The neuroendocrine transition in prostate cancer is dynamic and dependent on ASCL1

Lineage plasticity is a hallmark of cancer progression that impacts therapy outcomes, yet the mechanisms mediating this process remain unclear. Here, we introduce a versatile in vivo platform to interrogate neuroendocrine lineage transformation throughout prostate cancer progression. Transplanted mouse prostate organoids with human-relevant driver mutations (Rb1-/-; Trp53-/-; cMyc+ or Pten-/-; Trp53-/-; cMyc+) develop adenocarcinomas, but only those with Rb1 deletion advance to aggressive, ASCL1+ neuroendocrine prostate cancer (NEPC) resistant to androgen receptor signaling inhibitors. Notably, this transition requires an in vivo microenvironment not replicated by conventional organoid culture. Using multiplexed immunofluorescence and spatial transcriptomics, we reveal that ASCL1+ cells arise from KRT8+ luminal cells, progressing into transcriptionally heterogeneous ASCL1+;KRT8- NEPC. Ascl1 loss in established NEPC causes transient regression followed by recurrence, but its deletion before transplantation abrogates lineage plasticity, resulting in castration-sensitive adenocarcinomas. This dynamic model highlights the importance of therapy timing and offers a platform to identify additional lineage plasticity drivers.

Single-cell analysis of treatment-resistant prostate cancer: Implications of cell state changes for cell surface antigen-targeted therapies

Targeting cell surface molecules using radioligand and antibody-based therapies has yielded considerable success across cancers. However, it remains unclear how the expression of putative lineage markers, particularly cell surface molecules, varies in the process of lineage plasticity, wherein tumor cells alter their identity and acquire new oncogenic properties. A notable example of lineage plasticity is the transformation of prostate adenocarcinoma (PRAD) to neuroendocrine prostate cancer (NEPC)-a growing resistance mechanism that results in the loss of responsiveness to androgen blockade and portends dismal patient survival. To understand how lineage markers vary across the evolution of lineage plasticity in prostate cancer, we applied single-cell analyses to 21 human prostate tumor biopsies and two genetically engineered mouse models, together with tissue microarray analysis on 131 tumor samples. Not only did we observe a higher degree of phenotypic heterogeneity in castrate-resistant PRAD and NEPC than previously anticipated but also found that the expression of molecules targeted therapeutically, namely PSMA, STEAP1, STEAP2, TROP2, CEACAM5, and DLL3, varied within a subset of gene-regulatory networks (GRNs). We also noted that NEPC and small cell lung cancer subtypes shared a set of GRNs, indicative of conserved biologic pathways that may be exploited therapeutically across tumor types. While this extreme level of transcriptional heterogeneity, particularly in cell surface marker expression, may mitigate the durability of clinical responses to current and future antigen-directed therapies, its delineation may yield signatures for patient selection in clinical trials, potentially across distinct cancer types.

Assessment of TROP2, CEACAM5 and DLL3 in metastatic prostate cancer: Expression landscape and molecular correlates

Therapeutic approaches targeting proteins on the surface of cancer cells have emerged as an important strategy for precision oncology. To capitalize on the potential impact of drugs targeting surface proteins, detailed knowledge about the expression patterns of the target proteins in tumor tissues is required. In castration-resistant prostate cancer (CRPC), agents targeting prostate-specific membrane antigen (PSMA) have demonstrated clinical activity. However, PSMA expression is lost in a significant number of CRPC tumors. The identification of additional cell surface targets is necessary to develop new therapeutic approaches. Here, we performed a comprehensive analysis of the expression heterogeneity and co-expression patterns of trophoblast cell-surface antigen 2 (TROP2), delta-like ligand 3 (DLL3), and carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) in CRPC samples from a rapid autopsy cohort. We show that DLL3 and CEACAM5 exhibit the highest expression in neuroendocrine prostate cancer (NEPC), while TROP2 is expressed across different CRPC molecular subtypes, except for NEPC. We further demonstrated that AR alterations were associated with higher expression of PSMA and TROP2. Conversely, PSMA and TROP2 expression was lower in RB1-altered tumors. In addition to genomic alterations, we show a tight correlation between epigenetic states, particularly histone H3 lysine 27 methylation (H3K27me3) at the transcriptional start site and gene body of TACSTD2 (encoding TROP2), DLL3, and CEACAM5, and their respective protein expression in CRPC patient-derived xenografts. Collectively, these findings provide insights into patterns and determinants of expression of TROP2, DLL3, and CEACAM5 with implications for the clinical development of cell surface targeting agents in CRPC.

