Modeling African American prostate adenocarcinoma by inducing defined genetic alterations in organoids

Asparagine Dependency Is a Targetable Metabolic Vulnerability in TP53-Altered Castration-Resistant Prostate Cancer

TP53 tumor suppressor is frequently altered in lethal, castration-resistant prostate cancer (CRPC). However, to date there are no effective treatments that specifically target TP53 alterations. Using transcriptomic and metabolomic analyses, we have shown here that TP53-altered prostate cancer exhibits an increased dependency on asparagine (Asn) and overexpresses Asn synthetase (ASNS), the enzyme catalyzing the synthesis of Asn. Mechanistically, the loss or mutation of TP53 transcriptionally activated ASNS expression, directly and via mTORC1-mediated ATF4 induction, driving de novo Asn biosynthesis to support CRPC growth. TP53-altered CRPC cells were sensitive to Asn restriction by knockdown of ASNS or L-asparaginase treatment to deplete the intracellular and extracellular sources of Asn, respectively, and cell viability was rescued by Asn addition. Notably, pharmacological inhibition of intracellular Asn biosynthesis using a glutaminase inhibitor and depletion of extracellular Asn with L-asparaginase significantly reduced Asn production and effectively impaired CRPC growth. This study highlights the significance of ASNS-mediated metabolic adaptation as a synthetic vulnerability in CRPC with TP53 alterations, providing a rationale for targeting Asn production to treat these lethal prostate cancers. Significance: TP53-mutated castration-resistant prostate cancer is dependent on asparagine biosynthesis due to upregulation of ASNS and can be therapeutically targeted by approaches that deplete intracellular and extracellular asparagine.

Cancer stem cell in prostate cancer progression, metastasis and therapy resistance

Prostate cancer (PCa) is the most diagnosed malignancy in the men worldwide. Cancer stem cells (CSCs) are the sub-population of cells present in the tumor which possess unique properties of self-renewal and multilineage differentiation thus thought to be major cause of therapy resistance, disease relapse, and mortality in several malignancies including PCa. CSCs have also been shown positive for the common stem cells markers such as ALDH EZH2, OCT4, SOX2, c-MYC, Nanog etc. Therefore, isolation and characterization of CSCs specific markers which may discriminate CSCs and normal stem cells are critical to selectively eliminate CSCs. Rapid advances in the field offers a theoretical explanation for many of the enduring uncertainties encompassing the etiology and an optimism for the identification of new stem-cell targets, development of reliable and efficient therapies in the future. The emerging reports have also provided unprecedented insights into CSCs plasticity, quiescence, renewal, and therapeutic response. In this review, we discuss the identification of PCa stem cells, their unique properties, stemness-driving pathways, new diagnostics, and therapeutic interventions.

An overview of the latest in state-of-the-art murine models for prostate cancer

INTRODUCTION

Prostate cancer (PCa) is a complex, heterogenous and multifocal disease, which is debilitating for patients and often fatal - due to bone metastasis and castration-resistant cancer. The use of murine models that mimic human disease has been crucial in the development of innovative therapies and for better understanding the mechanisms associated with initiation and progression of PCa.

AREAS COVERED

This review presents a critical analysis of murine models for the study of PCa, highlighting their strengths, weaknesses and applications.

EXPERT OPINION

In animal models, disease may not occur exactly as it does in humans, and sometimes the levels of efficacy that certain treatments obtain in animal models cannot be translated into clinical practice. To choose the most appropriate animal model for each research work, it is crucial to understand the anatomical and physiological differences between the mouse and the human prostate, while it is also important to identify biological similarities and differences between murine and human prostate tumors. Although significant progress has already been made, thanks to many years of research and study, the number of new challenges and obstacles to overcome mean there is a long and difficult road still to travel.

