Sliding of HIV-1 reverse transcriptase over DNA creates a transient P pocket – targeting P-pocket by fragment screening

HIV-1 reverse transcriptase (RT) slides over an RNA/DNA or dsDNA substrate while copying the viral RNA to a proviral DNA. We report a crystal structure of RT/dsDNA complex in which RT overstepped the primer 3’-end of a dsDNA substrate and created a transient P-pocket at the priming site. We performed a high-throughput screening of 300 drug-like fragments by X-ray crystallography that identifies two leads that bind the P-pocket, which is composed of structural elements from polymerase active site, primer grip, and template-primer that are resilient to drug-resistance mutations. Analogs of a fragment were synthesized, two of which show noticeable RT inhibition. An engineered RT/DNA aptamer complex could trap the transient P-pocket in solution, and structures of the RT/DNA complex were determined in the presence of an inhibitory fragment. A synthesized analog bound at P-pocket is further analyzed by single-particle cryo-EM. Identification of the P-pocket within HIV RT and the developed structure-based platform provide an opportunity for the design new types of polymerase inhibitors.

Exploring New Scaffolds for the Dual Inhibition of HIV-1 RT Polymerase and Ribonuclease Associated Functions

Current therapeutic protocols for the treatment of HIV infection consist of the combination of diverse anti-retroviral drugs in order to reduce the selection of resistant mutants and to allow for the use of lower doses of each single agent to reduce toxicity. However, avoiding drugs interactions and patient compliance are issues not fully accomplished so far. Pursuing on our investigation on potential anti HIV multi-target agents we have designed and synthesized a small library of biphenylhydrazo 4-arylthiazoles derivatives and evaluated to investigate the ability of the new derivatives to simultaneously inhibit both associated functions of HIV reverse transcriptase. All compounds were active towards the two functions, although at different concentrations. The substitution pattern on the biphenyl moiety appears relevant to determine the activity. In particular, compound 2-{3-[(2-{4-[4-(hydroxynitroso)phenyl]-1,3-thiazol-2-yl} hydrazin-1-ylidene) methyl]-4-methoxyphenyl} benzamide bromide (EMAC2063) was the most potent towards RNaseH (IC50 = 4.5 mM)- and RDDP (IC50 = 8.0 mM) HIV RT-associated functions.

Repurposing Multi-Targeting Plant Natural Product Scaffolds In Silico Against SARS-CoV-2 Non-Structural Proteins Implicated in Viral Pathogenesis

<p>Background: Accessing COVID-19 vaccines is a challenge despite successful clinical trials. This burdens the COVID-19 treatment gap, thereby requiring accelerated discovery of anti-SARS-CoV-2 agents. Thus, this study explored the potential of anti-HIV reverse transcriptase (RT) phytochemicals as inhibitors of SARS-CoV-2 non-structural proteins (nsps) by targeting <i>in silico</i> key sites in the structures of SARS-CoV-2 nsps. Moreover, structures of the anti-HIV compounds were considered for druggability and toxicity. 104 anti-HIV phytochemicals were subjected to molecular docking with papain-like protease (nsp3), 3-chymotrypsin-like protease (nsp5), RNA-dependent RNA polymerase (nsp12), helicase (nsp13), SAM-dependent 2’-<i>O-</i>methyltransferase (nsp16) and its cofactor (nsp10), and endoribonuclease (nsp15). Drug-likeness and ADME (absorption, distribution, metabolism, and excretion) properties of the top ten compounds per nsp were predicted using SwissADME. Their toxicity was also determined using OSIRIS Property Explorer.</p> <p>Results: Among the twenty-seven top-scoring compounds, the polyphenolic natural products amentoflavone (<b>1</b>), robustaflavone (<b>4</b>), punicalin (<b>9</b>), volkensiflavone (<b>11</b>), rhusflavanone (<b>13</b>), morelloflavone (<b>14</b>), hinokiflavone (<b>15</b>), and michellamine B (<b>19</b>) were multi-targeting and had the strongest affinities to at least two of the nsps (Binding Energy = -7.7 to -10.8 kcal/mol). Friedelin (<b>2</b>), pomolic acid (<b>5</b>), ursolic acid (<b>10</b>), garcisaterpenes A (<b>12</b>), hinokiflavone (<b>15</b>), and digitoxigenin-3-<i>O-</i>glucoside (<b>17</b>) were computationally druggable. Moreover, compounds <b>5</b> and <b>17</b> showed good gastrointestinal absorptive property. Most of the compounds were also predicted to be non-toxic.</p> <p>Conclusions: Twenty anti-HIV RT phytochemicals showed multi-targeting inhibitory potential against SARS-CoV-2 nsp3, 5, 10, 12, 13, 15, and 16, and can therefore be used as prototypes for anti-COVID-19 drug design.</p>

Repurposing Multi-Targeting Plant Natural Product Scaffolds In Silico Against SARS-CoV-2 Non-Structural Proteins Implicated in Viral Pathogenesis

