Neuroendocrine Prostate Cancer Research Articles

Characterization of structural, biochemical, pharmacokinetic, and pharmacodynamic properties of the LSD1 inhibitor bomedemstat in preclinical models.

Lysine-specific demethylase 1 (LSD1) is emerging as a critical mediator of tumor progression in metastatic castration-resistant prostate cancer (mCRPC). Neuroendocrine prostate cancer (NEPC) is increasingly recognized as an adaptive mechanism of resistance in mCRPC patients failing androgen receptor axis-targeted therapies. Safe and effective LSD1 inhibitors are necessary to determine antitumor response in prostate cancer models. For this reason, we characterize the LSD1 inhibitor bomedemstat to assess its clinical potential in NEPC as well as other mCRPC pathological subtypes. Bomedemstat was characterized via crystallization, flavine adenine dinucleotide spectrophotometry, and enzyme kinetics. On-target effects were assessed in relevant prostate cancer cell models by measuring proliferation and H3K4 methylation using western blot analysis. In vivo, pharmacokinetic (PK) and pharmacodynamic (PD) profiles of bomedemstat are also described. Structural, biochemical, and PK/PD properties of bomedemstat, an irreversible, orally-bioavailable inhibitor of LSD1 are reported. Our data demonstrate bomedemstat has >2500-fold greater specificity for LSD1 over monoamine oxidase (MAO)-A and -B. Bomedemstat also demonstrates activity against several models of advanced CRPC, including NEPC patient-derived xenografts. Significant intra-tumoral accumulation of orally-administered bomedemstat is measured with micromolar levels achieved in vivo (1.2 ± 0.45 µM at the 7.5 mg/kg dose and 3.76 ± 0.43 µM at the 15 mg/kg dose). Daily oral dosing of bomedemstat at 40 mg/kg/day is well-tolerated, with on-target thrombocytopenia observed that is rapidly reversible following treatment cessation. Bomedemstat provides enhanced specificity against LSD1, as revealed by structural and biochemical data. PK/PD data display an overall safety profile with manageable side effects resulting from LSD1 inhibition using bomedemstat in preclinical models. Altogether, our results support clinical testing of bomedemstat in the setting of mCRPC.

An orthotopic prostate cancer model for new treatment development using syngeneic or patient-derived tumors.

There are limited preclinical orthotopic prostate cancer models due to the technical complexity of surgical engraftment and tracking the tumor growth in the mouse prostate gland. Orthotopic xenografts recapitulate the tumor microenvironment, tumor stromal interactions, and clinical behavior to a greater extent than xenografts grown at subcutaneous or intramuscular sites. This study describes a novel micro-surgical technique for orthotopically implanting intact tumors pieces from cell line derived (transgenic adenocarcinoma mouse prostate [TRAMP]-C2)or patient derived (neuroendocrine prostate cancer [NEPC])tumors in the mouse prostate gland and monitoring tumor growth using magnetic resonance (MR) imaging. The TRAMP-C2 tumors grew rapidly to a predetermined endpoint size of 10 mm within 3 weeks, whereas the NEPC tumors grew at a slower rate over 7 weeks. The tumors were readily detected by MRand confidently identified when they were approximately 2-3 mm in size. The tumors were less well-defined on CT. The TRAMP-C2 tumors were characterized by amorphous sheets of poorly differentiated cells similar to a high-grade prostatic adenocarcinoma and frequent macroscopic peritoneal and lymph node metastases. In contrast, the NEPC's displayed a neuroendocrine morphology with polygonal cells arranged in nests and solid sheets and high count. There was a local invasion of the bladder and other adjacent tissues but no identifiable metastases. The TRAMP-C2 tumors were more hypoxic than the NEPC tumors. This novel preclinical orthotopic prostate cancer mouse model is suitable for either syngeneic or patient derived tumors and will be effective in developing and advancing the current selection of treatments for patients with prostate cancer.

Development and Characterisation of a New Patient-Derived Xenograft Model of AR-Negative Metastatic Castration-Resistant Prostate Cancer

As the treatment landscape for prostate cancer gradually evolves, the frequency of treatment-induced neuroendocrine prostate cancer (NEPC) and double-negative prostate cancer (DNPC) that is deficient for androgen receptor (AR) and neuroendocrine (NE) markers has increased. These prostate cancer subtypes are typically refractory to AR-directed therapies and exhibit poor clinical outcomes. Only a small range of NEPC/DNPC models exist, limiting our molecular understanding of this disease and hindering our ability to perform preclinical trials exploring novel therapies to treat NEPC/DNPC that are urgently needed in the clinic. Here, we report the development of the CU-PC01 PDX model that represents AR-negative mCRPC with PTEN/RB/PSMA loss and CTNN1B/TP53/BRCA2 genetic variants. The CU-PC01 model lacks classic NE markers, with only focal and/or weak expression of chromogranin A, INSM1 and CD56. Collectively, these findings are most consistent with a DNPC phenotype. Ex vivo and in vivo preclinical studies revealed that CU-PC01 PDX tumours are resistant to mCRPC standard-of-care treatments enzalutamide and docetaxel, mirroring the donor patient’s treatment response. Furthermore, short-term CU-PC01 tumour explant cultures indicate this model is initially sensitive to PARP inhibition with olaparib. Thus, the CU-PC01 PDX model provides a valuable opportunity to study AR-negative mCRPC biology and to discover new treatment avenues for this hard-to-treat disease.

