Despite progress in the treatment of primary tumors, metastatic disease remains incurable. While all metastatic sites are important clinically, skeletal metastases are common in patients with breast, prostate, lung cancer, and other, with approximately 70% of women that die from metastatic breast cancer experiencing serious complications from bone metastases. Once established in the bone, tumors disrupt normal bone homeostasis leading to increased pain, fracture, and general morbidity. Our previous work has established the transcription factor Gli2 as a promising target for reducing tumor induced bone disease. After identifying the small molecule inhibitor, Gli Antagonist 58 (GANT58), as a promising inhibitor of Gli2 activity in bone metastatic tumors, we discovered the poor bioavailability of GANT58 limited its use in systemic delivery models. Thus, we developed polymeric NPs to solubilize, improve the pharmacokinetics (PK), and promote bioavailability of GANT58 (GANT58-NPs). The NPs comprised reactive oxygen species (ROS)-responsive poly(propylene sulfide-block- oligoethylene glycol acrylate) (PPS-b-POEGA). Intravenous injection of the 1st generation GANT58-NPs (Dh=93 nm) reduced TIBD in models of intratibial and intracardiac breast tumor cell inoculation and in a lung cancer model (3 unique models). GANT58-NPs were safe (did not elevate serum markers of liver/kidney toxicity or cause detectable histopathology. Our 2nd generation NPs were bone targeted (BT-GANT58-NPs), and the chemistry utilized enabled tuning of the density of the bone binding ligand, alendronate (ALN), a bioactive bisphosphonate (osteoclast inhibitor). While both formulations reduced tumor invasion into bone and reduced tumor proliferation by ki67 staining, they did not eliminate tumor and did not significantly reduce tumor bulk in models of established bone metastatic disease. Here, we propose to screen a broader polymer chemistry space focusing on: (1) Developing an alternative bone targeting strategy without inherent bioactivity; (2) Studying how NP core chemistry affects GANT58 loading, GANT58 triggerable release, and consequent in vivo PK; (3) Defining the maximum tolerated dose (MTD), dose-limiting toxicities, and dose dependent PK / PD. In addition, we will evaluate the efficacy of a co-loaded GANT58 and paclitaxel BT-NP formulation. Each of these formulations will be evaluated for detailed PK/PD and biodistribution properties to identify promising formulations to reduce tumor induced bone disease without inducing systemic toxicity. Our preliminary data show promising results that include low toxicity and efficacy in reducing tumor burden in bone and bone destruction. This proposal will explore the efficacy and PK/PD properties in more detail to develop a promising therapy for eventual translation. The results of these studies will help identify a novel and promising strategy to reduce tumor burden and bone destruction in patients with bone metastatic disease. Due to t...