Preclinical Models Of Prostate Cancer Research Articles

Kinesin Facilitates Phenotypic Targeting of Therapeutic Resistance in Advanced Prostate Cancer.

Understanding the mechanisms underlying resistance is critical to improving therapeutic outcomes in patients with metastatic castration-resistant prostate cancer (mCRPC). Previous work showed dynamic interconversions between epithelial-mesenchymal transition (EMT) to mesenchymal-epithelial transition (MET) defines the phenotypic landscape of prostate tumors, as a potential driver of emergence of therapeutic resistance. In this study, we use in vitro and in vivo preclinical MDA PCa PDX models of resistant human prostate cancer to determine molecular mechanisms of cross-resistance between anti-androgen therapy and taxane chemotherapy, underlying the therapeutically resistant phenotype. Transcriptomic profiling revealed that resistant and sensitive prostate cancer C4-2B cells have a unique differential gene signature response to cabazitaxel. Gene pathway analysis showed that sensitive cells exhibit increase in DNA damage, while resistant cells express genes associated with protein regulation in response to cabazitaxel. These PDX specimens are from patients who have metastatic lethal CRPC, treated with androgen-deprivation therapy (ADT), antiandrogens and chemotherapy including 2nd line taxane chemotherapy, cabazitaxel. Immunohistochemistry revealed high expression of E-cadherin and low expression of vimentin resulting in re-differentiation toward an epithelial phenotype. Furthermore, the mitotic kinesin-related protein (HSET) involved in microtubule binding and the SLCO1B3 transporter (implicated in cabazitaxel intracellular transport), associated with resistance in these prostate tumors. Combinational targeting of kinesins (ispinesib) with cabazitaxel was more effective than single monotherapies in inducing cell death in resistant prostate tumors. Implications: Our findings are of translational significance in identifying kinesin as a novel target of cross-resistance, towards enhancing therapeutic vulnerability and improved clinical outcomes in patients with advanced prostate cancer.

Enhancing surgical outcomes: accurate identification and removal of prostate cancer with B7-H3-targeted NIR-II molecular imaging.

One of the main reasons for prostate cancer (PCa) recurrence is the difficulty in identifying and removing cancerous lesions during surgery. Accurately localizing and excising cancerous tissue remains a significant challenge. The second near-infrared window (NIR-II, 1000-1700nm) fluorescence offers enhanced resolution, a high signal-to-noise ratio, and the potential for deeper tissue penetration. However, this technology is not currently employed for intraoperative imaging of PCa. This study aims to construct a new NIR-II probe targeting B7-H3 (AbB7-H3-800CW) for accurate intraoperative identification and resection of PCa. Based on the differential expression of B7-H3 in PCa, we designed a novel imaging probe to accurately identify and guide the resection of preclinical PCa models and ex vivo human PCa tissues using NIR-II fluorescence imaging technology. Analyzing tissue samples from 60 clinical cases of PCa, along with benign prostatic hyperplasia and normal prostate tissue from 22 cases, we observed a significant difference in B7-H3 protein expression levels (P < 0.001). Subcutaneous and orthotopic mouse models of PCa were imaged using NIR-II fluorescence after AbB7-H3-800CW injection, showing promising results with successful tumor targeting and high-contrast images achieved within 24-48h post-injection. The imaging also enabled the detection of occult PCa lesions approximately 1mm in diameter. In addition, imaging analysis of human PCa and adjacent tissues using AbB7-H3-800CW incubation revealed that cancer tissues exhibited a significantly higher fluorescence intensity than adjacent tissues (P < 0.05), which was conducive to the evaluation of tumor resection margin in vitro. The findings revealed that B7-H3 was a compelling imaging target for PCa. The AbB7-H3-800CW molecular imaging probe is capable of accurately identifying PCa lesions and guiding their removal. This approach can potentially reduce the rate of surgical margins under NIR-II fluorescence guidance.

Abstract 3223: Embryonic ectoderm development (EED) inhibitor APG-5918 (EEDi-5273) and MDM2 inhibitor alrizomadlin (APG-115) synergistically inhibit tumor growth in preclinical models of prostate cancer (PCa)

