Efficacy, safety and dose response of STS01, a topical controlled release nanoparticle formulation (dithranol/Prosilic), in adults with mild to moderate patchy alopecia areata: A randomised, double-blind, multicentre, phase 2 trial

In a randomized, double-blind, phase 2 trial involving 155 adults with mild to moderate patchy alopecia areata, the topical nanoparticle formulation STS01 demonstrated a clear dose-response relationship, with the 1% concentration significantly outperforming placebo in hair regrowth efficacy while maintaining a manageable safety profile characterized primarily by mild to moderate skin irritation.

The Gist

The "Smart Delivery" Hair Cream: A Simple Explanation of the STS01 Study

Imagine your hair follicles are like tiny, busy factories. In a condition called Alopecia Areata, your body's immune system gets confused and sends "security guards" (immune cells) to attack these factories, causing them to shut down and stop producing hair. This results in bald patches.

For years, doctors have had a "brute force" tool to fix this: a cream called Dithranol. Think of Dithranol as a very strong, old-fashioned fire extinguisher. It works by irritating the skin just enough to scare the immune system away from the hair follicles, letting the factories start working again.

But here's the problem with the old fire extinguisher:

• It's messy. It stains your skin purple/brown, your clothes, and your sheets.
• It burns. It feels like a bad sunburn.
• It's inconvenient. You have to apply it, wait 30 minutes, and then wash it all off immediately. It's a hassle most people can't deal with every day.

Because of these issues, this effective treatment fell out of favor, leaving millions of people with mild-to-moderate hair loss with no good options.

The New Solution: STS01 (The "Smart Drone" Delivery)

The researchers in this paper developed a new version of Dithranol called STS01.

If the old cream was a fire extinguisher thrown at the wall, STS01 is like a swarm of tiny, smart drones.

• The Technology: They wrapped the Dithranol in a special, biodegradable "honeycomb" shell made of silicon and lipids.
• The Magic: These tiny shells protect the drug from air (so it doesn't stain) and control exactly how much gets released. Instead of a messy explosion of irritation, it delivers a steady, controlled dose right to the hair follicle.
• The Benefit: You can apply it once in the morning, rub it in, and go about your day. No washing off. No purple stains.

The Experiment: Testing the "Drones"

The researchers wanted to see if this new "smart delivery" system actually worked better than a fake cream (placebo) and to find the perfect "dose" (how much drug to put in the shell).

The Setup:

• Who: 155 adults in the UK with patchy hair loss (losing between 10% and 50% of their hair).
• The Groups: They were split into five groups:
  1. Placebo (fake cream).
  2. STS01 0.25% (very low dose).
  3. STS01 0.5% (low dose).
  4. STS01 1% (medium dose).
  5. STS01 2% (high dose).
• The Duration: Everyone applied their cream once a day for 6 months.

The Results: Finding the "Goldilocks" Zone

After 6 months, the results were very clear:

1. It Works: The people using the real STS01 cream grew significantly more hair than the people using the fake cream.
2. The Dose Matters:
   • Too Low (0.25%): Didn't do much better than the fake cream.
   • Just Right (1%): This was the winner. About 76% of people in this group saw significant hair regrowth (at least 30% improvement), compared to only 37% in the fake group.
   • Too High (2%): While it grew hair, it caused too much skin irritation (redness and burning), making people stop using it.
3. The "Goldilocks" Conclusion: The 1% dose was the perfect balance. It grew hair effectively but didn't irritate the skin too much.

Key Stats:

• Hair Growth: The 1% group saw their hair loss score drop by 55% on average, while the fake group actually got slightly worse.
• Safety: The main side effect was mild skin redness (like a mild sunburn), which was manageable. Crucially, there was almost no staining (unlike the old cream), and no serious safety issues.

What Does This Mean for You?

Think of this study as finding the perfect recipe for a cake.

• The old recipe (standard Dithranol) tasted great but was messy and hard to eat.
• The new recipe (STS01) tastes just as good but is neat, easy to eat, and doesn't stain your fingers.

The Bottom Line:
This study proves that a modern, high-tech version of an old hair-loss treatment can be safe, effective, and easy to use. The 1% STS01 cream is now being prepared for a larger "Phase 3" test to see if it works for even more people. If successful, it could become the first licensed treatment for mild-to-moderate patchy hair loss, giving hope to millions who currently have no options.

In short: They took a messy, old hair-loss cure, wrapped it in a high-tech "smart shell," and found the perfect dose that grows hair without ruining your day.

Technical Summary

1. Problem Statement

• Unmet Clinical Need: Alopecia areata (AA) is an autoimmune condition causing non-scarring hair loss. While there are licensed treatments for severe AA (e.g., JAK inhibitors), there are no licensed treatments for patients with mild-to-moderate patchy AA (defined as 10%–50% scalp hair loss).
• Limitations of Existing Therapies:
  • JAK Inhibitors: Reserved for severe cases due to safety concerns (cardiovascular risk, thromboembolism, cancer) and lack of approval for milder forms.
  • Topical Dithranol: Historically recommended by British Association of Dermatology guidelines as an irritant therapy to stimulate regrowth. However, its use is limited in practice due to:
    • Rapid oxidation and instability in air/light.
    • Significant skin irritation and erythema.
    • Staining of skin, hair, and fabrics (purple/brown).
    • Inconvenient application (requires washing off after 30–60 minutes).
• Objective: To develop a novel formulation of dithranol that retains efficacy while mitigating irritation, staining, and application issues.

