How Olaparib Targets Ovarian Cancer Cells
Olaparib (Lynparza) inhibits poly(ADP-ribose) polymerase (PARP) enzymes, primarily PARP1 and PARP2. These enzymes repair single-strand DNA breaks by adding ADP-ribose chains to damaged sites, facilitating recruitment of repair proteins. In ovarian cancer cells with BRCA1 or BRCA2 mutations—common in high-grade serous ovarian cancer (up to 20% of cases)—homologous recombination repair (HRR) is already defective. Olaparib traps PARP on DNA, preventing repair and causing double-strand breaks that unrepaired HR-deficient cells cannot fix, leading to cell death via synthetic lethality.[1][2]
Role of BRCA Mutations and HRD
BRCA1/2 mutations impair HRR, making tumors vulnerable to PARP inhibition. Olaparib exploits this by stalling replication forks during DNA synthesis, collapsing them into double-strand breaks lethal in HR-deficient cells. It also shows efficacy in tumors with other HRD signatures (e.g., via RAD51 loss or genomic scarring), expanding beyond germline BRCA mutations to about 50% of high-grade serous cases.[1][3]
PARP Trapping vs. Catalytic Inhibition
Olaparib's key potency lies in PARP trapping—physically binding PARP-DNA complexes—more than just blocking enzymatic activity. This allosteric mechanism amplifies cytotoxicity in HRD cells, distinguishing it from weaker catalytic-only inhibitors. Studies confirm trapping correlates with antitumor activity in ovarian models.[2][4]
Clinical Evidence in Ovarian Cancer
Approved for maintenance after platinum response in BRCA-mutated or HRD-positive advanced ovarian cancer (e.g., SOLO-1 trial: PFS 56 vs. 14 months placebo). It reduces recurrence risk by 70% in BRCA cases. Used first-line with bevacizumab in HRD tumors (PAOLA-1: PFS 37 vs. 17 months).[1][5]
Differences from Other PARP Inhibitors
Compared to niraparib or rucaparib, olaparib has higher trapping efficiency and better BRCA/HRD selectivity, though all share core PARP inhibition. Niraparib works in non-HRD tumors via broader cytotoxicity; olaparib excels in genetically defined subsets.[3][4]
Resistance Mechanisms Emerging in Patients
Tumors revert BRCA mutations or upregulate drug efflux (e.g., ABC transporters), restoring HRR. Low PARP1 expression or fork protection via RAD51 also confer resistance, seen in 20-40% of progressed cases. Combination strategies (e.g., with ATR inhibitors) aim to counter this.[2][6]
[1]: FDA Lynparza Label
[2]: Nature Reviews Cancer: PARP Inhibitors
[3]: New England Journal of Medicine: SOLO-1 Trial
[4]: Cancer Discovery: PARP Trapping
[5]: NEJM: PAOLA-1 Trial
[6]: Clinical Cancer Research: Resistance