Leveraging PMN immune response to overcome ADT resistance in bone metastatic prostate cancer

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Metastatic castration-resistant prostate cancer (mCRPC) is deadly and currently incurable. Approximately 90% of patients CRPC become resistant to 2nd line androgen deprivation therapy (ADT; which primarily target androgen receptor (AR) signaling and present with bone metastatic disease. Although ADT remains a beneficial therapy for mCRPC patients, mechanisms of cancer resistance in mCRPC and specifically, in the bone environment, the most frequent site of CRPC metastasis, is poorly understood. Understanding contributing factors to PCa disease progression is needed for further development of efficacious therapies. ADT was previously shown to be critical for differentiation and function of polymorphonuclear leukocytes/neutrophils (PMNs) which are “first responder” innate immune cells that comprise ~40-50% of the bone marrow cavity. We recently showed that PMNs are protective against bone metastatic prostate cancer (BM-PCa) however, the PMN anti-tumoral immune response diminishes as the tumor progresses. To examine PMN phenotypical changes throughout PCa progression in patients, my group functionally and molecularly characterized peripheral blood PMNs from PCa patients at different stages: 1) Localized PCa, 2) bone metastatic hormone-sensitive (mCSPC), and 3) mCRPC patient. We found that PMN function was highly suppressed by 2nd line ADT through increased receptor 1 expression of transforming growth factor beta (TGFβ), an anti-inflammatory cytokine important for promoting BM-PCa and cancer-induced bone disease. Using preclinical bone metastasis mouse models, we were able to significantly suppress mCRPC growth in bone using 2nd line ADT in combination with either bipolar androgen therapy (BAT; exogenous testosterone) to boost PMN anti-tumor response OR PMN-specific genetic deletion of TβR1. Based on our preliminary findings, we hypothesize that: anti-tumor PMNs are suppressed/ “switched off” by androgen regulation via TβR1 signaling and this can be leveraged to improve mCRPC outcomes. This will be tested in the following aims: Aim 1. Define the impact of androgen regulation on PMN anti-tumor immune response. Aim 2. Determine the mechanism of TβR1-mediated PMN immune response in BM-PCa. Aim 3. Delineate the therapeutic potential of dual TβR1/AR regulation for improving mCRPC therapeutic outcomes. Primary Objective: To develop a novel immunotherapeutic strategy for treating BM-PCa by enhancing PMN anti-tumor response and overcoming PCa resistance to ADT. Study Design: For Aim 1, we will identify the impact of androgen signaling on PMN polarization ex vivo (using patient-derived PMNs and mouse bone marrow PMNs) and in vivo using normal PCa, non-metastatic and bone metastatic PCa cells) and in vivo (using mouse intratibial bone metastasis models). For Aim 2, we will delineate the role of TβR1 in PMN response to mCRPC using TβR1 knockout models. For Aim 3, we will define the therapeutic potential for using combination BAT with a novel bone-targeted TβR1 inhibitor.