Conventional anticancer therapy using cytotoxic drugs lacks selectivity and is prone to toxicity and drug resistance. Anticancer therapies targeting aberrant growth factor receptor signaling are gaining interest. The erbB receptor family belongs to the type I, the receptor tyrosine kinases class, and comprises EGFR, HER-2, HER-3, and HER-4. It has been targeted for solid tumor therapy, including breast, ovarian, colon, head-and-neck, and non-small-cell lung cancers. This review summarizes structural aspects of this class of growth factor receptors, their oncogenic expression, and various pharmacological interventions including biological products and small molecules that inhibit these enzymes. We have also discussed various mutations that occur in EGFR and their consequences on anticancer therapy.
The structures of the 16-residue fusion domain (or fusion peptide, FP) of the human immunodeficiency virus gp41 fusion protein, two of its mutants, and a shortened peptide (5-16) were studied by molecular dynamics simulation in an explicit palmitoyloleoylphosphoethanolamine bilayer. The simulations showed that the active wild-type FP inserts into the bilayer approximately 44 degrees +/- 6 degrees with respect to the bilayer normal, whereas the inactive V2E and L9R mutants and the inactive 5 to 16 fragment lie on the bilayer surface. This is the first demonstration by explicit molecular dynamics of the oblique insertion of the fusion domain into lipid bilayers, and provides correlation between the mode of insertion and the fusogenic activity of these peptides. The membrane structure of the wild-type FP is remarkably similar to that of the influenza HA(2) FP as determined by nuclear magnetic resonance and electron spin resistance power saturation. The secondary structures of the wild-type FP and the two inactive mutants are quite similar, indicating that the secondary structure of this fusion domain plays little or no role in affecting the fusogenic activity of the fusion peptide. The insertion of the wild-type FP increases the thickness of the interfacial area of the bilayer by disrupting the hydrocarbon chains and extending the interfacial area toward the head group region, an effect that was not observed in the inactive FPs.
In this early phase of the new era of molecularly targeted patient friendly cancer chemotherapy, there is a need for novel viable anticancer molecular targets. The MDM2 oncoprotein has been validated as a potential target for cancer drug development. MDM2 amplification and/or overexpression occur in a wide variety of human cancers, several of which can be treated experimentally with MDM2 antagonists. MDM2 interacts primarily with the p53 tumor suppressor protein in an autoregulatory negative feedback loop to attenuate p53's cell cycle arrest and apoptosis functions. Inhibition of the p53-MDM2 interaction has been shown to cause selective cancer cell death, as well as sensitize cancer cells to chemotherapy or radiation effects. Consequently, this interaction has been the main focus of anticancer drug discovery targeted to MDM2. The promotion of the proteasomal degradation of the p53 protein by MDM2 is central to its repression of the tumor suppressor functions of p53, and many proteins impinge upon this activity, either enhancing or inhibiting it. MDM2 also has oncogenic activity independent of its interaction with p53, but this has so far not been explored for drug discovery. Among the approaches for targeting MDM2 for cancer therapy, small molecule antagonists have recently featured as effective anticancer agents in experimental models, although the repertoire is currently limited and none has yet entered human clinical trials. Small molecules that have been reported to disrupt the p53-MDM2 binding, thereby enhancing p53 activity to elicit anticancer effects include the following: synthetic chalcones, norbornane derivatives, cis-imidazoline derivatives (Nutlins), a pyrazolidinedione sulfonamide and 1,4-benzodiazepine-2,5-diones, as well as tryptophan derivatives. In addition to compounds disrupting p53pMDM2 binding, three compounds have been discovered that are effective in inhibiting the E3 ligase activity of MDM2 towards p53, and should serve as leads for drug discovery targeting this aspect of the p53-MDM2 interaction as well. These compounds were discovered from library screening and/or structure-based rational drug design strategies.
An essential step in the HIV life cycle is integration of the viral DNA into the host chromosome. This step is catalyzed by a 32-kDa viral enzyme HIV integrase (IN). HIV-1 IN is an important and validated target, and the drugs that selectively inhibit this enzyme, when used in combination with reverse transcriptase (RT) and protease (PR) inhibitors, are believed to be highly effective in suppressing the viral replication. IN catalyzes two discrete enzymatic processes referred to as 3' processing and DNA strand transfer. As a part of a study to optimize new lead molecules we previously identified from a series of 2-mercaptobenzenesulfonamides (MBSAs), we applied three-dimensional quantitative structure-activity relationship methods, comparative molecular field analysis (CoMFA), and comparative molecular similarity indices analysis (CoMSIA) to training sets of up to 66 compounds. Two different conformational templates were used: Conf-d, obtained from docking into the HIV-1 IN active site and Conf-s obtained by a systematic conformational search, using lead compounds 1 and 14, respectively. Reliable models of good predictive power were obtained after removal of compounds with high residuals. The Conf-s models tended to perform better than the Conf-d models. Cross-validated coefficients (q(2)) of up to 0.719 (strand transfer CoMSIA, Conf-s) regression coefficients (r(2)) of up to 0.932 (strand transfer CoMSIA, Conf-d) were obtained, with the number of partial least squares (PLS) components varying from 3 to 6, and the number of outliers being 4 in most of the models. Because all biological data were determined under exactly the same conditions using the same enzyme preparation, our predictive models are promising for drug optimization. Therefore, these results combined with docking studies were used to guide the rational design of new inhibitors. Further synthesis of 12 new analogues was undertaken, and these were used as a test set for validation of the quantitative structure-activity relationship (QSAR) models. For compounds with closely related structures, binding energies given by the FlexX scoring function correlated with HIV-1 IN inhibitory activity.
The overexpression and/or mutation of the epidermal growth factor receptor family of tyrosine kinases, namely EGFR and HER-2, have been implicated in poor prognosis of human solid tumors and are under investigation as molecular targets for cancer therapy. To gain insights into selectivity in the interaction of inhibitors at the ATP site of the two kinases, we have carried out docking, comparative molecular field analysis (CoMFA), and comparative molecular similarity analysis (CoMSIA) 3D-QSAR studies on 50 benzylidene malonitrile derivatives. Docking studies indicate different binding modes (A, B, C, D, and E) that are dependent on the R(1) substituent of the compounds. Binding modes A and B are favored by compounds having a hydroxyl substituent at R(1) whereas a methoxy substituent at R(1) results in compounds occupying binding modes, C, D, and E. The compounds preferred modes A, B, and C in the apo-enzyme whereas modes B, D, and E were preferred in the enzyme in complex with erlotinib. For 3D QSAR studies, based on the multiple binding modes obtained from the docking, four composite alignment strategies (I, II, III, IV) were employed and compared with alignment V, which is based on pairwise atom alignment of the common structural elements. Alignments I and II produced models with better predictive ability than those from alignments III and IV against an external test set. In the EGFR kinase results, alignments I and II produced comparable 3D-QSAR models with alignment II being slightly better than I, whereas in the HER-2 results, alignment I was better than alignment II in its predictive ability. It appears that differences in binding mode preferences at the ATP site might constitute a reason for the selectivity of the dihydroxy compounds as inhibitors of EGFR relative to HER-2. They are more likely to have multiple binding modes at the ATP site of EGFR, i.e., either modes A or B, than in the ATP site of HER-2 where they are possibly limited to only binding mode, A. Selectivity of the methoxy compounds on the other hand appears to depend on hydrogen bonding interactions involving the cyano group and residue 751 in the ATP site.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.