Patient-derived Hormone-naive Prostate Cancer Xenograft Models Reveal Growth Factor Receptor Bound Protein 10 as an Androgen Receptor-repressed Gene Driving the Development of Castration-resistant Prostate Cancer

Defining the challenges and opportunities for using patient-derived models in prostate cancer research

BACKGROUND

There are relatively few widely used models of prostate cancer compared to other common malignancies. This impedes translational prostate cancer research because the range of models does not reflect the diversity of disease seen in clinical practice. In response to this challenge, research laboratories around the world have been developing new patient-derived models of prostate cancer, including xenografts, organoids, and tumor explants.

METHODS

In May 2023, we held a workshop at the Monash University Prato Campus for researchers with expertise in establishing and using a variety of patient-derived models of prostate cancer. This review summarizes our collective ideas on how patient-derived models are currently being used, the common challenges, and future opportunities for maximizing their usefulness in prostate cancer research.

RESULTS

An increasing number of patient-derived models for prostate cancer are being developed. Despite their individual limitations and varying success rates, these models are valuable resources for exploring new concepts in prostate cancer biology and for preclinical testing of potential treatments. Here we focus on the need for larger collections of models that represent the changing treatment landscape of prostate cancer, robust readouts for preclinical testing, improved in vitro culture conditions, and integration of the tumor microenvironment. Additional priorities include ensuring model reproducibility, standardization, and replication, and streamlining the exchange of models and data sets among research groups.

CONCLUSIONS

There are several opportunities to maximize the impact of patient-derived models on prostate cancer research. We must develop large, diverse and accessible cohorts of models and more sophisticated methods for emulating the intricacy of patient tumors. In this way, we can use the samples that are generously donated by patients to advance the outcomes of patients in the future.

Influence of ADT on B7-H3 expression during CRPC progression from hormone-naïve prostate cancer

Androgen deprivation therapy (ADT) is the standard care for advanced prostate cancer (PCa) patients. Unfortunately, although tumors respond well initially, they enter dormancy and eventually progress to fatal/incurable castration-resistant prostate cancer (CRPC). B7-H3 is a promising new target for PCa immunotherapy. CD276 (B7-H3) gene has a presumptive androgen receptor (AR) binding site, suggesting potential AR regulation. However, the relationship between B7-H3 and AR is controversial. Meanwhile, the expression pattern of B7-H3 following ADT and during CRPC progression is largely unknown, but critically important for identifying patients and determining the optimal timing of B7-H3 targeting immunotherapy. In this study, we performed a longitudinal study using our unique PCa patient-derived xenograft (PDX) models and assessed B7-H3 expression during post-ADT disease progression. We further validated our findings at the clinical level in PCa patient samples. We found that B7-H3 expression was negatively regulated by AR during the early phase of ADT treatment, but positively associated with PCa proliferation during the remainder of disease progression. Our findings suggest its use as a biomarker for diagnosis, prognosis, and ADT treatment response, and the potential of combining ADT and B7-H3 targeting immunotherapy for hormone-naïve PCa treatment to prevent fatal CRPC relapse.

Identification of Epigenetically Regulated Genes Distinguishing Intracranial from Extracranial Melanoma Metastases

Despite remarkable advances in treating patients with metastatic melanoma, the management of melanoma brain metastases remains challenging. Recent evidence suggests that epigenetic reprogramming is an important mechanism for the adaptation of melanoma cells to the brain environment. In this study, the methylomes and transcriptomes of a cohort of matched melanoma metastases were evaluated by integrated omics data analysis. The identified 38 candidate genes displayed distinct promoter methylation and corresponding gene expression changes in intracranial compared with extracranial metastases. The 11 most promising genes were validated on protein level in both tumor and surrounding normal tissue using immunohistochemistry. In accordance with the underlying promoter methylation and gene expression changes, a significantly different protein expression was confirmed for STK10, PDXK, WDR24, CSSP1, NMB, RASL11B, phosphorylated PRKCZ, PRKCZ, and phosphorylated GRB10 in the intracranial metastases. The observed changes imply a distinct intracranial phenotype with increased protein kinase B phosphorylation and a higher frequency of proliferating cells. Knockdown of PRKCZ or GRB10 altered the expression of phosphorylated protein kinase B and decreased the viability of a brain-specific melanoma cell line. In summary, epigenetically regulated cancer-relevant alterations were identified that provide insights into the molecular mechanisms that discriminate brain metastases from other organ metastases, which could be exploited by targeting the affected signaling pathways.