Activated ALK Cooperates with N-Myc via Wnt/β-Catenin Signaling to Induce Neuroendocrine Prostate Cancer

Neuroendocrine prostate cancer (NEPC) is an aggressive subtype of prostate cancer with poor prognosis, and there is a critical need for novel therapeutic approaches. NEPC is associated with molecular perturbation of several pathways, including amplification of MYCN. Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase involved in the pathogenesis of neuroblastoma and other malignancies where it cooperates with N-Myc. We previously identified the first case of ALK F1174C-activating mutation in a patient with de novo NEPC who responded to the ALK inhibitor, alectinib. Here, we show that coactivation of ALK and N-Myc (ALK F1174C/N-Myc) is sufficient to transform mouse prostate basal stem cells into aggressive prostate cancer with neuroendocrine differentiation in a tissue recombination model. A novel gene signature from the ALK F1174C/N-Myc tumors was associated with poor outcome in multiple human prostate cancer datasets. ALK F1174C and ALK F1174C/N-Myc tumors displayed activation of the Wnt/β-catenin signaling pathway. Chemical and genetic ALK inhibition suppressed Wnt/β-catenin signaling and tumor growth in vitro in NEPC and neuroblastoma cells. ALK inhibition cooperated with Wnt inhibition to suppress NEPC and neuroblastoma proliferation in vitro and tumor growth and metastasis in vivo. These findings point to a role for ALK signaling in NEPC and the potential of cotargeting the ALK and Wnt/β-catenin pathways in ALK-driven tumors. Activated ALK and N-Myc are well known drivers in neuroblastoma development, suggesting potential similarities and opportunities to elucidate mechanisms and therapeutic targets in NEPC and vice versa. SIGNIFICANCE: These findings demonstrate that coactivation of ALK and N-Myc induces NEPC by stimulating the Wnt/β-catenin pathway, which can be targeted therapeutically.

Current concepts in tumour-derived organoids

Cancer comprises a collection of highly proliferative and heterogeneous cells growing within an adaptive and evolving tumour microenvironment. Cancer survival rates have significantly improved following decades of cancer research. However, many experimental and preclinical studies do not translate to the bedside, reflecting the challenges of modelling the complexities and multicellular basis of human disease. Organoids are novel, complex, three-dimensional ex vivo tissue cultures that are derived from embryonic stem cells, induced pluripotent stem cells or tissue-resident progenitor cells, and represent a near-physiological model for studying cancer. Organoids develop by self-organisation, and can accurately represent the diverse genetic, cellular and pathophysiological hallmarks of cancer. In addition, co-culture methods and the ability to genetically manipulate these organoids have widened their utility in cancer research. Organoids thus offer a new and exciting platform for studying cancer and directing personalised therapies. This review aims to highlight how organoids are shaping the future of cancer research.

Histone methyltransferase DOT1L coordinates AR and MYC stability in prostate cancer

The histone methyltransferase DOT1L methylates lysine 79 (K79) on histone H3 and is involved in Mixed Lineage Leukemia (MLL) fusion leukemogenesis; however, its role in prostate cancer (PCa) is undefined. Here we show that DOT1L is overexpressed in PCa and is associated with poor outcome. Genetic and chemical inhibition of DOT1L selectively impaired the viability of androgen receptor (AR)-positive PCa cells and organoids, including castration-resistant and enzalutamide-resistant cells. The sensitivity of AR-positive cells is due to a distal K79 methylation-marked enhancer in the MYC gene bound by AR and DOT1L not present in AR-negative cells. DOT1L inhibition leads to reduced MYC expression and upregulation of MYC-regulated E3 ubiquitin ligases HECTD4 and MYCBP2, which promote AR and MYC degradation. This leads to further repression of MYC in a negative feed forward manner. Thus DOT1L selectively regulates the tumorigenicity of AR-positive prostate cancer cells and is a promising therapeutic target for PCa.

Histone methyltransferase, DOTL1 is implicated in the pathogenesis of MLL-rearranged leukemia, however, not much is known of its role in prostate cancer (PCa). Here, the authors report that DOTL1 inhibition suppresses both androgen receptor and MYC pathways in a negative feed forward manner to reduce growth of AR-positive PCa.

