No abstract

A series of indole derivatives was designed and synthesised to improve on activity and circumvent pharmacokinetic limitations experienced with the structurally related compound, ladostigil. The compounds consisted of a propargylamine moiety (a known MAO inhibitor and neuroprotector) at the 1 position and a ChE inhibiting diethyl-carbamate/urea moiety at the 5 or 6 position of the indole ring. In order to prevent or slow down the hydrolysis and deactivation associated with the carbamate function of ladostigil, a urea moeity was incorporated into selected compounds to obtain more metabolically stable structures. The majority of the synthesised compounds showed improved MAO-A inhibitory activity compared to ladostigil. The compounds possessing the propargylamine moiety showed good MAO-B inhibitory activity with and portraying IC values between 14-20 fold better than ladostigil. The ChE assay results indicated that the compounds have non-selective inhibitory activities on eeAChE and eqBuChE regardless of the type or position of substitution (IC: 2-5 μM). MAO-A and MAO-B docking results showed that the propargylamine moiety was positioned in close proximity to the FAD cofactor suggesting that the good inhibitory activity may be attributed to the propargylamine moiety and irreversible inhibition as confirmed in the reversibility studies. Docking results also indicated that the compounds have interactions with important amino acids in the AChE and BuChE catalytic sites. Compound was the most potent multifunctional agent showing better inhibitory activity than ladostigil on all enzymes tested (hMAO-A IC = 4.31 μM, hMAO-B IC = 2.62 μM, eeAChE IC = 3.70 μM, eqBuChE IC = 2.82 μM). Chemical stability tests confirmed the diethyl-urea containing compound to be more stable than its diethyl-carbamate containing counterpart compound. Compound also exerted significant neuroprotection (52.62% at 1 μM) against MPP insult to SH-SY5Y neural cells and has good predicted ADMET properties. The favourable neuronal enzyme inhibitory activity, likely improved pharmacokinetic properties and the potent neuroprotective ability of compound make it a promising compound for further development.

Mycobacterial efflux pumps play a major role in the emergence of antimycobacterial drug resistance. Of particular interest is the proteinaceous multi-drug efflux pump protein Rv1258c that encodes a tetracycline/aminoglycoside resistance (TAP-2)-like efflux pump which is active in susceptible and drug resistant Mycobacterium tuberculosis. Rv1258c is implicated in drug resistance to numerous antimycobacterials including first line drugs rifampicin and isoniazid as well as fluoroquinolone and aminoglycoside antibiotic classes. To date, compounds like verapamil and piperine have been shown to inhibit Rv1258c but no direct evidence for binding or mode of action exist. Therefore in the present study we generated an accurate 3D model of Rv1258c using MODELLER and validated its structure using molecular dynamic simulation studies with GROMACS software. The 3D-structures of Rv1258c and the homologous template 1pw4 were simulated within a POPE/POPG lipid bilayer and found to behave similar. Another important finding was the identification of one local energy minima state of the apo protein, which speaks to the flexibility of the protein and will be investigated further. Extraction of one of the open channel conformations of Rv1258c and blind docking of various structurally diverse putative inhibitors and substrates, allowed for the identification of a probable binding site. Spectinamide was found to bind to a different location on the outside surface of the protein suggesting its ability to avoid the efflux channel. We further identified 246 putative compounds that showed higher binding affinity values to Rv1258c compared to piperine and verapamil. Interaction analysis of the top 20 purchasable compounds identified crucial hydrogen bond interactions with Ser26, Ser45 and Glu243 as well as a pi-pi stacking interaction with Trp32 that accounted for the strong affinity of these compounds for Rv1258c. Future studies will entail purchasing a number of compounds for in vitro activity testing against Mycobacterium tuberculosis.

Drug resistance in Mycobacterium tuberculosis (M. tuberculosis) complicates management of tuberculosis. Efflux pumps contribute to low level resistance and acquisition of additional high level resistance mutations through sub-therapeutic concentrations of intracellular antimycobacterials. Various efflux pump inhibitors (EPIs) have been described for M. tuberculosis but little is known regarding the mechanism of efflux inhibition. As knowledge relating to the mechanism of action and drug target is central to the rational drug design of safe and sufficiently selective EPIs, this review aims to examine recent developments in the study of EPIs in M. tuberculosis from a rational drug development perspective and to provide an overview to facilitate systematic development of therapeutically effective EPIs. Review of literature points to a reduction in cellular energy or direct binding to the efflux pump as likely mechanisms for most EPIs described for M. tuberculosis. This review demonstrates that, where a direct interaction with efflux pumps is expected, both molecular structure and general physicochemical properties should be considered to accurately predict efflux pump substrates and inhibitors. Non-competitive EPIs do not necessarily demonstrate the same requirements as competitive inhibitors and it is therefore essential to differentiate between competitive and non-competitive inhibition to accurately determine structure activity relationships for efflux pump inhibition. It is also evident that there are various similarities between inhibitors of prokaryotic and eukaryotic efflux pumps but, depending on the specific chemical scaffolds under investigation, it may be possible to design EPIs that are less prone to inhibition of human P-glycoprotein, thereby reducing side effects and drug-drug interactions.