Danish drugmaker LEO Pharma has agreed to acquire the worldwide rights to dersimelagon from Tanabe Pharma in a deal valued at up to $435 million in upfront and near-term milestone payments, as the company expands its rare-disease portfolio and builds potential future growth drivers.

The transaction also includes potential downstream milestone payments and tiered royalties on net sales.

Dersimelagon is an investigational oral therapy being developed for erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP), rare genetic disorders that cause extreme sensitivity to sunlight and can trigger painful light-induced reactions.

The drug works by increasing melanin production, potentially helping protect patients from the painful effects of light exposure.

LEO Pharma CEO Christophe Bourdon said the unmet need in EPP is significant, with an estimated 5,000 patients in the US affected by the disease. 

The company expects the US Food and Drug Administration could approve dersimelagon for EPP and XLP as early as 2027, subject to regulatory review.

If approved, dersimelagon could become the first oral treatment for EPP and XLP, according to LEO Pharma.

The acquisition is part of LEO Pharma's broader strategy to strengthen its presence in rare genetic skin diseases. The company partnered with Boehringer Ingelheim on Spevigo in July 2025 and agreed to acquire US-based drug developer Replay in April 2026.

The transaction comes as LEO Pharma explores a potential stock-market listing, with the dersimelagon acquisition adding another potential growth asset to its pipeline.