Abstract Advanced PCa, especially castration-resistant PCa, represents an urgent unmet treatment need. Dysregulation of the polycomb repressive complex 2 (PRC2), which mediates trimethylation of histone H3 at lysine 27 (H3K27me3) and leads to gene silencing, is common in PCa and correlates with poor prognosis. EED, a core PRC2 component, is crucial for histone methyltransferase activity. MDM2, a negative regulator of p53, is often amplified or overexpressed in PCa and associated with metastasis and poor clinical outcomes. We evaluated antitumor activity and molecular mechanisms of EED inhibitor APG-5918/EEDi-5273 and MDM2 selective inhibitor alrizomadlin in preclinical PCa models. Human castration-resistant (22Rv1) and androgen-dependent (LNCaP) PCa cell lines were used in antiproliferation assays. Cell viability was determined by CellTiter-Glo luminescent assays. Western blotting was used to explore mechanisms of action. Subcutaneous 22Rv1 and LNCaP cell line-derived xenograft (CDX) models were established to evaluate antitumor effects of APG-5918 and alrizomadlin in vivo. Single-agent APG-5918 or alrizomadlin had limited inhibition on PCa cell growth; combined, they demonstrated synergistic antitumor activity. In the 22Rv1 CDX model, single-agent alrizomadlin (100 mg/kg) or APG-5918 (100 mg/kg) administered for 26 days exerted no/limited antitumor activity, with treatment-to-control (T/C) values of 93.39% and 49.89%, respectively. In contrast, the doublet enhanced antitumor activity (T/C value, 33.22%), with a synergistic index of 1.40. In the LNCaP CDX model, APG-5918 (100 mg/kg) administered for 28 days exhibited minimal antitumor effects (T/C value on last day of dosing, 80.32%). Alrizomadlin (100 or 50 mg/kg) showed limited antitumor activity (T/C value, 47.61%). Combined treatment significantly enhanced antitumor activity (T/C value, 15.69%), with a synergistic index of 2.44. Regarding putative mechanisms, western blot analyses showed that APG-5918 downregulated oncogenic drivers and DNA methylation factors (UHRF1, DNMT1) and on-target-related pharmacodynamic markers (H3K27me3, EED, EZH2). Alrizomadlin markedly downregulated UHRF1 and DNMT1, and upregulated p53 and p21 expression. Combined treatment further enhanced downregulation of DNMT1, UHRF1, cell cycle pathway proteins (pRb, CDK6), antiapoptotic protein MCL-1, and synergistically increased cleavage of PARP-1, a marker of apoptosis. In summary, we show that targeting EED and MDM2 synergistically enhances antitumor activity in PCa cell lines and CDX models. Mechanistically, this combination likely modulated pathways related to DNA methylation, cell cycle, and apoptosis. The findings provide a scientific rationale for future clinical development of APG-5918 and alrizomadlin for PCa patients. Citation Format: Yan Yin, Yun Yang, Eric Liang, Baisong Li, Hengbang Wang, Dajun Yang, Yifan Zhai. Embryonic ectoderm development (EED) inhibitor APG-5918 (EEDi-5273) and MDM2 inhibitor alrizomadlin (APG-115) synergistically inhibit tumor growth in preclinical models of prostate cancer (PCa) [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 3223.

Abstract 103: Prostate cancer bone metastasis: Therapeutic targeting of tumor associated macrophages

Abstract Introduction: Castration-resistant bone metastatic prostate cancer is a morbid and deadly disease with an exceedingly low response rates to available immunotherapies. Understanding the mechanisms behind immune evasion and tumor progression is critical to improving therapy. Historically, bone metastases have been challenging to model in the laboratory. Our foundational work was built upon fresh patient samples taken directly from the operating room for analysis across multiple platforms: IHC, single cell expression profiling, and spatial transcriptomics. We compared tumors from patients with bone metastatic disease to tumors from patients with disease localized to the prostate. Our work (Cancer Cell, 2021 and Nature Communications, 2023) has consistently pointed towards dysregulated myeloid populations within the tumor microenvironment, particularly TREM2+ tumor associated macrophages (TAMs), as key drivers of disease progression. Methods: Our patient samples and murine pre-clinical models of prostate cancer highlighted several specifically upregulated molecules and pathways in TAMs. Here we focus on TAMs in vitro and in vivo using a new and genetically tractable myeloid model to interrogate the mechanistic role of key pathways, and how they may contribute to T-cell immune suppression. The ER-Hoxb8 system of conditional myeloid differentiation permitted the generation of isogenic cell lines to interrogate the roles of key molecules TREM2, MSR1, APOE, and MERTK through overexpression or CRISPR/Cas9 knockout. Results: Using a system of co-culture in vitro, we quantified the role of these proteins in suppressing T-cell proliferation and cytokine production, as well as their role in TAM differentiation and function. In vivo, these lines were co-injected subcutaneously with syngeneic RM1-BM3 tumor cells to quantify their effect on tumor growth and T-cell suppression in vivo. In addition to localized subcutaneous tumors, bone metastatic disease was established by intracardiac injection. Furthermore, established tumors were treated with TAM-directed small molecule therapy (e.g., MERTK inhibition) as well as immune checkpoint inhibition (anti-PD1) alone, and in combination. Conclusions: TAMs are immune suppressive myeloid cells that are not found in normal tissues. They are specifically recruited to tumors and highly enriched in bone metastatic disease. Transcriptomic analyses highlighted signaling pathways potentially amenable to productive therapeutic targeting. The ER-Hoxb8 system was highly effective in generating a genetically tractable model of TAM for study in vitro and in vivo. Our work supports the hypothesis that the specific targeting of TAMs, by focusing on critical signaling pathways, can be effective in the treatment of pre-clinical models of prostate cancer. This new approach merits further study as a potential strategy for the treatment of patients with bone metastases. Citation Format: Hanyu Zhang, Shenglin Mei, Nathan E. Jeffries, Douglas M. Dahl, Chin-Lee Wu, Philip J. Saylor, David B. Sykes. Prostate cancer bone metastasis: Therapeutic targeting of tumor associated macrophages [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 103.

Abstract 6034: PSMA targeted alpha radiopharmaceutical [211At]PSAt-3 inhibits tumor growth in a preclinical model of prostate cancer

Abstract Introduction: Prostate cancer continues to be a highly prevalent cancer diagnosis among men and a leading cause of cancer related deaths worldwide. With the introduction[177Lu]Lu-PSMA-617, targeted radionuclide therapy has proven successful in increasing survival time for patients with metastasized castration resistant prostate cancer. However, despite encouraging results, such patients tend to develop progressive disease, and thus, enhanced efficacy is warranted. To this end, the use of radiopharmaceuticals harnessing alpha-emitters is a promising venue due to the potent energy deposition and short range of alpha particles in tissue. Here, we employ the PSMA targeting vector, [211At]PSAt-3, for targeted alpha radionuclide therapy in a preclinical prostate cancer model. Methods: [211At]PSAt-3, a structural derivative of PSMA-617, in which the L-2-naphtylalanine was replaced by L-3-[211At]astato-phenylalanine, was obtained by electrophilic [211At]astatodesilylation. Evaluation of [211At]PSAt-3 was conducted in male inbred nude mice of Balb/c background xenografted subcutaneously with human prostate cancer cells (LNCaP). Prior biodistribution studies were carried out with approximately 100 kBq intravenous injections, and subsequent biodistribution 2, 6 and 24h post injection (P.I.). For establishment of therapeutic effect, a single intravenous dose of [211At]PSAt-3 was administered. To asses hematological toxicity, blood cell composition was assessed weekly. Results: Favorable tumor uptake of 15.2±6 %ID/g was observed 2h after injection of [211At]PSAt-3 in LNCaP xenografted nude mice, with subsequent 9±5.1% ID/g and 6.4±2.4% ID/g 6 and 24h P.I., respectively. [211At]PSAt-3 cleared mainly by the kidneys, in which uptake was 72, 38 and 6% ID/g at 2, 6 and 24h P.I., respectively. Thyroid/throat uptake remained low at ~0.1% ID for all timepoints investigated, indicating a low degree of de-astatination. Initial efficacy studies using a single intravenous dose of 0.5 MBq (~20 MBq/kg) demonstrated significant growth delay and tumor volume reduction compared with control mice (saline). Blood platelet count was reduced after administration of [211At]PSAt-3 and subsequently recovered. No signs of severe toxicity, and no significant weight loss between control and treated mice was observed, suggesting that the treatment is well tolerated. Conclusion: 0.5 MBq [211At]PSAt-3 was well tolerated in mice and demonstrated tumor volume reduction and significant delay of tumor growth. These findings suggest [211At]PSAt-3 as a promising candidate for clinical translation. Citation Format: Lars Hvass, Marius Müller, Anne Clausen, Matthias Herth, Andreas Kjaer. PSMA targeted alpha radiopharmaceutical [211At]PSAt-3 inhibits tumor growth in a preclinical model of 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 6034.

Abstract 170: Targeting of macrophage PI3Kγin prostate cancer using Eganelisib (IPI-549) reprograms immune-suppressive infiltrating macrophages to enhance anti-tumor immune responses and promote immunologically mediated tumor growth

