Current Topics in Medicinal Chemistry - Volume 15, Issue 1, 2015

Drug repositioning is an important component of therapeutic stratification in the precision medicine paradigm. Molecular profiling and more sophisticated analysis of longitudinal clinical data are refining definitions of human diseases, creating needs and opportunities to re-target or reposition approved drugs for alternative indications. Drug repositioning studies have demonstrated success in complex diseases requiring improved therapeutic interventions as well as orphan diseases without any known treatments. An increasing collection of available computational and experimental methods that leverage molecular and clinical data enable diverse drug repositioning strategies. Integration of translational bioinformatics resources, statistical methods, chemoinformatics tools and experimental techniques (including medicinal chemistry techniques) can enable the rapid application of drug repositioning on an increasingly broad scale. Efficient tools are now available for systematic drug-repositioning methods using large repositories of compounds with biological activities. Medicinal chemists along with other translational researchers can play a key role in various aspects of drug repositioning. In this review article, we briefly summarize the history of drug repositioning, explain concepts behind drug repositioning methods, discuss recent computational and experimental advances and highlight available open access resources for effective drug repositioning investigations. We also discuss recent approaches in utilizing electronic health record for outcome assessment of drug repositioning and future avenues of drug repositioning in the light of targeting disease comorbidities, underserved patient communities, individualized medicine and socioeconomic impact.

The traditional knowledge of medicinal plants that are in use by the indigenous Jaintia tribes residing in few isolated pockets of North-East India is documented here. The present study was carried out through the personal discussion with the president of the Jaintia Indigenous Herbal Medicine Association, Dr.H.Carehome Pakyntein from Jowai, Meghalaya. The plants being used generation after generation by his family of herbalists to cure ailments like tuberculosis, cancer and diabetes were selected for the present study. In order to scientifically validate the use of these selected plants for the cure of selected diseases, phytochemical analyses, characterization and molecular docking studies of some of the selected compounds from these plants have been carried out. The compounds 2-hydroxy-4-methoxy- Benzaldehyde from methanolic extract of Strophanthus Wallichii and DL tetrahydropalmatine from Stephania Hernandifolia have been confirmed after determining their molecular structures, justifying the activity of these two plants against TB and cancer, respectively. The present study covers the potentials of some of the medicinal plants of North east India in curing common diseases due to which millions of people suffer and die. The presence of certain compounds in these plants related to the cure of the diseases deserves further studies.

Ribonucleotide reductase subunit R2 regulates catalytic action of the enzyme to provide DNA synthesis material via reduction. It has been continuously investigated as anticancer drug target for design and discovery of its inhibitors. Present studies aim to design novel heterocyclic/aryl substituted and adamantyl added thiosemicarbazones out fitted with improved cell permeability and effective RNR inhibition. Design strategy renders significant use of virtual screening and molecular docking studies to converge search of selective molecules for synthesis and further experimental studies. Selected candidates were synthesized and evaluated in vitro for their RNR inhibitory activity (IC50, uM) on MCF-7 cells, breast cancer cell lines. Molecular docking results (docking scores) and experimental results (IC50, uM) were found to be correlated and in agreement. Structure-based and ligandbased studies of results substantiate regulative role of water molecules at catalytic site (H2O: 2057) as well as at RNR inhibitor binding site (H2O: 2023, 2047, 2060 and 2070). Admantyl group has testified constant spatial position in docked poses and involved in steric interactions with Cys271, Asp272, Phe237, Gly234 and Val238. Heterocyclic/aryl substitutions equally offered H-bonds with water molecules (H2O: 2028, 2054, 2061 and 2073) along with amino acids Ser264, Asp272, Tyr324 and Asn346. Present efforts to design new inhibitors incur new characteristics in RNR Inhibition.

Human immunodeficiency virus type 1 (HIV-1) integrase (IN) is an essential enzyme in the viral replication cycle as it catalyzes the insertion of the reverse transcribed viral DNA into host chromosome. The structure of prototype foamy virus (PFV) IN has structural and functional homology with HIV-1 IN (no full-length structure available). In this study, we have used PFV IN-DNA complex as a surrogate model for HIV-1 IN-DNA complex to investigate the binding modes of N-methyl pyrimidones (NMPs) by QMpolarized ligand docking (QPLD), binding free energy calculations and molecular dynamics simulations. The O,O,O donor atom triad of NMPs show metal chelation with divalent Mg2+ ions in the active site of PFV IN, in perfect agreement with the proposed mechanism of IN strand transfer inhibitors (INSTIs). The results also show that the benzyl group of compounds fit into a pocket to displace the 3'-terminal adenosine of viral DNA from the IN active site making it unavailable for the nucleophile to attack the target DNA in the strand transfer (ST) reaction. The halobenzyl moiety show hydrophobic interactions with conserved PFV IN Tyr212 and Pro214 residues, corresponding to HIV-1 IN Tyr143 and Pro145, respectively. Molecular dynamics (MD) simulations gave important insights into the structural and chemical basis involved in ST inhibition. Based on MD results, hydrogen bond with Tyr212, coordinate bonds with Mg2+ ions, and hydrophobic interactions play an important role in the stabilization of compounds. Our results provide additional insight into the possible mechanism of action and binding mode of NMPs, and might have implications for rational design of specific HIV-1 INSTIs with improved affinity and selectivity.

