mCRPC Patients Research Articles

Bellmunt risk score as a survival predictor in patients with metastatic castration-resistant prostate cancer.

The prognosis of metastatic castration-resistant prostate cancer (mCRPC) is influenced by numerous individual factors. Despite various proposed prognostic models, the clinical application of these remains limited, probably due to complexity. Our study aimed to evaluate the predictive value of the Bellmunt risk score, which is well-known for urothelial carcinoma and easily assessed, in mCRPC patients. The Bellmunt risk score was calculated from three risk factors (Eastern Cooperative Oncology Group Performance Status (ECOG PS) ≥1, serum hemoglobin <10 g/dL, presence of liver metastases) in 125 patients who received first-line mCRPC treatment between 2005 and 2023. In addition, a modified score was established (one point each for hemoglobin <10 g/dL and the presence of liver metastases added to the ECOG PS). Associations with overall survival (OS) under first- and second-line therapy were tested using Cox regression analyzes, log-rank tests, concordance index (C-index) and time-dependent receiver operating characteristic. There is a significant correlation between the level of the Bellmunt risk score and shorter OS (hazard ratio: 3.23, 95% confidence interval: 2.06-5.05; log-rank p < 0.001; C-index: 0.724). The semi-quantitative modified risk score showed even better prognostic discrimination (log-rank p < 0.001, C-index: 0.764). The score and its dynamics were also predictive in the second-line setting (log-rank p < 0.001 and = 0.01; C-index: 0.742 and 0.595). The Bellmunt risk score is easy to assess and provides useful prognostic information in mCRPC, and can support physicians in their treatment decisions.

A phase 2, single-arm trial evaluating 131 I-PSMA-1095 targeted radioligand therapy for metastatic castration-resistant prostate cancer.

Metastatic castration-resistant prostate cancer (mCRPC) remains uniformly lethal. Prostate specific membrane antigen (PSMA) is a transmembrane glycoprotein overexpressed in prostate cancer. 131 I-PSMA-1095 (also known as 131 I-MIP-1095) is a PSMA-targeted radioligand which selectively delivers therapeutic radiation to cancer cells and the tumor microenvironment. We conducted a single-arm, phase 2 trial to assess efficacy and tolerability of 131 I-PSMA-1095 in mCRPC patients who had exhausted all lines of approved therapy. All patients underwent 18 F-DCFPyL PET and 18 F-FDG PET to determine PSMA-positive tumor volume, and patients with >50% PSMA-positive tumor volume were treated with up to four doses of 131 I-PSMA-1095. The primary endpoint was the response rate of prostate specific antigen (PSA). Secondary endpoints included rates of radiographic response and adverse events. Overall and radiographic progression-free survival were also analyzed. Eleven patients were screened for inclusion and nine patients received 131 I-PSMA-1095. The median baseline PSA was 162 µg/l, and six patients demonstrated a >50% PSA decrease. One patient demonstrated a confirmed radiographic response. Median overall survival was 10.3 months, and median progression-free survival was 5.4 months. Four patients experienced adverse events of grade 3 or higher, the most frequent being thrombocytopenia and anemia. 131 I-PSMA-1095 is highly active against heavily-pretreated PSMA-positive mCRPC, significantly decreasing tumor burden as measured by PSA. Adverse events, mainly hematologic toxicity, were not infrequent, likely related to off-target irradiation. This hematologic toxicity, as well as a higher logistical burden associated with use, could represent relative disadvantages of 131 I-PSMA-1095 compared to 177 Lu-PSMA-617.

Baseline serum testosterone and differential efficacy of bipolar androgen therapy and enzalutamide in the randomized TRANSFORMER trial.