<p>Background: Accessing COVID-19 vaccines is a challenge despite successful clinical trials. This burdens the COVID-19 treatment gap, thereby requiring accelerated discovery of anti-SARS-CoV-2 agents. Thus, this study explored the potential of anti-HIV reverse transcriptase (RT) phytochemicals as inhibitors of SARS-CoV-2 non-structural proteins (nsps) by targeting <i>in silico</i> key sites in the structures of SARS-CoV-2 nsps. Moreover, structures of the anti-HIV compounds were considered for druggability and toxicity. 104 anti-HIV phytochemicals were subjected to molecular docking with papain-like protease (nsp3), 3-chymotrypsin-like protease (nsp5), RNA-dependent RNA polymerase (nsp12), helicase (nsp13), SAM-dependent 2’-<i>O-</i>methyltransferase (nsp16) and its cofactor (nsp10), and endoribonuclease (nsp15). Drug-likeness and ADME (absorption, distribution, metabolism, and excretion) properties of the top ten compounds per nsp were predicted using SwissADME. Their toxicity was also determined using OSIRIS Property Explorer.</p> <p>Results: Among the twenty-seven top-scoring compounds, the polyphenolic natural products amentoflavone (<b>1</b>), robustaflavone (<b>4</b>), punicalin (<b>9</b>), volkensiflavone (<b>11</b>), rhusflavanone (<b>13</b>), morelloflavone (<b>14</b>), hinokiflavone (<b>15</b>), and michellamine B (<b>19</b>) were multi-targeting and had the strongest affinities to at least two of the nsps (Binding Energy = -7.7 to -10.8 kcal/mol). Friedelin (<b>2</b>), pomolic acid (<b>5</b>), ursolic acid (<b>10</b>), garcisaterpenes A (<b>12</b>), hinokiflavone (<b>15</b>), and digitoxigenin-3-<i>O-</i>glucoside (<b>17</b>) were computationally druggable. Moreover, compounds <b>5</b> and <b>17</b> showed good gastrointestinal absorptive property. Most of the compounds were also predicted to be non-toxic.</p> <p>Conclusions: Twenty anti-HIV RT phytochemicals showed multi-targeting inhibitory potential against SARS-CoV-2 nsp3, 5, 10, 12, 13, 15, and 16, and can therefore be used as prototypes for anti-COVID-19 drug design.</p>

'I think they might just go to the doctor': qualitatively examining the (un)acceptability of newer HIV testing approaches among Vietnamese-born migrants in greater-Brisbane, Queensland, Australia

Background In high-income countries (HICs), migrants often have higher rates of late diagnosis of HIV than the host population. Timely HIV testing has significant implications for HIV prevention and management. Newer HIV testing approaches, namely provider-initiated testing and counselling (PITC), HIV rapid testing (HIV RT) and HIV self-testing (HIV ST), aim to reach those populations most at risk and, particularly, those who have not previously tested for HIV. Methods: This study used semi-structured interviews to examine the (un)acceptability, barriers and facilitators to newer HIV testing approaches (i.e. PITC, HIV RT and HIV ST) among Vietnamese-born migrants (n = 10) in greater-Brisbane, Queensland, Australia. Results: Vietnamese-born migrants had mixed perspectives on the (un)acceptability of newer HIV testing approaches. PITC was largely viewed by participants as a facilitator to HIV testing for Vietnamese-born migrants. Likewise, HIV RT (undertaken by a doctor in a medical setting, as opposed to a trained community member in a community setting) was generally considered to facilitate HIV testing. HIV ST was largely not considered acceptable to Vietnamese-born migrants and they would prefer to go to a doctor for HIV testing. Several factors were identified that either facilitate or act as barriers to newer HIV testing approaches, including privacy; cost of (accessing) HIV testing; comfort and convenience; healthcare provider relationship; risk perception; symptoms; and technical and emotional support. Conclusions: There is a need to understand migrants’ HIV testing preferences if poorer HIV-related outcomes are to be overcome. The findings from this study show a preference for doctor-centred HIV testing, due to enhanced privacy, accuracy and support.

Rational in silico drug design of HIV-RT inhibitors through G-QSAR and molecular docking study of 4-arylthio and 4-aryloxy-3-iodopyridine-2(1-H)-one derivative