Abstract LB161: Discovery of an oral, potent, and selective CDK9 molecular glue degrader SLX-3065 active in aggressive variant prostate cancers (AVPC)

Abstract Background: The use of new potent targeted therapies in prostate cancers has led to the resistance and development of highly aggressive variant prostate cancers (AVPC), including neuroendocrine prostate cancers (NEPC). N-MYC and C-MYC oncogenes overexpress in all aggressive prostate cancers (PCa). This overexpression is highly prevalent in these lethal subtypes of cancers, detected in 2% of all Prostate Cancers and over 10-17% of mCRPC patients. Transcriptional targets of CDK9 are MYCs, which act as an oncogenic driver, sufficient to transform human-derived prostate cancer cells to take on AVPC and NEPC phenotypic changes. Additionally, N-MYC and C-MYC play key roles in tumor drug resistance, and their downregulation, through CDK9 inhibition or degradation lowers tumor growth. Our efforts have demonstrated that targeting drivers of NEPC and mCRPC with highly selective CDK9 molecular glue degraders SLX-3064 SLX-3065 was designed from reversible SLX-3039 for therapeutic intervention of mCRPC, AVPC, and NEPCs. Materials and Methods: We employed our MolecuLernTM-trained molecular glue library design strategies and in vitro CDK9 kinase binding assays. Other experiments include cellular efficacies of single-agent Molecular Glue degraders and their effect in combination experiments on 22Rv1, LASCPC-01, C4-2, and C4-2B MYC expressed PCa cells. Kinase selectivity, Nano BRET, ADME-Tox, in vitro safety, secondary pharmacological assays, Cell engraftment mouse tumor mode, and PK studies were performed. Results: We designed and synthesized a series of novel small molecule CDK9 Molecular Glue degraders based on our initial CDK9 inhibitor lead SLX-3030 and SLX-3039. The SLX-3064 and SLX-3065 reversibly bind to CDK9 with an IC50 of 9 and 7 nM in kinase binding, in target engagement assays, elicit pharmacological responses in N-MYC, C-MYC, driven prostate cancer cells in vitro in LASCPC-01 (21, 35 nM), 22Rv1 (108, 236 nM), C4-2B (15, 12 nM), C4-2 (2.7, 1.5 nM) and VCap (86, 73 nM) cell lines. SLX-3064 and SLX-3065 exhibited potent activity degrading total, pCDK9, MYCs, Mcl-1, and its downstream RNA Pol II, Ser 2, 5, 7, and pAR Ser-81 in a dose-dependent manner. Additionally, we performed in vitro ADME-Tox, hERG, P450, safety panel screen, and in vivo PK experiments in rodent and beagle dog species. Conclusion: In summary, both SLX-3064 and SLX-3065 molecular glues display complete degradation of CDK9 and its downstream markers, and these degraders possess ideal developable criteria as oral agents. With these characteristics, SLX-3065 was selected as a candidate that had the appropriate developable properties and our plans for conducting additional IND-enabling studies and future clinical trial plans will also be discussed. Citation Format: Chenyu Lin, Zhaoliang Li, Kyle Medley, David J. Bearss, Hariprasad Vankayalapati. Discovery of an oral, potent, and selective CDK9 molecular glue degrader SLX-3065 active in aggressive variant prostate cancers (AVPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB161.

Abstract LB217: Novel organoid models of lineage plasticity in castration resistant prostate cancer

Abstract The development of next-generation AR-targeted drugs, such as abiraterone and enzalutamide, has improved survival of patients with castration-resistant prostate cancer (CRPC). However, many patients eventually progress to therapy-resistant lethal prostate cancer. CRPC exhibits variant cellular states, including AR-pathway active prostate cancer (ARPC), AR activity-low prostate cancer (ARLPC), neuroendocrine prostate cancer (NEPC), amphicrine prostate cancer co-expressing AR and neuroendocrine genes (AMPC), and double-negative prostate cancer (DNPC) lacking both AR expression and neuroendocrine differentiation, indicating that lineage plasticity facilitates therapeutic resistance. While molecular characteristics of ARPC and NEPC are well described, other common forms of CRPC, such as DNPC which occurs in 20-25% of CRPC patients, remain poorly understood. Therefore, characterization of pre-clinical models of DNPC and identification of novel regulators of lineage plasticity in DNPC are urgent necessities for the development of effective treatment for lethal prostate cancer.In our studies, we have generated a new mouse model of CRPC in which Pten and Smad4 are deleted in distal luminal cells upon tamoxifen administration (Nkx3.1CreERT2/+; Ptenfl/fl; Smad4fl/fl; R26R-eYFP/+, NPS). We observed a molecular transition from ARPC to ARLPC and DNPC in the prostate tumors derived from NPS mice during tumor progression. Moreover, a combination of castration and enzalutamide treatment promoted a partial epithelial-mesenchymal transition (EMT) in DNPC. To identify the evolutionary trajectories of cancer progression and drivers of lineage plasticity in CRPC, we have established organoid lines from the prostate tumor cells of NPS mice. Single-cell RNA-sequencing (scRNA-seq) and marker validation analyses shown that these organoid lines display overt lineage plasticity, corresponding to ARPC, ARLPC, partial EMT-absent DNPC, and partial EMT-present DNPC. Orthotopic grafts derived from the established NPS organoid lines show consistent molecular phenotypes and confirm that AR-targeted therapies facilitate partial EMT in vivo. Furthermore, cross-species bioinformatic analyses using scRNA-seq datasets indicate that the established NPS organoid lines partially recapitulate the spectrum of lineage plasticity in human CRPC.In summary, we have established prostate cancer organoid lines from a novel mouse model of CRPC, which not only provide large and reproducible sources of two distinct forms of DNPC (partial EMT-absent DNPC and partial EMT-present DNPC) for molecular analyses, but also can capture the regulatory complexity of lineage plasticity in human CRPC. Therefore, NPS mice provide an excellent pre-clinical model of CRPC, especially DNPC, to identify novel regulators that drive lineage plasticity and to pursue assays for development of candidate drugs that can inhibit or even possibly convert therapy-resistant forms of CRPC to therapy-sensitive ones. Citation Format: Jinqiu Lu, Michael M. Shen. Novel organoid models of lineage plasticity in castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB217.

Co-targeting BET, CBP, and p300 inhibits neuroendocrine signalling in androgen receptor-null prostate cancer.