Bipolar androgen therapy (BAT) is effective in a subset of metastatic castration-resistant prostate cancer (mCRPC) patients. Treatment selection biomarkers are needed due to other therapies that can be equally efficacious. We performed post-hoc analysis to determine whether baseline serum testosterone (T) is a treatment selection marker in the TRANSFORMER study, a randomized trial of abiraterone-pretreated mCRPC patients assigned to BAT (n = 94) or enzalutamide (n = 101). The findings suggest that patients with poor outcomes to abiraterone and serum T ≥ 20 ng/dL may benefit preferentially from BAT over enzalutamide. Baseline testosterone could be considered in the treatment selection process when BAT is an option.

Outcomes and patterns of use of Radium-223 in metastatic castration-resistant prostate cancer.

Radium-223 dichloride (Ra-223) is recommended as a treatment option for metastatic castration-resistant prostate cancer (mCRPC) patients with symptomatic bone metastases and no visceral disease, after docetaxel failure, or in patients who are not candidates to receive it. In this study, we aimed to ambispectively analyze overall survival (OS) and prognostic features in mCRPC in patients receiving Ra-223 as per clinical routine practice and identify the most suitable treatment sequence. This study is observational, multicentric, and ambispective. Eligibility criteria included mCRPC patients treated with Ra-223, with an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2, without visceral metastases, and no more than three cm involved lymph nodes. A total of 145 patients were included; the median age was 73.97 years, and a Gleason score of more than or equal to 7 in 61 (48%) patients; 73 (81%) had previously received docetaxel. The most important benefit was reached by those patients who received Ra-223 in the second-line setting, with a median OS of 17 months (95% CI, 12-21), and by patients who received six cycles of treatment, with a median OS of 19 months (95% CI, 14-21). An alkaline phosphatase (ALP) decrease was also identified as a prognosis marker. When performing the multivariate analysis, the time to develop castration-resistant disease longer than 24 months was the most important prognostic factor to predict the evolution of the patients receiving Ra-223. Ra-223 was well tolerated, with thrombocytopenia, anemia, and diarrhea being the main adverse events. There is a benefit for those patients who received Ra-223 in the second-line setting, regardless of prior use of docetaxel. In addition, a survival benefit for patients presenting with a decline in ALP was observed.

Comparison of novel PSMA-targeting [177Lu]Lu-P17-087 with its albumin binding derivative [177Lu]Lu-P17-088 in metastatic castration-resistant prostate cancer patients: a first-in-human study.

Prostate-specific membrane antigen (PSMA) is a promising target for diagnosis and radioligand therapy (RLT) of prostate cancer. Two novel PSMA-targeting radionuclide therapy agents, [177Lu]Lu-P17-087, and its albumin binder modified derivative, [177Lu]Lu-P17-088, were evaluated in metastatic castration-resistant prostate cancer (mCRPC) patients. The primary endpoint was dosimetry evaluation, the second endpoint was radiation toxicity assessment (CTCAE 5.0) and PSA response (PCWG3). Patients with PSMA-positive tumors were enrolled after [68Ga]Ga-PSMA-11 PET/CT scan. Five mCRPC patients received [177Lu]Lu-P17-087 and four other patients received [177Lu]Lu-P17-088 (1.2 GBq/patient). Multiple whole body planar scintigraphy was performed at 1.5, 4, 24, 48, 72, 120 and 168h after injection and one SPECT/CT imaging was performed at 24h post-injection for each patient. Dosimetry evaluation was compared in both patient groups. Patients showed no major clinical side-effects under this low dose treatment. As expected [177Lu]Lu-P17-088 with longer blood circulation (due to its albumin binding) exhibited higher effective doses than [177Lu]Lu-P17-087 (0.151 ± 0.036 vs. 0.056 ± 0.019 mGy/MBq, P = 0.001). Similarly, red marrow received 0.119 ± 0.068 and 0.048 ± 0.020 mGy/MBq, while kidney doses were 0.119 ± 0.068 and 0.046 ± 0.022 mGy/MBq, respectively. [177Lu]Lu-P17-087 demonstrated excellent tumor uptake and faster kinetics; while [177Lu]Lu-P17-088 displayed a slower washout and higher average dose (7.75 ± 4.18 vs. 4.72 ± 2.29 mGy/MBq, P = 0.018). After administration of [177Lu]Lu-P17-087 and [177Lu]Lu-P17-088, 3/5 and 3/4 patients showed reducing PSA values, respectively. [177Lu]Lu-P17-088 and [177Lu]Lu-P17-087 displayed different pharmacokinetics but excellent PSMA-targeting dose delivery in mCRPC patients. These two agents are promising RLT agents for personalized treatment of mCRPC. Further studies with increased dose and frequency of RLT are warranted to evaluate the potential therapeutic efficacy. 177Lu-P17-087/177Lu-P17-088 in Patients with Metastatic Castration-resistant Prostate Cancer (NCT05603559, Registered at 25 October, 2022). URL OF REGISTRY: https://classic. gov/ct2/show/NCT05603559 .

