Project Summary: PARP inhibitors-based synthetic lethal therapy, such as BMN673 (Talazoparib), shows great efficacy for BRCA mutated (or homologous recombination repair (HRR)-deficient) cancers in preclinical and clinical studies, but demonstrates limited efficacy for majority of cancer types that are HRR proficient. To improve the PARPi efficacy and extend their therapeutic application, additional combination approaches are necessary. 5-azacytidine (AZA) is a DNA methylation inhibitor, which shows increasing clinical use for epigenetic therapy of solid tumors. AZA has been reported to enhance PARPi response through trapping large DNMT-PARP1 complexes to DNA break sites and enhancing formation of cytotoxic double-strand breaks (DSBs). Based on our preliminary data and data from others, AZA may also affect DNA repair, inducing HRR defects and sensitizing tumors to PARPi. Moreover, we hypothesize that combination of AZA with BMN673 may enhance the tumor immune response through generation of novel neoantigens and upregulation of MHC class I molecules. However, the effectiveness of this combination therapy is limited by the poor bioavailability of the two drugs and the challenge of codelivery to tumors due to the distinct physiochemical properties of BMN and Aza. In our preliminary studies, we developed a small sized nanocarrier that could selectively accumulate in the tumors and effectively penetrate to the core of experimental tumors, importantly, it could efficiently load both hydrophilic AZA and hydrophobic agent BMN673 and was more effective in suppressing tumor growth in PARPi-insensitive NSCLC tumor models at relatively lower doses. We propose to further optimize the BMN/PAZA formulation (Aim 1) and evaluate their in vivo pharmacokinetics, biodistribution and tumor penetration efficiency using tumor models that closely mimic human NSCLC (Aim 2). We will also investigate the therapeutic efficacy and the underlying mechanism (Aim 3). These studies will address the issues of off-target toxicity of AZA and PARPi, and provide a promising and safe strategy to expand the clinical use of synthetic lethal therapy to both HRR-deficient and HRR-proficient cancer patients.