There are diverse phenotypes of castration-resistant prostate cancer, including neuroendocrine disease, that vary in their sensitivity to drug treatment. The efficacy of BET and CBP/p300 inhibitors in prostate cancer is attributed, at least in part, to their ability to decrease androgen receptor (AR) signalling. However, the activity of BET and CBP/p300 inhibitors in prostate cancers that lack the AR is unclear. In this study, we showed that BRD4, CBP, and p300 were co-expressed in AR-positive and AR-null prostate cancer. A combined inhibitor of these three proteins, NEO2734, reduced the growth of both AR-positive and AR-null organoids, as measured by changes in viability, size, and composition. NEO2734 treatment caused consistent transcriptional downregulation of cell cycle pathways. In neuroendocrine models, NEO2734 treatment reduced ASCL1 levels and other neuroendocrine markers, and reduced tumour growth in vivo. Collectively, these results show that epigenome-targeted inhibitors cause decreased growth and phenotype-dependent disruption of lineage regulators in neuroendocrine prostate cancer, warranting further development of compounds with this activity in the clinic. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Abstract LB259: Cell context-dependent role of KDM5D in ATR and CHK1 inhibitor sensitivity in prostate cancer

Abstract Epigenetic regulation plays an important role in prostate cancer progression and metastasis. KDM5D is a male-specific histone-modifying enzyme encoded on the Y chromosome that demethylates di- and tri-methylated forms of lysine 4 in histone H3, resulting in transcriptional repression of certain genes. In this study, we investigated the role of KDM5D in resistance to inhibitors targeting the G2/M cell cycle checkpoint kinase CHK1. Loss of KDM5D expression was associated with reduced cell proliferation and resistance to the CHK1 inhibitor SRA737 in castration-resistant (CRPC) and neuroendocrine (NEPC) prostate cancer cell lines. In KDM5D expressing cells, depletion of KDM5D differentially impacted the proliferation of prostate cancer cell lines. The androgen-sensitive LNCaP cell line was particularly sensitive to the knockdown of KMD5D. On the other hand, in CRPC cell line 22Rv1, the knockdown of KDM5D caused resistance to both inhibitors, indicating a dual role of KDM5D in mediating ATR and CHK1 inhibitor sensitivity and cell proliferation in prostate cancer cells. Further analysis demonstrated a self-regulatory cycle between CHK1 and KDM5D in 22Rv1 cells, where depletion of KMD5D reduced CHK1 mRNA, while decreased CHK1 caused upregulation of KDM5D and overexpression of KDM5D resulted in increased CHK1 expression. The relevance of this regulatory mechanism to ATR and CHK1 inhibitor sensitivity is currently under investigation, along with several potential mediators of the differential responses to these inhibitors. Additional ATR and CHK1 inhibitors will also be examined in this context. This study may uncover novel biomarkers for ATR and CHK1 inhibitors that are currently in clinical trials for various cancers. KDM5D may be used to stratify prostate cancer patients receiving these highly potent anticancer agents. Citation Format: Wenxiao Zheng, Yuzhou Chen, Qiming J. Wang. Cell context-dependent role of KDM5D in ATR and CHK1 inhibitor sensitivity in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB259.

Integrative molecular analyses of the MD Anderson prostate cancer patient-derived xenograft (MDA PCa PDX) series.

Develop and deploy a robust discovery platform that encompasses heterogeneity, clinical annotation, and molecular characterization and overcomes the limited availability of prostate cancer (PCa) models. This initiative builds on the rich MD Anderson (MDA) PCa patient-derived xenograft (PDX) resource to complement existing publicly available databases by addressing gaps in clinically annotated models reflecting the heterogeneity of potentially lethal and lethal PCa. We performed whole-genome, targeted, and RNA sequencing in representative samples of the same tumor from 44 PDXs derived from 38 patients linked to donor tumor metadata and corresponding organoids. The cohort includes models derived from different morphologic groups, disease states, and involved organ sites (including circulating tumor cells), as well as paired samples representing heterogeneity or stages before and after therapy. The cohort recapitulates clinically reported alterations in PCa genes, providing a data resource for clinical and molecular interrogation of suitable experimental models. Paired samples displayed conserved molecular alteration profiles, suggesting the relevance of other regulatory mechanisms (e.g., epigenomic) influenced by the microenvironment and/or treatment. Transcriptomically, models were grouped based on morphological classification. DNA damage response-associated mechanisms emerged as differentially regulated between adenocarcinoma and neuroendocrine PCa in a cross-interrogation of PDX/patient datasets. We addressed the gap in clinically relevant PCa models through comprehensive molecular characterization of MDA PCa PDXs, providing a discovery platform that integrates with patient data and benchmarked to therapeutically relevant consensus clinical groupings. This unique resource supports robust hypothesis generation and testing from basic, translational, and clinical perspectives.

Abstract 3577: The role of PLXND1 in lineage plasticity and progression to neuroendocrine prostate cancer