Inter- and Intra-Patient Repeatability of Radiomic Features from Multiparametric Whole-Body MRI in Patients with Metastatic Prostate Cancer.

(1) Background: We assessed the test-re-test repeatability of radiomics in metastatic castration-resistant prostate cancer (mCPRC) bone disease on whole-body diffusion-weighted (DWI) and T1-weighted Dixon MRI. (2) Methods: In 10 mCRPC patients, 1.5 T MRI, including DWI and T1-weighted gradient-echo Dixon sequences, was performed twice on the same day. Apparent diffusion coefficient (ADC) and relative fat-fraction-percentage (rFF%) maps were calculated. Per study, up to 10 target bone metastases were manually delineated on DWI and Dixon images. All 106 radiomic features included in the Pyradiomics toolbox were derived for each target volume from the ADC and rFF% maps. To account for inter- and intra-patient measurement repeatability, the log-transformed individual target measurements were fitted to a hierarchical model, represented as a Bayesian network. Repeatability measurements, including the intraclass correlation coefficient (ICC), were derived. Feature ICCs were compared with mean ADC and rFF ICCs. (3) Results: A total of 65 DWI and 47 rFF% targets were analysed. There was no significant bias for any features. Pairwise correlation revealed fifteen ADC and fourteen rFF% feature sub-groups, without specific patterns between feature classes. The median intra-patient ICC was generally higher than the inter-patient ICC. Features that describe extremes in voxel values (minimum, maximum, range, skewness, and kurtosis) showed generally lower ICCs. Several mostly shape-based texture features were identified, which showed high inter- and intra-patient ICCs when compared with the mean ADC or mean rFF%, respectively. (4) Conclusions: Pyradiomics texture features of mCRPC bone metastases varied greatly in inter- and intra-patient repeatability. Several features demonstrated good repeatability, allowing for further exploration as diagnostic parameters in mCRPC bone disease.

Increase of prostate-specific antigen doubling time predicts survival in metastatic castration-resistant prostate cancer patients undergoing radium therapy.

Radium-223 (Ra-223) is an important treatment modality for bone-dominant metastatic castration-resistant prostate cancer (mCRPC). However, there is currently a lack of effective markers to monitor treatment response during treatment. We aim to investigate the response in prostate-specific antigen doubling time (PSADT) as a potential marker for assessing Ra-223 treatment in mCRPC patients. We retrospectively collected data from mCRPC patients who underwent radium treatment at our institution between August 2020 and June 2023. Prostate-specific antigen (PSA) measurements prior to treatment and during treatment were collected. Baseline PSADT was calculated from PSA measurements prior to Ra-223 treatment; interim PSADT was calculated from PSA measurements before Ra-223 treatment and prior to the fourth course injection. Overall survival was calculated from the start of treatment to the date of death. Univariable and multivariable analysis using the Cox proportional hazards model were performed to examine the association of factors with overall survival. We included 35 patients from our institution, with a median overall survival of 13.3months. Eighteen (51.4%) completed all six courses of treatment. PSA dynamic response (interim PSADT > baseline PSADT or decreased PSA) was observed in 20 patients. Overall survival was associated with a PSA dynamic response (HR = 0.318, 95% CI 0.133-0.762, p = 0.010) when compared to patients without response. Dynamic changes in PSADT were associated with survival in mCRPC patients receiving radium therapy. Comparing interim and baseline PSADT could serve as a valuable marker for determining treatment benefits.

