Binding of Multivalent Anionic Porphyrins to V3 Loop Fragments of an HIV-1 Envelope and Their Antiviral Activity

Repurposing anti-cancer porphyrin derivative drugs to target SARS-CoV-2 envelope

Antiviral medicines to treat COVID-19 are still scarce. Porphyrins and porphyrin derivatives (PDs) usually present broad-spectrum antiviral activity with low risk of resistance development. In fact, some PDs are clinically approved to be used in anti-cancer photodynamic therapy and repurposing clinically approved PDs might be an alternative to treat COVID-19. Here, we characterize the ability of temoporfin, verteporfin, talaporfin and redaporfin to inactivate SARS-CoV-2 infectious particles. PDs light-dependent and -independent effect on SARS-CoV-2 infectivity were evaluated. PDs photoactivation successfully inactivated SARS-CoV-2 with very low concentrations and light dose. However, only temoporfin and verteporfin inactivated SARS-CoV-2 in the dark, being verteporfin the most effective. PDs treatment reduced viral load in infected Caco-2 cells, while not inducing cytotoxicity. Furthermore, light-independent treatment with temoporfin and verteporfin act on early stages of viral infection. Using lipid vehicles as membrane models, we characterized PDs interaction to the viral envelope. Verteporfin presented the lowest IC50 for viral inactivation and the highest partition coefficients (Kp) towards lipid bilayers. Curiously, although temoporfin and redaporfin presented similar Kps, redaporfin did not present light-independent antiviral activity, and only temoporfin and verteporfin caused lipid membrane disorder. In fact, redaporfin is located closer to the bilayer surface, while temoporfin and verteporfin are located closer to the centre. Our results suggest that viral envelope affinity, with penetration and destabilization of the lipid bilayer, seems critical to mediate PDs antiviral activity. Altogether, these findings open new avenues for the off-label application of temoporfin and verteporfin in the systemic treatment of COVID-19.

Porphyrins with combinations of 4-carboxyphenyl and 4-hydroxyphenyl substituents in meso-positions as anti-HIV-1 agents

A series of 4-carboxyphenyl/4-hydroxyphenyl meso-substituted porphyrins were synthesized, purified, and characterized. The compounds exhibited anti-HIV-1 activities, in vitro, under both non-photodynamic (non-PDT) and photodynamic (PDT) conditions. Specifically, the porphyrins inhibited HIV-1 virus entry, with c-PB2(OH)2 and PB(OH)3 showing significant anti-HIV-1 activity. All of the porphyrins inhibited HIV-1 subtype B and C virus entry under PDT conditions. Our study demonstrated that the compounds bearing combinations of 4-carboxyphenyl/4-hydroxyphenyl moieties were not toxic even at higher concentrations, as compared to the reference porphyrins 5,10,15,20-tetra-(4-carboxyphenyl)porphyrin (TCPP) and 5,10,15,20-tetra-(4-hydroxyphenyl)porphyrin (THPP), under PDT conditions. This study underscores the promising potential of these compounds as HIV entry inhibitors in both non-PDT and PDT scenarios.

A recombinant adenovirus-based vector elicits a specific humoral immune response against the V3 loop of HIV-1 gp120 in mice through the "Antigen Capsid-Incorporation" strategy

Background

Due to potential advantages, human adenoviral vectors have been evaluated pre-clinically as recombinant vaccine vectors against several cancers and infectious diseases, including human immunodeficiency virus (HIV) infection. The V3 loop of HIV-1 glycoprotein 120 (gp120) contains important neutralizing epitopes and plays key roles in HIV entry and infectivity.

Methods

In order to investigate the humoral immune response development against portions of the V3 loop, we sought to generate four versions of adenovirus (Ad)-based V3 vectors by incorporating four different antigen inserts into the hypervariable region 1 (HVR1) of human adenovirus type 5 (hAd5) hexon. The strategy whereby antigens are incorporated within the adenovirus capsid is known as the “Antigen Capsid-Incorporation” strategy.

Results

Of the four recombinant vectors, Ad-HVR1-lgs-His₆-V3 and Ad-HVR1-long-V3 had the capability to present heterologous antigens on capsid surface, while maintaining low viral particle to infectious particle (VP/IP) ratios. The VP/IP ratios indicated both high viability and stability of these two vectors, as well as the possibility that V3 epitopes on these two vectors could be presented to immune system. Furthermore, both Ad-HVR1-lgs-His₆-V3 and Ad-HVR1-long-V3 could, to some extent escape the neutralization by anti-adenovirus polyclonal antibody (PAb), but rather not the immunity by anti-gp120 (902) monoclonal antibody (MAb). The neutralization assay together with the whole virus enzyme-linked immunosorbent assay (ELISA) suggested that these two vectors could present V3 epitopes similar to the natural V3 presence in native HIV virions. However, subsequent mice immunizations clearly showed that only Ad-HVR1-lgs-His₆-V3 elicited strong humoral immune response against V3. Isotype ELISAs identified IgG2a and IgG2b as the dominant IgG isotypes, while IgG1 comprised the minority.

