New Immunotherapy Shows Promise for Advanced Prostate Cancer

A new immunotherapy drug, VIR-5500, is demonstrating encouraging results in early clinical trials for the treatment of advanced prostate cancer, offering potential hope for patients who have stopped responding to conventional therapies. The drug utilizes a novel approach to harness the body’s immune system to fight the disease.

How VIR-5500 Works

VIR-5500 is a T-cell engager, engineered to simultaneously bind to the body’s T-cells and prostate-specific membrane antigen (PSMA), a protein found on the surface of prostate cancer cells. Researchers at The Institute of Cancer Research, London, explain that this process brings the T-cells into close contact with the cancer cells, facilitating their destruction.

A key innovation of VIR-5500 is its “cloaking device,” designed to keep the drug inactive until it reaches the tumor site. This feature aims to minimize side effects, a common challenge with other T-cell engagers that can trigger severe inflammatory responses. The cloaking mechanism also allows the drug to remain in the bloodstream for a longer duration, potentially reducing the frequency of doses needed.

Phase I Trial Results

The phase I clinical trial, involving 58 patients with advanced prostate cancer who had ceased responding to other treatments, focused on assessing the safety of VIR-5500 and determining the optimal dosage. Results presented at the American Society of Clinical Oncology (ASCO) Genitourinary Cancers Symposium showed promising outcomes:

• 88% of patients experienced only mild side effects.
• In 17 patients receiving the highest dose, 82% saw a reduction of at least 50% in prostate-specific antigen (PSA) levels.
• 53% experienced a PSA level reduction of at least 90%.
• 29% saw a PSA level reduction of at least 99%.
• Among 11 patients with measurable tumors, five exhibited tumor shrinkage.
• In one case, a 63-year-old patient with cancer spread to the liver experienced the complete resolution of 14 cancerous liver lesions after six cycles of treatment.

Implications and Future Research

Professor Johann de Bono of The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, who led the trial, described the results as “stunning,” particularly given that prostate cancer is often considered “immune-cold,” meaning it doesn’t readily respond to immunotherapy. He expressed optimism that such treatments could potentially lead to cures in the long term.

Charlotte Bevan, professor of cancer biology at Imperial College London, noted that this advancement in immunotherapy for prostate cancer is potentially very exciting, opening up a new class of drugs. Bevan emphasized the importance of conducting studies with diverse patient ethnicities, as disparities exist in prostate cancer outcomes.

Simon Grieveson, assistant director of research at Prostate Cancer UK, highlighted the urgent need for new treatments, noting that over 12,000 men die from prostate cancer annually in the UK. Prostate Cancer UK is funding further clinical trials to evaluate the drug’s effectiveness in larger patient populations.

Ongoing Research

Additional research is underway to explore the potential of immunotherapy in prostate cancer, including studies focused on overcoming the immune suppression caused by hormone therapy. Researchers at the University of Sheffield are investigating the use of nanoparticles to stimulate T-cells and delay resistance to hormone therapy, a common issue in prostate cancer treatment.