Background Human immunodeficiency virus infection and acquired immune deficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV). Antiretroviral therapy (ART) against HIV infection offers the promise of controlling disease progression and prolonging the survival of HIV-infected patients. Reverse transcriptase (RT) inhibitors remain the cornerstone of the drug regimen to treat AIDS. In this direction, by using group-based QSAR study (G-QSAR), identification of the structural need for the development of lead structure with reverse transcriptase inhibition on 97 reported structures was carried out. Docking analysis was performed further and suggested the structural properties required for binding affinity with the receptor. The molecules in the data set were fragmented into six (R1, R2, R3, R4, R5, and R6) by applying the fragmentation pattern. Three G-QSAR models were selected based on the statistical significance of the model. The molecular docking study was performed to explain the structural properties required for the design of potent HIV-RT inhibitors. Results The statistically validated QSAR models reveal the presence of higher hydrophobic groups containing single-bonded –Br atom, 2 aromatic bonded –NH group with less electronegativity, and entropic interaction fields at R2 essential for better anti-HIV activity. The presence of a lipophilic group at R3, oxygen and sulfur connected with two aromatic bonds at R4, and –CH3 group at R5 was fruitful for reverse transcriptase inhibition. Docking studies of the selected inhibitors with the active site of reverse transcriptase enzyme showed hydrogen bond, Van der Waal’s, charge, aromatic, and π–π interactions with residues present at the active site. Conclusion The results of the generated models provide significant site-specific insight into the structural requirements for reverse transcriptase inhibition during the design and development of novel anti-HIV compounds. Molecular docking study revealed the binding interaction between the ligand and the receptor which gave insight towards the structure-based design for the discovery of more potent compounds with better activity against HIV infection.

Translesion Synthesis by MmLV-, AMV-, and HIV-Reverse Transcriptases Using RNA Templates Containing Inosine, Guanosine, and Their 8-oxo-7,8-Dihydropurine Derivatives

ABSTRACTInosine is ubiquitous and essential in many biological processes, including RNA-editing. In addition, oxidative stress on RNA has been a topic of increasing interest due, in part, to its potential role in the development/progression of disease. In this work we probed the ability of three reverse transcriptases to catalyze the synthesis of cDNA in the presence of RNA templates containing inosine (I), 8-oxo-7,8-dihydroinosine (8oxo-I), guanosine (G), or 8-oxo-7,8-dihydroguanosine (8-oxoG), and explored the impact that these purine derivatives have as a function of position. To this end, we used 29-mers of RNA (as template) containing the modifications at position-18 and reverse transcribed DNA using 17-mers, 18-mers, or 19-mers (as primers). Generally reactivity of the viral RTs, MMLV / AMV / HIV, towards cDNA synthesis was similar for templates containing G or I, as well as for those with 8-oxoG or 8-oxoI. Notable differences are 1) that templates containing I enabled the incorporation of dT when using 17-mers (for exploring incorporation of dNTPs opposite the site of interest); 2) that the use of 18-mers of DNA (to explore cDNA synthesis past the lesion) led to DNA elongation inhibition in the case when a G:dA wobble pair was present, while the presence of I, 8-oxoI, or 8-oxoG led to full synthesis of the corresponding cDNA, with the latter two displaying a more efficient process; 3) that HIV-RT is more sensitive to modified base pairs in the vicinity of cDNA synthesis; and 4) that the presence of a modification two positions away from transcription initiation has an adverse impact on the overall process. Steady-state kinetics were established to determine substrate specificities towards canonical dNTPs (N = G, C, T, A). Overall we found evidence that RNA templates containing inosine are likely to incorporate dC > dT > > dA, where reactivity in the presence of dA was found to be pH dependent (process abolished at pH 7.3); and that the absence of the C2-exocyclic amine, as displayed with templates containing 8-oxoI, leads to increased selectivity towards incorporation of dA over dC. The data will be useful in assessing the impact that the presence of inosine and/or oxidatively generated lesions have on viral processes and adds to previous reports where I codes exclusively like G.

Hepatitis B virus resistance to tenofovir: fact or fiction? A synthesis of the evidence to date

ABSTRACTBackgroundTenofovir (TFV) is a widely used antiviral treatment for chronic hepatitis B virus (HBV) infection. There is a high genetic barrier to the selection of TFV resistance-associated mutations (RAMs), but the distribution and clinical significance of TFV RAMs are not well understood, and the topic remains contentious. We here present assimilated evidence for putative TFV RAMs with the aims of cataloguing and characterising mutations that have been reported, and starting to develop insights into the mechanisms of resistance and potential clinical significance.MethodsWe carried out a systematic literature search in PubMed to identify clinical, in vitro and in silico evidence of TFV resistance. The structure of HBV reverse transcriptase (RT) has not been solved; we therefore compared HBV RT to the crystal structure for HIV RT to map the likely sites of RAMs.ResultsWe identified a ‘long-list’ of 37 putative TFV RAMs in HBV RT, occurring within and outside sites of enzyme activity, some of which can be mapped onto a homologous HIV RT structure. Based on quality and quantity of supporting data, we generated a ‘short-list’ of nine sites that are supported by the most robust evidence. Most resistance arises as a result of suites of multiple RAMs. Other factors including adherence, viral load, HBeAg status, HIV coinfection and NA dosage may also influence viraemic suppression.ConclusionThere is emerging evidence for polymorphisms that may reduce susceptibility to TVF. A better understanding of HBV drug resistance is imperative to optimise approaches to public health elimination targets.