Investigating mechanisms of bladder cancer metastasis

The major cause of bladder cancer deaths is due to metastasis, yet to date metastatic bladder cancer (mMIBC) has not been extensively studied and many salient issues remain unresolved. One of the major challenges that has hampered progress in studying mMIBC is the lack of suitable models to investigate metastatic progression in vivo. We have now generated novel genetically-engineered mouse models (GEMMs) that develop highly penetrant mMIBC. These new are based on our established GEMM, in which bladder-specific co-inactivation of the Pten and p53 tumor suppressors leads to invasive disease with a low incidence of metastasis. Crossing these Pten; p53 mice with mice harboring loss-of-function of Arid1a, an epigenetic regulator that is dysregulated in a high percentage of human bladder cancers, results in lethal bladder cancer with >80% incidence of metastasis. In addition, treatment of the Pten; p53 mice with a low dose of the carcinogen N-butyl- N-(4-hydroxybutyl)-nitrosamine (BBN) leads to mMIBC with >60% incidence. In parallel, we have implemented state-of-the-art systems biology approaches to identify mechanistic determinants—master regulators (MRs)—of metastatic progression in the GEMMs. MRs enriched in metastatic tumors in the GEMMs are conserved with human bladder cancer, and are enriched for those associated with lineage plasticity. To identify drugs that target these conserved MRs, we implemented OncoTreat, a computational algorithm that prioritizes drugs based on their ability to invert the activities of biologically-relevant MR. To validate these drugs, we have generated an extensive biobank of human patient derived organoid models. Leveraging these GEMMs, human patient derived organoids and systems approaches, we are ideally poised to investigate the hypothesis that the transition from pre-invasive to metastatic disease is driven by the sequential activities of master regulators, including for lineage plasticity, which can be elucidated and targeted by studying metastatic progression in these GEMMs. We will pursue three Specific Aims: In Aim 1, we will leverage our GEMMs of mMIBC to systematically investigate the biological processes and molecular mechanisms underlying metastatic progression in vivo. In Aim 2, we will elucidate master regulators of metastatic progression, focusing on those associated with the transition from pre- metastatic to metastatic MIBC, and/or that distinguish tumors from their corresponding metastases, metastases to different organ sites, and, as feasible, pre-metastatic clusters from overt metastases. We will prioritize MRs that are conserved with human bladder cancer, as well as those associated with lineage plasticity. In Aim 3, we will seek to identify new drugs for mMIBC using the OncoTreat algorithm to identify compounds that invert the activity of MRs of metastasis. We will prioritize candidate drugs that (1) target lineage plasticity mechanisms, and/or (2) are inferred for patients that do not have evident actionable driver mutations. Altogether, our studies will provide a comprehensive analysis of the biology, mechanisms, and treatments for mMIBC, with the translational goal of identifying new therapeutic targets that may improve patient outcomes.