Men with metastatic hormone-resistant prostate cancer (mCRPC) given Lynparza® (olaparib), a breast and ovarian cancer treatment, lived a clinically meaningful longer time without disease progression or death compared to those given standard treatment with Xtandi® (enzalutamide) or Zytiga® (abiraterone) in a Phase 3 trial. These eligible patients had a mutation in one of 15 DNA repair genes involved in the homologous recombination (HR) pathway. Specifically, these positive benefits were seen in patients with mutations in BRCA1, BRCA2, or ATM, the most common among HR gene mutations; the first two are also strongly linked with familial breast and ovarian cancers. Overall, HR mutations occur in approximately 25% of men diagnosed with mCRPC.
The multicenter, open-label PROfound study (NCT02987543) compared the efficacy and safety of Lynparza® to that of Xtandi® (from Astellas and Pfizer Oncology) and Zytiga® (from Janssen) in mCRPC patients whose disease had progressed while on these newer hormone treatments.
Lynparza®, an oral PARP (poly ADP-ribose polymerase) enzyme inhibitor marketed by AstraZeneca and Merck, is intended to prevent cancer cells from repairing their DNA errors, thereby causing their death. It is approved for some breast and ovarian cancers.
Patients in PROfound were treated with 300 mg twice daily of Lynparza®, or investigators’ choice of Xtandi® (160 mg daily) or Zytiga® (1,000 mg daily, plus prednisone). Lynparza’s safety and tolerability results were generally consistent with previous trials. The PROfound trial is expected to fully conclude in February 2021.
“This is the only positive Phase 3 trial of any PARP inhibitor in metastatic hormone-resistant prostate cancer, where the need for new, effective therapies is high,” according to José Baselga, AstraZeneca’s executive vice president, Oncology R&D. “The PROfound trial also demonstrates the potential value of genomic testing in this at-risk patient population.” Roy Baynes, senior vice president, head of global clinical development and chief medical officer at Merck Research Laboratories, said trial results “represent the potential for a new, oral, and targeted treatment option for this patient population.”
Lynparza® is being tested in other prostate cancer trials, including the international PROpel Phase 3 study testing the addition of Lynparza® to Zytiga® as a first-line treatment of mCRPC patients who have not been given chemotherapy or newer hormonal agents (NCT03732820). PROpel is currently enrolling up to 720 men at sites across the U.S., Canada, Europe and elsewhere.
The material above was summarized from an article appearing in Prostate Cancer News Today, August 12, 2019 to which an e mail subscription is highly recommended.
Additional note on how PARP inhibitors work. DNA is damaged thousands of times during each cell multiplication cycle, and that damage must be repaired, including in normal as well as in cancer cells (which multiply and grow faster than normal cells). Otherwise, if DNA damage is not repaired, cells may die due to this damage. BRCA1, BRCA2 and PALB2 are proteins in cells that are important for the repair of double-strand DNA breaks by the error-free homologous recombinational repair, or HRR, pathway. PARP1 is a protein that is important for repairing single-strand breaks (‘nicks’ in the DNA). Drugs that inhibit PARP1 cause multiple double strand DNA breaks to form in this way, and in tumors with BRCA1, BRCA2 or PALB2 mutations, these double strand breaks cannot be efficiently repaired, leading to the death of the cells. Normal cells that don’t replicate their DNA as often as cancer cells, and that lack any mutated BRCA1 or BRCA2 still have homologous repair system operating, which allows them to survive the inhibition of PARP by drugs like Lynparza®.