CB-03-01, also known as Breezula™ or clascoterone, is a topical medication generating interest as a potential therapy for androgenetic alopecia (AGA). It was developed by Cassiopea (now owned by Cosmo Pharmaceuticals) and is a synthetic androgen receptor antagonist. While it is primarily recognized for its potential in combating hair loss, particularly AGA, CB-03-01 has also exhibited efficacy in treating conditions like acne, hirsutism, polycystic ovary syndrome (PCOS), and seborrheic dermatitis. In this overview, we look at whether  CB-03-01  can impact hair follicles and its potential in treating hair loss, and we will also look at CB-03-01’s safety profile and mechanism of action, drawing from clinical trials and research findings.

Key Takeaways

• Drug. CB-03-01, also known as Breezula™ or clascoterone, is a topical synthetic androgen receptor antagonist developed by Cassiopea (now owned by Cosmo Pharmaceuticals). It competes with natural androgens like dihydrotestosterone (DHT) for binding to androgen receptors, making it a promising treatment for hair loss that may be caused by androgen signaling, particularly androgenetic alopecia.
• Clinical Data. Three Phase II trials for CB-03-01 have been conducted – two for male and one for female AGA – the results of one of these trials were not published. The published studies are summarized below:
  • Study 1: A study involving 293 women aged 18-55 with AGA. Of various treatments used, a 5% formulation of CB-03-01 was the only treatment that significantly improved, and only in women under 30.^[1]Cassiopea Spa, (2021). Cassiopea SpA Announces Topline Results of Phase II Proof of Concept Trial of Clascoterone Solution for the Treatment of Androgenetic Alopecia in Females. Bloomberg. Available … Continue reading 
  • Study 2: A study involving 400 men aged 18-55 with mild to moderate AGA.  A 7.5% concentration of CB-03-01 led to statistically significant improvements in hair length and width in the treated area. All treatment groups showed relative improvement compared to the control.^[2]Cassiopea Spa, (2021). Cassiopea Announces Very Positive Phase II Twelve Months Results for Breezula® (Clascoterone) in Treating Androgenetic Alopecia Bloomberg. Available at: … Continue reading 
  • Phase III trials of CB-03-01 are expected to be completed in January 2025.
• Safety. CB-03-01 has reportedly demonstrated minimal side effects, with common issues being mild skin reactions such as scaling, redness, and itching. However, there is too little published data to make a definitive statement regarding the safety of CB-03-01.
• Evidence Quality. CB-03-01 scored 36/100 for evidence quality by our metrics.
• Best Practices. This product is not currently available at a 5% concentration for treatment of AGA. However, when available, this may be most effective when used twice daily by women with AGA under 30, based on the available data.

What is CB-03-01?

CB-03-01, known by its brand name Breezula™ or clascoterone, is a topical synthetic androgen receptor antagonist owned by Cosmo Pharmaceuticals.^[3]Cosmo, (no date). Breezula. Cosmo Pharmaceuticals Available at: https://www.cosmopharma.com/pipeline/breezula (Accessed: 17 October 2023) An androgen receptor antagonist is a substance that can interfere with or block androgen hormones from working as they normally would.^[4]Kokal, M., Mirzakhani, K., Pungsrinont, T., Baniahmad, A. (2020). Mechanisms of Androgen Receptor Agonist- and Antagonist-Mediated Cellular Senescence in Prostate Cancer. Cancers (Basel). 12(7). … Continue reading CB-03-01 is a competitive antagonist, meaning it competes with natural androgen hormones in our bodies, such as dihydrotestosterone (DHT), for binding to the androgen receptor. CB-03-01 is primarily recognized for its potential in treating hair loss, particularly androgenetic alopecia. However, it has also been used to treat acne (under the brand name Winlevi), hirsutism (excess/unwanted facial hair in women), polycystic ovary syndrome (PCOS), and seborrheic dermatitis (Figure 1).

How Does CB-03-01 Work?

