'Remarkable' results in study on new prostate cancer drug
Almost half of the 11 patients who could be evaluated after receiving the highest dose - saw their tumour shrink.
A drug for advanced prostate cancer has shown "remarkable" results in an early-stage trial, experts have said.
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.
The news was welcomed by cancer experts who said that 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.
But 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.
Reporting their findings at the American Society of Clinical Oncology (ASCO) Genitourinary Cancers Symposium, researchers described how the drugs was 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%) saw their tumour shrink, according to the team led by Professor Johann de Bono at the Institute of Cancer Research (ICR), London, and the Royal Marsden NHS Foundation Trust.
Meanwhile, 88% 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%) saw their their levels of prostate-specific antigen (PSA), a blood marker which indicates prostate disease, levels drop by 90%. And 82% 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.
The ICR said 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 looks at the safety and efficacy of the drug before it is tested on a wider group.
Prof de Bono said: "T-cell engagers empower the body's own immune system to give cancer cells the kiss of death.
"It is really remarkable to see early signs that this T-cell engager drug can have a profound anti-cancer effect for patients with advanced prostate cancer, who desperately need new treatments.
"It's very positive to see that very few patients have experienced major side-effects, as this has been a key challenge in treating prostate cancers with immunotherapies in the past.
"This clinical trial is ongoing, and the drug will now progress into larger trials so that we can study its effect on patients' long-term outcomes.
"There is certainly hope that drugs such as this will increase the likelihood of a cure even from advanced prostate cancer that has already spread, in the not-too-distant future."
Professor Kristian Helin, chief executive of the Institute of Cancer Research, London, said: "Immunotherapy has transformed the outcomes for many people with cancer but for those with prostate cancer its benefits have often remained out of reach.
"It's encouraging to see this innovative approach showing promising effects in early clinical studies, and I look forward to following its continued development.
"I hope that VIR-5500 may offer a new treatment option for patients with advanced prostate cancer, who urgently need more effective therapies."
Simon Grieveson, assistant director of research at Prostate Cancer UK, said: "With over 12,000 men dying from prostate cancer each year in the UK, we urgently need new and innovative ways to treat the disease. Immunotherapy has shown huge benefits to patients in several other cancers, but to date it has not had the same impact in prostate cancer.
"This is an exciting early-phase trial testing an innovative way to harness the body's immune system to target prostate cancer. These early results are extremely promising, with a number of men on the study responding positively to the treatment with minimal side effects. I look forward to seeing this now tested in larger trials, with the hope that this treatment will offer men more valuable time with their loved ones."