Nanoformulated Talazoparib enhances the efficacy and reduces the toxicity of this PARP inhibitor in a preclinical model of BRCA‐deficient breast cancer

BRCA mutations are the leading cause of hereditary breast cancer. PARP inhibitors have shown promising activities in clinical trials for breast cancer by inducing synthetic lethality, particularly in patients with BRCA deficiency. Moreover, the utility of PARP inhibitors could potentially extend beyond BRCA mutations by targeting defects in homologous recombination, and thus impact up to 75% of triple negative breast cancer patients and 33% of breast cancer patients overall. However, conventional oral delivery of PARP inhibitors is hindered by limited bioavailability and significant off‐target toxicities, thus compromising the therapeutic benefits and quality of life in patients. Therefore, we developed a new nanoparticle delivery system for PARP inhibitors and hypothesize that nanoformulated Talazoparib can enhance efficacy by increasing drug concentrations in the tumor and reduce off‐target toxicities. The nanoparticle formulation includes polymer brushes to prolong the circulation time, enabling tumor accumulation through the enhanced permeability and retention effect. The therapeutic efficacy of Nano‐Talazoparib (Nano‐TLZ) was assessed after i.v. injection in Brca1Co/Co;MMTV‐Cre; p53+/− mice with established tumors and compared to vehicle control (saline, i.v.), empty nanoparticles (i.v.), free Talazoparib (i.v.), and free Talazoparib (gavage). Treatment was started when the tumor was 4 mm in diameter and ended when the tumor size reached defined IACUC endpoints. Nano‐TLZ significantly (p<0.05) prolonged the life span of BRCA deficient mice from 11.6±2.6 days with saline injection and 18.3±3.6 days with empty nanoparticles injection to 82.2±10.5 days with i.v. Nano‐TLZ. Nano‐TLZ induced growth arrest in 100% of the tumors and regression (> 50% reduction in tumor volume) in 80% of the tumors. Established tumors regressed more rapidly, and therefore progression free survival significantly improved in the nanoformulated Talazoparib group (p<0.05). Moreover, Nano‐TLZ is better tolerated than free Talazoparib with no significant weight lost or alopecia. In a biomarker study following 10 days of treatment, Nano‐TLZ increased double strand DNA breaks (γ‐H2AX) and decreased proliferation (PCNA) compared to the saline controls. Interestingly, Nano‐TLZ significantly (p<0.05) decreased myeloid derived suppressor cells in both the tumor (41.6±4.7% to 11.2±2.9%) and spleen (10.0±3.2% to 3.7±0.6%) compared to the saline control. Nano‐TLZ also significantly (p<0.05) decreased the percentage of tumor‐associated macrophages in the mammary gland from 7.4±2.0% in the saline control group to 2.5±0.2% in the Nano‐TLZ group. The changes in immune populations suggest potential immunomodulatory effects of Talazoparib. These results demonstrate that the delivery of Talazoparib as a nanoformulation induces superior treatment outcomes with reduced off‐target toxicity in BRCA deficient mice, and provides a novel delivery strategy for PARP inhibitors in patients. Support or Funding Information DoD CDMRP Breakthrough Award This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .