Pentacycloundecane-based inhibitors of wild-type C-South African HIV-protease

Understanding Drug Resistance of Wild-Type and L38HL Insertion Mutant of HIV-1 C Protease to Saquinavir

Acquired immunodeficiency syndrome (AIDS) is one of the most challenging infectious diseases to treat on a global scale. Understanding the mechanisms underlying the development of drug resistance is necessary for novel therapeutics. HIV subtype C is known to harbor mutations at critical positions of HIV aspartic protease compared to HIV subtype B, which affects the binding affinity. Recently, a novel double-insertion mutation at codon 38 (L38HL) was characterized in HIV subtype C protease, whose effects on the interaction with protease inhibitors are hitherto unknown. In this study, the potential of L38HL double-insertion in HIV subtype C protease to induce a drug resistance phenotype towards the protease inhibitor, Saquinavir (SQV), was probed using various computational techniques, such as molecular dynamics simulations, binding free energy calculations, local conformational changes and principal component analysis. The results indicate that the L38HL mutation exhibits an increase in flexibility at the hinge and flap regions with a decrease in the binding affinity of SQV in comparison with wild-type HIV protease C. Further, we observed a wide opening at the binding site in the L38HL variant due to an alteration in flap dynamics, leading to a decrease in interactions with the binding site of the mutant protease. It is supported by an altered direction of motion of flap residues in the L38HL variant compared with the wild-type. These results provide deep insights into understanding the potential drug resistance phenotype in infected individuals.

Improved Production of HIV-1 Subtype C Protease from Transgenic E. Coli

Background:

Human Immunodeficiency Virus 1 (HIV-1) subtype C is responsible for the majority of infections of patients in Southern Africa. The HIV protease is a primary target for the development of highly efficient anti-retroviral pharmaceuticals because of its pivotal role in the maturation of the virus in the host cell. For target validation of novel HIV protease inhibitors, there is a need for the availability of an abundance of this protease.

Objective:

This study reports an optimized method to produce HIV-1 protease derived from HIV-1 subtype C.

Methods:

It involves the use of a transgenic E. coli strain that overexpresses the native form of the enzyme via inclusion bodies. A stringent method for the isolation, purification, and renaturation resulted in the production of highly pure active HIV-1 protease. In order to facilitate an increase in protease yields, an optimized growth strategy was developed. In this regard, a chemically defined medium with lower glucose content and devoid of essential amino acids of the TCA cycle was used as an alternative to the widely used nutrient-rich Luria Bertani (LB) medium.

Results:

Results indicated an increase in protease yield up to twice the amount, thereby making this medium an attractive alternative for increasing biomass and HIV protease production for future research.

Conclusion:

An optimized method for HIV-1 protease derived from HIV-1 subtype C production using chemically defined media was established. This was achieved using a known method to isolate and purify the enzyme with the use of a specialized feeding strategy.

Recent Progress in the Development of HIV-1 Protease Inhibitors for the Treatment of HIV/AIDS

HIV-1 protease inhibitors continue to play an important role in the treatment of HIV/AIDS, transforming this deadly ailment into a more manageable chronic infection. Over the years, intensive research has led to a variety of approved protease inhibitors for the treatment of HIV/AIDS. In this review, we outline current drug design and medicinal chemistry efforts toward the development of next-generation protease inhibitors beyond the currently approved drugs.

Binding Free Energy Calculations of Nine FDA-approved Protease Inhibitors Against HIV-1 Subtype C I36T↑T Containing 100 Amino Acids Per Monomer

In this work, have investigated the binding affinities of nine FDA-approved protease inhibitor drugs against a new HIV-1 subtype C mutated protease, I36T↑T. Without an X-ray crystal structure, homology modelling was used to generate a three-dimensional model of the protease. This and the inhibitor models were employed to generate the inhibitor/I36T↑T complexes, with the relative positions of the inhibitors being superimposed and aligned using the X-ray crystal structures of the inhibitors/HIV-1 subtype B complexes as a reference. Molecular dynamics simulations were carried out on the complexes to calculate the average binding free energies for each inhibitor using the molecular mechanics generalized Born surface area (MM-GBSA) method. When compared to the binding free energies of the HIV-1 subtype B and subtype C proteases (calculated previously by our group using the same method), it was clear that the I36T↑T proteases mutations and insertion had a significant negative effect on the binding energies of the non-pepditic inhibitors nelfinavir, darunavir and tipranavir. On the other hand, ritonavir, amprenavir and indinavir show improved calculated binding energies in comparison with the corresponding data for wild-type C-SA protease. The computational model used in this study can be used to investigate new mutations of the HIV protease and help in establishing effective HIV drug regimes and may also aid in future protease drug design.

Pentacycloundecane lactam vs lactone norstatine type protease HIV inhibitors: binding energy calculations and DFT study

Background

Novel pentacycloundecane (PCU)-lactone-CO-EAIS peptide inhibitors were designed, synthesized, and evaluated against wild-type C-South African (C-SA) HIV-1 protease. Three compounds are reported herein, two of which displayed IC₅₀ values of less than 1.00 μM. A comparative MM-PB(GB)SA binding free energy of solvation values of PCU-lactam and lactone models and their enantiomers as well as the PCU-lactam-NH-EAIS and lactone-CO-EAIS peptide inhibitors and their corresponding diastereomers complexed with South African HIV protease (C-SA) was performed. This will enable us to rationalize the considerable difference between inhibitory concentration (IC₅₀) of PCU-lactam-NH-EAIS and PCU-lactone-CO-EAIS peptides.

Results

The PCU-lactam model exhibited more negative calculated binding free energies of solvation than the PCU-lactone model. The same trend was observed for the PCU-peptide inhibitors, which correspond to the experimental activities for the PCU-lactam-NH-EAIS peptide (IC₅₀ = 0.076 μM) and the PCU-lactone-CO-EAIS peptide inhibitors (IC₅₀ = 0.850 μM). Furthermore, a density functional theory (DFT) study on the natural atomic charges of the nitrogen and oxygen atoms of the three PCU-lactam, PCU-lactim and PCU-lactone models were performed using natural bond orbital (NBO) analysis. Electrostatic potential maps were also used to visualize the electron density around electron-rich regions. The asymmetry parameter (η) and quadrupole coupling constant (χ) values of the nitrogen and oxygen nuclei of the model compounds were calculated at the same level of theory. Electronic molecular properties including polarizability and electric dipole moments were also calculated and compared. The Gibbs theoretical free solvation energies of solvation (∆G_solv) were also considered.

Conclusions

A general trend is observed that the lactam species appears to have a larger negative charge distribution around the heteroatoms, larger quadrupole constant, dipole moment and better solvation energy, in comparison to the PCU-lactone model. It can be argued that these characteristics will ensure better eletronic interaction between the lactam and the receptor, corresponding to the observed HIV protease activities in terms of experimental IC₅₀ data.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-015-0115-5) contains supplementary material, which is available to authorized users.

The impact of active site mutations of South African HIV PR on drug resistance: Insight from molecular dynamics simulations, binding free energy and per-residue footprints

Molecular dynamics simulations and binding free energy calculations were used to provide an understanding of the impact of active site drug-resistant mutations of the South African HIV protease subtype C (C-SA HIV PR), V82A and V82F/I84V on drug resistance. Unique per-residue interaction energy 'footprints' were developed to map the overall drug-binding profiles for the wild type and mutants. Results confirmed that these mutations altered the overall binding landscape of the amino acid residues not only in the active site region but also in the flaps as well. Four FDA-approved drugs were investigated in this study; these include ritonavir (RTV), saquinavir (SQV), indinavir (IDV), and nelfinavir (NFV). Computational results compared against experimental findings were found to be complementary. Against the V82F/I84V variant, saquinavir, indinavir, and nelfinavir lose remarkable entropic contributions relative to both wild-type and V82A C-SA HIV PRs. The per-residue energy 'footprints' and the analysis of ligand-receptor interactions for the drug complexes with the wild type and mutants have also highlighted the nature of drug interactions. The data presented in this study will prove useful in the design of more potent inhibitors effective against drug-resistant HIV strains.