Abstract Background: Neuroendocrine prostate cancer (NEPC) is a lethal subtype of prostate cancer and is commonly associated with therapy resistance and poor prognosis. Treatment-induced NEPC (t-NEPC) predominantly develops by lineage plasticity from adenocarcinoma in response to androgen receptor signaling inhibitors, such as enzalutamide. However, the mechanisms underlying the lineage plasticity and progression to NEPC are unclear. PLXND1 (PlexinD1) is a cellular receptor of the semaphorin family and has important functions in modulating the cytoskeleton and cell adhesion. However, the role of PLXND1 in lineage plasticity to NEPC development and progression is not well established. Methods: We performed transcriptomic analysis on NEPC patients’ cohorts and the enzalutamide-resistant prostate cancer cell lines. Correlation of PLXND1 with neuroendocrine feature genes and AR-targeting genes was determined. Kaplan-Meier method and the Cox proportional hazards model was used to estimate the correlation between PLXND1 expression level and patients’ survival. Immunohistochemistry was used to analyze PLXND1 expression in prostate adenocarcinoma and NEPC. Cell viability was determined in C4-2B MDVR, CWR22Rv1, and H660 cells after knocking down PLXND1 using siRNA or knocking out PLXND1 using CRISPR/CAS9. Organoids viability of patient-derived xenografts was measured after knocking down or knocking out PLXND1. Results: Our analysis on different patient cohorts suggests that PLXND1 is highly expressed in NEPC patients, and the expression of PLXND1 is positively correlated with neuroendocrine feature genes (CHGA, ENO2, SYP, and NCAM1). Kaplan-Meier survival analysis shows that high expression of PLXND1 is significantly associated with the poor prognosis of prostate cancer patients. PLXND1 is overexpressed and negatively regulated by androgen receptor signaling in enzalutamide-resistant cells and prostate cancer patients’ cohorts. Furthermore, downregulation of PLXND1 expression suppressed proliferation of the NEPC cells and viability of the PDX tumor organoids. Conclusions: PLXND1 expression is elevated in NEPC and correlated with the poor survival of prostate cancer patients, suggesting it is a potential molecular indicator and therapy target for NEPC. Citation Format: Bo Chen, Pengfei Xu, Joy C. Yang, Shu Ning, Leyi Wang, Christopher Nip, Allen C. Gao, Chengfei Liu. The role of PLXND1 in lineage plasticity and progression to neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3577.

Abstract 3036: Sensitivity of ONC201/TIC10 cancer therapeutic on neuroendocrine prostate cancer (NEPC) and neuroendocrine differentiation (NED)

Abstract Although androgen deprivation therapy and androgen receptor (AR) blockade are highly effective therapies for metastatic prostate cancer (PCa), most patients develop resistance, leading to castration-resistant prostate cancer (CRPC). A subset of CRPC shows neuroendocrine prostate cancer (NEPC) features, which are associated with poor prognosis and limited therapeutic strategies. NEPC is characterized by oncogenic driver activation and epigenetic changes, partly controlled by transcription factors like BRN2 and SOX2. AR has been shown to suppress BRN2 transcription, which is required for NEPC, and BRN2-dependent regulation of the NEPC marker SOX2 (Bishop et al., 2017). Dordaviprone (ONC201/TIC10) is a first-in-class small molecule that antagonizes DRD2, induces tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and activates the integrated stress response (ISR). Neuroendocrine tumors express significant DRD2 levels, suggesting ONC201 as a potential therapeutic strategy in NEPC or when drivers for disease progression are overexpressed (OE). PCa cell lines PC3, DU145, LNCaP, and 22RV1 are ONC201 sensitive, with IC50=2.87 μM, 3.18 μM, 1.31 μM, and 1.16 μM, respectively (Ding et al., 2023). To characterize the association of BRN2/SOX2 dysregulation with ONC201 sensitivity, we transiently OE BRN2/SOX2 in PCa. We hypothesized that markers of neuroendocrine differentiation (NED), activation of the ISR, TRAIL, and ClpP and dopamine receptor expression contribute to NEPC cell death and sensitivity to ONC201. We performed CellTiter-Glo experiments to assess viability after 96 hours ± BRN2 OE. DU145 cells with BRN2 OE increased their sensitivity to ONC201 (IC50=2.75 µM) compared to empty vector (IC50=3.03 µM). Colony formation assays were conducted in PCa and analyzed 7 days after ONC201 treatment to show ONC201 effect on PCa cell lines. DU145 was treated at 0.5, 1, and 2 µM of ONC201. There were 95 ± 3.22 colonies for the control group, 83 ± 5.22 colonies with 0.5 µM, 74 ± 3.64 colonies with 1 µM, and 8 ± 2.03 colonies with 2 µM ONC201. DU145 showed a significant reduction in colony-forming ability when treated with 1 and 2 uM ONC201 compared to the control, with P values of <0.05 and <0.0001, respectively. We OE BRN2 and observed changes in NED markers and ISR pathway. In PC3, FoxO1 and ATF4 levels increased. In DU145, FoxO1, ENO2, PGP9.5, CgA, and ATF4 levels decreased. We reveal that DU145 OE at 48 hours does not result in greater expression of NEPC markers. BRN2 OE significantly increased PCa cell sensitivity to ONC201 and was evident without an increase in common phenotypical markers used for NEPC assessment (FoxO1, ENO2, PGP9.5, CgA). Expression change was not shown when PCa had an integral AR pathway. Ongoing efforts are observing ONC201 treatment effects on NED markers and the TRAIL pathway due to BRN2 OE and showing increased sensitivity of PCa to ONC201 with BRN2 OE. Citation Format: Elizabeth C. Ding, Maximilian Pinho-Schwermann, Shengliang Zhang, Connor Purcell, Wafik S. El-Deiry. Sensitivity of ONC201/TIC10 cancer therapeutic on neuroendocrine prostate cancer (NEPC) and neuroendocrine differentiation (NED) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3036.

