Precision cancer drugs called PARP inhibitors have a previously unknown ability to boost the immune system, and could help many more patients benefit from immunotherapy, a new study reveals.
Scientists found that PARP inhibitors sparked a powerful immune response when used against cancer cells with weaknesses in repairing their DNA.
The study changes our understanding of how PARP inhibitors work – and suggests they could be used alongside immunotherapies to boost their effectiveness. Clinical trials have already started to assess this combination.
Some patients have benefited dramatically from a new generation of immunotherapies – but often only between 10 and 20 per cent of patients will respond, with many others’ cancers able to hide from the immune system.
Scientists at The Institute of Cancer Research, London, and the Institut Gustave Roussy, France, led by Professor Chris Lord and Dr Sophie Postel-Vinay, found that PARP inhibitors could unmask some of these cancers that can currently evade detection by immune cells.
Their study is published in the Journal of Clinical Investigation and was funded by Breast Cancer Now and Cancer Research UK, with additional support from Siric Socrates, the Philanthropia Foundation and the Inserm ATIP-Avenir programme.
Immune response against the tumours
PARP inhibitors such as olaparib block one of the systems which cells use to repair their DNA. They are designed to attack tumours that are already defective at DNA repair, especially ovarian and breast cancers in women with inherited BRCA mutations.
The researchers looked at lung tumours taken from patients, and found those with deficiencies in their DNA repair contained significantly more immune cells within the tumours, compared with tumours in patients with a functioning DNA repair system. This suggested that the DNA repair mutations were stimulating an immune response against the tumours.
They also studied cancer cells from non-small cell lung cancers and triple-negative breast cancers with mutations in DNA repair genes such as ERCC1 or BRCA, to assess whether PARP inhibitors could increase this immune response.
When cancer cells with defective repair systems are treated with PARP inhibitors to block their remaining system of DNA repair, they can no longer repair any DNA damage so accumulate more and more DNA mutations until they die.
provided by The Institute of Cancer Research.