2. Methodology

• Study Design: A randomized, double-blind, multicentre, Phase 2 trial conducted in the UK (10 centres) from March 2022 to May 2024.
• Intervention:
  • Drug: STS01, a novel topical controlled-release nanoparticle formulation combining dithranol with ProSilic® (a biodegradable hybrid of porous elemental silicon, lipids, and amino acids). The ProSilic matrix creates a "honeycomb" colloidal structure to control drug release, reduce surface area exposure to air, and target the immune response.
  • Dosing: Daily topical application for 6 months.
  • Arms: Five parallel groups: Placebo (ProSilic base) and STS01 at four concentrations (0.25%, 0.5%, 1%, 2%).
• Population:
  • N: 155 randomized and treated adults (Full Analysis Set).
  • Inclusion: Age ≥18, active mild-to-moderate patchy AA (10%–50% scalp hair loss), duration ≥6 months.
  • Exclusion: Other alopecia types, significant scalp inflammation, recent use of JAK inhibitors, systemic immunosuppressants, or topical hair loss treatments (within 6 weeks).
• Endpoints:
  • Primary: Proportion of patients achieving ≥30% improvement in Severity of Alopecia Tool (SALT) score at 6 months; LS mean percentage change in SALT score.
  • Secondary: Clinical responder rates at higher thresholds (≥40%, ≥50%, ≥60%, 100%), patch area reduction (ImageJ), and Clinical Global Impression-Improvement (CGI-I).
  • Safety: Treatment-emergent adverse events (TEAEs), specifically skin irritation and staining.
• Statistical Analysis: Full Analysis Set (FAS) using ANCOVA for continuous variables and Fisher's exact test/logistic regression for responder rates. Dose-response modeling (Emax) was utilized.

3. Key Contributions

• Novel Formulation: Successfully demonstrated that encapsulating dithranol in a nanoparticle controlled-release system (ProSilic) allows for once-daily application without the need to wash off, significantly improving patient convenience compared to traditional dithranol.
• Mechanism Validation: Provided clinical evidence that controlled-release dithranol can effectively downregulate the autoimmune response in AA without relying solely on severe irritation to generate efficacy.
• Dose-Response Characterization: Mapped the therapeutic window for STS01, identifying the optimal balance between efficacy and tolerability.

4. Key Results

• Efficacy (Primary Endpoint):
  • STS01 1% met the primary endpoint significantly better than placebo: 75.9% of patients achieved ≥30% SALT improvement vs. 36.7% for placebo ($p=0.0037$).
  • Complete Regrowth (100% SALT improvement): Achieved by 25.0% in the 2% group and 21.4% in the 0.5% group, both significantly higher than placebo (3.3%).
  • SALT Score Reduction: The LS mean percentage change from baseline at 6 months was -55.0% for the 1% group vs. +0.6% (deterioration) for placebo ($p<0.01$).
  • Time Course: Significant improvements were observed as early as 2 months and continued to increase through 6 months.
  • Dose Response: A clear sigmoidal dose-response curve was established. The 0.5% dose was minimally effective, and the 2% dose was the maximum tolerated, with the 1% dose showing the optimal efficacy profile.
• Safety and Tolerability:
  • Adverse Events: Skin irritation reactions were the most common TEAEs (STS01: 70.0–93.5% vs. Placebo: 21.9%).
  • Severity: Most reactions were mild (56.7–71.0%) or moderate (13.3–35.5%). Severe reactions were rare (0–9.7%).
  • Staining: Skin discolouration was reported in ≤10% of patients, a marked improvement over historical dithranol data.
  • Discontinuation: 12.2% of STS01 patients discontinued due to TEAEs (mostly irritation) vs. 6.3% for placebo.
  • No Serious Adverse Events (SAEs) or deaths were reported.
• Risk-Benefit Analysis: The 1% dose demonstrated the best balance of high efficacy, manageable safety profile, and compliance.

5. Significance and Conclusion

• Clinical Impact: This study represents the first Phase 2 randomized, double-blind, placebo-controlled trial specifically for mild-to-moderate patchy AA, an area with no currently licensed treatments.
• Therapeutic Advance: STS01 offers a convenient, once-daily, wash-free treatment option that overcomes the major historical barriers of dithranol (staining, irritation, application frequency).
• Future Directions: Based on the risk-benefit analysis, the 1% dose has been selected for further characterization in a planned Phase 3 clinical trial.
• Mechanistic Insight: The results suggest that STS01 modulates the local immune environment (potentially via cytokine modification) to permit hair regrowth, validating the controlled-release nanoparticle approach for autoimmune dermatological conditions.

In summary, STS01 1% demonstrated statistically significant and clinically relevant hair regrowth with a manageable safety profile, positioning it as a promising candidate to fill the critical treatment gap for mild-to-moderate alopecia areata.