Single Cell Analysis of Treatment-Resistant Prostate Cancer: Implications of Cell State Changes for Cell Surface Antigen Targeted Therapies

Targeting cell surface molecules using radioligand and antibody-based therapies has yielded considerable success across cancers. However, it remains unclear how the expression of putative lineage markers, particularly cell surface molecules, varies in the process of lineage plasticity, wherein tumor cells alter their identity and acquire new oncogenic properties. A notable example of lineage plasticity is the transformation of prostate adenocarcinoma (PRAD) to neuroendocrine prostate cancer (NEPC)--a growing resistance mechanism that results in the loss of responsiveness to androgen blockade and portends dismal patient survival. To understand how lineage markers vary across the evolution of lineage plasticity in prostate cancer, we applied single cell analyses to 21 human prostate tumor biopsies and two genetically engineered mouse models, together with tissue microarray analysis (TMA) on 131 tumor samples. Not only did we observe a higher degree of phenotypic heterogeneity in castrate-resistant PRAD and NEPC than previously anticipated, but also found that the expression of molecules targeted therapeutically, namely PSMA, STEAP1, STEAP2, TROP2, CEACAM5, and DLL3, varied within a subset of gene-regulatory networks (GRNs). We also noted that NEPC and small cell lung cancer (SCLC) subtypes shared a set of GRNs, indicative of conserved biologic pathways that may be exploited therapeutically across tumor types. While this extreme level of transcriptional heterogeneity, particularly in cell surface marker expression, may mitigate the durability of clinical responses to novel antigen-directed therapies, its delineation may yield signatures for patient selection in clinical trials, potentially across distinct cancer types.

The neuroendocrine transition in prostate cancer is dynamic and dependent on ASCL1

Lineage plasticity is a recognized hallmark of cancer progression that can shape therapy outcomes. The underlying cellular and molecular mechanisms mediating lineage plasticity remain poorly understood. Here, we describe a versatile in vivo platform to identify and interrogate the molecular determinants of neuroendocrine lineage transformation at different stages of prostate cancer progression. Adenocarcinomas reliably develop following orthotopic transplantation of primary mouse prostate organoids acutely engineered with human-relevant driver alterations (e.g., Rb1-/-; Trp53-/-; cMyc+ or Pten-/-; Trp53-/-; cMyc+), but only those with Rb1 deletion progress to ASCL1+ neuroendocrine prostate cancer (NEPC), a highly aggressive, androgen receptor signaling inhibitor (ARSI)-resistant tumor. Importantly, we show this lineage transition requires a native in vivo microenvironment not replicated by conventional organoid culture. By integrating multiplexed immunofluorescence, spatial transcriptomics and PrismSpot to identify cell type-specific spatial gene modules, we reveal that ASCL1+ cells arise from KRT8+ luminal epithelial cells that progressively acquire transcriptional heterogeneity, producing large ASCL1+;KRT8- NEPC clusters. Ascl1 loss in established NEPC results in transient tumor regression followed by recurrence; however, Ascl1 deletion prior to transplantation completely abrogates lineage plasticity, yielding adenocarcinomas with elevated AR expression and marked sensitivity to castration. The dynamic feature of this model reveals the importance of timing of therapies focused on lineage plasticity and offers a platform for identification of additional lineage plasticity drivers.

ERG activates a stem-like proliferation-differentiation program in prostate epithelial cells with mixed basal-luminal identity

To gain insight into how ERG translocations cause prostate cancer, we performed single cell transcriptional profiling of an autochthonous mouse model at an early stage of disease initiation. Despite broad expression of ERG in all prostate epithelial cells, proliferation was enriched in a small, stem-like population with mixed-luminal basal identity (called intermediate cells). Through a series of lineage tracing and primary prostate tissue transplantation experiments, we find that tumor initiating activity resides in a subpopulation of basal cells that co-express the luminal genes Tmprss2 and Nkx3.1 (called BasalLum) but not in the larger population of classical Krt8+ luminal cells. Upon ERG activation, BasalLum cells give rise to the highly proliferative intermediate state, which subsequently transitions to the larger population of Krt8+ luminal cells characteristic of ERG-positive human cancers. Furthermore, this proliferative population is characterized by an ERG-specific chromatin state enriched for NFkB, AP-1, STAT and NFAT binding, with implications for TF cooperativity. The fact that the proliferative potential of ERG is enriched in a small stem-like population implicates the chromatin context of these cells as a critical variable for unmasking its oncogenic activity.

