Prostate Cancer Immunotherapy Shows Tumor Shrinkage in Early Trial
A T-cell engager drug called VIR-5500 demonstrated tumor shrinkage or growth halt in 45% of evaluable patients with advanced prostate cancer in a phase 1 trial, with 88% experiencing only mild side-effects.
A drug for advanced prostate cancer has shown "remarkable" results in an early-stage trial. The treatment, a type of immunotherapy which harnesses the body's immune system to fight cancer, was found to shrink tumours or halt their growth in patients whose disease had stopped responding to other treatments.
The new drug, known as VIR-5500, uses a so-called cloaking device and only activates when it reaches the tumour, minimising the risk of side-effects. Until now, prostate cancer has seen little benefit from immunotherapies as they have not shown much benefit in shrinking tumours and patients have experienced severe side-effects.
Reporting their findings at the American Society of Clinical Oncology (ASCO) Genitourinary Cancers Symposium, researchers described how the drugs were tested on 58 men with advanced prostate cancer that had stopped responding to other treatments. Of the 11 patients who could be evaluated after being treated at the highest dose, almost half (45 per cent) saw their tumour shrink. Meanwhile, 88 per cent of all the patients, who were recruited from eight sites around the world, only experienced very mild side-effects.
Of the 17 patients who were given the highest dose of the drug, half (53 per cent) saw their levels of prostate-specific antigen (PSA), a blood marker which indicates prostate disease, drop by 90 per cent. And 82 per cent saw their PSA levels halved. "Pending further clinical validation, available data are suggestive of a generally favourable safety profile, with evidence of meaningful anti-tumour activity," according to the abstract presented at the conference.
The drug is called a "T-cell engager" and works by binding to the body's immune T-cells and to a protein found on the surface of prostate cancer cells. When it binds to the cancer cells, wherever they are in the body, it brings the T-cells into contact with them, enabling the attack.
VIR-5500 also contains a "cloaking device" which keeps it inactive until it reaches the cancerous cell, which helps to prevent side-effects from occurring. This also enables the drug to stay in the blood stream for longer, meaning fewer doses may need to be given to patients, according to the study, which was funded by Vir Biotechnology.
Researchers presented details of specific cases to the conference, including a 63-year-old man whose cancer had spread to his liver. Some 14 cancerous liver lesions were "completely resolved" after six cycles of treatment. A 70-year-old whose cancer had spread outside the prostate saw a "complete resolution" of these additional small tumours and reported that he was enjoying an "excellent" quality of life. Meanwhile, a 77-year-old man involved in the study had "undetectable" levels of PSA after 17 cycles of treatment.
The study was a phase 1 trial that looks at the safety and efficacy of the drug before it is tested on a wider group. The trial, led by researchers at the Institute of Cancer Research, London, and the Royal Marsden NHS Foundation Trust, is ongoing, and the drug will now progress into larger trials.