The following are all current UCLA Prostate SPORE research projects.
Project II: Developing an N-Terminal Inhibitor of the Androgen Receptor
Matthew B. Rettig, MD, Clinical Co-Leader
Michael E. Jung, PhD, Basic Co-Leader
The overarching goal of this project is to bring a lead compound that targets the androgen receptor (AR) N-terminal domain to early phase clinical trials with the long-term goal of bringing a drug to regulatory approval that prolongs life expectancy and improves the quality of life of patients with the metastatic castration resistant prostate cancer (mCRPC), the stage and state of prostate cancer that accounts for virtually all prostate cancer-specific mortality. Thus, the key focus of this project is drug discovery and development. Several years of preclinical studies and subsequent proof-of-principle clinic trials established a pathophysiologic role for the AR in the emergence of CRPC. Unfortunately, primary or secondary resistance to all currently available drugs emerges in all patients. Thus, there is an unmet clinical need to develop effective therapies that can be applied as single agents in the post-abiraterone/post-enzalutamide setting and potentially in combination with current secondary generation AR inhibitory agents to improve the quality and quantity of life of mCRPC patients. Importantly, the C-terminal ligand binding domain (LBD) of the AR represents the direct or indirect molecular target of all hormonally acting agents in clinical use. Other major domains of the AR, including the centrally located DNA binding domain (DBD) and N-terminal transactivation domain (TAD), have yet to be directly targeted and exploited for therapeutic benefit. Given that the AR principally functions as a transcription factor and its genotropic effects are required for the development of castration resistance, we hypothesized that approaches to inhibit AR transcriptional activity by interfering with the TAD will suppress the growth of AR-dependent CRPC cells. In pursuit of this hypothesis, the PIs have collaborated for the last several years to identify a series (the “JN” series) of potent AR inhibitors with the following characteristics: 1) AR TAD as the molecular target, 2) direct, selective, high affinity and covalent binding to the AR, 3) drug-induced rapid degradation of the full-length AR (ARFL) and constitutively active AR splice variants that lack a functional LBD (ARSVs), 4) selective cytoreductive effects on AR expressing prostate cancer cell lines, including ARΔLBD expressing cell lines, 5) growth inhibition of CRPC xenografts, and 6) inhibition of AR-driven gene expression. In the advancement of the pre-clinical and clinical development of JN series compounds, we propose to elucidate the detailed mechanism of action of the JN series compounds and identify a lead compound through further structure activity relationship analysis that will be pre-clinically validated and tested in IND-enabling studies. In year 5 of the award, we will initiate a first-in-human phase 1 study of our lead compound.
Project III: Developing CAR T Cell Therapies to Target Tumor Heterogeneity in Advanced Prostate Cancer
Owen N. Witte, MD, Basic Co-Leader
Stephen J. Forman, MD, Clinical Co-Leader
Therapies that inhibit androgen biosynthesis and target the androgen receptor are the mainstay of treatment for patients with advanced prostate cancer. However, most men will eventually develop resistant disease that is called castration-resistant prostate cancer (CRPC). Metastatic CRPC is not curable and treatments at this stage are aimed at extending and improving quality of life. CRPC is a heterogeneous disease composed of at least two subtypes including prostate adenocarcinoma and neuroendocrine prostate cancer (NEPC). Both CRPC subtypes are found together in many lethal, treatment-resistant prostate cancers. New and potent therapies that account for and eliminate the heterogeneity of CRPC are urgently needed. Chimeric antigen receptor (CAR) T cell therapy is a revolutionary advance in oncology that combines precision targeting with powerful killing of tumor cells. In this approach, a patient’s own immune T cells are collected from the blood, genetically engineered to recognize and kill his/her specific cancer and reintroduced into the patient. This technology has the potential to transform the treatment of cancer including those that have been considered incurable. Our group has pushed forward the first CAR T cell therapy for metastatic CRPC to a clinical trial by building on a series of scientific accomplishments. We discovered that prostate stem cell antigen (PSCA) is a protein expressed on the surface of the majority of prostate adenocarcinomas, developed antibodies that bind specifically to PSCA, and extensively engineered and tested PSCA CAR T cell therapy in laboratory models of prostate cancer. Recently, we have also found that another protein, carcinoembryonic antigen related cell adhesion molecule 5 (CEACAM5), is expressed on the surface of most NEPCs. In the proposed research, we will initiate a phase I clinical trial to evaluate our PSCA CAR T cells in patients with metastatic CRPC and interrogate patient specimens to elucidate mechanisms of treatment resistance with particular attention given to the emergence of NEPC. We will also engineer and evaluate CARs aimed at safely and specifically targeting CEACAM5 in laboratory models of NEPC. Lastly, we will determine whether a strategy combining PSCA CAR T and CEACAM5 CAR T cells can safely address tumor heterogeneity in CRPC by eradicating both prostate adenocarcinoma and NEPC.