Abstract 1725: Role of PRMT5 in neuroendocrine prostate cancer development

Abstract Background: Neuroendocrine prostate cancer (NEPC) is a lethal subtype of prostate cancer responsible for an estimated 20-30% of castration resistant prostate cancer (CRPC) deaths. While NEPC can arise de novo, the majority of these cases emerge as treatment-induced NEPC (tNEPC). Our data establish PRMT5:MEP50 as a key epigenetic regulator in NEPC and provide a potential predictive biomarker for tNEPC. Methods: Here we generated an in vitro cell culture model and mouse model to mimic the clinical conditions in androgen signaling inhibitor (ASI) or androgen deprivation treatment (ADT) We developed an in vitro cell culture and in vivo model to mimic the clinical conditions in enzalutamide-resistant prostate cancer. Regulation and role of protein arginine methyltransferase 5 (PRMT5) and its cofactor methylosome protein 50 (MEP50) were determined by treating cells and mice tumors with doxycycline inducible-shRNAs and catalytic inhibitors followed by analysis of cell viability, neurite growth, and effects on neuroendocrine related gene transcription. Pro-NEPC development effects were analyzed by immunofluorescence, immunohistochemical analysis, and western blot. PRMT5:MEP50-dependent methyltransferase activity was further validated by observing histone deposition levels via western blot and ChIP-qPCR. For clinical correlation, PRMT5 and MEP50 expression levels were comprehensively analyzed in both CRPC and NEPC patient prostate tissue samples. Results: Our clinical and computational analyses have identified increased expression of PRMT5:MEP50 in NEPC. Overexpression of PRMT5 and MEP50 in prostate cancer cells is sufficient to induce neuroendocrine differentiation (NED) in prostate cancer cells. Gene depletion of PRMT5 and MEP50 prevented the NE phenotype induced by androgen receptor inhibition and resensitized the prostate cancer cells to ASI/ADT. PRMT5 and MEP50 facilitate chromatin modulation through the dimethylation of H4R3, which is highly correlated with the NED phenotype. Moreover, overexpression of PRMT5 and MEP50 in mouse prostate induces NEPC development, and gene downregulation can prevent NED in a xenograft mouse model. Elevated PRMT5 and MEP50 correlated with increased recurrence in prostate cancer patients receiving ADT and their recurrence probability after the treatment. Conclusion: Our data establish PRMT5:MEP50 as a key epigenetic regulator in NEPC and provide a potential predictive biomarker for tNEPC. Citation Format: Hye Seung Nam, Xuehong Deng, Chang-Deng Hu. Role of PRMT5 in neuroendocrine prostate cancer development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1725.

Abstract 948: A novel combinatorial therapy for lethal neuroendocrine prostate cancer

Abstract Background: Neuroendocrine prostate cancer (NEPC) is a highly aggressive subtype of prostate cancer that can arise de novo, but more commonly develops after hormone therapies for advanced prostate adenocarcinoma. Current treatment options for NEPC are only palliative, and most patients die within several months. Additionally, single-agent clinical trials targeting NEPC so far have only produced disappointing results, highlighting the clear need to develop effective combinatorial therapies for NEPC. RB1 loss, a pivotal event in the development of NEPC, can sensitize cancer cells to ferroptosis in multiple cancer cell types, including prostate cancer. Here, we aim to identify an optimal combinatorial therapy for NEPC based on targeting ferroptosis. Methods: We determined the cell-killing efficacy of ferroptosis inducers and several current and emerging treatment regimens for NEPC as single agents, then performed drug synergism analyses of the above two potent treatments. Lastly, we investigated the molecular mechanisms of drug synergism by examining the major types of cell death induced by combinatorial treatment through molecular and biochemical assays. Results: Our results demonstrated that both ferroptosis inducers and BCL2 inhibitors as single agents led to robust cell death in NEPC cell lines tested. In contrast, cisplatin, the standard of care for NEPC, and Aurora kinase A inhibitor showed modest to no cell-killing effect. Furthermore, suboptimal doses of ferroptosis inducers and BCL-2 inhibitors synergistically induced cell death in NEPC cell lines. Unexpectedly, we found that low-dose ferroptosis inducer led to increased production of mitochondria ROS, which in turn exacerbated BCL-2 suppression-induced apoptosis. Conclusions: Our findings reveal a novel combinatorial therapy for NEPC. Based on our in vitro data, we will further test the in vivo therapeutic efficacy of ferroptosis inducers combined with BCL-2 inhibitors against NEPC growth. Citation Format: Mu-En Wang, Wei-Ling Tu, Yi Lu, Jinjin Wu, Alyssa Bawcom, Andrew J. Armstrong, Qianben Wang, Yuzhuo Wang, Jiaoti Huang, Ming Chen. A novel combinatorial therapy for lethal neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 948.

Abstract 473: PVT1 exon 9 overexpression induces AR null phenotype and cellular reprogramming in prostate cancer

Abstract Plasmacytoma variant translocation 1 (PVT1) is an oncogenic long-noncoding RNA (lncRNA) gene located directly downstream of MYC on chromosome 8q24. PVT1 is an oncogene overexpressed in prostate cancer (PCa) and can promote oncogenesis by altering gene expression directly or acting as a noncoding RNA sponge. Beyond functioning as a lncRNA, PVT1 gene encodes six microRNAs that each have independent functions. Our group identified overexpression of PVT1 exon 9 in PCa samples derived from men of African Ancestry and overexpression may explain why this population group experiences more aggressive disease. We overexpressed PVT1 exon 9 in RWPE1 prostate epithelial cells (RWPE1_ex9) and found enhanced migration and invasion compared to empty vector (RWPE1_ev). Implantation of RWPE1_ex9 cells into mice led to the formation of tumors with the neuroendocrine PCa (NEPC) phenotype that was histopathologically confirmed. RNA-sequencing analysis of PVT1 exon 9 overexpression showed significant (p-value < 0.05) upregulation of 141 genes. The majority of pathways impacted by PVT1 exon 9 overexpression were interferon type 1 signaling (RSAD2, CMPK2), developmental NOTCH signaling (HES7), cargo-transport (STX16) and tumor microenvironment promoting factors (HS3ST3A1). We found loss of androgen receptor (AR) expression at mRNA and protein levels in RWPE1_ex9 cells, a hallmark of NEPC, which further supports our hypothesis that PVT1 exon 9 overexpression plays a role in NEPC development. Validation of RNA-sequencing confirmed upregulation of RSAD2, CMPK2, STX16, HES7 and HS3ST3A1 within RWPE1_ex9 cells compared to RWPE1_ev and RWPE1 wild-type, suggestive of cellular reprogramming of prostate epithelial cells. We further analyzed expression profile in a novel circulating tumor cell model of castration-resistant 22RV1 cells (C22OH) and found enhanced expression of PVT1 exon 9, suppression of AR, phosphorylation of AR serine residue 308 and enhanced CDK11 activity compared to the primary 22RV1 cell line T22OH suggestive of a cell-cycle mediated regulatory mechanism. We further found enhanced expression of chromogramin A in the C22OH cell line, a marker of NEPC. These results suggest PVT1 exon 9 overexpression may play a critical role in NEPC development from normal epithelial cells via cellular reprogramming as well as facilitating a transition to NEPC from a castration resistant phenotype. PVT1 exon 9 may be a useful predictive biomarker that can identify populations which are likely to have disease progression from castration resistance to NEPC and further highlights the need to identify therapeutic strategies to target PVT1 exon 9 overexpression. Citation Format: Rachel E. Sexton-Bonacci, Chinedum Udekwu, Baris Boylu, Olorunseun O. Ogunwobi. PVT1 exon 9 overexpression induces AR null phenotype and cellular reprogramming in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 473.