Abstract Background: Prostate cancer (PCa) is traditionally considered an immunologically 'cold’ indication, as evidenced in part by significant infiltration of immunosuppressive tumor associated macrophages (TAMs) and few activated effector CD8+ T cells. Attempts to (re)invigorate an anti-prostate cancer immune response with immune checkpoint blockade (ICB) such as anti-CTLA-4 and anti-PD-1 have been largely ineffective clinically, despite promising results in other cancers. This is likely due to a multitude of immunosuppressive cell types and secreted factors within the tumor microenvironment (TME) that diminish T cell activation and trafficking. Reducing the immunosuppressive burden intratumorally by targeting TAMs is a clinically attractive approach and offers opportunity to sensitize PCa to immune checkpoint blockade. While PI3K signaling is ubiquitous in most cell types, specific catalytic isoforms and regulatory elements are differentially expressed depending on cell type, with PI3Kγ being significantly enriched in myeloid cells and therefore offering a unique therapeutic opportunity for specific targeting. Methods: Utilizing novel syngeneic prostate cancer tumors, PI3Kγ deletion and antagonism using Eganelisib (a small molecule inhibitor for PI3Kγ), we tested our hypothesis that targeting PI3Kγ signaling in PCa TAMs would lead to tumor growth inhibition and anti-tumor immune responses. Results: We show here that PCa tumor cells do not express the PI3Kγ isoform and, therapeutic inhibition of PI3Kγ with Eganelisib reduces the TAM suppressive phenotype. We also show PI3Kγ signaling is essential to monocyte anti-apoptotic signaling, and inhibition of PI3Kγ can enhance anti-tumor immune responses in preclinical models of PCa. Specifically, inhibition of PI3Kγ alone is sufficient to enhance anti-tumor immune responses in the less aggressive B6CaP PCa model, but insufficient in the more aggressive RM-1 PCa model. However, treatment of RM-1 tumors with Eganelisib produces improved tumor control when combined with anti-PD-1 therapy, relative to Eganelisib or anti-PD1 as a monotherapy. Conclusions: Altogether, these data highlight the integral role of PI3Kγ signaling in TAMs and the potential for therapeutic targeting with Eganelisib to sensitize PCa to ICB. Citation Format: Kenneth M. Adusei, Thomas R. Nirschl, Alex J. Lee, Fan Shen, Xiaoxu Wang, Monali Praharaj, Jade Alvarez, Iyana Gross, Kara A. Lombardo, Tamara L. Lotan, Judith A. Varner, Jelani C. Zarif. Targeting of macrophage PI3Kγin prostate cancer using Eganelisib (IPI-549) reprograms immune-suppressive infiltrating macrophages to enhance anti-tumor immune responses and promote immunologically mediated tumor growth [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 170.

A Compound that Inhibits Glycolysis in Prostate Cancer Controls Growth of Advanced Prostate Cancer.

Metastatic castration-resistant prostate cancer remains incurable regardless of recent therapeutic advances. Prostate cancer tumors display highly glycolytic phenotypes as the cancer progresses. Non-specific inhibitors of glycolysis have not been utilized successfully for chemotherapy, because of their penchant to cause systemic toxicity. This study reports the preclinical activity, safety, and pharmacokinetics of a novel small molecule preclinical candidate, BKIDC-1553, with antiglycolytic activity. We tested a large battery of prostate cancer cell lines for inhibition of cell proliferation, in vitro. Cell cycle, metabolic and enzymatic assays were used to demonstrate their mechanism of action. A human PDX model implanted in mice and a human organoid were studied for sensitivity to our BKIDC preclinical candidate. A battery of pharmacokinetic experiments, absorption, distribution, metabolism, and excretion experiments, and in vitro and in vivo toxicology experiments were carried out to assess readiness for clinical trials. We demonstrate a new class of small molecule inhibitors where antiglycolytic activity in prostate cancer cell lines is mediated through inhibition of hexokinase 2. These compounds display selective growth inhibition across multiple prostate cancer models. We describe a lead BKIDC-1553 that demonstrates promising activity in a preclinical xenograft model of advanced prostate cancer, equivalent to that of enzalutamide. BKIDC-1553 demonstrates safety and pharmacologic properties consistent with a compound that can be taken into human studies with expectations of a good safety margin and predicted dosing for efficacy. This work supports testing BKIDC-1553 and its derivatives in clinical trials for patients with advanced prostate cancer.

Stat5 induces androgen receptor (AR) gene transcription in prostate cancer and offers a druggable pathway to target AR signaling.

Androgen receptor (AR) drives prostate cancer (PC) growth and progression, and targeting AR signaling is the mainstay of pharmacological therapies for PC. Resistance develops relatively fast as a result of refueled AR activity. A major gap in the field is the lack of understanding of targetable mechanisms that induce persistent AR expression in castrate-resistant PC (CRPC). This study uncovers an unexpected function of active Stat5 signaling, a known promoter of PC growth and clinical progression, as a potent inducer of AR gene transcription. Stat5 suppression inhibited AR gene transcription in preclinical PC models and reduced the levels of wild-type, mutated, and truncated AR proteins. Pharmacological Stat5 inhibition by a specific small-molecule Stat5 inhibitor down-regulated Stat5-inducible genes as well as AR and AR-regulated genes and suppressed PC growth. This work introduces the concept of Stat5 as an inducer of AR gene transcription in PC. Pharmacological Stat5 inhibitors may represent a new strategy for suppressing AR and CRPC growth.

Effect of combined treatment with sipuleucel-T and IL-15 on tumor control, tumor-infiltrating immune effectors, and key mediators of immunoresistance in a preclinical prostate cancer model.