Timing of treatment shapes the path to androgen receptor signaling inhibitor resistance in prostate cancer

There is optimism that cancer drug resistance can be addressed through appropriate combination therapy, but success requires understanding the growing complexity of resistance mechanisms, including the evolution and population dynamics of drug-sensitive and drug-resistant clones over time. Using DNA barcoding to trace individual prostate tumor cells in vivo , we find that the evolutionary path to acquired resistance to androgen receptor signaling inhibition (ARSI) is dependent on the timing of treatment. In established tumors, resistance occurs through polyclonal adaptation of drug-sensitive clones, despite the presence of rare subclones with known, pre-existing ARSI resistance. Conversely, in an experimental setting designed to mimic minimal residual disease, resistance occurs through outgrowth of pre-existing resistant clones and not by adaptation. Despite these different evolutionary paths, the underlying mechanisms responsible for resistance are shared across the two evolutionary paths. Furthermore, mixing experiments reveal that the evolutionary path to adaptive resistance requires cooperativity between subclones. Thus, despite the presence of pre-existing ARSI-resistant subclones, acquired resistance in established tumors occurs primarily through cooperative, polyclonal adaptation of drug-sensitive cells. This tumor ecosystem model of resistance has new implications for developing effective combination therapy.

Strategies to decrease inequalities in cancer therapeutics, care and prevention: Proceedings on a conference organized by the Pontifical Academy of Sciences and the European Academy of Cancer Sciences, Vatican City, February 23-24, 2023

Analyses of inequalities related to prevention and cancer therapeutics/care show disparities between countries with different economic standing, and within countries with high Gross Domestic Product. The development of basic technological and biological research provides clinical and prevention opportunities that make their implementation into healthcare systems more complex, mainly due to the growth of Personalized/Precision Cancer Medicine (PCM). Initiatives like the USA-Cancer Moonshot and the EU-Mission on Cancer and Europe's Beating Cancer Plan are initiated to boost cancer prevention and therapeutics/care innovation and to mitigate present inequalities. The conference organized by the Pontifical Academy of Sciences in collaboration with the European Academy of Cancer Sciences discussed the inequality problem, dependent on the economic status of a country, the increasing demands for infrastructure supportive of innovative research and its implementation in healthcare and prevention programs. Establishing translational research defined as a coherent cancer research continuum is still a challenge. Research has to cover the entire continuum from basic to outcomes research for clinical and prevention modalities. Comprehensive Cancer Centres (CCCs) are of critical importance for integrating research innovations to preclinical and clinical research, as for ensuring state-of-the-art patient care within healthcare systems. International collaborative networks between CCCs are necessary to reach the critical mass of infrastructures and patients for PCM research, and for introducing prevention modalities and new treatments effectively. Outcomes and health economics research are required to assess the cost-effectiveness of new interventions, currently a missing element in the research portfolio. Data sharing and critical mass are essential for innovative research to develop PCM. Despite advances in cancer research, cancer incidence and prevalence is growing. Making cancer research infrastructures accessible for all patients, considering the increasing inequalities, requires science policy actions incentivizing research aimed at prevention and cancer therapeutics/care with an increased focus on patients' needs and cost-effective healthcare.