The mechanism of action of CB-03-01 (clascoterone) involves its interaction with androgen receptors in the skin, particularly in hair follicles and sebaceous glands. This compound is a selective androgen receptor antagonist with a specific affinity for androgen receptors.^[6]Cosmo, (no date). Breezula. Cosmo Pharmaceuticals Available at: https://www.cosmopharma.com/pipeline/breezula (Accessed: 17 October 2023) Androgens are a group of hormones that include testosterone and dihydrotestosterone (DHT), which play a role in the development and growth of hair, but which can also contribute to conditions like androgenetic alopecia (AGA, also known as male pattern hair loss) and acne when androgen hormone activity becomes abnormal or excessive.^[7]Handelsman, D.J. (2020). Androgen Physiology, Pharmacology, Use and Misuse. Endotext [Internet]. South Dartmouth (MA). Available at: https://www.ncbi.nlm.nih.gov/books/NBK279000/ (Accessed: 17 … Continue reading

Androgens like DHT normally activate androgen receptors to mediate their biological effects. CB-03-01 interferes with the ability of androgens to activate these receptors. In the context of hair loss, reducing androgen signaling can help slow down the miniaturization of hair follicles associated with androgenetic alopecia. By reducing the impact of androgens on hair follicles, CB-03-01 may help prevent hair follicle miniaturization and hair loss.

What is the Impact of CB-03-01 on Hair Follicle Biology?

There is one in vitro (or ‘test tube’) study that we could find that looks at how CB-03-01 could affect hair follicle biology. The study looked at dermal papilla cells (DPCs), which can be thought of as the hair follicle’s signaling center and which are negatively affected by testosterone in patients with AGA. DPCs from balding scalps grow slower than those of healthy scalps. They undergo a process called premature senescence, in which cells lose their ability to divide and grow.^[8]Bahta, A.W., Farjo, N., Farjo, B., Philpott, M. Premature senescence of balding dermal papilla cells in vitro is associated with p16(INK4a) expression. Journal of Investigative Dermatology. 218(5). … Continue reading 

Firstly, the researchers wanted to show that CB-03-01 could, in principle,  interfere with androgen receptor signaling. They used an experimental tool called androgen receptor reporter cells, which are commonly used to study the activity of androgen receptors. These cells were treated with 0.4 nM testosterone in the presence or absence of CB-03-01 or finasteride. The IC₅₀ value –  the drug concentration required to give half the maximal response  – was then calculated. CB-03-01 (called clascoterone here) had an IC₅₀ of  1.55×10^-6M, compared to 2.89×10^-6 M for finasteride. As a lower IC₅₀ value indicates that a drug is more effective, the results show that clascoterone is at least as potent as finasteride in inhibiting testosterone-induced androgen receptor activity; their IC₅₀ values are in the same order of magnitude (Figure 2).^[9]Rosetter, C., Rosette, N., Mazzetti, A., Moro, L., Gerloni, M. Cortexolone 17ɑ-Proprionate (Clascoterone) is an Androgen Receptor Antagonist in Dermal Papilla Cells in Vitro. Journal of Drugs in … Continue reading 

The researchers then treated reporter cells with 200 μM DHT with or without finasteride or CB-03-01 under three conditions (Figure 3).

1. Treated with DHT plus androgen receptor inhibitor (finasteride of CB-03-01) for 24 hours (to mimic once-daily application)
2. Treated with DHT plus androgen receptor inhibitor for 12 hours, then washed off and treated with DHT alone for a further 12 hours (to mimic once daily application and examine the metabolism of the drug)
3. Treated with DHT plus androgen receptor inhibitor for 12 hours, then washed off and treated with DHT plus androgen receptor inhibitor for a further 12 hours (to mimic twice-daily application)

In conditions 1 and 3, where CB-03-01 was continuously present, AR activity was significantly inhibited. This suggests that continuous exposure to the inhibitor effectively blocks androgen receptor activity. In condition 2, where CB-03-01 was removed after 12 hours, and the cells were exposed to DHT alone, the inhibitor’s effectiveness significantly decreased. The drug’s IC₅₀ was much higher in this case. This indicates a need for a continuous presence of the inhibitor for sustained antagonism of DHT-induced AR activity. The study also found finasteride was more effective when present for 24 hours than 12 hours (Figure 3), and CB-03-01 seemed to be as effective as finasteride at a similar concentration.