The future of patient-derived xenografts in prostate cancer research

Patient-derived xenografts (PDXs) are generated by engrafting human tumours into mice. Serially transplantable PDXs are used to study tumour biology and test therapeutics, linking the laboratory to the clinic. Although few prostate cancer PDXs are available in large repositories, over 330 prostate cancer PDXs have been established, spanning broad clinical stages, genotypes and phenotypes. Nevertheless, more PDXs are needed to reflect patient diversity, and to study new treatments and emerging mechanisms of resistance. We can maximize the use of PDXs by exchanging models and datasets, and by depositing PDXs into biorepositories, but we must address the impediments to accessing PDXs, such as institutional, ethical and legal agreements. Through collaboration, researchers will gain greater access to PDXs representing diverse features of prostate cancer.

Treatment of Prostate Cancer with CD46-targeted 225Ac Alpha Particle Radioimmunotherapy

PURPOSE

Radiopharmaceutical therapy is changing the standard of care in prostate cancer and other malignancies. We previously reported high CD46 expression in prostate cancer and developed an antibody-drug conjugate and immunoPET agent based on the YS5 antibody, which targets a tumor-selective CD46 epitope. Here, we present the preparation, preclinical efficacy, and toxicity evaluation of [225Ac]DOTA-YS5, a radioimmunotherapy agent based on the YS5 antibody.

EXPERIMENTAL DESIGN

[225Ac]DOTA-YS5 was developed, and its therapeutic efficiency was tested on cell-derived (22Rv1, DU145), and patient-derived (LTL-545, LTL484) prostate cancer xenograft models. Biodistribution studies were carried out on 22Rv1 tumor xenograft models to confirm the targeting efficacy. Toxicity analysis of the [225Ac]DOTA-YS5 was carried out on nu/nu mice to study short-term (acute) and long-term (chronic) toxicity.

RESULTS

Biodistribution study shows that [225Ac]DOTA-YS5 agent delivers high levels of radiation to the tumor tissue (11.64% ± 1.37%ID/g, 28.58% ± 10.88%ID/g, 29.35% ± 7.76%ID/g, and 31.78% ± 5.89%ID/g at 24, 96, 168, and 408 hours, respectively), compared with the healthy organs. [225Ac]DOTA-YS5 suppressed tumor size and prolonged survival in cell line-derived and patient-derived xenograft models. Toxicity analysis revealed that the 0.5 μCi activity levels showed toxicity to the kidneys, likely due to redistribution of daughter isotope 213Bi.

CONCLUSIONS

[225Ac]DOTA-YS5 suppressed the growth of cell-derived and patient-derived xenografts, including prostate-specific membrane antigen-positive and prostate-specific membrane antigen-deficient models. Overall, this preclinical study confirms that [225Ac]DOTA-YS5 is a highly effective treatment and suggests feasibility for clinical translation of CD46-targeted radioligand therapy in prostate cancer.

PDZRN4 suppresses tumorigenesis and androgen therapy-resistance in prostate cancer

Background: PDZRN4 (PDZ domain-containing RING finger 4), a member of the LNX (ligand of numb protein-X) family that regulates the levels of NUMB, plays a critical role in suppressing the proliferation and invasion of hormone-related malignant tumours. There are few studies on the role of PDZRN4 in the pathogenesis of prostate cancer (PCa). We aimed to examine whether PDZRN4 regulates the growth and development of PCa.

Methods: Cell transduction and Western blotting were used to establish and confirm PDZRN4 knock down in PC cells. Using the MTT, wound healing, transwell migration, and animal experiments, we explored the biological function of PDZRN4 knockdown (PDZRN4-kd) cells. Via PCR and immunohistochemistry, the mRNA and protein expression of PDZRN4 was examined in PC cells and tissues.

Results: Hormone-dependent (LNCap) and hormone-independent (DU145, PC3, and C4-2) PC lines were transfected with lentivirus carrying PDZRN4 shRNA. The Western blotting results showed that the expression of PDZRN4 was stably downregulated in PDZRN4 knockdown (PDZRN4-kd) cells. The proliferation, invasion and migration of PDZRN4-kd cells were dramatically increased in vivo. To explore the expression of PDZRN4 in prostate cancer samples, we analysed TCGA data and found that PDZRN4 was negatively correlated with the development of PC. PDZRN4 levels were downregulated by androgen deprivation in hormone-sensitive cells. Moreover, PDZRN4 failed to induce proliferation in DU145 cells with androgen deprivation.

Conclusions: PDZRN4 is a functional suppressor of prostate cancer growth and development and is a potential target of biochemical therapy in hormone-resistant PC.

