Project Description Triple negative breast cancer (TNBC) is the most challenging subtype to treat among all breast cancer cases due to lack of cell surface receptors. Patients with metastatic TNBC have median overall survival of only 13.3 months with treatment. Newly approved immune checkpoint inhibitors such as PD-1 antibody only extend the survival by 2-4 months when used with chemotherapy, and the efficacy highly relies on expression of targets such as PD-L1 in tumors. Despite new treatment options, metastatic TNBC is predominantly treated by highly potent chemotherapy, with combination therapy being advantageous over single agents regarding response rate and overall survival. However, the drugs in combination chemotherapy have distinct physicochemical properties that hinders formulation into single dosage; their distinct pharmacokinetic behavior hinders the in vivo synergism. Furthermore, these drugs are non-specific to cancer cells and often show systemic toxicity. Our long-term goal is to develop advanced and well-characterized drug delivery approaches to improve treatment outcomes of drugs and drug combinations. In this project, we propose a dual-drug loaded dual-peptide ligand incorporated drug combination nanoparticle (DCNP) approach for targeting and inhibition of metastatic TNBC. The lipid-based DCNP leverage on effective gemcitabine and paclitaxel combination in clinic to deliver both drugs in prolonged and synchronized manner. Through incorporation of two peptide ligands that targets TNBC cells (through ICAM- 1) and tumor vasculature (through endoglin), the DCNP could target both primary tumor and metastasis for enhanced chemotherapy. Furthermore, both drugs are reported to upregulate PD-L1 and reduce population of myeloid derived suppressor cells (MDSCs) in the tumor. These effects can sensitize TNBC cells for PD-1/PD-L1 therapy. The DCNPs that synchronize and co-deliver both drugs may further augment such effects thus generate improved chemoimmuno therapeutic outcomes. The objectives of this project are to validate the concepts of improved targeting and chemotherapy of metastatic TNBC with a dual-targeting DCNP approach and enhanced combination therapy with immune checkpoint inhibitors. In Aim 1, we will prepare ligands-incorporated DCNPs with high drug loading, proper size, and good stability, and test their cellular binding and efficacy, and effects on cancer cell expression of PD-L1. In Aim 2, we will validate enhanced in vivo targeting efficiency with the dual- ligand strategy and correlate it with expression levels of receptors and evaluate inhibition of primary tumor and metastasis with monitoring of survival. In Aim 3, we will assess the upregulation of PD-L1 and reduction of MDSCs by the DCNPs and carry out a pilot survival study with a chemoimmuno combination regimen. If successful, this targeted drug combination strategy could substantially improve the treatment of metastatic TNBC. Through tuning composition and targetin...