Wuppertal, Germany, July 24, 2025 - Aicuris Anti-infective Cures AG today announced the completion of patient enrollment in its pivotal Phase 3 trial, PRIOH-1, evaluating pritelivir for the treatment of refractory and/or treatment resistant herpes simplex virus (HSV) infections in immunocompromised patients. The company’s lead candidate is a small molecule specifically inhibiting the viral helicase-primase complex, which represents a novel mechanism of action distinct from current HSV therapies.
While HSV infections are typically manageable, they can become severe and difficult to treat in individuals with a weakened immune system. In this patient population, failure to respond to marketed antiviral agents such as acyclovir and foscarnet occurs more frequently. This leaves patients and their clinicians with limited approved treatment options. By targeting an alternative step in the viral replication cycle, pritelivir may provide an oral therapeutic alternative for patients with refractory HSV.
“An HSV infection can be a serious health burden for immunocompromised patients, particularly when the virus no longer responds to standard treatments,” said Cynthia Wat, MD, CMO of Aicuris. “Despite this high medical need, no new HSV therapies have been approved in over two decades, leaving clinicians with limited therapeutic choices, which are often not well tolerated, in a clinically vulnerable patient population. Pritelivir showed a promising efficacy and safety/tolerability profile in earlier development stages and is already delivering clinical impact to patients through our compassionate use program. We believe it holds strong potential to address a critical gap in care with the ability to redefine the treatment landscape for immunocompromised patients facing HSV infections.”
“Completion of patient enrollment in our pivotal Phase 3 trial is a major milestone for Aicuris and a key step towards delivering a much-needed therapy to patients facing refractory HSV infections,” stated Larry Edwards, CEO of Aicuris. “After PREVYMIS®, pritelivir is the second candidate from our pipeline reaching this stage, further validating our R&D strategy and solidifying our position as a leader in antiviral innovation. We are now focusing on preparing for study completion and the data readout, while advancing our regulatory and commercial strategy to bring pritelivir to patients in need.”
The study (2023-510088-37-00) aims to demonstrate superior efficacy and safety of pritelivir vs. investigator’s choice for refractory HSV infections in immunocompromised patients. The study recruited 157 participants across 12 countries in Europe, North America and Australia. Patients received 100 mg of pritelivir orally once daily after an initial loading dose of 400 mg on the first day of treatment.
In the acyclovir-refractory part of the trial, HSV patients were randomized 1:1 and treated with pritelivir or investigator´s choice to demonstrate superior efficacy (percentage of fully healed lesions) and a more favorable safety profile of pritelivir. Apart from the randomized part of the study, HSV patients were treated in two additional cohorts: an acyclovir-refractory and foscarnet-refractory/intolerant arm and an acyclovir-susceptible arm.
The study builds on pritelivir’s previous clinical success, demonstrating favorable tolerability and pharmacokinetic properties and promising clinical efficacy in patients with refractory HSV. Notably, pritelivir received a Breakthrough Therapy designation in 2020 from the FDA, and Aicuris supports expanded access to treatment for eligible patients. Topline results are expected for Q4 2025 with a detailed analysis presented at a medical conference in H1 2026.
About Herpes Simplex Virus
Herpes Simplex Virus (HSV) includes two types, HSV-1 and HSV-2, both of which cause lifelong infections. HSV-1 typically leads to labile herpes, typically resulting in cold sores, while HSV-2 is commonly associated with genital herpes. These viruses can cause recurrent painful lesions and sores, and in severe cases, complications such as encephalitis, meningitis, disseminated disease, keratitis and neonatal herpes. HSV infections are widespread globally, with a significant impact on public health, especially in immunocompromised patients, in whom more severe, more frequent and refractory manifestations may occur.
About Pritelivir
Pritelivir, a novel helicase-primase inhibitor developed by Aicuris, targets both HSV-1 and HSV-2. These viruses are responsible for genital, oral or disseminated infections with increasing severity and resistance development in immunocompromised people. Unlike traditional antivirals, pritelivir blocks viral DNA synthesis by inhibiting the helicase-primase complex, a mechanism distinct from marketed nucleoside analogues. As pritelivir does not require activation by viral proteins it may be less susceptible to resistance development.1 Earlier Phase 1 and Phase 2 trials in immunocompetent and immunocompromised individuals showed a favorable safety profile and an improved clinical efficacy compared to standard of care treatments like valaciclovir and foscarnet (including resistant or refractory strains) pritelivir has currently enrolled the last patient in a pivotal Phase 3 trial. The results of this trial will serve as a basis for filing for marketing authorization in 2026.
About Aicuris
Aicuris is meeting the needs of the growing population of immunocompromised people who require precise therapies to effectively treat infection. Our flagship product, PREVYMIS®, marketed by our partner MSD, prevents CMV in a defined group of transplant recipients. Our pivotal Phase 3 candidate, pritelivir, aims to address refractory HSV infections in a broad population of patients with weakened immune systems. For immunocompromised people, an otherwise manageable infection can mean life or death. Aicuris, with its expertise and growing pipeline, is committed to providing 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: aicuris@trophic.eu
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. https://doi.org/10.1002/rmv.2574
