FDA grants priority review to dersimelagon for erythropoietic protoporphyria and X-linked protoporphyria

An oral option for erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP), rare genetic photodermatoses that usually begin in early childhood, is nearing a regulatory decision. The FDA has accepted the new drug application (NDA) for dersimelagon and granted it priority review, with a Prescription Drug User Fee Act target date expected by the end of February 2027.¹ LEO Pharma has also closed its acquisition of worldwide rights to the once-daily melanocortin 1 receptor (MC1R) agonist from Tanabe Pharma.¹

"Patients living with EPP or XLP face a devastating lifelong burden of sunlight-induced pain and a significant impact on their daily lives," said Christophe Bourdon, CEO of LEO Pharma.¹ "The FDA's Priority Review brings us one step closer to potentially providing a new treatment option for patients."

Dersimelagon phase 3 INSPIRE trial design and efficacy in EPP and XLP

The NDA is supported by the global, randomized, double-blind, placebo-controlled phase 3 INSPIRE trial, which enrolled 165 patients aged 12 to 75 years with EPP or XLP.² Participants received dersimelagon 200 mg or placebo once daily for 16 weeks. A 36-week open-label extension is ongoing.²

Dersimelagon met the primary endpoint. It prolonged average daily sunlight exposure time to first prodromal symptom (burning, tingling, itching, or stinging) during weeks 12 to 16, with a placebo-adjusted least-squares mean difference of 23.19 minutes (P = .004).² At week 16, a supplementary analysis showed a difference of 29.64 minutes (P = .004).² Key secondary endpoints were also met, including Patient Global Impression of Change (difference, −1.83; P < .001) and a 39% reduction in total sunlight-induced pain events (P = .004).²

The adverse events that occurred more often with dersimelagon than with placebo were melanocytic nevi, headache, nausea, diarrhea, and skin hyperpigmentation.² The results have not yet appeared in a peer-reviewed journal.

Disease burden of EPP and XLP in children and adolescents

EPP results from ferrochelatase (FECH) mutations. XLP results from gain-of-function aminolevulinic acid synthase-2 (ALAS2) mutations. Both cause protoporphyrin to accumulate in erythrocytes and tissues.² Prodromal symptoms can appear less than 10 minutes after direct sun exposure, and continued exposure leads to severe phototoxic pain.² Some patients also develop liver damage.¹ Estimated prevalence in Europe ranges from about 1 in 75,000 to 1 in 200,000, and US prevalence is unknown.²

Management has relied largely on sun avoidance. Afamelanotide, a melanocortin receptor agonist given as a subcutaneous implant every 2 months, is available for adults.⁴ No pharmacologic therapy is approved for adolescents.²

MC1R agonist mechanism and phase 2 dersimelagon data

Dersimelagon is an oral, nonpeptide small molecule that selectively activates MC1R and increases eumelanin in the skin.²,³ In the phase 2 ENDEAVOR trial, adults were randomized 1:1:1 to placebo, dersimelagon 100 mg, or dersimelagon 300 mg daily for 16 weeks.³ Both doses significantly increased symptom-free sunlight exposure.³ Nausea, freckles, headache, and hyperpigmentation were the most common adverse events.³ The drug holds FDA fast track and orphan drug designations.²

Interpreting dersimelagon efficacy ahead of the 2027 FDA decision

Amy Yeung, MD, MSc, co-director of the Porphyria Center at Massachusetts General Hospital, said the results "show a clinical improvement in light tolerance before experiencing pain."²

The absolute benefit, roughly 23 to 30 more minutes of daily sun exposure before symptoms, comes from a 16-week controlled period and from patient-reported diaries. Because MC1R agonists visibly darken the skin, keeping patients blinded is inherently difficult. Researchers have also questioned the ethics of placebo arms in EPP trials when an approved therapy exists.⁴

Several questions remain open. No head-to-head data against afamelanotide exist. The share of adolescents in INSPIRE and their subgroup outcomes have not been reported. Long-term safety, including nevus surveillance, will depend on the open-label extension.²

References

1. LEO Pharma. LEO Pharma announces FDA acceptance of dersimelagon NDA with priority review and closes acquisition from Tanabe Pharma. News release. Business Wire. September 18, 2026. Accessed September 23, 2026. https://www.businesswire.com/news/home/20260918178750/en/

2. Tanabe Pharma. Tanabe Pharma announces positive data from phase 3 INSPIRE study of dersimelagon in EPP and XLP. News release. March 30, 2026. Accessed September 23, 2026. https://www.tanabe-pharma.com/en/news/rel_260330/main/0/link/e_rel_260330.pdf

3. Balwani M, Bonkovsky HL, Levy C, et al; Endeavor Investigators. Dersimelagon in erythropoietic protoporphyrias. N Engl J Med. 2023;388(15):1376-1385. doi:10.1056/NEJMoa2208754

4. Barman-Aksözen J, Andreoletti M, Blasimme A. Current trials in erythropoietic protoporphyria: are placebo controls ethical? Orphanet J Rare Dis. 2023;18. doi:10.1186/s13023-023-02941-w