Trifluoperazine exhibits broad-spectrum antiviral activity against arboviruses

This study identifies the FDA-approved antipsychotic Trifluoperazine as a potent broad-spectrum antiviral against arboviruses like JEV, DENV, and CHIKV that functions by inducing eIF2α phosphorylation and ER stress, thereby demonstrating significant therapeutic potential for repurposing in both in vitro and in vivo models.

The Gist

Imagine the world is currently under siege by a group of sneaky invaders called arboviruses. These are viruses like Dengue, Chikungunya, and Japanese Encephalitis, carried by mosquitoes. They are notorious because they can cause everything from a bad fever to deadly brain inflammation or hemorrhagic shock. Currently, doctors have no "magic bullets" (antiviral drugs) to fight them; they can only offer supportive care, like giving fluids and painkillers while the body tries to fight the battle on its own.

This paper introduces a new hero: an old, well-known drug called Trifluoperazine (TFP).

The Hero: A Drug with a New Job

Think of Trifluoperazine as a retired soldier who used to fight a different enemy. Originally, it was an antipsychotic medication used to calm the mind and treat mental health conditions. It's been on the market for decades, so doctors know exactly how it works in the human body and that it's generally safe.

The researchers in this study asked a simple question: "Can we repurpose this old soldier to fight these new viral invaders?"

The Strategy: Turning the Factory Against the Invaders

To understand how TFP works, imagine your cells are factories.

• The Virus: When a virus infects a cell, it hijacks the factory's machinery. It forces the factory to stop making normal products and start churning out thousands of copies of the virus.
• The ER (Endoplasmic Reticulum): Inside the factory, there's a specific assembly line called the ER. This is where the virus builds its protein parts.
• The Problem: The virus is so good at this that it clogs the assembly line, causing a massive traffic jam. This is called "ER stress." Usually, the cell tries to fix this jam, but the virus often outsmarts the cell.

The TFP Trick:
The researchers discovered that TFP acts like a saboteur who intentionally creates a controlled traffic jam in the factory's assembly line.

1. Inducing Stress: TFP messes with the cell's internal calcium levels, causing the assembly line (ER) to get stressed.
2. The Alarm Bell: This stress triggers an alarm system inside the cell (specifically, it phosphorylates a protein called eIF2α).
3. The Shutdown: The alarm tells the factory to slow down production. It's like hitting the "Pause" button on the assembly line.
4. The Result: Because the virus needs that assembly line to copy itself, the virus gets stuck. It can't make new copies, and the infection dies out.

The Proof: Lab and Animal Tests

The team tested this "saboteur" against three different viral enemies:

1. Japanese Encephalitis Virus (JEV): In mice, the drug didn't just stop the virus; it saved lives. Mice treated with TFP survived a lethal dose that would have killed untreated mice. Their brains were protected from the inflammation that usually causes paralysis and death.
2. Chikungunya Virus: In mice, the drug stopped the painful swelling in the paws (a hallmark of Chikungunya) and cleared the virus from the blood much faster.
3. Dengue Virus: Here, the story had a twist. The drug worked perfectly in human liver cells and in mice that had a normal immune system. However, it failed in a specific type of mouse that lacks a key immune defense (Interferon). This suggests that for Dengue, TFP needs a "two-pronged attack": it stresses the factory and relies on the body's immune system to finish the job.

The "Undo" Button

To prove that the "traffic jam" (ER stress) was actually the reason the virus died, the researchers used a chemical "chaperone" called 4PBA. Think of 4PBA as a traffic cop that clears the jam.

• When they gave the virus-infected cells both TFP (the saboteur) and 4PBA (the traffic cop), the virus started replicating again!
• This confirmed that TFP's power comes entirely from its ability to stress the cell's assembly line.

Why This Matters

This is a big deal for three reasons:

1. Broad-Spectrum: It works against multiple different types of viruses, not just one.
2. Repurposing: Since TFP is already FDA-approved and safe for humans, it could be fast-tracked to become a treatment for these deadly diseases without needing years of new safety testing.
3. Hard to Resist: Because TFP targets the cell's machinery rather than the virus itself, it's much harder for the virus to mutate and become resistant to the drug. It's like changing the factory rules rather than just shooting at the workers; the virus can't easily evolve to break the new rules.

The Bottom Line

The researchers found an old antipsychotic drug that can be repurposed to act as a broad-spectrum shield against mosquito-borne viruses. By intentionally stressing the cell's internal factory, it shuts down the virus's ability to copy itself, offering hope for a future where we have effective treatments for diseases like Dengue and Chikungunya.

Technical Summary

1. Problem Statement

Mosquito-borne arboviruses, including Japanese Encephalitis Virus (JEV), Dengue Virus (DENV), and Chikungunya Virus (CHIKV), pose a significant global health threat, causing hundreds of thousands of deaths and millions of infections annually. Current clinical management is limited to supportive care as there are no specific antiviral therapies available for these infections. The geographical expansion of these viruses and the lack of broad-spectrum treatments necessitate the urgent development of novel therapeutic strategies. Targeting host cellular machinery rather than viral proteins is proposed as a viable strategy to overcome viral resistance and address emerging strains.

2. Methodology

The study employed a multi-faceted approach combining in vitro cell culture assays, ex vivo immune cell models, and in vivo animal models to evaluate the repurposing potential of Trifluoperazine (TFP), an FDA-approved antipsychotic drug.