Propagation of human prostate tissue from induced pluripotent stem cells

Primary culture of human prostate organoids and patient-derived xenografts is inefficient and has limited access to clinical tissues. This hampers their use for translational study to identify new treatments. To overcome this, we established a complementary approach where rapidly proliferating and easily handled induced pluripotent stem cells enabled the generation of human prostate tissue in vivo and in vitro. By using a coculture technique with inductive urogenital sinus mesenchyme, we comprehensively recapitulated in situ 3D prostate histology, and overcame limitations in the primary culture of human prostate stem, luminal and neuroendocrine cells, as well as the stromal microenvironment. This model now unlocks new opportunities to undertake translational studies of benign and malignant prostate disease.

Engineering Prostate Cancer from Induced Pluripotent Stem Cells-New Opportunities to Develop Preclinical Tools in Prostate and Prostate Cancer Studies

One of the key issues hampering the development of effective treatments for prostate cancer is the lack of suitable, tractable, and patient-specific in vitro models that accurately recapitulate this disease. In this review, we address the challenges of using primary cultures and patient-derived xenografts to study prostate cancer. We describe emerging approaches using primary prostate epithelial cells and prostate organoids and their genetic manipulation for disease modelling. Furthermore, the use of human prostate-derived induced pluripotent stem cells (iPSCs) is highlighted as a promising complimentary approach. Finally, we discuss the manipulation of iPSCs to generate 'avatars' for drug disease testing. Specifically, we describe how a conceptual advance through the creation of living biobanks of "genetically engineered cancers" that contain patient-specific driver mutations hold promise for personalised medicine.

Small-Molecule MYC Inhibitors Suppress Tumor Growth and Enhance Immunotherapy

Small molecules that directly target MYC and are also well tolerated in vivo will provide invaluable chemical probes and potential anti-cancer therapeutic agents. We developed a series of small-molecule MYC inhibitors that engage MYC inside cells, disrupt MYC/MAX dimers, and impair MYC-driven gene expression. The compounds enhance MYC phosphorylation on threonine-58, consequently increasing proteasome-mediated MYC degradation. The initial lead, MYC inhibitor 361 (MYCi361), suppressed in vivo tumor growth in mice, increased tumor immune cell infiltration, upregulated PD-L1 on tumors, and sensitized tumors to anti-PD1 immunotherapy. However, 361 demonstrated a narrow therapeutic index. An improved analog, MYCi975 showed better tolerability. These findings suggest the potential of small-molecule MYC inhibitors as chemical probes and possible anti-cancer therapeutic agents.

EPHB4 inhibition activates ER stress to promote immunogenic cell death of prostate cancer cells

The EPHB4 receptor is implicated in the development of several epithelial tumors and is a promising therapeutic target, including in prostate tumors in which EPHB4 is overexpressed and promotes tumorigenicity. Here, we show that high expression of EPHB4 correlated with poor survival in prostate cancer patients and EPHB4 inhibition induced cell death in both hormone sensitive and castration-resistant prostate cancer cells. EPHB4 inhibition reduced expression of the glucose transporter, GLUT3, impaired glucose uptake, and reduced cellular ATP levels. This was associated with the activation of endoplasmic reticulum stress and tumor cell death with features of immunogenic cell death (ICD), including phosphorylation of eIF2α, increased cell surface calreticulin levels, and release of HMGB1 and ATP. The changes in tumor cell metabolism after EPHB4 inhibition were associated with MYC downregulation, likely mediated by the SRC/p38 MAPK/4EBP1 signaling cascade, known to impair cap-dependent translation. Together, our study indicates a role for EPHB4 inhibition in the induction of immunogenic cell death with implication for prostate cancer therapy.