Project IV: Targetable Master Regulator of Lethal Prostate Cancer
Michael R. Freeman, PhD, Basic Co-Leader
Isla Garraway, MD, PhD, Clinical Co-Leader
Castration-resistant prostate cancer (CRPC) emerges following androgen deprivation therapy (ADT), where variable degrees of dependence on the androgen receptor (AR) are observed, and features of neuroendocrine (NE) carcinoma often arise. We have identified the developmental transcription factor, ONECUT2 (OC2/HNF6β), as a master regulator of AR networks in metastatic (m)CRPC. OC2 governs a lethal differentiation program, drives metastasis, and interacts with the AR at several levels, including as a multiprotein complex and a transcriptional regulator of AR target genes. Our studies indicate that OC2 appears to override AR-dependent mechanisms in a subset of mCRPC and activates an NE differentiation program within the context of adenocarcinoma. To inhibit OC2, we developed a novel class of small molecules that bind OC2 directly and suppress growth and metastasis of AR/AR-V7-positive mCRPC xenografts. Additionally, we have developed profiling and immunohistochemistry (IHC) methods to identify OC2 activity in clinical specimens, laying a foundation for an OC2-targeted treatment approach in select patients. This project will test the hypothesis that OC2 is an actionable target in a subset of aggressive prostate cancer where OC2 is active. The Specific Aims are: Aim 1. Study the mechanism by which OC2 activity promotes aggressive behavior of CRPC. Determine whether OC2 can compensate for AR in CRPC. Determine whether OC2 upregulation can confer independence from AR. Determine whether OC2 interactors in AR-dependent and AR-independent transcription complexes are distinct. Determine whether OC2 is required for NE differentiation and growth of NE-CRPC. Aim 2. Develop and optimize OC2 inhibitors for use in patients with early mCRPC. Synthesize and test derivatives of the OC2 targeting compound CSRM617. Perform in silico and high-throughput screening for structurally unrelated OC2 inhibitors. Test the safety and efficacy of OC2 inhibitors in pre-clinical models. Aim 3. Identify the clinical scenarios where OC2-driven tumors emerge. Refine multiplex IHC detection of OC2/AR expression in OC2-active tumors. Determine the correlation between OC2 activity and IHC detection of OC2 and AR in independent sets of clinical samples. Evaluate OC2 activity along the clinical spectrum of prostate cancer progression, including sequential pre/post-ADT tumor specimens, metastases and xenograft models. Measure OC2/AR activity in diagnostic prostate needle biopsies (PNBX) of untreated men with high-grade prostate cancer and determine the impact of OC2 activity on clinical outcome in univariate and multivariate analyses. These experiments will help clarify the role of alternative drivers of progression and ADT resistance that emerge to cause lethal disease. They will also advance, toward a phase I clinical trial, a therapeutic approach against a novel master regulator that we estimate operates in 1/3 or more of all patients with CRPC tumors.