A new immunotherapy drug, VIR-5500, has demonstrated promising results in a phase one clinical trial for men with advanced prostate cancer, shrinking tumours in some patients and significantly reducing levels of a key cancer biomarker, researchers announced on Wednesday.
The trial, led by Professor Johann de Bono of the Institute of Cancer Research, London, and The Royal Marsden NHS Foundation Trust, involved 58 men whose prostate cancer had stopped responding to other treatments. Results presented at the American Society of Clinical Oncology (ASCO) Genitourinary Cancers Symposium in San Francisco showed that the majority of patients experienced only mild side effects, a significant improvement over previous T-cell engager therapies.
VIR-5500 is a T-cell engager, designed to bind both to the body’s immune T-cells and to prostate-specific membrane antigen (PSMA) found on the surface of cancer cells. This process brings the T-cells into contact with the tumour cells, facilitating their destruction. A key innovation of VIR-5500 is its “cloaking device,” which keeps the drug inactive until it reaches the tumour site, minimising systemic side effects and potentially allowing for fewer doses.
Researchers assessed prostate-specific antigen (PSA) levels, a biomarker used to monitor prostate cancer. For 17 men receiving the highest dose of VIR-5500, 14 (82%) saw their PSA levels fall by at least half. Nine (53%) experienced a reduction of at least 90%, and five (29%) saw a fall of at least 99%. Among 11 patients with measurable tumours, five showed evidence of shrinkage. In one case, a 63-year-old man with cancer that had spread to his liver experienced the complete resolution of 14 cancerous lesions after six cycles of treatment.
“We believe that such treatments may in the long term lead to cures,” said Professor de Bono. He described the results as unprecedented for a disease historically considered “immune-cold,” meaning resistant to immunotherapy.
The phase one trial was funded by Vir Biotechnology. Researchers are now planning further clinical trials to confirm these early findings. Simon Grieveson, assistant director of research at Prostate Cancer UK, called the results “extremely promising,” noting that over 12,000 men die from prostate cancer each year in the UK. “We urgently need new and innovative ways to treat the disease,” he said.
Charlotte Bevan, professor of cancer biology at Imperial College London, who was not involved in the study, cautioned that future studies should include patients of diverse ethnicities, given disparities in prostate cancer outcomes. Prostate cancer is the most common cancer among men in many countries, with approximately 1.5 million diagnoses worldwide annually.
