Deciphering Prostate Cancer Cell Dormancy Drivers

It is well established that cancer metastases develop from early disseminated tumor cells (DTCs), which can stay dormant but reactivate into overt proliferation. Studies on dormant cancer cells across multiple cancers have revealed the nuclear receptor NR2F1 as a key indicator and determinant for cellular dormancy. Global epigenetic modulators such as 5-aza-C and retinoic acid, or specific agonist C26 increased NR2F1 protein levels and enhanced NR2F1- dependent dormancy programs in pre-clinical in vivo models of breast cancer and head and neck squamous cell cancer, suggesting the clinical potential of NR2F1 to induce DTC dormancy for delay of metastatic onset. In prostate cancer (PCa), NR2F1 was also a dormancy marker and expressed highly in the dormant PCa cells in the bone microenvironment. However, the mechanistic understanding of PCa DTC dormancy in the bone microenvironment remains lacking, which limits the development of therapeutic approaches that directly act on DTCs to stop the lethal bone metastases. Specifically, whether manipulation of NR2F1 protein levels can benefit PCa patients is elusive. The NR2F1 expression is decreased in PCa tumors compared to normal prostate and further decreases in metastatic tumors; intriguingly, NR2F1 does NOT have a prognostic effect in PCa patients. Although NR2F1 levels consistently increase in dormant DTC cells in the bone microenvironment, our preliminary data suggested that overexpression and knockout of NR2F1 did not affect PCa cells’ dormancy responses. We hypothesize that NR2F1 is a dispensable downstream effector in the dormancy program; instead, an unexplored upstream transcription regulator (UTR) determines the PCa DTCs dormancy. The objectives of this proposal are to identify the master UTR and NR2F1- independent downstream effectors. The long-term goal of this proposal is to develop targeted therapies to manipulate tumor dormancy in PCa patients so that we can either prevent metastasis and relapse or eliminate dormant DTCs. We propose two specific aims to test our hypothesis. Specific Aim 1. Determine the upstream transcription regulators (UTRs) of NR2F1 in PCa dormancy. Using an unbiased novel loci-specific proteomic approach and a targeted screen against a pre-determined candidate list from RNA-Seq, we will determine the driver of PCa cell dormancy using NR2F1 as one of the markers. Specific Aim 2. Determine the NR2F1-independent dormancy effector in PCa dormancy. Using a targeted screen in PCa cells with NR2F1 KO, against an up-regulated gene list from RNA-Seq of dormant PCa cells, we will identify the indispensable downstream effectors of PCa dormancy. The successful identification of dormancy drivers, including the UTRs and downstream effectors, will yield a better understanding of how PCa cells respond to dormancy induction signals from the bone microenvironment and also facilitate the development of targeted therapies to induce or maintain the DTCs as dormant, thus stopping the lethal bone metastases.