Abstract 4567: Dual targeting of HSP70 and AURKA improves treatment in neuroendocrine prostate cancer

Abstract Background: Neuroendocrine prostate cancer (NEPC) is the most aggressive type of prostate cancer with no effective treatments. Therefore, there is an urgent need to develop new treatment strategies. N-Myc plays a key role in driving NEPC progression, and Aurora kinase A (AURKA) prevents N-Myc degradation by interact with N-Myc and disallowing the intervention of ubiquitin ligases. The AURKA inhibitor Alisertib inhibits NEPC tumor growth by disrupting N-Myc signaling, but it is failed in a phase II clinical trial. In this study, we tested the synergy of novel HSP70 allosteric inhibitor JG231 and Alisertib in NEPC cells, organoids, and patient derived xenograft (PDX) models, which will provide new therapeutic strategies for the NEPC treatment. Methods: RT-PCR, western blotting, or immunohistochemistry (IHC) were used to determine the expression of N-Myc, neuroendocrine maker (NSE, SYP, CHGA, etc) in different prostate cancer cell lines and PDX tumors. After the knockdown of HSP70 and AURKA by siRNA transfection, cell proliferation and N-Myc expression were assessed by using cell viability assay, RT-PCR and Western blotting respectively. The co-immunoprecipitation assay was performed to detect the N-Myc ubiquitination. RNA-sequencing, gene set enrichment analysis was employed to determine the changes of JG231 on gene programs. The effects of JG231 and Alisertib on the proliferation were examined in NEPC cell lines and PDX organoids models. Results: We determined that PC3, CWR22Rv1, H660 cell lines, LuCaP49, and LuCaP93 PDX tumors had significantly increased the expression of N-Myc and neuroendocrine makers. Knockdown of HSP70 or using the HSP70 inhibitor, JG231, significantly inhibit the growth of H660 and CWR22Rv1 cells and leads to a synergistic effect with Alisertib (p<0.001). JG231 combined with Alisertib also inhibits growth and induces the death of LuCaP93 and H660 tumor derived organoids in a dose-dependent manner (p<0.001). Mechanistically, JG231 inhibits the protein expression of N-Myc through the ubiquitin-proteasome system and promote STUB1 to enter the nucleus to bind to N-Myc. Conclusions: JG231, a novel HSP70 inhibitor, can improves the treatment efficacy of AURKA inhibitor Alisertib against NEPC through the regulation of N-Myc protein homeostasis. Citation Format: Pengfei Xu, Joy C. Yang, Bo Chen, Shu Ning, Leyi Wang, Christopher Nip, Christopher P. Evans, Marc A. Dall'Era, Allen C. Gao, Jason Gestwicki, Chengfei Liu. Dual targeting of HSP70 and AURKA improves treatment in neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4567.

Abstract 5795: Potent and selective degradation of KAT2A and KAT2B induces profound cell state changes and inhibits growth of AML, SCLC and NEPC model systems

Abstract Phenotypic plasticity, or the ability of cancer cells to switch between cell states, has recently been recognized as a key hallmark of cancer. Cancer cells can hijack normal developmental pathways, preventing terminal differentiation or causing de-differentiation or transdifferentiation to a more proliferative, plastic cell state similar to those found in early development. Using our proprietary AI/ML platform AURIGIN, we created a high-resolution atlas to define the drivers of normal cell states during human development. After mapping primary human tumors to the atlas, we identified the histone acetyltransferase KAT2A as a key driver of tumor cell plasticity in a subset of acute myeloid leukemias (AML), small cell lung cancer (SCLC) and neuroendocrine prostate cancer (NEPC). Targeting KAT2A was genetically validated in MOLM-13 (AML) cells, where knockdown resulted in significant cell growth inhibition and induction of cell state changes consistent with a more mature differentiation phenotype. Similarly, an early tool heterobifunctional degrader of KAT2A and KAT2B (AUR101) resulted in potent growth inhibition and granulocytic differentiation in MOLM-13 cells and in 5/12 primary AML patient samples grown ex vivo. Treatment of NCI-H1048 SCLC cells with AUR101 potently degraded KAT2A/B, induced a significant shift from a dedifferentiated cell state to a more differentiated epithelial cell state and potently inhibited cell growth both in vitro and in vivo. The strong biological validation of KAT2A/B in SCLC and AML tumors, led us to develop AUR1545, a novel sub-nanomolar degrader of KAT2A and KAT2B. AUR1545, with its improved drug like properties, was tested across representative models of AML, SCLC and NEPC. In vitro, treatment with AUR1545 inhibited proliferation and promoted profound cell state changes in MOLM-13 (AML) cells. In NCI-H1048 (SCLC), LASPC-01 (NEPC) cell lines as well as a primary NEPC organoid model, AUR1545 demonstrated potent antiproliferative effects. In vivo, AUR1545 significantly inhibited tumor growth in an NCI-H1048 xenograft model. Taken together, these data genetically and pharmacologically validate KAT2A and KAT2B as key drivers of cell state plasticity in SCLC, NEPC and AML tumors and point to their utility as novel targets in these aggressive, metastatic and drug resistant cancers. Citation Format: Kimberly S. Straley, James Neef, Ileana Antony-Debre, Maulasri Bhatta, Sambad Sharma, Sara Sinicropi-Yao, Joe DeBartolo, Andrew McRiner, Betty Chan, Henry Wilson, Christina S. Lee, Zied Boudhraa, Mohamed El Ezzy, Umar Sharif, Mark Bittinger, Laura Antipov, Thomas G. Graeber, Stephane de Botton, Katharine E. Yen, David S. Millan. Potent and selective degradation of KAT2A and KAT2B induces profound cell state changes and inhibits growth of AML, SCLC and NEPC model systems [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5795.

Abstract 5067: Exploring the genomic landscape of de novo neuroendocrine prostate cancer: Insights for innovative therapies from spatial gene expression analysis

Abstract Introduction & Objectives Neuroendocrine prostate cancer (NEPC) accounts for less than 1% of all prostate cancers but has a worse prognosis than androgen receptor-positive prostate adenocarcinoma (ARPC). Rare cases exist where both de novo NEPC and ARPC are found in the same tissue sample. Our study examines one such unique case: a 78-year-old male treated at Ehime University Hospital who was diagnosed with both ARPC and adjacent de novo metastatic NEPC. This case provides an excellent opportunity for studying gene expression in these two types of prostate cancer. Materials & Methods We used Visium CytAssist Spatial Gene Expression technology from 10x Genomics to analyze formalin-fixed, paraffin-embedded (FFPE) tissue samples from this unique patient. Results We observed elevated expression levels of specific neuroendocrine markers like PEG10, DLL3, NCAM1, SYP, and CHGA in de novo NEPC regions. In contrast, androgen receptor markers such as KLK3, ACPP, TMPRSS2, and NKX3.1 were more prevalent in ARPC areas. Furthermore, genes like Chek1, BRCA1/2, TOP2A, and FANCA were also elevated in NEPC, suggesting that PARP and TOP2 inhibitors could be effective. Expression levels of Rbfox3 and SFRTM2 were lower in NEPC areas, implying possible roles in epithelial-mesenchymal transition (EMT) and Wnt signaling pathways. Additionally, fibrotic markers like HGF, HMOX1, ELN, and GREM1 were upregulated, suggesting that de novo NEPC tumors might be 'immune cold,' thus requiring treatments to boost the effectiveness of immune checkpoint inhibitors. Conclusion The data from additional cases could open the door for new treatment options for NEPC and improve survival rates for castration-resistant prostate cancer patients. Our research serves as a pioneering application of Visium CytAssist on FFPE samples and is the first to examine gene expression in both ARPC and de novo NEPC. A subset of these findings was published in the International Journal of Molecular Science (IJMS) in May 2023. Citation Format: Ryuta Watanabe, Noriyoshi Miura, Mie Kurata, Riko Kitazawa, Tadahiko Kikugawa, Takashi Saika. Exploring the genomic landscape of de novo neuroendocrine prostate cancer: Insights for innovative therapies from spatial gene expression analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5067.

Abstract 2898: Development of the lipid kinase PIKfyve PROTAC degrader against neuroendocrine prostate cancer

Abstract Therapies targeting the androgen receptor (AR) as the main driver of prostate cancer (PCa) can lead to various mechanisms of resistance and promote progression to castration-resistant PCa (CRPC), which has a median survival of only 13-23 months. Amongst recurrent CRPC, 17%-30% of patients develop neuroendocrine prostate cancer (NEPC), which is a PCa subtype characterized by a unique histology. NEPC exhibits a loss of AR signaling during neuroendocrine transdifferentiation which results in resistance to AR-targeted therapies and gain of cell characteristics resembling poorly differentiated neuroendocrine tumors. Despite advances in the understanding of NEPC development, treatment options remain limited, with platinum-based chemotherapy as the first-line treatment for both de novo and treatment-induced NEPC. However, response to first-line chemotherapy in NEPC is short, with a median survival of only seven months. The poor prognosis of NEPC is attributed in part to late diagnosis and a lack of effective therapeutic agents. Our previous work demonstrated that NEPC and AR-negative PCa exhibit higher dependency on the lipid kinase PIKfyve than AR-positive CRPC. Thus, development of PIKfyve inhibitory therapies targeting the emergent vulnerabilities of NEPC or AR-negative forms of PCa is a promising approach. Using a proteolysis targeting chimera (PROTAC) technology, we designed a class of PIKfyve specific degrader. The in vitro degradation efficiency were determined by immunoblotting, and DC50s (degradation concentration at 50%) were calculated for top candidates. Pharmacokinetic and pharmacodynamic were evaluated for in vivo study. In summary, we have developed a class of PIKfyve specific degrader using the E3 ligase von Hippel-Lindau (VHL) as a ligand via a diverse set of linkers. Mechanistic studies revealed that it induced PIKfyve degradation in a VHL- and proteasome-dependent manner. Citation Format: Yuanyuan Qiao, Chungen Li, Yang Zheng, Xia Jiang, Sarah Nicole Yee, Caleb Cheng, Yi Bao, Yuping Zhang, Yuzhuo Wang, Zhen Wang, Ke Ding, Arul Chinnaiyan. Development of the lipid kinase PIKfyve PROTAC degrader against neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2898.