Recent patents and emerging therapeutics for HIV infections: a focus on protease inhibitors

The inclusion of protease inhibitors (PIs) in highly active antiretroviral therapy has significantly improved clinical outcomes in HIV-1-infected patients. To date, PIs are considered to be the most important therapeutic agents for the treatment of HIV infections. Despite high anti-HIV-1 potency, poor oral bioavailability of PIs has been a major concern. For achieving therapeutic concentrations, large doses of PIs are administered, which results in unacceptable systemic toxicities. Such severe and long-term toxicities necessitate the development of safer and potentially promising PIs. Recently, considerable attention has been paid to the development of newer compounds capable of inhibiting wild-type and resistant HIV-1 protease. Some of these PIs have displayed potent HIV-1 protease inhibitory activity. In this review, we have made an attempt to provide an overview on clinically approved and newly developing PIs, and related recent patents in the development of novel PIs.

Antiproliferative and antiviral activity of three libraries of adamantane derivatives

Three libraries of adamantane derivatives were synthesized and evaluated for antiviral and antiproliferative activities against a broad variety of DNA and RNA viruses. Whereas none of the compounds exhibit antiviral activity at subtoxic concentrations, antiproliferative activity was found against murine leukemia cells (L1210), human T-lymphocyte cells (CEM), and cervix carcinoma cells (HeLa) for 4, 8, and 10.

Preparation and complete (1) H and (13)C assignment of some pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione (PCUD) derivatives

The preparation of a number of alkyl and alkoxy derivatives of pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione derivatives utilising a cheap, practical, low energy, 'green', single-pass continuous flow photochemical reactor is reported. Their (1)H and (13)C NMR spectra are fully assigned, revealing some general characteristics not previously reported for this class of compound, which should aid the assignment and prediction of the NMR spectra of PCUD derivatives.

Synthesis, screening and computational investigation of pentacycloundecane-peptoids as potent CSA-HIV PR inhibitors

Herein, we present the first pentacycloundecane (PCU) diol peptoid derived HIV protease inhibitors with IC(50) values ranging from 6.5 to 0.075 μM. Five derivatives were synthesized in an attempt to understand the structure activity relationship of this class of compounds for HIV protease inhibition. NMR spectroscopy (new Efficient Adiabatic Symmetrized Rotating Overhauser Effect Spectroscopy, EASY-ROESY) was employed to determine the predominant conformation of the active compound. In this study docking studies and MD simulations provided insight into the binding theme of this class of peptoid inhibitors to the CSA-HIV PR active site. Conserved and stable hydrogen bonding between the hydroxyl groups of the inhibitors and the active site Asp25/Asp25' residues were observed from the docking and along the MD trajectories.

Synthesis, 2D-NMR and molecular modelling studies of pentacycloundecane lactam-peptides and peptoids as potential HIV-1 wild type C-SA protease inhibitors

In this study, eight non-natural peptides and peptoids incorporating the pentacycloundecane (PCU) lactam were designed and synthesized as potential inhibitors of the wild type C-SA HIV-protease. Five of these inhibitors gave IC(50) values ranging from 0.5 up to 0.75 µM against the resistance-prone wild type C-South African HIV-protease. NMR EASY-ROESY studies enabled us to describe the secondary structure of three of these compounds in solution. The 3D structures of the selected cage peptides were also modelled in solution using QM/MM/MD simulations. Satisfactory agreement between the NMR observations and the low energy calculated structures exists. Only one of these inhibitors (11 peptoid), which showed the best IC(50)(0.5 µM), exhibited a definable 3-D structure in solution. Autodock4 and AutodockVina were used to model the potential interaction between these inhibitors and the HIV-PR. It appears that the docking results are too crude to be correlated with the relative narrow range of experimental IC(50) values (0.5-10 µM). The PCU-peptides and peptoides were several orders less toxic (145 μM for 11 and 102 μM for 11 peptoid) to human MT-4 cells than lopinavir (0.025 μM). This is the first example of a polycyclic cage framework to be employed as an HIV-PR transition state analogue inhibitor and can potentially be utilized for other diseases related proteases. [Figure: see text].