Bayer has launched a first-in-human Phase I clinical trial evaluating 225Ac-GPC3 (BAY 3547926), a novel targeted alpha radiopharmaceutical designed to treat patients with advanced hepatocellular carcinoma (HCC). The announcement was made during the 2025 American Association for Cancer Research (AACR) Annual Meeting, marking Bayer's third targeted alpha therapy program in clinical development.
BAY 3547926 combines a high-affinity monoclonal antibody that targets Glypican-3 (GPC3) with actinium-225, a potent alpha particle-emitting radionuclide. GPC3, an oncofetal protein, is overexpressed in 70-75% of HCC tumors while remaining largely absent in healthy adult tissues, making it an ideal target for precision oncology approaches.
Mechanism of Action and Scientific Rationale
The investigational therapy works by delivering highly potent alpha particles directly to GPC3-expressing cancer cells. Once bound to tumor cells, the radiolabeled antibody emits alpha particles that cause lethal double-strand DNA breaks—damage that cancer cells typically cannot repair. The short path length of alpha emissions helps confine the cytotoxic effects to malignant cells while minimizing damage to surrounding healthy tissue.
"The launch of the Phase I trial using the 225Ac-GPC3 radionuclide therapy marks an important milestone in our commitment to develop new medicines targeting cancer cells with high effect size," said Dr. Dominik Ruettinger, Global Head of Research and Early Development for Oncology at Bayer's Pharmaceuticals Division. "Through continued research innovation we can unlock the full potential of targeted alpha therapies which is an emerging class of targeted radionuclide therapy and a strategic focus area for Bayer's precision oncology development portfolio."
Trial Design and Patient Population
The Phase I dose-escalation study (NCT06764316) will evaluate BAY 3547926 both as a monotherapy and in combination regimens in patients with advanced HCC. Primary endpoints include safety and tolerability, while secondary measures will explore pharmacokinetics and preliminary anti-tumor efficacy.
Preclinical characterization of the asset, presented at AACR, demonstrated low uptake and fast clearance from normal organs as well as induction of tumor regression in in vivo models. The therapy's inclusion in AACR's "New Drugs on the Horizon" session underscores its potential significance in the treatment landscape.
Addressing a Significant Unmet Need
Liver cancer, including HCC, represents the third leading cause of cancer-related deaths worldwide, with approximately 900,000 new cases diagnosed annually. In the United States, it is the most rapidly growing cause of cancer deaths, accounting for about 2% of new cancer cases but 5% of cancer-related mortality.
"Hepatocellular carcinoma continues to be a devastating disease for millions of patients and a pressing unmet need in cancer care," Dr. Ruettinger noted. Despite recent scientific advancements, many clinicians remain dissatisfied with the therapeutic benefits provided by currently available treatments.
Expanding Targeted Alpha Therapy Portfolio
BAY 3547926 joins Bayer's growing targeted alpha therapy (TAT) portfolio, which includes 225Ac-Pelgifatamab and 225Ac-PSMA-Trillium, both currently in Phase I clinical trials for advanced metastatic castration-resistant prostate cancer. This new candidate represents Bayer's first investigational targeted radiopharmaceutical specifically for HCC.
Targeted alpha therapy has emerged as a promising approach for addressing high unmet medical needs across various cancer types. The technology combines alpha particle-emitting radionuclides with specific targeting moieties to deliver radiation precisely where needed.
Actinium-225, with its 9.9-day half-life, delivers highly ionizing radiation over a short range, potentially inducing irreparable DNA damage in cancer cells while limiting toxicity to surrounding healthy tissues. This localized delivery mechanism represents a significant advancement in precision oncology.
Future Implications
As Bayer advances its third TAT program into clinical development, the company continues to strengthen its position in the radiopharmaceutical space. The strategic focus on targeted alpha therapies aligns with the growing interest in radiopharmaceuticals as a promising modality for cancer treatment.
If successful in clinical development, BAY 3547926 could potentially offer a new treatment option for patients with advanced HCC, a population with limited therapeutic alternatives and poor prognosis. The targeted nature of the therapy may provide an improved therapeutic window compared to conventional treatments, potentially delivering more effective treatment with fewer side effects.
The development of BAY 3547926 reflects Bayer's commitment to addressing significant unmet needs in oncology through innovative approaches and precision medicine strategies. As the trial progresses, it will provide valuable insights into the potential of targeted alpha therapies in the treatment of liver cancer.