Abstract 6268: A study of orphan nuclear receptor SHP (NR0B2) in prostate cancer progression

Abstract Prostate cancer (PCa) is a significant male cancer in many countries accounting for around 14% of new cancer cases globally in 2020 and ranked as 3rd common cancer in males in Hong Kong. The major risk factors include old age, high-fat diet, and genetics. Compared to other cancers, PCa is unique as its initial and advanced growth is androgen dependent. As tumor progresses, it accumulates numerous genetic alterations. Main therapeutic options include surgery, radiotherapy and or active surveillance. Upon treatment failure or when metastasis develops, androgen-deprivation therapy (ADT) with the use of potent androgen receptor (AR) antagonists and androgen biosynthesis inhibitors (e.g. Enzalutamide and abiraterone acetate) aiming to suppress AR signaling axis are the standard treatment options. However, the effect of these treatments is short-lived, in which nearly all patients will inevitably relapse to a hormone-independent and metastatic stage known as metastatic castration-resistant prostate cancer (mCRPC) within few years and further drive progression to a more lethal subtype, described as treatment-induced neuroendocrine prostate cancer (NEPC). The treatment options are limited and therefore resulted in high mortality, representing an emerging clinical problem. Recent studies have illustrated that NEPC progression follows a lineage plasticity model with a phenotypic transition to AR loss and neuroendocrine transdifferentiation. Our preliminary study has identified a nuclear receptor NR0B2 (SHP, small heterodimer partner SHP), which is a unique ligand-independent orphan nuclear receptor without a DNA-binding domain, that displays a significant up-regulation in clinical NEPC and prostate cancer cells with NEPC phenotype. Mechanistic studies revealed that SHP could directly interact with AR utilizing its NR Box1 motif while inducing repression on the AR transactivation via its another NR Box2 motif. Based on this, we conducted in vitro growth studies and revealed that NR0B2 overexpression could promote growth differentially in AR-negative PCa cells. However, AR-positive PCa cells were insensitive to AR blockade, providing supporting evidence that NR0B2 may be involved in repressing AR activity in prostate cancer cells. Multiple key NEPC and oncogenic TGFβ signaling markers showed significant upregulation in gene expression. Based on this, we hypothesize that upregulation of NR0B2 could play an important role in driving the advanced progression of CRPC via its direct interference of AR signaling axis and through other AR-independent signaling pathways, including activation of TGFβ signaling. (Study supported by a CUHK Direct Grant for Research 2022-2023, Project No. 2022.081) Citation Format: Hau Tak Daniel Lam, Franky Leung Chan. A study of orphan nuclear receptor SHP (NR0B2) in prostate cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6268.

Abstract 3232: LSD1 inhibition transcriptionally reprograms neuroendocrine prostate cancer exposing unique therapeutic vulnerabilities

Abstract Therapeutics have been developed to target castration-resistant prostate cancer (CRPC) classified as adenocarcinoma (CRPC-Adeno). However, an increasing frequency of CRPC-Adeno tumors progress to the highly aggressive and lethal neuroendocrine prostate cancer (NEPC) by acquiring a neuroendocrine (NE) phenotype as a mechanism of therapeutic resistance. This transformation from CRPC-Adeno to NEPC requires distinct epigenetic reprogramming by lysine-specific demethylase 1 (LSD1), which can be exploited for development of novel therapies to target NEPC. LSD1 is upregulated in NEPC and promotes a stem-like transition state through lineage plasticity which enables the cancer cell to undergo NE differentiation. We have shown that LSD1 inhibition reduces the NE program, driving NEPC towards a non-neuroendocrine state through ASCL1 suppression and YAP1 re-expression. This less aggressive non-neuroendocrine state exposes unique vulnerabilities for the development of novel combination therapies to treat this lethal disease. Citation Format: Sumer M. Jasmine, Adel Mandl, Susan L. Dalrymple, Sunghyun Kim, Jennifer Dias, Maria Kleppe, Cassandra Celatka, Amy Tapper, Ilsa Coleman, Peter Nelson, Hugh Rienhoff, Samuel R. Denmeade, W. Nathaniel Brennen. LSD1 inhibition transcriptionally reprograms neuroendocrine prostate cancer exposing unique therapeutic vulnerabilities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3232.

Abstract 6020: GPC3-targeted radiopharmaceutical therapy for neuroendocrine prostate cancer

Abstract Introduction: Glypican-3 (GPC3) is a membrane-anchored oncofetal protein with minimal expression in normal tissues. Besides hepatocellular carcinoma, upregulation of GPC3 protein has been observed in a significant subset of treatment-emergent neuroendocrine prostate cancer (NEPC), which accounts for to 30% of prostate cancer cases refractory to anti-androgen and other therapies. The differential expression of GPC3 between NEPC cells and normal tissues provides a theranostic opportunity for targeted radiopharmaceutical therapy (RPT). Methods: The novel RPT agent RYZ-GPC3 comprises a small macrocyclic peptide binder with high affinity to GPC3 linked with a tetraxetan moiety capable of chelating a variety of radioisotopes. The expression of GPC3 in NEPC cells was assessed by flow cytometry and immunohistochemistry (IHC). The affinity of peptide binders to GPC3 was determined by surface plasma resonance (SPR) and radioligand binding assays. In vivo biodistribution of [177Lu]Lu-RYZ-GPC3 and anti-tumor therapy with [177Lu]Lu-RYZ-GPC3 or [225Ac]Ac-RYZ-GPC3 were performed in NEPC xenografts. Results: The novel agent is a highly potent and selective peptide binder to GPC3 of human, mouse and NHP origins, and is compatible with multiple radiometal isotopes. In vivo biodistribution study of [177Lu]Lu-RYZ-GPC3 in GPC3-positive NEPC xenografts showed sustained tumor uptake of 10.8, 12.6, 5.1, and 2.2 %ID/g at 2, 24, 72 and 168 hours post dose, respectively, with fast renal clearance. Minimal or no uptake was observed in other normal tissues. A single injection of [225Ac]Ac-RYZ-GPC3 (11.1 kBq) resulted in significant tumor growth inhibition (TGI 109%) with durable regression and prolonged survival. All treatments were well tolerated. Conclusion: Preclinical in vitro and in vivo data demonstrated the potential of the novel binder as a theranostic agent for the treatment of patients with GPC3+ NEPC. Citation Format: Renee Clift, Fanching Lin, Katrina Salvador, Matt Guest, Daniel Kim, Guangzhou Han, Gary Li. GPC3-targeted radiopharmaceutical therapy for neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6020.