Blocking the interaction between two dengue virus (DENV) nonstructural proteins, NS3 and NS4B, with a newly developed small-molecule inhibitor resulted in potent antiviral activity in mouse models, according to an international collaborative study led by scientists at the University of Leuven (KU Leuven), CD3 the Centre for Drug Design and Discovery in Leuven, and Janssen Pharmaceutica in Beerse, Belgium.

This protein interaction represents a promising new target for the development of pan-serotype DENV inhibitors with a high barrier to resistance, with the potency of the inhibition warranting further development of these compounds, the authors reported in the October 6, 2021, edition of Nature.

"This is the first study to show that blocking the NS3/NS4B interaction has potent antiviral activity in mice warranting the further development of such inhibitors," said study co-leader Johan Neyts, professor of virology at KU Leuven.

Dengue is currently among the leading threats to global public health, with an estimated 96 million individuals developing dengue disease, which is probably an underestimation.

In addition, the incidence of dengue has increased approximately 30-fold over the past 50 years. DENV is now endemic in the subtropical regions of 128 countries, with an estimated 4 billion people at risk of infection, predicted to increase to 6 billion by 2080.

This dengue upsurge is driven by various factors, most notably rapid urbanization and the spread of the Aedes mosquito vectors due to climate change.

The DENV has four serotypes that are further classified into genotypes, which are increasingly co-circulating in endemic regions. Antibodies to infection with one serotype can lead to a more severe second infection with a different serotype increases the risk of potentially life-threatening severe dengue.

The DENV vaccine Dengvaxia (Sanofi-Pasteur), which has been approved in several countries for individuals aged at least 9 years, is only recommended for those with previous DENV exposure.

Moreover, there are currently no available antiviral agents for dengue prevention or treatment, while development of pan-serotype DENV inhibitors has proven challenging.

"The major developmental challenge has been to obtain ultrapotent antivirals that also have equipotent activity against the four DENV serotypes," Neyts told BioWorld Science.

Such drugs should lower viral loads during an ongoing infection, thereby reducing dengue-associated morbidity and mortality, as well as transmission.

In their new Nature study, researchers co-led by Neyts, Patrick Chaltin, managing director of CD3 the Centre for Drug Design and Discovery, and Marnix Van Loock, R&D Lead Emerging Pathogens, Janssen Global Public Health at Janssen Pharmaceutica, identified potential new DENV inhibitors using large-scale cell-based anti-DENV-2 screening.

"We screened tens of thousands of molecules and interesting hits were further optimized to eventually obtain JNJ-A07 and other ultrapotent and selective analogues, with roughly 2,000 analogues being synthesized and tested," said Neyts.

Notably, the promising small molecule JNJ-A07 was demonstrated to have nanomolar to picomolar activity against a panel of 21 clinical isolates representing the natural genetic diversity of known DENV genotypes and serotypes.

The molecule was then shown to have a high barrier to resistance "by months of culturing the dengue virus in suboptimal concentrations of the inhibitor," Neyts said.

JNJ-A07 was then shown to prevent formation of the viral replication complex by blocking the interaction between the nonstructural proteins NS3 and NS4B, thereby revealing a previously undescribed mechanism of antiviral action.

JNJ-A07 was further demonstrated to have a favorable pharmacokinetic (PK) profile resulting in outstanding efficacy against DENV infection in mouse models.

"JNJ-A07's favorable PK profile resulted from optimization of the ADME [absorption, distribution metabolism and excretion] properties of the analogues within this chemical series," Janssen's Van Loock told BioWorld Science.

"This enabled us to administer the compound [twice daily] in mice and assess its efficacy, which resulted in a significantly reduced viral load and protected against mortality in a mouse lethal challenge model."

However, "additional research will be required in preclinical models, to understand how these findings reflect those in humans, as currently no translational models are available to assess the potential effect in humans," noted Van Loock.

Delaying treatment commencement until peak viremia had developed was shown to result in a rapid and significant reduction in viral load in the mouse models of infection.

This is an important finding, as "one wants an antiviral effect that is independent of how much [viral] replication is ongoing," Van Loock said.

"In these mice, the reduction in viral load was also very pronounced if the treatment was initiated on the day of peak viral load, when the effect was quantified 24 hours later."

On safety, said Neyts, as JNJ-A07 and its analogues "target specific viral proteins that have no homologues in eukaryotic cells, we expect a considerable safety window, with these agents being very well tolerated." The safety and potency of DENV inhibition established in this study justifies the further development of these novel antivirals, with an analogue being currently in further development.

Further development will include "using our know-how to also develop drugs against the other member of the flavivirus family to which DENV belongs, including Japanese encephalitis, Zika, yellow fever, West Nile virus, et cetera," said Neyts.

Meanwhile, "Janssen has moved the compound into clinical development and continues to work closely in this regard with teams at KU Leuven and elsewhere," said Van Loock.

"We will be sharing information about progress of the compound's clinical development during the American Society of Tropical Medicine and Hygiene meeting this November."