ASSESSMENT OF CELL SURFACE TARGETS IN METASTATIC PROSTATE CANCER: EXPRESSION LANDSCAPE AND MOLECULAR CORRELATES

Therapeutic approaches targeting proteins on the surface of cancer cells have emerged as an important strategy for precision oncology. To fully capitalize on the potential impact of drugs targeting surface proteins, detailed knowledge about the expression patterns of the target proteins in tumor tissues is required. In castration-resistant prostate cancer (CRPC), agents targeting prostate-specific membrane antigen (PSMA) have demonstrated clinical activity. However, PSMA expression is lost in a significant number of CRPC tumors, and the identification of additional cell surface targets is necessary in order to develop new therapeutic approaches. Here, we performed a comprehensive analysis of the expression and co-expression patterns of trophoblast cell-surface antigen 2 (TROP2), delta-like ligand 3 (DLL3), and carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) in CRPC samples from a rapid autopsy cohort. We show that DLL3 and CEACAM5 exhibit the highest expression in neuroendocrine prostate cancer (NEPC), while TROP2 is expressed across different CRPC molecular subtypes, except for NEPC. We observed variable intra-tumoral and inter-tumoral heterogeneity and no dominant metastatic site predilections for TROP2, DLL3, and CEACAM5. We further show that AR amplifications were associated with higher expression of PSMA and TROP2 but lower DLL3 and CEACAM5 levels. Conversely, PSMA and TROP2 expression was lower in RB1-altered tumors. In addition to genomic alterations, we demonstrate a tight correlation between epigenetic states, particularly histone H3 lysine 27 methylation (H3K27me3) at the transcriptional start site and gene body of TACSTD2 (encoding TROP2), DLL3, and CEACAM5, and their respective protein expression in CRPC patient-derived xenografts. Collectively, these findings provide novel insights into the patterns and determinants of expression of TROP2, DLL3, and CEACAM5 with important implications for the clinical development of cell surface targeting agents in CRPC.

Exportin 1 inhibition prevents neuroendocrine transformation through SOX2 down-regulation in lung and prostate cancers

In lung and prostate adenocarcinomas, neuroendocrine (NE) transformation to an aggressive derivative resembling small cell lung cancer (SCLC) is associated with poor prognosis. We previously described dependency of SCLC on the nuclear transporter exportin 1. Here, we explored the role of exportin 1 in NE transformation. We observed up-regulated exportin 1 in lung and prostate pretransformation adenocarcinomas. Exportin 1 was up-regulated after genetic inactivation of TP53 and RB1 in lung and prostate adenocarcinoma cell lines, accompanied by increased sensitivity to the exportin 1 inhibitor selinexor in vitro. Exportin 1 inhibition prevented NE transformation in different TP53/RB1-inactivated prostate adenocarcinoma xenograft models that acquire NE features upon treatment with the aromatase inhibitor enzalutamide and extended response to the EGFR inhibitor osimertinib in a lung cancer transformation patient-derived xenograft (PDX) model exhibiting combined adenocarcinoma/SCLC histology. Ectopic SOX2 expression restored the enzalutamide-promoted NE phenotype on adenocarcinoma-to-NE transformation xenograft models despite selinexor treatment. Selinexor sensitized NE-transformed lung and prostate small cell carcinoma PDXs to standard cytotoxics. Together, these data nominate exportin 1 inhibition as a potential therapeutic target to constrain lineage plasticity and prevent or treat NE transformation in lung and prostate adenocarcinoma.

Chromatin regulation of transcriptional enhancers and cell fate by the Sotos syndrome gene NSD1

Nuclear receptor-binding SET-domain protein 1 (NSD1), a methyltransferase that catalyzes H3K36me2, is essential for mammalian development and is frequently dysregulated in diseases, including Sotos syndrome. Despite the impacts of H3K36me2 on H3K27me3 and DNA methylation, the direct role of NSD1 in transcriptional regulation remains largely unknown. Here, we show that NSD1 and H3K36me2 are enriched at cis-regulatory elements, particularly enhancers. NSD1 enhancer association is conferred by a tandem quadruple PHD (qPHD)-PWWP module, which recognizes p300-catalyzed H3K18ac. By combining acute NSD1 depletion with time-resolved epigenomic and nascent transcriptomic analyses, we demonstrate that NSD1 promotes enhancer-dependent gene transcription by facilitating RNA polymerase II (RNA Pol II) pause release. Notably, NSD1 can act as a transcriptional coactivator independent of its catalytic activity. Moreover, NSD1 enables the activation of developmental transcriptional programs associated with Sotos syndrome pathophysiology and controls embryonic stem cell (ESC) multilineage differentiation. Collectively, we have identified NSD1 as an enhancer-acting transcriptional coactivator that contributes to cell fate transition and Sotos syndrome development.