 

DPCs were treated with 200 μM DHT or vehicle control (0.1% DMSO) for 24 hours. The researchers found that exposure to high levels of DHT increased the expression of the androgen receptor in healthy dermal papilla cells. This mimicked the conditions found in the balding scalp, where DHT sensitivity contributes to hair loss. Additionally, the experiment revealed that exposure to high levels of DHT significantly increased the secretion of two cytokines: Interleukin-6 (IL-6) and basic fibroblast growth factor (bFGF) by DPCs (Figure 4A & B). 

The researchers then investigated whether clascoterone (CB-03-01) could antagonize the synthesis and secretion of these cytokines. They used enzalutamide as a positive control because it also acts as an androgen receptor antagonist, competing with DHT for binding to the androgen receptor. However, it would have been more useful to compare to finasteride, which is commonly used to treat AGA.

Clascoterone was found to be more effective at reducing the secretion of IL-6 compared to enzalutamide. The IC₅₀ (the concentration at which it inhibits 50% of IL-6 secretion) for clascoterone was much lower than that of enzalutamide, indicating that clascoterone more effectively reduced the secretion of this inflammatory cytokine (Figure 4B). However, neither of the drugs had any effect on bFGF (Figure 4C). 

The researchers finally performed cell viability assays to ensure the results were not due to cell death – this is important because cell viability changes could affect cytokine secretion. These assays showed that neither clascoterone nor enzalutamide significantly affected cell viability, indicating that the results were not an artifact caused by variations in cell death (Figure 4D).

 

So, we know that CB-03-01 can effectively compete with DHT for the androgen receptor, reducing the harmful effects of the hormone. However, these experiments were conducted in cells in a dish. Let’s move on to studies conducted on human patients.

Is CB-03-01 Clinically Effective at Treating Hair Loss?

CB-03-01 has undergone three Phase II trials, which have informed the dosage for an upcoming Phase III trial that is expected to be completed in 2025.  The first Phase II trial was a proof-of-concept study conducted in 2014 with 95 males with androgenetic alopecia. However, the Phase II trial results for male AGA were not publicly disclosed or published.^[13]Clinical Trials, (2017). A Phase 2 Study to Evaluate the Safety and Efficacy of CB-03-01 Solution, a Comparator Solution and Vehicle Solution in Males with Androgenetic Alopecia. Clinical Trials. … Continue reading

The second Phase II study was another proof-of-concept study for the use of CB-03-01 in the treatment of female pattern baldness. Once again, there have yet to be fully published results. However, Bloomberg did publish a press release summarizing the main findings.^[14]Cassiopea Spa, (2021). Cassiopea SpA Announces Topline Results of Phase II Proof of Concept Trial of Clascoterone Solution for the Treatment of Androgenetic Alopecia in Females. Bloomberg. Available … Continue reading. The trial enrolled 293 women aged 18 to 55, all experiencing androgenetic alopecia (AGA). The participants were divided into groups, with each group containing 70 individuals. The trial’s main objective was to evaluate the effects of different treatments over six months, comparing them to a control group that received a placebo (vehicle) and another group that used a 2% minoxidil solution.

All participants applied their assigned treatment twice daily. The treatment groups included two concentrations of CB-03-01, specifically 5% and 7.5%. The primary outcome measurements were changes in hair count and assessing hair growth over the six months of treatment.

Interestingly, only a subgroup of women under 30 using the 5% CB-03-01 solution showed statistically significant improvements in hair count, which was unexpected. Cassiopea mentioned that they were encouraged by the data and would further analyze it to identify further subgroups. However, since female-pattern hair loss typically occurs later in life for women (in their 50s or 60s), this treatment may not be appropriate for most patients. Therefore, further research is needed to determine its broader applicability.^[15]Fabbrocini, G., Cantelli, M., Masara, A., Annunziata, M.C., Marasca, C., Cacciapuoti, S. (2018). Female pattern hair loss: A clinical, pathophysiologic, and therapeutic review. International Journal … Continue reading 

Furthermore, although the press release mentioned that some participants were treated with 2% minoxidil, there was no information on how CB-03-01 performed compared to this. This highlights the issue of using press releases instead of peer-reviewed journal articles, as important data can be omitted.

