Discovery and Application of Biologically Active Molecules on the Privileged Structure-Based Strategy in the Drug Discovery and Abused Drug Biosensor

Abstract

Over the past 20 years the privileged structure concept has emerged as a fruitful approach to the discovery of novel biologically active molecules. Biologically active compounds obtained from library based on the privileged structure, which is a molecular scaffold with versatile binding properties, have been applied to the drug discovery such as kinase inhibitor and the biosensor construction including abused drug biosensor system. In chapter I, were introduced discovery and development of the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor originated from the adenosine triphosphate (ATP) as the privileged structure. The EGFR family of receptor tyrosine kinases (EGFR/HER-1, HER-2, HER-3, and HER-4) has been implicated in a variety of cancers. In particular, activating mutations such as the L858R point mutation in exon 21 and the small in-frame deletions in exon 19 of the EGFR tyrosine kinase domain are correlated with sensitivity to EGFR tyrosine kinase inhibitors (e.g. gefitinib and erlotinib) in non–small cell lung cancer (NSCLC) patients. But the clinical treatment of patients is limited due to the development of drug resistance resulting mainly from a gatekeeper mutation (EGFR T790M). In addition, other subtype such as HER-2 is overexpressed in 20-25% of metastatic breast or gastric cancers and is associated with an aggressive tumor type and reduced survival rate. Therefore, HER-2 targeted therapy such as trastuzumab (monoclonal antibody) or lapatinib is beneficial for patients with high HER-2 expression level. However, the majority of cancers that initially respond to HER-2 targeted therapy begin to progress again within 1 year. Thus, in the EGFR targeted therapy area, there have been unmet medical needs associated with resistance. For the discovery of new EGFR tyrosine kinase inhibitor, novel series of (S)-1-acryloyl-N-[4-(arylamino)-7-(alkoxy)quinazolin-6-yl]pyrrolidine-2-carboxamides and N4-(3-chloro-phenyl)-5-(oxazol-2-yl)pyrimidine-4,6-diamines were synthesized and evaluated as HER-1/HER-2 dual inhibitors. In contrast to previously approved HER-1 selective inhibitors (gefitinib and erlotinib) or HER-1/HER-2 dual inhibitor (lapatinib), our novel compounds are irreversible inhibitors of HER-1 and HER-2 tyrosine kinases with the potential to overcome clinically relevant drug resistance. The selected compounds (19c, 19d, and 38a) showed good HER-1 and HER-2 inhibition activity even toward the T790M mutation of HER-1 tyrosine kinase with excellent selectivity. The pharmacokinetic profiles of these compounds in animals (19c, 19d, and 38a) and in vivo efficacy in an A431 xenograft model (19c and 19d) clearly demonstrate that they merit further investigation as novel therapeutic agents for EGFR-targeting treatment of solid tumors. In succession, the promising candidate HM781-36B was discovered and evaluated for the therapeutic potential of an irreversible pan-HER inhibitor. The results from this study show that HM781-36B is a potent inhibitor of EGFR including the EGFR-acquired resistance mutation (T790M), HER-2 and HER-4 compared with other EGFR tyrosine kinases inhibitors such as erlotinib, lapatinib, and BIBW2992. HM781-36B treatment of EGFR DelE746_A750-harboring erlotinib-sensitive HCC827 and EGFR L858R/T790M-harboring erlotinib-resistant NCI-H1975 NSCLC cells results in the inhibition of EGFR phosphorylation and the subsequent deactivation of downstream signaling proteins. Additionally, HM781-36B shows an excellent efficacy in a variety of EGFR- and HER-2-dependent tumor xenograft models, including erlotinib-sensitive HCC827 NSCLC cells, erlotinib-resistant NCI-H1975 NSCLC cells, HER-2 overexpressing Calu-3 NSCLC cells, NCI-N87 gastric cancer cells, SK-Ov3 ovarian cancer cells, and EGFR-overexpressing A431 epidermoid carcinoma cancer cells. On the basis of these preclinical results, HM781-36B is the most potent pan-HER inhibitor, which will be advantageous for the treatment of patients with NSCLC including clinical limitation caused by acquired mutation (EGFR T790M), breast cancer, and gastric cancer. In chapter II, was introduced construction of biosensor for abused antibiotics using the pharmacophore information of fluoroquinolone as a privileged structure. We developed fluorescent biosensor systems that are general or selective to fluoroquinolone antibiotics by using a single-chain variable-fragment (scFv) as a recognition element. The selectivity and generality of these biosensors to fluoroquinolone antibiotics were rationally tuned through the structural modification on the pharmacophore of fluoroquinolone antibiotics and the subsequent selection of scFv receptor modules with these antibiotics-based antigens using phage display. The resulting A2 and F9 scFvs bound to their representative antigen with a moderate affinty (KD in micromolar range as determined by surface plasmon resonance). A2 is a specific binder for enrofloxacin and did not cross-react with other fluoroquinolone antibiotics including structurally similar ciprofloxacin, while F9 is a general fluoroquinolone binder likely bound to the antigen at the common pyridone-carboxylic acid pharmacophore. These scFv-based receptors were successfully applied to the development of one-step fluorescent biosensor which can detect fluoroquinolone antibiotics at concentrations below the level suggested in animal drug application guidelines. The strategy described in this report can be applied to developing convenient field biosensors that can quantitatively detect overused/misused antibiotics in drinking water of the livestock.