Association among plasma 1,25(OH)2 D, ratio of 1,25(OH)2 D to 25(OH)D, and prostate cancer aggressiveness

BACKGROUND

African-American (AA) men tend to present with more aggressive prostate cancer (Gleason score >7) than European-American (EA) men. Vitamin D and its metabolites are implicated in prostate cancer biology with vitamin D deficiency, indicated by its metabolite levels in serum or plasma, usually observed in AA men.

OBJECTIVE

To determine if 1, 25-dihydroxy vitamin D3 [1,25(OH)2 D] plasma levels in AA and EA prostate cancer patients alter the risk of having aggressive prostate cancer.

DESIGN

Research subjects from the North Carolina-Louisiana Prostate Cancer Project (AA n = 435 and EA n = 532) were included. Plasma metabolites 1,25(OH)2 D and 25-hydroxyvitamin D3 [25(OH)D] were measured using liquid chromatography with tandem mass spectrophotometry. Research subjects were classified into low (Gleason sum < 7, stage T1-T2, and Prostate-specific antigen (PSA) < 9 ng/mL) or high (Gleason sum > 8 or Gleason sum = 7 with 4 + 3, or PSA > 20 ng/mL, or Gleason sum = 7 and stage T3-T4) aggressive disease.

RESULTS

Research subjects in the second and third tertiles of plasma levels of 1, 25(OH)2 D had lower odds of high aggressive prostate cancer (AA [ORT2vsT1 : 0.66, 95%CI: 0.39-1.12; ORT3vsT1 : 0.83, 95%CI: 0.49-1.41] and EA [ORT2vsT1 : 0.68, 95%CI: 0.41-1.11; ORT3vsT1 : 0.67, 95%CI: 0.40-1.11]) compared with the first tertile, though confidence intervals included the null. Greater 1,25(OH)2 D/25(OH)D molar ratios were associated with lower odds of high aggressive prostate cancer more evidently in AA (ORQ4vsQ1 : 0.45, CI: 0.24-0.82) than in EA (ORQ4vsQ1 : 0.64, CI: 0.35-1.17) research subjects.

CONCLUSIONS

The 1,25(OH)2 D/25(OH)D molar ratio was associated with decreased risk of high aggressive prostate cancer in AA men, and possibly in EA men. Further studies analyzing vitamin D polymorphisms, vitamin D binding protein levels, and prostatic levels of these metabolites may be useful. These studies may provide a better understanding of the vitamin D pathway and its biological role underlying health disparities in prostate cancer.

Cytochrome c Deficiency Confers Apoptosome and Mitochondrial Dysfunction in African-American Men with Prostate Cancer

Although African-American (AA) patients with prostate cancer tend to develop greater therapeutic resistance and faster prostate cancer recurrence compared with Caucasian-American (CA) men, the molecular mechanisms of this racial prostate cancer disparity remain undefined. In this study, we provide the first comprehensive evidence that cytochrome c deficiency in AA primary tumors and cancer cells abrogates apoptosome-mediated caspase activation and contributes to mitochondrial dysfunction, thereby promoting therapeutic resistance and prostate cancer aggressiveness in AA men. In AA prostate cancer cells, decreased nuclear accumulation of nuclear respiration factor 1 (Nrf1) and its subsequent loss of binding to the cytochrome c promoter mediated cytochrome c deficiency. The activation of cellular Myc (c-Myc) and NF-κB or inhibition of AKT prevented nuclear translocation of Nrf1. Genetic and pharmacologic inhibition of c-Myc and NF-κB or activation of AKT promoted Nrf1 binding to cytochrome c promoter, cytochrome c expression, caspase activation, and cell death. The lack of p-Drp1^S616 in AA prostate cancer cells contributed to defective cytochrome c release and increased resistance to apoptosis, indicating that restoration of cytochrome c alone may be insufficient to induce effective apoptosis. Cytochrome c deficiency promoted the acquisition of glycolytic phenotypes and mitochondrial dysfunction, whereas cytochrome c restoration via inhibition of c-Myc and NF-κB or activation of AKT attenuated glycolysis in AA prostate cancer cells. Inhibition of c-Myc and NF-κB enhanced the efficacy of docetaxel in tumor xenografts. Therefore, restoring cytochrome c may overcome therapeutic resistance and prostate cancer aggressiveness in AA men. Overall, this study provides the first comprehensive experimental, mechanistic, and clinical evidence for apoptosome and mitochondrial dysfunction in prostate cancer racial disparity. SIGNIFICANCE: Mechanistic insights on prostate cancer health disparity among American men provide novel approaches to restore mitochondrial function, which can address therapeutic resistance and aggressiveness in African-American men with prostate cancer.