Salbutamol forms an important and widely administered β2 agonist prescribed in the symptomatic treatment of bronchial asthma. Unfortunately, a subset of patients show refractoriness to it owing to ADRB2 gene variant (rs 1800888). The variant substitutes Thr to Ile at the position 164 in the β2 adrenergic receptor leading to sub-optimal binding of agonists. The present study aims to associate the Salbutamol response with the variant and select the bioactive conformer of Sabutamol with optimal binding affinity against mutated receptor by in silico approaches. To assess bronchodilator response spirometry was performed before and 15 min after Salbutamol (200 mcg) inhalation. Responders to Salbutamol were categorized if percentage reversibility was greater than or equal to 12%, while those showing FEV1 reversibility less than 12% were classified as non-responders. Among the 344 subjects screened, 238 were responders and 106 were non-responders. The frequency of mutant allele “T” was significantly higher in case of non-responders (p < 0.05). In silico process involved generation of Salbutamol conformer ensembles supported by systematic search algorithm. 4369 conformers were generated of which only 1882 were considered bioactive conformers (threshold RMSD≤1 in reference to normalized structure of salbutamol). All the bioactive conformers were evaluated for the binding affinity against (Thr164 Ile) receptor through MolDock aided docking algorithm. One of the bioactive conformer (P.E. = -57.0038, RMSD = 0.6) demonstrated 1.54 folds greater affinity than the normal Salbutamol in the mutated receptor. The conformer identified in the present study may be put to pharmacodynamic and pharmacokinetic studies in future ahead.

Since the discovery of Hsp90, a decade ago, it has surfaced as a potential target in breast cancer therapy along with other cancers. In present study, we have selected seven established Hsp inhibitors viz., PU3, CCT-018159, CNF-2024, SNX-5422, NVP (AUY-922), EGCG and IPI-504 used in the treatment of cancer. Considering these seven inhibitors as a parent compound, ligand based search was carried out with 90% similarity in Pubchem database (31 million compounds). All the similar molecules belonging to respective parent compound along with similar compound were subjected to virtual screening using MolDock and PLP algorithm aided molecular docking. Compounds with highest docking rerank scores were selected and filtered through Lipinski’s drug-likeness filters and toxicity parameters. New candidate (Pubchem CID: 11363378) qualified to demonstrate considerable affinity towards Hsp90. The selected compound was further pharmcophorically incited for receptor- ligand interactions like H-bond, electrostatic, hydrophobic interactions etc.

Currently available antiviral drugs target the pol-encoded retroviral enzymes or integrases, in addition, inhibitors that target HIV-1 envelope-receptor interactions have also been recently approved. Recent understanding of the interactions between HIV-1 and host restriction factors has provided fresh avenues for development of novel antiviral drugs. For example, viral infectivity factor (Vif) now surfaced as an important therapeutic target in treatment of HIV infection. Vif suppresses A3G antiviral activity by targeting these proteins for polyubiquitination and proteasomal degradation. In the present study we analyzed the inhibitory potential of VEC5 and RN18 to inhibit the Vif-A3G interaction through protein- protein docking studies. Perusal of the study showed that, VEC5 and RN18 though inhibits the interaction however showed sub optimal potential. To overcome this set back, we identified 35 structural analogues of VEC5 and 18 analogues of RN18 through virtual screening approach. Analogue with PubCID 71624757 and 55358204 (AKOS006479723) -structurally akin to VEC5 and RN18 respectively showed much appreciable interaction than their respective parent compound. Evident from Vif-A3G; protein - protein docking studies, analogue PubCID 71624757 demonstrated 1.08 folds better inhibitory potential than its parent compound VEC5 while analogue PubCID 55358204 was 1.15 folds better than RN18. Further these analogues passed drug likeness filters and predicted to be non- toxic. We expect these analogues can be put to pharmacodynamic studies that can pave way the breakthrough in HIV therapeutics.

Tubulin has picked up great focus as a major target in drug discovery and consequently, tubulin inhibitors have pulling in a considerable attention as anticancer agents. Numerable naturally occurring agents have focused on tubulin system act as an imperative target of cancer chemotherapy. Substantial number of tubulin inhibitors has been discovered so far and these agents are classified as indicated by their interaction. They are colchicine site binder, vinca- alkaloid related drugs and those interacting with the Taxol binding site and functioning as stabilising agents. We review the recent advances in the advancement of tubulin interfering agents and will render the current trend in the improvement of tubulin inhibitors as anticancer agents.