A Phase II clinical trial led by The Institute of Cancer Research, London (ICR), and The Royal Marsden NHS Foundation Trust has shown that Pfizer’s precision drug talazoparib could help treat advanced prostate cancer.
The experimental anticancer drug is a poly ADP ribose polymerase (PARP) inhibitor that selectively acts on cancer cells with faulty DNA repair genes.
Named TALAPRO-1, the Pfizer-funded Phase II trial enrolled more than 100 advanced prostate cancer patients with tumours that had alterations in one or more of 11 DNA repair genes.
These subjects received prior treatment with chemotherapy and enzalutamide and/or abiraterone.
During the trial, talazoparib slowed down tumour growth in certain patients with no other alternate therapies. Of the 104 patients treated with the drug, 31 had a response.
ICR researchers noted that participants who had BRCA mutations particularly experienced a good response to talazoparib.
Nearly 50% of subjects with BRCA2 or BRCA1 defects had a response to the drug, which stopped tumour growth in some patients. The response was observed in 46% and 50% of patients with BRCA2 and BRCA1 mutations, respectively.
This is the first trial to show the safety and effectiveness of talazoparib in prostate cancer, ICR said.
In addition, some patients who had tumours harbouring PALB2 or ATM mutations also experienced a response to the treatment.
The trial also revealed that the drug delayed the progression of the disease by an average of 11.2 months in prostate cancer patients with faulty BRCA genes.
Among talazoparib-treated participants with any of the 11 faulty DNA repair genes, the overall length of time before worsening of their cancer was an average of 5.6 months.
The most frequent adverse effect was anaemia and only a few subjects discontinued the treatment due to the side effects. Overall, the drug was well-tolerated.
Study lead and ICR experimental cancer medicine professor Johann de Bono said: “These results are yet another demonstration that PARP inhibitors work well in some men with prostate cancer – delaying the spread of the disease and extending their lives so they can have more quality time with their families.”
Talazoparib is currently in a follow-up Phase III TALAPRO-2 trial and expected to potentially be one of the first genetically targeted drugs for prostate cancer.