Modified cyclodextrins as broad-spectrum antivirals
Viral infections kill millions of people and new antivirals are needed. Nontoxic drugs that irreversibly inhibit viruses (virucidal) are postulated to be ideal. Unfortunately, all virucidal molecules described to date are cytotoxic. We recently developed nontoxic, broad-spectrum virucidal gold nanoparticles. Here, we develop further the concept and describe cyclodextrins, modified with mercaptoundecane sulfonic acids, to mimic heparan sulfates and to provide the key nontoxic virucidal action. We show that the resulting macromolecules are broad-spectrum, biocompatible, and virucidal at micromolar concentrations in vitro against many viruses [including herpes simplex virus (HSV), respiratory syncytial virus (RSV), dengue virus, and Zika virus]. They are effective ex vivo against both laboratory and clinical strains of RSV and HSV-2 in respiratory and vaginal tissue culture models, respectively. Additionally, they are effective when administrated in mice before intravaginal HSV-2 inoculation. Lastly, they pass a mutation resistance test that the currently available anti-HSV drug (acyclovir) fails.
INTRODUCTION
Viruses can negatively affect society at several levels: from viral infections of food crops and livestock to the serious health impacts of viruses that infect humans, such as HIV, Ebola, and Zika virus (ZIKV). When prevention is not possible, drugs must be administered to limit viral replication and aid the immune systems fight against the infection, if they are available. Unfortunately, most existing antivirals act intracellularly, with related problems of permeability and toxicity, are virus specific (1), and/or have a reversible (virustatic) effect (2–4).
Broad-spectrum antivirals like heparin or heparin-like materials (5–8) have been developed that mimic the cell surface sugars responsible for initial viral attachment, such as heparan sulfate (HS). Unfortunately, upon dilution, the viruses are no longer bound to the drug and are still infectious; thus, the clinical efficacy remains unproven (2–4). A drug with an irreversible action, i.e., a virucidal drug, could be ideal to fight viral infection, given that it would not be subject to loss of efficacy upon dilution and have long-lasting effects. All previously identified virucidal molecules have toxic side effects that render their clinical use impossible (9). To the best of our knowledge, there is currently no approved drug that shows virucidal activity.
Recently, we have shown that highly sulfonated gold nanoparticles display broad-spectrum virucidal properties in vitro, ex vivo, and in vivo (10). In that work, a slight modification to the nanoparticle structure, relative to published work (6), altered the antiviral mode of action from virustatic to virucidal, with nanomolar median effective concentrations (EC50’s). This allowed us to maintain the broad-spectrum and nontoxic properties of virustatic nanoparticles while imparting a virucidal mechanism. Unfortunately, there are concerns with the use of gold nanoparticles as drugs due to their unknown clearance mechanism and possible long-term toxicity (11). Nonetheless, the principle of displaying multiple viral attachment ligands to create a virucidal drug remains compelling.
Cyclodextrins (CDs) are naturally occurring glucose derivatives, with a rigid cyclic structure, consisting of α(1-4)–linked glucopyranoside units. The most common CDs, referred to as α, β, and γ, have 6-, 7-, and 8-glucopyranoside units, respectively. They have found use in many commercial applications including drug delivery, air fresheners, cosmetics, and food (12, 13). Sulfonated CDs have shown antiviral properties only against HIV (14–18); however, their action was found to be reversible (virustatic) and virus specific. Here, we attach highly sulfonated chemicals to a U.S. Food and Drug Administration (FDA)–approved CD scaffold and achieve highly efficient virucidal broad-spectrum molecules, effective in vitro, ex vivo, and in an animal model.
RESULTS AND DISCUSSION
To test whether a modified CD (CD1; Fig. 1A) has antiviral activity like its nanogold counterpart (10), we used sodium undec-10-enesulfonate to synthesize a modified CD (CD1) (see figs. S1 and S2 for characterization) that exposes the sulfonate groups in a similar manner. In addition, two other modified CDs were synthesized. To alter the length of the linker, we synthesized CD2 (Fig. 1A), which bears a seven-carbon sulfonated alkyl chain (see figs. S1 and S3 for characterization). While CD1 showed strong inhibition of the growth of herpes simplex virus type 2 (HSV-2), with an EC50 of 28.51 ± 2.319 μg/ml, CD2 showed no significant effect (Fig. 1B). To alter the nature of the linker, we also synthesized a nonalkyl linker of similar overall length to sodium undec-10-enesulfonate (CD3) (see figs. S1 and S4 for characterization). We hypothesized that removing the flexibility of the linker would result in stronger binding to the virus and improved overall antiviral effect. Continue to read the full publication here