177 Background: Sipuleucel-T (sip-T) is an autologous therapeutic vaccine produced using a tumor antigen-cytokine fusion protein, and the only FDA approved cellular immunotherapy for metastatic castration-resistant prostate cancer (mCRPC) patients. Sip-T significantly improves overall survival (OS), but has limited impact on PSA and radiographic responses. Here, we present the first high dimensional analysis of the sip-T product; we used a preclinical model of human prostate cancer to show the effects of IL-15 on anti-tumor efficacy, tumor infiltration of effector cells, and reversal of immunosuppressive mediators. Methods: We performed a comprehensive assessment of the sip-T product collected from prostate cancer patients using mass cytometry (CyTOF). Control and IL-15 stimulated sip-T were evaluated, and changes in leukocyte subsets as well as markers of activation and exhaustion were identified. Using a preclinical mouse model of human prostate cancer, we examined the effects of IL-15 treatment on sip-T. CyTOF, flow cytometry, RNAseq, and qPCR were used to evaluate the effects of IL-15 on sip-T phenotype, function, and in vitro and in vivo efficacy. Results: CyTOF analysis revealed that CD3+ T cells constituted the highest proportion of sip-T, followed by B-cells, natural killer (NK) cells, NKT, and monocytes, with only a small percentage of dendritic cells. Following sip-T stimulation with IL-15, a significant expansion and activation of CD8+ T-cell and NK cell populations was seen. Co-culture of sip-T with IL-15 and control or prostate-relevant antigens showed significant activation and expansion of CD8 T and NKT cells in an antigen-specific manner, with significantly increased tumor cytotoxicity and evidence of antigen spread. IL-15 treatment combined with sip-T in a preclinical mouse model showed significant suppression of tumor growth compared to sip-T alone, with increased tumor-infiltrating lymphocytes (TIL). A significant increase in interferon (IFN)-γ producing CD8+ T and NKT cells within the tumor microenvironment was seen in the IL-15 group. Tumor transcriptomic analyses revealed IL-15 treatment was able to reverse immunoresistance, with significant decreases in PD-L1, CTLA, TIGIT, B7-H3, and others compared to sip-T alone. Conclusions: This is the first study to evaluate the sip-T product using CyTOF, and the first pre-clinical in vivo prostate tumor modeling of sip-T. IL-15 treatment significantly enhances anti-tumor efficacy, effector immune cell activation and tumor infiltration, and reverses key mediators of immune suppression. Studies with modified IL-15 cytokines are ongoing and will be presented.

Palladium-Mediated S-Arylation of Cysteine Residues with 4-[18F]Fluoroiodobenzene ([18F]FIB).

Transition-metal-mediated bioconjugation chemistry has been used extensively to design and synthesize molecular probes to visualize, characterize, and quantify biological processes within intact living organisms at the cellular and subcellular levels. We demonstrate the development and validation of chemoselective [18F]fluoro-arylation chemistry of cysteine residues using Pd-mediated S-arylation chemistry with 4-[18F]fluoroiodobenzene ([18F]FIB) as an aryl electrophile. The novel bioconjugation technique proceeded in excellent radiochemical yields of 73-96% within 15 min under ambient and aqueous reaction mixture conditions, representing a versatile novel tool for decorating peptides and peptidomimetics with short-lived positron emitter 18F. The chemoselective S-arylation of several peptides and peptidomimetics containing multiple reactive functional groups confirmed the versatility and functional group compatibility. The synthesis and radiolabeling of a novel prostate-specific membrane antigen (PSMA) binding radioligand [18F]6 was accomplished using the novel labeling protocol. The validation of radioligand [18F]6 in a preclinical prostate cancer model with PET resulted in favorable accumulation and retention in PSMA-expressing LNCaP tumors. At the same time, a significantly lower salivary gland uptake was observed compared to clinical PSMA radioligand [18F]PSMA-1007. This finding coincides with ongoing discussions about the molecular basis of the off-target accumulation of PSMA radioligands currently used for clinical imaging and therapy of prostate cancer.