The third phase II study recruited more than 400 male participants in Germany, aged 18-55, with mild to moderate AGA. All participants applied CB-03-01 at concentrations of 2.5%, 5%, 7.5% twice daily, or 7.5% once daily. The control group applied a  vehicle solution (once- or twice daily).^[16]Cassiopea Spa, (2021). Cassiopea Announces Very Positive Phase II Twelve Months Results for Breezula® (Clascoterone) in Treating Androgenetic Alopecia Bloomberg. Available at: … Continue reading Once again, the results were only available via a press release, so while some data was present we do not know if any has been omitted. It is reported that the results showed statistically significant improvements in target area hair counts and hair growth assessment scores across all active groups compared to the vehicle control. Notably, the highest change occurred in the 7.5% twice-daily group. This group also showed the highest statistically significant improvements in hair width in the treated area.

Two Phase III studies are awaiting recruitment, with expected completion dates in January 2025.^[17]Clinical Trials, (no date). CB-03-01. NIH. Available at: https://clinicaltrials.gov/search?cond=Hair%20Loss%2FBaldness&term=CB-03-01 (Accessed: 17 October 2023)

Is CB-03-01 Safe?

According to the Bloomberg press release, treatment-emergent adverse events (TEAEs) were mostly minimal, mild, or trace and unrelated to the study drug. However, very little detail is given. The most frequently observed local skin reactions across all treatment groups were minimal to mild scaling, redness, or minimal itching.^[18]Cassiopea Spa, (2021). Cassiopea SpA Announces Topline Results of Phase II Proof of Concept Trial of Clascoterone Solution for the Treatment of Androgenetic Alopecia in Females. Bloomberg. Available … Continue reading

In a Phase III trial of CB-03-01 for patients with facial acne, TEAEs were also generally mild in severity and similar to the control. The most common were pain, dryness, hypersensitivity at the site of application, redness, contact dermatitis, and headache.^[19]Hebert, A., Thiboutot, D., Gold, L.S., Cartwright, M., Gerlonim M., Fragasso, E., Mazzetti, A. (2020). Efficacy and Safety of Topical Clascoterone Cream, 1% for Treatment in Patients with Facial … Continue reading

CB-03-01 has yet to receive FDA approval for hair loss treatment, and certainly, more information on its safety and efficacy is required. The results from the upcoming Phase III studies should provide more information.

Can I Make CB-03-01 at Home?

We want to make it clear here – we do not endorse the use of homemade CB-03-01 (or any other treatment) as there may be issues with the purity of CB-03-01 and may lead to other unintended side effects. However, some people are buying powdered CB-03-01 and making a topical solution at home. CB-03-01 powder is widely available online for research and is easy to buy. As for a vehicle, some are using ethanol, propylene glycol (PG), and diethylene glycol monoethyl ether (DEGEE) at a 1:1:1 ratio, whereas others are using ethanol and PG alone.^[20]Reddit, (2020). Anyone know how to make your own CB0301 vehicle? Reddit. Available at: https://www.reddit.com/r/tressless/comments/l5y0di/anyone_know_how_to_make_your_own_cb0301_vehicle/ (Accessed: … Continue reading According to Selleckchem, it is soluble in both dimethylsulfoxide (DMSO) and ethanol.^[21]Selleckchem, (no date). Clascoterone. Selleckchem. Available at: https://www.selleckchem.com/datasheet/clascoterone-S689601-DataSheet.html (Accessed 17 October 2023)

Is CB-03-01 for Me?

While CB-03-01 is available under the brand name Winlevi for acne at a 1% concentration, it will not be available at the 5% dosage (which seemed effective in Phase II studies) until Phase III studies have been completed and FDA approval application has begun.

However, when it is available, you may want to try this treatment if:

• You are male or female 
• You are female and 30 or under
• You have AGA (this treatment targets androgen receptors, so it will not be beneficial for those with other types of hair loss)