Conclusions

Our findings demonstrated that human adenovirus (hAd) vectors which present HIV antigen via the “Antigen Capsid-Incorporation” strategy could successfully elicit antigen-specific humoral immune responses, which could potentially open an avenue for the development of Ad-based HIV V3 vaccines.

Design and synthesis of biotin- or alkyne-conjugated photoaffinity probes for studying the target molecules of PD 404182

To investigate the mechanism of action of the potent antiviral compound PD 404182, three novel photoaffinity probes equipped with a biotin or alkyne indicator were designed and synthesized based on previous structure-activity relationship studies. These probes retained the potent anti-HIV activity of the original pyrimidobenzothiazine derivatives. In photoaffinity labeling studies using HIV-1-infected H9 cells (H9IIIB), eight potential proteins were observed to bind PD 404182.

Structure–Activity Relationship Study of PD 404182 Derivatives for the Highly Potent Anti-HIV Agents

Using facile synthetic approaches to pyrimido[1,2-c][1,3]benzothiazin-6-imines and related tricyclic derivatives, the parallel structural optimizations were investigated for the central 1,3-thiazin-2-imine core, the benzene part, and the cyclic amidine part of PD 404182. Replacement of the 6-6-6 pyrimido[1,2-c][1,3]benzothiazin-6-imine framework with 5-6-6 or 6-6-5 derivatives led to a significant loss of anti-HIV activity, and introduction of a hydrophobic group at the 9- or 10-positions improved the potency. The most potent PD 404182 derivative exerts anti-HIV effects at an early stage of viral infection including binding and fusion.

Structure-activity relationship study of pyrimido[1,2-c][1,3]benzothiazin-6-imine derivatives for potent anti-HIV agents

3,4-Dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine (PD 404182) is an antiretroviral agent with submicromolar inhibitory activity against human immunodeficiency virus-1 (HIV-1) and HIV-2 infection. In the current study, the structure-activity relationships of accessory groups at the 3- and 9-positions of pyrimido[1,2-c][1,3]benzothiazin-6-imine were investigated for the development of more potent anti-HIV agents. Several different derivatives containing a 9-aryl group were designed and synthesized using Suzuki-Miyaura cross-coupling and Ullmann coupling reactions. Modification of the m-methoxyphenyl or benzo[d][1,3]dioxol-5-yl group resulted in improved anti-HIV activity. In addition, the 2,4-diazaspiro[5.5]undec-2-ene-fused benzo[e][1,3]thiazine derivatives were designed and tested for their anti-HIV activities. The most potent 9-(benzo[d][1,3]dioxol-5-yl) derivative was two-threefold more effective against several strains of HIV-1 and HIV-2 than the parent compound, PD 404182.

Dominant structural factors for complexation and denaturation of proteins using carboxylic acid receptors

Complexation accompanied by denaturation of protein with synthetic carboxylic acid receptors was investigated, to evaluate the key factors for recognition of proteins. The synthetic receptors used were tetraphenylporphyrin (TPP) derivatives and receptors bearing multiple (2-8) carboxylic acid groups. The complexation behavior was quantified from the absorption in the far UV CD spectrum attributed to the secondary structure of the protein. TPP derivatives bearing multiple carboxylic acid groups in the side chains exhibited higher affinity than other receptors that were smaller and had fewer carboxylic acid groups. As the degree of complexation was influenced by the pH and ionic strength in aqueous solution, electrostatic interaction was one of the most important factors for the recognition of proteins. Complexation was also estimated by observation of fluorescence quenching of the TPP derivatives. The stoichiometry of the complexes between lysozyme and the porphyrins was investigated by quantitative analysis of the denaturation using CD spectra. From the results of Job plots and slope analysis for the amount of denatured protein, formation of 1:1 complexes was confirmed. The equilibrium association constants (K(ass)) for lysozyme and the TPP receptors ranged from 0.6×10(6) to 1.1×10(6)M(-1). The lytic activity of lysozyme was partially lost in the presence of anionic TPP derivatives, due to complexation and denaturation.