Modeling Androgen Deprivation Therapy-Induced Prostate Cancer Dormancy and Its Clinical Implications

Treatment-induced tumor dormancy is a state in cancer progression where residual disease is present but remains asymptomatic. Dormant cancer cells are treatment-resistant and responsible for cancer recurrence and metastasis. Prostate cancer treated with androgen-deprivation therapy (ADT) often enters a dormant state. ADT-induced prostate cancer dormancy remains poorly understood due to the challenge in acquiring clinical dormant prostate cancer cells and the lack of representative models. In this study, we aimed to develop clinically relevant models for studying ADT-induced prostate cancer dormancy. Dormant prostate cancer models were established by castrating mice bearing patient-derived xenografts (PDX) of hormonal naïve or sensitive prostate cancer. Dormancy status and tumor relapse were monitored and evaluated. Paired pre- and postcastration (dormant) PDX tissues were subjected to morphologic and transcriptome profiling analyses. As a result, we established eleven ADT-induced dormant prostate cancer models that closely mimicked the clinical courses of ADT-treated prostate cancer. We identified two ADT-induced dormancy subtypes that differed in morphology, gene expression, and relapse rates. We discovered transcriptomic differences in precastration PDXs that predisposed the dormancy response to ADT. We further developed a dormancy subtype-based, predisposed gene signature that was significantly associated with ADT response in hormonal naïve prostate cancer and clinical outcome in castration-resistant prostate cancer treated with ADT or androgen-receptor pathway inhibitors.

IMPLICATIONS

We have established highly clinically relevant PDXs of ADT-induced dormant prostate cancer and identified two dormancy subtypes, leading to the development of a novel predicative gene signature that allows robust risk stratification of patients with prostate cancer to ADT or androgen-receptor pathway inhibitors.

Immunosuppressive environment in response to androgen deprivation treatment in prostate cancer

RATIONALE

To invest the role of androgen deprivation therapy (ADT) on the tumor immune microenvironment of prostate cancer.

METHODS

Here we have profiled the transcriptomes of 19,227 single cells from 4 prostate tumors, including two cases who received ADT. To validated the single-cell analysis we use another group of patients receiving neoadjuvant ADT.

RESULTS

After receiving ADT treatment, the killing effect of prostate cancer immune cells on tumors is weakened, the interaction between immune cells and tumor cells is weakened, and the proportion of immunosuppressive cells Myeloid-derived suppressor cell (MDSC) and Regulatory T cells (Treg) cells increases.

CONCLUSIONS

Our results highlight that ADT induces immunosuppressive in the prostate tumor microenvironment. These data have important implications for combining ADT with immunotherapy.

The MURAL collection of prostate cancer patient-derived xenografts enables discovery through preclinical models of uro-oncology

Preclinical testing is a crucial step in evaluating cancer therapeutics. We aimed to establish a significant resource of patient-derived xenografts (PDXs) of prostate cancer for rapid and systematic evaluation of candidate therapies. The PDX collection comprises 59 tumors collected from 30 patients between 2012-2020, coinciding with availability of abiraterone and enzalutamide. The PDXs represent the clinico-pathological and genomic spectrum of prostate cancer, from treatment-naïve primary tumors to castration-resistant metastases. Inter- and intra-tumor heterogeneity in adenocarcinoma and neuroendocrine phenotypes is evident from bulk and single-cell RNA sequencing data. Organoids can be cultured from PDXs, providing further capabilities for preclinical studies. Using a 1 x 1 x 1 design, we rapidly identify tumors with exceptional responses to combination treatments. To govern the distribution of PDXs, we formed the Melbourne Urological Research Alliance (MURAL). This PDX collection is a substantial resource, expanding the capacity to test and prioritize effective treatments for prospective clinical trials in prostate cancer.

ZRSR2 overexpression is a frequent and early event in castration-resistant prostate cancer development

BACKGROUND

Androgen deprivation therapy (ADT) remains the leading systemic therapy for locally advanced and metastatic prostate cancers (PCa). While a majority of PCa patients initially respond to ADT, the durability of response is variable and most patients will eventually develop incurable castration-resistant prostate cancer (CRPC). Our research objective is to identify potential early driver genes responsible for CRPC development.

METHODS

We have developed a unique panel of hormone-naïve PCa (HNPC) patient-derived xenograft (PDX) models at the Living Tumor Laboratory. The PDXs provide a unique platform for driver gene discovery as they allow for the analysis of differentially expressed genes via transcriptomic profiling at various time points after mouse host castration. In the present study, we focused on genes with expression changes shortly after castration but before CRPC has fully developed. These are likely to be potential early drivers of CRPC development. Such genes were further validated for their clinical relevance using data from PCa patient databases. ZRSR2 was identified as a top gene candidate and selected for further functional studies.