NSD2 maintains lineage plasticity and castration-resistance in neuroendocrine prostate cancer

The clinical use of potent androgen receptor (AR) inhibitors has promoted the emergence of novel subtypes of metastatic castration-resistant prostate cancer (mCRPC), including neuroendocrine prostate cancer (CRPC-NE), which is highly aggressive and lethal 1 . These mCRPC subtypes display increased lineage plasticity and often lack AR expression 2-5 . Here we show that neuroendocrine differentiation and castration-resistance in CRPC-NE are maintained by the activity of Nuclear Receptor Binding SET Domain Protein 2 (NSD2) 6 , which catalyzes histone H3 lysine 36 dimethylation (H3K36me2). We find that organoid lines established from genetically-engineered mice 7 recapitulate key features of human CRPC-NE, and can display transdifferentiation to neuroendocrine states in culture. CRPC-NE organoids express elevated levels of NSD2 and H3K36me2 marks, but relatively low levels of H3K27me3, consistent with antagonism of EZH2 activity by H3K36me2. Human CRPC-NE but not primary NEPC tumors expresses high levels of NSD2, consistent with a key role for NSD2 in lineage plasticity, and high NSD2 expression in mCRPC correlates with poor survival outcomes. Notably, CRISPR/Cas9 targeting of NSD2 or expression of a dominant-negative oncohistone H3.3K36M mutant results in loss of neuroendocrine phenotypes and restores responsiveness to the AR inhibitor enzalutamide in mouse and human CRPC-NE organoids and grafts. Our findings indicate that NSD2 inhibition can reverse lineage plasticity and castration-resistance, and provide a potential new therapeutic target for CRPC-NE.

Effect of Janus kinase (JAK) signaling inhibition on lineage plasticity and drug sensitivity in castrate resistant prostate cancer

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Background: Despite the remarkable successes of targeted cancer therapies, certain cancers, including lung, breast, and prostate cancer and melanoma, invariably become resistant to therapy. One mechanism of secondary resistance—lineage plasticity—arises when cells alter their identity and transition into aggressive states. In the case of prostate cancer, cells can acquire a neuroendocrine histology. This is often associated with a loss of tumor suppressor genes, such as TP53, RB1, and PTEN. However, while these genomic events initiate plasticity, tumor progression is not always associated with successive genomic alterations. This, in essence, not only poses a clinical challenge, but also confronts us with a wide-open biological question—what are the molecular underpinnings of lineage plasticity, and importantly, can the process be reversed? Methods: To study the temporal evolution of lineage plasticity and its relationship to androgen receptor signaling inhibitor (ARSI) resistance, we utilized genetically engineered mouse models (GEMMs) and murine organoids that were deleted for Tp53, Rb1, and/or Pten. Single cell RNA analyses were utilized to dissect which genes and pathways were up-regulated and most associated with the progression of plasticity. Plasticity-associated genes and pathways were perturbed using FDA-approved inhibitors or genetic editing tools. The presence of these pathways was confirmed in a subset of metastatic index lesions obtained by radiologically guided biopsies and as visualized by metabolic imaging. Furthermore, relevant findings were functionally validated in human tumor derived organoids (“tumoroids”). Results: Using GEMMs and organoid models, we found the lineage plasticity depended on increased Janus Kinase (JAK) and fibroblast growth factor receptor (FGFR) activity. Pharmacologic inhibition using FDA–approved inhibitors of JAK/STAT (ruxolitinib) and FGFR (erdafinitib), or through genetic knockdown, demonstrated increased androgen receptor (AR) signaling and restored ARSI sensitivity. These findings were further validated in a subset of ARSI-insensitive human tumoroids. By performing single cell RNA sequencing on mCRPC tumors biopsies, the presence of highly plastic JAK/STAT- and FGFR-high cells were confirmed, with implications for stratifying patients for clinical trials. Conclusions: JAK/STAT and FGFR signaling pathways promote lineage plasticity and result in complete insensitivity to androgen receptor signaling inhibitors (ARSIs). FDA-approved inhibitors of JAK/STAT (ruxolitinib) and FGFR (erdafitinib) synergize to reverse lineage plasticity and restore ARSI sensitivity.

An immunocompetent rectal cancer model to study radiation therapy

We describe a mouse model of rectal cancer (RC) involving rapid tumor organoid engraftment via orthotopic transplantation in an immunocompetent setting. This approach uses simple mechanical disruption to allow engraftment, avoiding the use of dextran sulfate sodium. The resulting RC tumors invaded from the mucosal surface and metastasized to distant organs. Histologically, the tumors closely resemble human RC and mirror remodeling of the tumor microenvironment in response to radiation. This murine RC model thus recapitulates key aspects of human RC pathogenesis and presents an accessible approach for more physiologically accurate, preclinical efficacy studies.

