Wuppertal, Germany, July 24, 2025 – Aicuris announced today that it has completed patient enrollment for PRIOH-1, its Phase 3 pivotal trial. This trial is assessing pritelivir as a treatment for herpes simplex virus (HSV) infections that are refractory and/or treatment-resistant in patients with compromised immune systems. The company’s primary drug candidate is a small molecule that uniquely inhibits the viral helicase-primase complex, setting it apart from existing HSV treatments.

While HSV infections are usually manageable, they can become severe and challenging to treat in individuals with weakened immunity. In this group, standard antiviral medications like acyclovir and foscarnet often fail. This leaves both patients and their doctors with few approved treatment options. By targeting a different stage in the viral replication process, pritelivir could offer an oral treatment option for individuals with refractory HSV.

“HSV infections can pose a significant health challenge for immunocompromised patients, particularly when standard treatments are ineffective,” stated Cynthia Wat, MD, CMO of Aicuris. “Despite this pressing need, there have been no new HSV therapies approved in over two decades, leaving clinicians with limited and often poorly tolerated choices for this vulnerable population. Pritelivir has demonstrated encouraging efficacy and a favorable safety/tolerability profile in earlier trials and is already making a clinical difference through our compassionate use program. We believe it has the potential to significantly improve care and change the treatment landscape for immunocompromised patients with HSV infections.”

“Completing patient enrollment in our Phase 3 pivotal trial marks a major achievement for Aicuris and a crucial step toward providing a much-needed therapy for patients battling refractory HSV infections,” said Larry Edwards, CEO of Aicuris. “Following PREVYMIS®, pritelivir is the second candidate from our pipeline to reach this stage, further validating our R&D strategy and reinforcing our leadership in antiviral innovation. We are now focused on preparing for study completion and data analysis, while also advancing our regulatory and commercial plans to make pritelivir available to patients who need it.”

The study’s goal is to show that pritelivir is more effective and safer than the investigator’s choice of treatment for refractory HSV infections in immunocompromised patients. The trial enrolled 157 participants from 12 countries across Europe, North America, and Australia. Patients received a daily oral dose of 100 mg of pritelivir after an initial loading dose of 400 mg on the first day.

In the part of the trial focused on acyclovir-refractory HSV, patients were randomly assigned in a 1:1 ratio to receive either pritelivir or the investigator’s choice of treatment. This was done to demonstrate that pritelivir has superior efficacy (percentage of completely healed lesions) and a better safety profile. In addition to the randomized part, HSV patients were treated in two more groups: one with acyclovir-refractory and foscarnet-refractory/intolerant HSV, and another with acyclovir-susceptible HSV.

The study is based on pritelivir’s prior clinical successes, which showed good tolerability, favorable pharmacokinetic properties, and promising clinical efficacy in patients with refractory HSV. The FDA granted pritelivir Breakthrough Therapy designation in 2020, and Aicuris is supporting expanded access to treatment for eligible patients. Topline results are expected in Q4 2025, and a detailed analysis will be presented at a medical conference in H1 2026.

About Herpes Simplex Virus
Herpes Simplex Virus (HSV) has two types, HSV-1 and HSV-2, both causing lifelong infections. HSV-1 usually causes oral herpes, leading to cold sores, while HSV-2 is generally linked to genital herpes. These viruses can result in recurring painful lesions and sores, and in serious cases, complications like encephalitis, meningitis, disseminated disease, keratitis, and neonatal herpes. HSV infections are common worldwide and have a considerable impact on public health, especially among immunocompromised patients, who may experience more severe, frequent, and refractory symptoms.

About Pritelivir
Pritelivir, a novel helicase-primase inhibitor created by Aicuris, targets both HSV-1 and HSV-2. These viruses cause genital, oral, or disseminated infections that are becoming more severe and resistant in immunocompromised individuals. Unlike traditional antivirals, pritelivir inhibits viral DNA synthesis by targeting the helicase-primase complex, a different mechanism from currently available nucleoside analogs. Because pritelivir doesn’t need activation by viral proteins, it may be less prone to resistance development.1 Earlier Phase 1 and Phase 2 trials in immunocompetent and immunocompromised individuals showed a good safety profile and improved clinical efficacy compared to standard treatments like valaciclovir and foscarnet (including resistant or refractory strains). Pritelivir has now completed patient enrollment in its pivotal Phase 3 trial, and the results will be used to apply for marketing authorization in 2026.

About Aicuris
Aicuris is dedicated to meeting the needs of the increasing number of immunocompromised individuals who require specialized therapies for effective infection treatment. Our main product, PREVYMIS®, is marketed by our partner MSD and prevents CMV in specific groups of transplant recipients. Our Phase 3 pivotal candidate, pritelivir, is intended to treat refractory HSV infections in a broad range of patients with weakened immune systems. For immunocompromised individuals, a manageable infection can be life-threatening. Aicuris, with its expertise and expanding pipeline, is committed to delivering therapeutic solutions for them now and in the future.

Contact:
Aicuris Anti-infective Cures AG
info@aicuris.com

Trophic Communications
Dr. Stephanie May and Dr. Charlotte Spitz
Phone: +49 171 3512733
Email:

1 Sallée, L. and Boutolleau, D. (2024), Management of Refractory/Resistant Herpes Simplex Virus Infections in Haematopoietic Stem Cell Transplantation Recipients: A Literature Review. Rev Med Virol, 34: e2574.

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