrane segment, a protein kinase domain, and a carboxyterminal tail. The binding of ligands, such as epidermal growth factor (EGF), to EGFRs on the surface of cells results in exposure of the dimer interface and homodimerization with another EGFR or heterodimerization with other family member [[2], [3], [4]]. Dimerization results in RTK activation and phosphorylation of specific tyrosine residues, which initiates a mitogenic signalling cascade and other cellular activities [[5], [6], [7]]. Over-expression and mutation of EGFR are involved in lung, breast, stomach, colorectal, head and neck, and pancreatic carcinomas and glioblastoma, making EGFR an ideal target for anticancer drugs. The monoclonal antibodies cetuximab and panitumumab have been clinically used as EGFR inhibitors for anticancer therapy; however, these drugs showed a low clinical response rate (approximately 15%) [8]. The poor clinical response rate is associated with intrinsic and acquired drug resistance, which may be attributed to heterodimerization with other receptors in the family and heterogeneity on the surface of EGFR molecules [5,6,9,10]; therefore, targeting the dimer interface, which is highly conserved and directly involved in the homo- or heterodimerization of EGFR, may be an effective strategy for improving the clinical response of anti-EGFR therapies. Pertuzumab is an approved monoclonal antibody that prevents dimerization of HER2, and its epitope was identified to be located in the β-hairpin loop of the dimer interface [[11], [12], [13], [14]]. The β-hairpin loop of EGFR is a highly conserved sequence that spans residues 237–267 (EGFR237−267) and has 100% sequence identity between human and mouse EGFRs. We have reported a peptide vaccine and a monoclonal antibody (EGFR dimer mAb 5G9) targeting the β-hairpin loop of EGFR, which could effectively inhibit the growth of EGFR-overexpressing tumour cells [15,16]. Nanobodies, also known as the variable domain of the heavy chain of heavy chain antibodies (VHHs), are a new type of antibodies with broad application prospects. Nanobodies have the advantages of small size, good solubility and stability, and the ability to reach their target cells inside tumour tissue. Furthermore, nanobodies can be produced on a large scale using bacterial and yeast systems, which makes them a new class of cost-effective therapeutic antibodies [[17], [18], [19], [20]]. To investigate the feasibility of nanobodies targeting the dimer interface of EGFR as anti-EGFR drugs, a novel nanobody identified from a commercial humanized phage antibody library using the EGFR237−267 peptide as the antigen was reported in this paper.