Anaplastic Lymphoma Kinase Mutation (ALK F1174C) in Small Cell Carcinoma of the Prostate and Molecular Response to Alectinib

Purpose: Small cell carcinoma of the prostate (SCCP) is an aggressive disease that can arise de novo or by transdifferentiation from prostate adenocarcinoma. Alterations in anaplastic lymphoma kinase (ALK) gene are involved in neuroblastoma, lung cancer, and other malignancies, but its role in SCCP has not been documented. We describe a patient with refractory de novo SCCP with ALK F1174C-activating mutation who obtained clinical benefit from treatment with ALK inhibitor.Experimental Design: Next-generation sequencing (NGS) was used to analyze primary and circulating tumor DNA (ctDNA). Prostate cancer databases were queried for alterations in ALK gene, mRNA, and its impact in clinical outcomes. In vitro prostate cell line/organoid models were generated by lentiviral-mediated expression of ALK and ALK F1174C and assessed for response to ALK inhibitors crizotinib and alectinib.Results: NGS analysis of the primary tumor and ctDNA of a 39-year-old patient with refractory SSCP identified ALK F1174C mutation. Treatment with second-generation ALK inhibitor alectinib resulted in radiographic stable disease for over 6 months, symptomatic improvement, and significant molecular response as reflected by declining ctDNA allele fraction. Analysis of prostate cancer datasets showed that ALK amplification was associated with poor outcome. In prostate cancer cells and organoids, ALK F1174C expression enhanced growth and induced expression of the neuroendocrine marker neuron-specific enolase. Alectinib was more effective than crizotinib in inhibiting ALK F1174C-expressing cell growth.Conclusions: These findings implicate ALK-activating mutations in SCCP pathogenesis and suggest the therapeutic potential of targeting ALK molecular alterations in some patients with SCCP. Clin Cancer Res; 24(12); 2732-9. ©2018 AACR.

Organoids model distinct Vitamin E effects at different stages of prostate cancer evolution

Vitamin E increased prostate cancer risk in the Selenium and Vitamin E Cancer Prevention Trial (SELECT) through unknown mechanisms while Selenium showed no efficacy. We determined the effects of the SELECT supplements on benign (primary), premalignant ( RWPE-1) and malignant (LNCaP) prostate epithelial organoids. While the supplements decreased proliferation and induced cell death in cancer organoids, they had no effect on the benign organoids. In contrast, Vitamin E enhanced cell proliferation and survival in the premalignant organoids in a manner that recapitulated the SELECT results. Indeed, while Vitamin E induced a pro-proliferative gene expression signature, Selenium alone or combined with Vitamin E produced an anti-proliferative signature. The premalignant organoids also displayed significant downregulation of glucose transporter and glycolytic gene expression pointing to metabolic alterations. Detached RWPE-1 cells had low ATP levels due to diminished glucose uptake and glycolysis which was rescued by Vitamin E through the activation of fatty acid oxidation (FAO). FAO inhibition abrogated the ATP rescue, diminished survival of the inner matrix detached cells, restoring the normal hollow lumen morphology in Vitamin E treated organoids. Organoid models therefore clarify the paradoxical findings from SELECT and demonstrate that Vitamin E promotes tumorigenesis in the early stages of prostate cancer evolution.