Genomic analysis of early-stage lung cancer reveals a role for TP53 mutations in distant metastasis

Patients with non-small cell lung cancer (NSCLC) who have distant metastases have a poor prognosis. To determine which genomic factors of the primary tumor are associated with metastasis, we analyzed data from 759 patients originally diagnosed with stage I-III NSCLC as part of the AACR Project GENIE Biopharma Collaborative consortium. We found that TP53 mutations were significantly associated with the development of new distant metastases. TP53 mutations were also more prevalent in patients with a history of smoking, suggesting that these patients may be at increased risk for distant metastasis. Our results suggest that additional investigation of the optimal management of patients with early-stage NSCLC harboring TP53 mutations at diagnosis is warranted in light of their higher likelihood of developing new distant metastases.

Lineage plasticity in prostate cancer depends on JAK/STAT inflammatory signaling

Drug resistance in cancer is often linked to changes in tumor cell state or lineage, but the molecular mechanisms driving this plasticity remain unclear. Using murine organoid and genetically engineered mouse models, we investigated the causes of lineage plasticity in prostate cancer and its relationship to antiandrogen resistance. We found that plasticity initiates in an epithelial population defined by mixed luminal-basal phenotype and that it depends on increased Janus kinase (JAK) and fibroblast growth factor receptor (FGFR) activity. Organoid cultures from patients with castration-resistant disease harboring mixed-lineage cells reproduce the dependency observed in mice by up-regulating luminal gene expression upon JAK and FGFR inhibitor treatment. Single-cell analysis confirms the presence of mixed-lineage cells with increased JAK/STAT (signal transducer and activator of transcription) and FGFR signaling in a subset of patients with metastatic disease, with implications for stratifying patients for clinical trials.

Allosteric interactions prime androgen receptor dimerization and activation

The androgen receptor (AR) is a nuclear receptor that governs gene expression programs required for prostate development and male phenotype maintenance. Advanced prostate cancers display AR hyperactivation and transcriptome expansion, in part, through AR amplification and interaction with oncoprotein cofactors. Despite its biological importance, how AR domains and cofactors cooperate to bind DNA has remained elusive. Using single-particle cryo-electron microscopy, we isolated three conformations of AR bound to DNA, showing that AR forms a non-obligate dimer, with the buried dimer interface utilized by ancestral steroid receptors repurposed to facilitate cooperative DNA binding. We identify novel allosteric surfaces which are compromised in androgen insensitivity syndrome and reinforced by AR's oncoprotein cofactor, ERG, and by DNA-binding motifs. Finally, we present evidence that this plastic dimer interface may have been adopted for transactivation at the expense of DNA binding. Our work highlights how fine-tuning AR's cooperative interactions translate to consequences in development and disease.

Understanding Drug Sensitivity and Tackling Resistance in Cancer

Decades of research into the molecular mechanisms of cancer and the development of novel therapeutics have yielded a number of remarkable successes. However, our ability to broadly assign effective, rationally targeted therapies in a personalized manner remains elusive for many patients, and drug resistance persists as a major problem. This is in part due to the well-documented heterogeneity of cancer, including the diversity of tumor cell lineages and cell states, the spectrum of somatic mutations, the complexity of microenvironments, and immune-suppressive features and immune repertoires, which collectively require numerous different therapeutic approaches. Here, we describe a framework to understand the types and biological causes of resistance, providing translational opportunities to tackle drug resistance by rational therapeutic strategies.