PC Kz is the novel human prostate cancer model in vitro and in vivo

BACKGROUND: The use of relevant in vitro and in vivo model systems is important in preclinical studies of anticancer agents. The process of creating tumor models is methodically complicated and has a number of disadvantages. Among tumor models of prostate cancer, the most accessible are 2D models (DU145, 22Rv1, PC3, LNCaP, VCaP cell lines), their xenograft models in immunodeficient mice and some patient-derived xenograft models. However, this panel of experimental models is not perfect and needs further expansion.&#x0D; AIM: To create a new preclinical prostate cancer model, characterize it (morphology, tumorigenicity, tumor growth kinetics in vivo, verification of prostate-specific membrane antigen expression status, testosterone production, sensitivity to CYP17A1 inhibitors), and develop resistance to the steroid CYP17A1 inhibitor — abiraterone.&#x0D; METHODS: CYP17A1 expression in PC Kz cell line was evaluated by reverse transcription polymerase chain reaction. Testosterone concentration was determined with an enzyme-linked immunosorbent assay. The sensitivity to antitumor agents was studied with the MTT test. Tumorigenicity was evaluated by transplantation of PC Kz cell line into Balb/c nude mice. The prostate-specific membrane antigen expression status was assessed using the indirect reaction of surface immunofluorescence.&#x0D; RESULTS: The PC Kz cell line is characterized by a high level of CYP17A1 messenger RNA expression, comparable to that of the commercial 22Rv1 cell line. Immunophenotypic analysis demonstrated negative prostate-specific membrane antigen expression status of PC Kz cell line. A significant decrease (18%) in testosterone concentration in vitro was found, compared to the value in the control. This effect can be associated with the suppression of CYP17A1 gene expression.&#x0D; The studied PC Kz cell line is tumorigenic in Balb/c nude mice (100% tumorigenicity was detected during the first passage at a transplantation dose of 107 cells/mouse). A pathomorphological study of the structures of the obtained subcutaneous PC Kz xenografts verified their identity to the histological image of human prostate cancer. Furthermore, PC Kz/AA cell line was obtained, resistant to abiraterone; the index of resistance was 3.4.&#x0D; CONCLUSION: The derived PC Kz cell line was adapted for in vitro and in vivo growth, characterized by the main biological parameters, and can be recommended as an adequate test system to use in preclinical studies of new antitumor agents for the human prostate cancer treatment.

Bioanalysis of the Ex Vivo Labile PACE4 Inhibitory Peptide Ac-[d-Leu]LLLRVK-Amba in Whole Blood Using Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry Quantification.

The calcium-dependent serine endoprotease PACE4 is evaluated as a therapeutic target for prostate cancer. The peptide Ac-[d-Leu]LLLRVK-amba inhibits PACE4 with high affinity and has shown efficacy in preclinical mice xenograft models of prostate cancer. To support in vivo examinations of the potential therapeutic peptide Ac-[d-Leu]LLLRVK-amba, we established a highly sensitive assay for its quantification in mouse whole blood microsamples based on UPLC-MS/MS determination. Ac-[d-Leu]LLLRVK-amba was very labile during sample processing, which was particularly pronounced in plasma. High resolution mass spectrometric investigations of the metabolism/degradation in plasma revealed that no peptide bond hydrolysis generated products were formed, leaving the cause of the observed consumption of the peptide elusive. As a consequence, whole-blood quantification was developed relying on the immediate snap-freezing of blood samples after collection and immediate sample processing after serial thawing to ensure accurate and reliable quantification. The assay was validated according to the applicable recommendations of the FDA and EMA in a range of 10-10,000 ng/mL and applied to determine the pharmacokinetics of Ac-[d-Leu]LLLRVK-amba after intravenous and intraperitoneal administration to mice. Individual pharmacokinetic profiles were assessed using four microsamplings per animal. Intraperitoneal absorption was found to be efficient, demonstrating that this well-manageable route of administration is feasible for preclinical efficacy experiments with Ac-[d-Leu]LLLRVK-amba.

P-170 - Evaluation of lysine modifications in the PSMA-targeting pharmacophore using positron emission tomography imaging in a preclinical model of human prostate cancer

P-170 - Evaluation of lysine modifications in the PSMA-targeting pharmacophore using positron emission tomography imaging in a preclinical model of human prostate cancer

Abstract A052: Discovery and characterization of a p300-selective degrader demonstrates potent anti-tumor activity in preclinical models of prostate cancer

