New features that improve the pharmacophore tools from Accelrys.

Generating a pharmacophore is often the first step towards understanding the interactions between a receptor and a ligand and can be pivotal to a successful drug discovery project. The pharmacophore tools at Accelrys have been used to assist in many different projects over the years, such as lead generation, scaffold hopping, mining ligand databases as well as many more. In this article, we will review the pharmacophore tools that have been developed at Accelrys. These will include the often used and well validated ligand based algorithms, HipHop and HypoGen and as well as extensions of these algorithms, HipHopRefine and HypoGenRefine. Recently we also developed new pharmacophore tools in the area of structure based design - deriving pharmacophores from the receptor as well as the receptor-ligand complex - which will also be discussed in this paper.

Fully automated molecular mechanics based induced fit protein-ligand docking method.

We describe a method for docking a ligand into a protein receptor while allowing flexibility of the protein binding site. The method employs a multistep procedure that begins with the generation of protein and ligand conformations. An initial placement of the ligand is then performed by computing binding site hotspots. This initial placement is followed by a protein side-chain refinement stage that models protein flexibility. The final step of the process is an energy minimization of the ligand pose in the presence of the rigid receptor. Thus the algorithm models flexibility of the protein at two stages, before and after ligand placement. We validated this method by performing docking and cross docking studies of eight protein systems for which crystal structures were available for at least two bound ligands. The resulting rmsd values of the 21 docked protein-ligand complexes showed values of 2 A or less for all but one of the systems examined. The method has two critical benefits for high throughput virtual screening studies. First, no user intervention is required in the docking once the initial binding site selection has been made in the protein. Second, the initial protein conformation generation needs to be performed only once for a given binding region. Also, the method may be customized in various ways depending on the particular scenario in which dockings are being performed. Each of the individual steps of the method is fully independent making it straightforward to explore different variants of the high level workflow to further improve accuracy and performance.

Using pharmacophore models to gain insight into structural binding and virtual screening: an application study with CDK2 and human DHFR.

This study provides results from two case studies involving the application of the HypoGenRefine algorithm within Catalyst for the automated generation of excluded volume from ligand information alone. A limitation of pharmacophore feature hypothesis alone is that activity prediction is based purely on the presence and arrangement of pharmacophoric features; steric effects remained unaccounted. Recently reported studies have illustrated the usefulness of combining excluded volumes to the pharmacophore models. In general, these excluded volumes attempt to penalize molecules occupying steric regions that are not occupied by active molecules. The HypoGenRefine algorithm in Catalyst accounts for steric effects on activity, based on the targeted addition of excluded volume features to the pharmacophores. The automated inclusion of excluded volumes to pharmacophore models has been applied to two systems: CDK2 and human DHFR. These studies are used as examples to illustrate how ligands could bind in the protein active site with respect to allowed and disallowed binding regions. Additionally, automated refinement of the pharmacophore with these excluded volume features provides a more selective model to reduce false positives and a better enrichment rate in virtual screening.

DNA recognition by the anthracycline antibiotic respinomycin D: NMR structure of the intercalation complex with d(AGACGTCT)2.

Respinomycin D is a member of the anthracycline family of antitumour antibiotics that interact with double stranded DNA through intercalation. The clinical agents daunomycin and doxorubicin are the most well-studied of this class but have a relatively simple molecular architecture in which the pendant daunosamine sugar resides in the DNA minor groove. Respinomycin D, which belongs to the nogalamycin group of anthracyclines, possesses additional sugar residues at either end of the aglycone chromophore that modulate the biological activity but whose role in molecular recognition is unknown. We report the NMR structure of the respinomycin D-d(AGACGTCT)2 complex in solution derived from NOE restraints and molecular dynamics simulations. We show that the drug threads through the DNA double helix forming stabilising interactions in both the major and minor groove, the latter through a different binding geometry to that previously reported. The bicycloaminoglucose sugar resides in the major groove and makes specific contacts with guanine at the 5'-CpG intercalation site, however, the disaccharide attached at the C4 position plays little part in drug binding and DNA recognition and is largely solvent exposed.