RESULTS

ZRSR2 is significantly upregulated in our PDX models during the early phases of CRPC development after mouse host castration and remains consistently high in fully developed CRPC PDX models. Moreover, high ZRSR2 expression is also observed in clinical CRPC samples. Importantly, elevated ZRSR2 in PCa samples is correlated with poor patient treatment outcomes. ZRSR2 knockdown reduced PCa cell proliferation and delayed cell cycle progression at least partially through inhibition of the Cyclin D1 (CCND1) pathway.

CONCLUSION

Using our unique HNPC PDX models that develop into CRPC after host castration, we identified ZRSR2 as a potential early driver of CRPC development.

GRB10 sustains AR activity by interacting with PP2A in prostate cancer cells

Prostate cancer (PCa) progression is driven by androgen receptor (AR) signaling. Unfortunately, androgen-deprivation therapy and the use of even more potent AR pathway inhibitors (ARPIs) cannot bring about a cure. ARPI resistance (ie, castration-resistant PCa, CRPC) will inevitably develop. Previously, we demonstrated that GRB10 is an AR transcriptionally repressed gene that functionally contributes to CRPC development and ARPI resistance. GRB10 expression is elevated prior to CRPC development in our patient-derived xenograft models and is significantly upregulated in clinical CRPC samples. Here, we analyzed transcriptomic data from GRB10 knockdown in PCa cells and found that AR signaling is downregulated. While the mRNA expression of AR target genes decreased upon GRB10 knockdown, AR expression was not affected at the mRNA or protein level. We further found that phosphorylation of AR serine 81 (S81), which is critical for AR transcriptional activity, is decreased by GRB10 knockdown and increased by its overexpression. Luciferase assay using GRB10-knockdown cells also indicate reduced AR activity. Immunoprecipitation coupled with mass spectrometry revealed an interaction between GRB10 and the PP2A complex, which is a known phosphatase of AR. Further validations and analyses showed that GRB10 binds to the PP2Ac catalytic subunit with its PH domain. Mechanistically, GRB10 knockdown increased PP2Ac protein stability, which in turn decreased AR S81 phosphorylation and reduced AR activity. Our findings indicate a reciprocal feedback between GRB10 and AR signaling, implying the importance of GRB10 in PCa progression.

Cancer-driven IgG promotes the development of prostate cancer though the SOX2-CIgG pathway

BACKGROUND

Although androgen deprivation therapy (ADT) is the initial treatment strategy for prostate cancer (PCa), recurrent castration-resistant prostate cancer (CRPC) eventually ensues. In this study, cancer-derived immunoglobulin G (CIgG) is found to be induced after ADT, identifying CIgG as a potential CRPC driver gene.

METHODS

The expression of CIgG and its clinical significance in PCa tissue was analyzed by The Cancer Genome Atlas database and immunohistochemistry. Subsequently, the sequence features of prostate cell line VHDJH rearrangements were analyzed. We also assessed the effect of CIgG on the migratory, invasive and proliferative abilities of PCa cells in vitro and vivo. Suspended microsphere, colony formation and drug-resistant assays were performed using PC3 cells with high CIgG expression (CIgG^high ) and low CIgG expression (CIgG^-/low ), and A nonobese diabetic/severe combined immunodeficiency mouse tumor xenograft model was developed for the study of the tumorigenic effects of the different cell populations. The SOX2-CIgG signaling pathway was validated by immunohistochemistry, immunofluorescence, quantitative reverse transcription-polymerase chain reaction, Western blot, luciferase, and chromatin immunoprecipitation assays and bioinformatics analyses. Finally, we investigated the effect of RP215 inhibition on the progression of PCa in vivo using a Babl/c nude mouse xenograft model.

RESULTS

CIgG is frequently expressed in PCa and associated with clinicopathological characteristics, moreover, CIgG transcripts with unique patterns of VHDJH rearrangements are found in PCa cells. Functional analyses identified that CIgG was induced by ADT and upregulated by SOX2 (SRY (sex determining region Y)-box 2) in PCa, promoting the development of PCa. In addition, our findings underscore a novel role of CIgG signaling in the maintenance of stemness and the progression of cancer through mitogen activated protein kinase/extracellular-signal-regulated kinase and AKT in PCa. In vivo experiments further demonstrated that depleting CIgG significantly suppressed the growth of PCa cell xenografts. Furthermore, a CIgG monoclonal antibody named RP215 exhibits tumor inhibitory effect as well.

CONCLUSION

Our data suggests that CIgG could be a driver of PCa development, and that targeting the SOX2-CIgG axis may therefore inhibit PCa development after ADT.