Abstract PR09: Macrophage promotion of anti-androgen resistance in prostate cancer bone disease

Metastatic castration resistant prostate cancer (mCRPC) is the final stage of prostate cancer (PC) that acquires resistance to androgen deprivation therapies (ADT). Despite many recent progresses in the mechanistic understanding of ADT resistance, the specific contribution of the metastatic microenvironment in mCRPC remains largely unknown. A novel in vivo model of androgen dependent bone metastatic PC was developed in address this question. Our identified that macrophages are the major stromal cells in bone metastatic PC. Using multiple genetic models, we demonstrated that macrophages, both monocyte-derived and bone resident populations, were critical for bone metastatic PC to develop resistance to enzalutamide, a clinically used anti-androgen. Mechanistically, macrophages drove resistance through induction of a wound healing like response in prostate cancer cells, which was strongly supported by bioinformatics analysis of multiple patient mCRPC datasets. Furthermore, macrophage depletion or SRC inhibition using a novel specific inhibitor significantly inhibited resistant growth of mCRPC. Together, our findings elucidated a novel mechanism of macrophage-induced anti-androgen resistance of metastatic PC and a promising therapeutic approach to treat this deadly disease.

Citation Format: Xue-Feng Li, Cigdem Selli, Asier Unciti-Broceta, Neil O. Carragher, Hai-Yan Hu, Charles L. Sawyers, Bin-Zhi Qian. Macrophage promotion of anti-androgen resistance in prostate cancer bone disease [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr PR09.

Rapid interrogation of cancer cell of origin through CRISPR editing

The increasing complexity of different cell types revealed by single-cell analysis of tissues presents challenges in efficiently elucidating their functions. Here we show, using prostate as a model tissue, that primary organoids and freshly isolated epithelial cells can be CRISPR edited ex vivo using Cas9-sgRNA (guide RNA) ribotnucleoprotein complex technology, then orthotopically transferred in vivo into immunocompetent or immunodeficient mice to generate cancer models with phenotypes resembling those seen in traditional genetically engineered mouse models. Large intrachromosomal (∼2 Mb) or multigenic deletions can be engineered efficiently without the need for selection, including in isolated subpopulations to address cell-of-origin questions.

Abstract PO-134: Identification of the cells of origin and tumor heterogeneity in neuroendocrine prostate cancer (NEPC) by single-cell analysis

Lineage plasticity has emerged as an important mechanism of therapeutic resistance in prostate cancer treated with a newer generation of AR signaling inhibitor (ARSi). As a consequence of lineage plasticity, treatment resistant prostate cancer loses epithelial cell identity, acquires stem cell-like properties and transforms into a neuroendocrine lineage. Loss of function mutations in Tp53, Rb1 and Pten are enriched in human neuroendocrine prostate cancer (NEPC). To understand the cell of origin and the molecular mechanism underlying lineage plasticity and NEPC development, we have used single-cell RNA-sequencing (scRNA-seq) technology to profile a genetically engineered mouse model with probasin-Cre driven Tp53, Rb1 and Pten deletions (referred to as TKO mouse) and Rb1 and Pten deletions (referred to as DKO mouse). We have profiled ~70,000 single cells from 16 mice of various ages and 6 additional mice that have undergone castration with or without testosterone addback. Our scRNA-seq analysis captures a developmental trajectory from luminal adenocarcinoma to neuroendocrine tumor, suggesting a newly discovered luminal cell type (L2) within the normal prostate may be the preferred cell of origin for NEPC development. Furthermore, combining scRNA-seq, flow cytometry and immunofluorescence analysis, we reveal tremendous heterogeneity within the neuroendocrine tumors with differential expression of several putative drivers, including SOX2, EZH2, AURKA, NMYC and POU2F3. Many of these genes have been previously implicated as drivers of NEPC development, while POU2F3 has been identified as a defining marker for a Tuft-variant small cell lung cancer (SCLC). Lastly, we have preliminary evidence that castration may have the potential to accelerate the transition from adenocarcinoma to NEPC, while adding back testosterone may delay the process in the TKO mice. Overall, in this study, we have identified a luminal L2 population as the putative preferred cell of origin for NEPC in the TKO model and revealed a previous under-appreciated heterogeneity within NEPC with differential expression of driver transcriptional, epigenetic and cell cycle regulators, which mirrors what has been described in the SCLC field.

Citation Format: Jimmy L. Zhao, Samir Zaidi, Joseph Chan, Kristine Wadosky, Wouter Karthaus, Danielle Choi, Aura Agudelo Rivera, Anuradha Gopalan, Dana Rathkopf, Brett Carver, Wassim Abida, Howard Scher, Yu Chen, David Goodrich, Dana Pe’er, Charles L. Sawyers. Identification of the cells of origin and tumor heterogeneity in neuroendocrine prostate cancer (NEPC) by single-cell analysis [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-134.