Abstract Strategies targeting androgen receptor (AR) in the treatment of prostate cancer (PrCa) have shown clear clinical benefit. However, a variety of AR-signaling bypass mechanisms ultimately result in progression to metastatic castrate resistant prostate cancer (mCRPC), and therapies for these patients remain an urgent unmet need. The histone acetyltransferase paralogs p300 and CBP, key coactivators of AR, are currently under investigation as attractive therapeutic targets to abrogate aberrant AR signaling but face a challenging clinical toxicity profile in hematopoietic cells. We postulate that p300 serves as a key regulator of AR signaling, and by sparing CBP we should retain potency against AR-driven PrCa while providing a larger safety margin. We discovered potent heterobifunctional degraders with demonstrated selectivity for p300 over CBP. Our tool compound exhibits degradation of p300 within 2 hours (DC50 = 7.5nM, Dmax = 79%) with minimal impact on CBP at 48 h (DC50 &amp;gt;1uM, Dmax = 5%). The AR/ARv7 driven VCaP PrCa cell line demonstrated exceptional sensitivity to this p300 degrader in proliferation assays (gIC50 = 0.8 nM) comparable to the dual p300/CBP inhibitor, CCS-1477, or the AR degrader, ARV-110 and undergoes a cytotoxic response. Profiled against known AR target genes, our degrader was able to suppress KLK2, KLK3 and FKBP5 transcript levels akin to CCS-1477 in both LNCaP and VCaP PrCa cell lines, supporting the hypothesis that p300, not CBP, acts as the primary coactivator of AR signaling. In addition, our compound led to greater downregulation of full-length AR, ARv7 and cMyc compared to CCS-1477. Subsequent assessment in an in vivo model (VCaP CDX) demonstrated tumor growth inhibition at the highest dose tested (88%; p=2.6e-4). Lastly, we profiled our p300 degrader in human bone marrow derived hematopoietic progenitor colony-forming assays where we observed a significant reduction in toxicity (IC50 = 3.9uM) compared to either CCS-1477 (IC50 = 121nM) or a dual degrader tool compound (IC50 = 16nM), supporting the hypothesis that a p300-specific mechanism will offer an improved therapeutic index. Treatment with our p300-specific degrader resulted in a potent anti-tumor effect on PrCa cells both in vitro and in vivo, comparing favorably to both dual p300/CBP inhibitor or AR degrader strategies. Furthermore, selective degradation of p300 has the potential to minimize toxicity to hematopoietic cells commonly observed with dual targeting of CBP and p300. Taken together, these results support the role p300 may play in driving AR-mediated signaling in PrCa and demonstrate that a p300-specific degrader may serve as an effective therapeutic modality in this disease setting. Citation Format: Mike Russell, Cassandra L Lowenstein, Xuqing Zhang, Jeremy Roach, Jianing Song, Rakesh Nagilla, Peter Orth, Matt Tudor, Qiaolin Deng, Zhihua Sui, Corey Strickland, Larry J Jolivette, E Scott Priestley, Helai P Mohammad. Discovery and characterization of a p300-selective degrader demonstrates potent anti-tumor activity in preclinical models of prostate cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A052.

Clinically Translatable Hyperpolarized 13C Bicarbonate pH Imaging Method for Use in Prostate Cancer.

Solid tumors such as prostate cancer (PCa) commonly develop an acidic microenvironment with pH 6.5-7.2, owing to heterogeneous perfusion, high metabolic activity, and rapid cell proliferation. In preclinical prostate cancer models, disease progression is associated with a decrease in tumor extracellular pH, suggesting that pH imaging may reflect an imaging biomarker to detect aggressive and high-risk disease. Therefore, we developed a hyperpolarized carbon-13 MRI method to image the tumor extracellular pH (pHe) and prepared it for clinical translation for detection and risk stratification of PCa. This method relies on the rapid breakdown of hyperpolarized (HP) 1,2-glycerol carbonate (carbonyl-13C) via base-catalyzed hydrolysis to produce HP 13CO32-, which is neutralized and converted to HP H13CO3-. After injection, HP H13CO3- equilibrates with HP 13CO2 in vivo and enables the imaging of pHe. Using insights gleaned from mechanistic studies performed in the hyperpolarized state, we solved issues of polarization loss during preparation in a clinical polarizer system. We successfully customized a reaction apparatus suitable for clinical application, developed clinical standard operating procedures, and validated the radiofrequency pulse sequence and imaging data acquisition with a wide range of animal models. The results demonstrated that we can routinely produce a highly polarized and safe HP H13CO3- contrast agent suitable for human injection. Preclinical imaging studies validated the reliability and accuracy of measuring acidification in healthy kidney and prostate tumor tissue. These methods were used to support an Investigational New Drug application to the U.S. Food and Drug Administration. This methodology is now ready to be implemented in human trials, with the ultimate goal of improving the management of PCa.

Ultrasound targeted microbubble destruction using docetaxel and Rose Bengal loaded Microbubbles for targeted Chemo-Sonodynamic therapy treatment of prostate cancer

Docetaxel (DTX) chemotherapy is commonly used in the treatment of patients with advanced prostate cancer demonstrating modest improvements in survival. As these patients are often elderly and the chemotherapy treatment is not targeted, it is often poorly tolerated. More targeted approaches that increase therapeutic efficacy yet reduce the amount of toxic chemotherapy administered are needed. In this manuscript, we investigate the potential of ultrasound targeted microbubble destruction (UTMD) to deliver a combination of docetaxel chemotherapy and Rose Bengal mediated sonodynamic therapy (SDT) in pre-clinical prostate cancer models. A Rose Bengal modified phospholipid was synthesized and used as a component lipid to prepare a microbubble (MB) formulation that was also loaded with DTX. The DTX-MB-RB formulation was used in the UTMD mediated treatment of androgen sensitive and androgen resistant 3D spheroid and murine models of prostate cancer. Results from the 3D spheroid experiments showed UTMD mediated DTX-MB-RB chemo-sonodynamic therapy to be significantly more effective at reducing cell viability than UTMD mediated DTX or SDT treatment alone. In an androgen sensitive murine model of prostate cancer, UTMD mediated DTX-MB-RB chemo-sonodynamic therapy was as effective as androgen deprivation therapy (ADT) at controlling tumour growth. However, when both treatments were combined, a significant improvement in tumour growth delay was observed. In an androgen resistant murine model, UTMD mediated DTX-MB-RB chemo-sonodynamic therapy was significantly more effective than standard DTX monotherapy. Indeed, the DTX dose administered using the DTX-MB-RB formulation was 91% less than standard DTX monotherapy. As a result, UTMD mediated DTX-MB-RB treatment was well tolerated while animals treated with DTX monotherapy displayed significant weight loss which was attributed to acute toxic effects. These results highlight the potential of UTMD mediated DTX-MB-RB chemo-sonodynamic therapy as a targeted, well tolerated alternative treatment for advanced prostate cancer.