• Cell Models: Various cell lines were used based on viral tropism: Neuro2a (mouse neuroblastoma) for JEV, Huh7 (human hepatocarcinoma) for DENV-2, and ERMS (human rhabdomyosarcoma) for CHIKV. Bone Marrow-Derived Macrophages (BMDMs) from C57BL/6 (wild-type) and AG129 (IFN receptor-deficient) mice were used for ex vivo studies.
• Viral Assays: Antiviral efficacy was measured via qRT-PCR for viral RNA levels and plaque/foci-forming assays for infectious viral titers. Cytotoxicity was assessed using MTT assays to determine Selectivity Indices (SI).
• Mechanistic Studies:
  • ER Stress Induction: Western blotting was performed to detect phosphorylation of eIF2$\alpha$ (p-eIF2$\alpha$) and PERK, markers of Endoplasmic Reticulum (ER) stress.
  • Rescue Experiments: Cells were co-treated with TFP and 4-phenylbutyric acid (4PBA), a chemical chaperone known to alleviate ER stress, to determine if ER stress mediation is essential for the antiviral effect.
• Animal Models:
  • JEV: 3-week-old C57BL/6 mice were infected with a lethal dose of JEV S3 isolate.
  • DENV: 6-8 week old AG129 mice (IFN-deficient) were used due to the lack of a susceptible wild-type mouse model for DENV.
  • CHIKV: 8-10 week old C57BL/6 mice were infected subcutaneously to model arthritis/edema.
  • Treatment: Mice received oral TFP (1 mg/kg) starting 4 hours post-infection (hpi) daily.
• Pathogenesis Markers: Viral load in tissues (brain/serum), blood-brain barrier (BBB) permeability (Evans blue dye assay), and neuroinflammation (cytokine bead array for IFN$\beta$, IL-6, TNF$\alpha$, RANTES) were quantified.

3. Key Contributions and Results

A. Broad-Spectrum Antiviral Activity In Vitro

TFP demonstrated potent antiviral activity against all three arboviruses with high selectivity indices (SI):

• JEV: SI = 308 (IC50 = 0.1 $\mu$M; CC50 = 30.8 $\mu$M).
• DENV-2: SI = 16.7 (IC50 = 2.9 $\mu$M; CC50 = 48.4 $\mu$M).
• CHIKV: SI = 66.5 (IC50 = 0.74 $\mu$M; CC50 = 49.2 $\mu$M).
  TFP treatment resulted in a 50–90% reduction in viral RNA and a 50–70% reduction in infectious titers across all tested cell lines.

B. In Vivo Efficacy and Pathogenesis Reduction

• JEV Model: TFP treatment significantly improved survival rates in lethal JEV infection (72% survival vs. 27% in untreated controls). It reduced brain viral loads by 2–3 log10, prevented BBB leakage (reduced Evans blue leakage), and suppressed neuroinflammation (lowered levels of IFN$\beta$, IL-6, TNF$\alpha$, and RANTES).
• CHIKV Model: TFP treatment significantly reduced paw edema (arthropathy) and serum viremia (~70% reduction at 2 dpi) in C57BL/6 mice.
• DENV Model (Limitation): In AG129 mice (lacking IFN receptors), TFP failed to improve survival or reduce viral load. However, in BMDMs from wild-type C57BL/6 mice, TFP was effective. This suggests that TFP's anti-DENV activity is dependent on a functional Interferon (IFN) response, which is absent in the AG129 model.

C. Mechanism of Action: ER Stress Induction

The study identified ER stress as the central mechanism of TFP's antiviral activity:

• TFP treatment induced rapid phosphorylation of eIF2$\alpha$ (p-eIF2$\alpha$) and increased total eIF2$\alpha$ levels in Neuro2a, Huh7, and ERMS cells.
• Unlike Thapsigargin (Tg), TFP induced an adaptive ER stress response (characterized by p-eIF2$\alpha$ induction without immediate PERK phosphorylation shifts).
• Crucial Validation: Co-treatment with the chemical chaperone 4PBA (which relieves ER stress) completely abolished the antiviral effect of TFP, restoring viral replication to control levels. This confirms that TFP-mediated ER stress is necessary for its broad-spectrum antiviral efficacy.

4. Significance

• Drug Repurposing: The study validates Trifluoperazine, a well-characterized FDA-approved drug with a known safety profile, as a potent broad-spectrum antiviral candidate. This could significantly accelerate clinical translation compared to novel drug development.
• Host-Directed Therapy: By targeting the host's ER stress pathways rather than viral enzymes, TFP offers a strategy to combat viral resistance, a major hurdle in antiviral therapy.
• Mechanistic Insight: The findings highlight the critical role of adaptive ER stress and the Interferon response in controlling arboviral infections. Specifically, it elucidates why TFP works against JEV and CHIKV in immunocompetent hosts but fails in DENV models lacking IFN signaling.
• Therapeutic Potential: The drug's ability to cross the blood-brain barrier and reduce neuroinflammation makes it particularly promising for neurotropic viruses like JEV.

5. Limitations

• DENV Model: The lack of a suitable wild-type mouse model for DENV limited the in vivo validation of TFP against Dengue. The study relies on the AG129 model, which does not fully recapitulate human DENV pathogenesis due to the absence of IFN signaling.
• Mechanism Nuance: While ER stress is the primary driver, the specific interplay between TFP-induced stress granules and the IFN response in DENV control requires further investigation.

Conclusion

This study establishes Trifluoperazine as a promising broad-spectrum antiviral agent against major arboviruses (JEV, DENV, CHIKV) through the induction of adaptive ER stress. Its efficacy in reducing viral load, preventing tissue damage, and improving survival in animal models supports its potential for repurposing as a clinical therapeutic for arboviral outbreaks.