Establishment and characterization of patient-derived xenografts for hormone-naïve and castrate-resistant prostate cancers to improve treatment modality evaluation

Prostate cancer (PC) is a heterogeneous disease characterized by variable morphological patterns. Thus, establishing a patient-derived xenograft (PDX) model that retains the key features of the primary tumor for each type of PC is important for appropriate evaluation. In this study, we established PDX models of hormone-naïve (D17225) and castration-resistant (B45354) PC by implanting fresh tumor samples, obtained from patients with advanced PC under the renal capsule of immune-compromised mice. Supplementation with exogenous androgens shortened the latent period of tumorigenesis and increased the tumor formation rate. The PDX models exhibited the same major genomic and phenotypic features of the disease in humans and maintained the main pathological features of the primary tumors. Moreover, both PDX models showed different outcomes after castration or docetaxel treatment. The hormone-naïve D17225 PDX model displayed a range of responses from complete tumor regression to overt tumor progression, and the development of castrate-resistant PC was induced after castration. The responses of the two PDX models to androgen deprivation and docetaxel were similar to those observed in patients with advanced PC. These new preclinical PC models will facilitate research on the mechanisms underlying treatment response and resistance.

An actionable sterol-regulated feedback loop modulates statin sensitivity in prostate cancer

OBJECTIVE

The statin family of cholesterol-lowering drugs has been shown to induce tumor-specific apoptosis by inhibiting the rate-limiting enzyme of the mevalonate (MVA) pathway, HMG-CoA reductase (HMGCR). Accumulating evidence suggests that statin use may delay prostate cancer (PCa) progression in a subset of patients; however, the determinants of statin drug sensitivity in PCa remain unclear. Our goal was to identify molecular features of statin-sensitive PCa and opportunities to potentiate statin-induced PCa cell death.

METHODS

Deregulation of HMGCR expression in PCa was evaluated by immunohistochemistry. The response of PCa cell lines to fluvastatin-mediated HMGCR inhibition was assessed using cell viability and apoptosis assays. Activation of the sterol-regulated feedback loop of the MVA pathway, which was hypothesized to modulate statin sensitivity in PCa, was also evaluated. Inhibition of this statin-induced feedback loop was performed using RNA interference or small molecule inhibitors. The achievable levels of fluvastatin in mouse prostate tissue were measured using liquid chromatography-mass spectrometry.

RESULTS

High HMGCR expression in PCa was associated with poor prognosis; however, not all PCa cell lines underwent apoptosis in response to treatment with physiologically-achievable concentrations of fluvastatin. Rather, most cell lines initiated a feedback response mediated by sterol regulatory element-binding protein 2 (SREBP2), which led to the further upregulation of HMGCR and other lipid metabolism genes. Overcoming this feedback mechanism by knocking down or inhibiting SREBP2 potentiated fluvastatin-induced PCa cell death. Notably, we demonstrated that this feedback loop is pharmacologically-actionable, as the drug dipyridamole can be used to block fluvastatin-induced SREBP activation and augment apoptosis in statin-insensitive PCa cells.

CONCLUSION

Our study implicates statin-induced SREBP2 activation as a PCa vulnerability that can be exploited for therapeutic purposes using clinically-approved agents.

Application of Prostate Cancer Models for Preclinical Study: Advantages and Limitations of Cell Lines, Patient-Derived Xenografts, and Three-Dimensional Culture of Patient-Derived Cells

Various preclinical models have been developed to clarify the pathophysiology of prostate cancer (PCa). Traditional PCa cell lines from clinical metastatic lesions, as exemplified by DU-145, PC-3, and LNCaP cells, are useful tools to define mechanisms underlying tumorigenesis and drug resistance. Cell line-based experiments, however, have limitations for preclinical studies because those cells are basically adapted to 2-dimensional monolayer culture conditions, in which the majority of primary PCa cells cannot survive. Recent tissue engineering enables generation of PCa patient-derived xenografts (PDXs) from both primary and metastatic lesions. Compared with fresh PCa tissue transplantation in athymic mice, co-injection of PCa tissues with extracellular matrix in highly immunodeficient mice has remarkably improved the success rate of PDX generation. PDX models have advantages to appropriately recapitulate the molecular diversity, cellular heterogeneity, and histology of original patient tumors. In contrast to PDX models, patient-derived organoid and spheroid PCa models in 3-dimensional culture are more feasible tools for in vitro studies for retaining the characteristics of patient tumors. In this article, we review PCa preclinical model cell lines and their sublines, PDXs, and patient-derived organoid and spheroid models. These PCa models will be applied to the development of new strategies for cancer precision medicine.