UP49 - Anti-tumor effects of antipsychotic drug penfluridol in preclinical prostate cancer models

UP49 - Anti-tumor effects of antipsychotic drug penfluridol in preclinical prostate cancer models

P01 - Personalization of oncolytic virus therapy: Heterogeneous anti-tumor responses in preclinical prostate and bladder cancer models

P01 - Personalization of oncolytic virus therapy: Heterogeneous anti-tumor responses in preclinical prostate and bladder cancer models

The Balance Between the Therapeutic Efficacy and Safety of [177Lu]Lu-NeoB in a Preclinical Prostate Cancer Model.

Radiolabeled NeoB is a promising gastrin-releasing peptide receptor (GRPR)-targeting radiopharmaceutical for theranostics of GRPR-expressing malignancies, e.g., prostate cancer (PCa). The aim of this study was to evaluate the effect of different doses of [177Lu]Lu-NeoB on the balance between therapeutic efficacy and safety in a preclinical PCa model. To determine the efficacy of [177Lu]Lu-NeoB, PC-3 xenografted mice received 3 sham injections (control group) or 3 injections of 30 MBq/300 pmol, 40 MBq/400 pmol, or 60 MBq/600 pmol [177Lu]Lu-NeoB (groups 1, 2, and 3, respectively) 1 week apart. To quantify tumor uptake, single-photon emission computed tomography/computed tomography (SPECT/CT) imaging was performed 4 h after the first, second, and third injection on a separate group of animals. For safety evaluations, pancreatic and renal tissues of non-tumor-bearing mice treated with the abovementioned [177Lu]Lu-NeoB doses were evaluated 12 and 24 weeks post-treatment. Treatment of PC-3 tumors with all three studied [177Lu]Lu-NeoB doses was effective. Median survival times were significantly (p < 0.0001) improved for treatment groups 1, 2, and 3 versus the control group (82 days, 89 days, 99 days versus 19 days, respectively). However, no significant differences were observed between treatment groups. Quantification of SPECT/CT images showed minimal differences in the average absolute radioactivity uptake, especially after the third injection. Histopathological analysis revealed no clear signs of treatment-related pancreatic toxicity. For the kidneys, atrophy and fibrosis were observed for one animal from group 1 and a chronic inflammatory response was observed for both animals from group 3 at 24 weeks post-treatment. Treatment with [177Lu]Lu-NeoB is effective in a preclinical PCa model. Adjusting the administered dose could positively impact the risk-benefit balance as a higher dose might not lead to an increased therapeutic effect, but it may lead to an increase in toxicological effects in healthy organs such as the kidneys.

Poly-l-glutamic acid modification modulates the bio-nano interface of a therapeutic anti-IGF-1R antibody in prostate cancer

Modifying biological agents with polymers such as polyethylene glycol (PEG) has demonstrated clinical benefits; however, post-market surveillance of PEGylated derivatives has revealed PEG-associated toxicity issues, prompting the search for alternatives. We explore how conjugating a poly-l-glutamic acid (PGA) to an anti-insulin growth factor 1 receptor antibody (AVE1642) modulates the bio-nano interface and anti-tumor activity in preclinical prostate cancer models. Native and PGA-modified AVE1642 display similar anti-tumor activity in vitro; however, AVE1642 prompts IGF-1R internalization while PGA conjugation prompts higher affinity IGF-1R binding, thereby inhibiting IGF-1R internalization and altering cell trafficking. AVE1642 attenuates phosphoinositide 3-kinase signaling, while PGA-AVE1642 inhibits phosphoinositide 3-kinase and mitogen-activated protein kinase signaling. PGA conjugation also enhances AVE1642's anti-tumor activity in an orthotopic prostate cancer mouse model, while PGA-AVE1642 induces more significant suppression of cancer cell proliferation/angiogenesis than AVE1642. These findings demonstrate that PGA conjugation modulates an antibody's bio-nano interface, mechanism of action, and therapeutic activity.