Efficacité et tolérance du dichlorure de radium 223 chez les patients traités pour cancer de la prostate résistant à la castration avec métastases osseuses

IntroductionThe aim of our study was to evaluate the efficacy and tolerance of 223RaCl2 in patients with mCRPC with bone metastases, then analyse the impact of any change in treatment protocol on the efficacy of 223RaCl2 in mCRPC patients with bone metastases, by determining overall survival, progression-free survival and events occurring during therapeutic monitoring. Materiel and methodsOur retrospective, analytical and descriptive study, carried out in Luxembourg, included patients eligible for le 223RaCl2 treatment who were assessed during and at the end of treatment, and 3 to 4months after the end of treatment. ResultsOur sample included 41 cases. The mean age of patients was 74years (min=52, max=87), with 32 (78.1%) deaths recorded. Median overall survival was 18.0months (95% CI: 12.1–23.9): 11months for those who experienced progression during treatment versus 47 months for those who experienced a partial response. Median progression-free survival was 15.0 months (95% CI: 0.0–36.4). Overall survival was positively correlated with progression-free survival (Rho Spearman=0.713, P-value<0.001); however, a one-month increase in progression-free survival decreased the risk of death by 6% and thus increased overall survival (HR=0.937, 95% CI : 0.903–0.973, P<0.001). ConclusionAdministration of the complete 223RaCl2 protocol improved overall survival and progression-free survival in patients treated for mCRPC with bone metastases, with good hematological tolerability despite the occurrence of complications such as epiduritis and fractures.

Predicting abiraterone efficacy in advanced prostate cancer: Insights from marker of proliferation Ki67.

KI67 is a well-known biomarker reflecting cell proliferation. We aim to elucidate the predictive role of KI67 in the efficacy of abiraterone for patients with advanced prostate cancer (PCa). Clinicopathological data of 152 men with metastatic PCa, who received abiraterone therapy were retrospectively collected. The KI67 positivity was examined by immunohistochemistry using the prostate biopsy specimen. The predictive value of KI67 on the therapeutic efficacy of abiraterone was explored using Kaplan-Meier curve and Cox regression analysis. The endpoints included prostate-specific antigen (PSA) progression-free survival (PSA-PFS), radiographic PFS (rPFS), and overall survival (OS). In total, 85/152 (55.9%) and 67/152 (44.1%) cases, respectively, received abiraterone at metastatic hormone-sensitive (mHSPC) and castration-resistant PCa (mCRPC) stage. The median KI67 positivity was 20% (interquartile range: 10%-30%). Overall, KI67 rate was not correlated with PSA response. Notably, an elevated KI67-positive rate strongly correlated with unfavorable abiraterone efficacy, with KI67 ≥ 30% and KI67 ≥ 20% identified as the optimal cutoffs for prognosis differentiation in mHSPC (median PSA-PFS: 11.43 Mo vs. 26.43 Mo, p < 0.001; median rPFS: 16.63 Mo vs. 31.90 Mo, p = 0.003; median OS: 21.77 Mo vs. not reach, p = 0.005) and mCRPC (median PSA-PFS: 7.17 Mo vs. 12.20 Mo, p = 0.029; median rPFS: 11.67 Mo vs. 16.47 Mo, p = 0.012; median OS: 21.67 Mo vs. not reach, p = 0.073) patients, respectively. Multivariate analysis supported the independent predictive value of KI67 on abiraterone efficacy. In subgroup analysis, an elevated KI67 expression was consistently associated with unfavorable outcomes in the majority of subgroups. Furthermore, data from another cohort of 79 PCa patients with RNA information showed that those with KI67 RNA levels above the median had a significantly shorter OS than those below the median (17.71 vs. 30.72 Mo, p = 0.035). This study highlights KI67 positivity in prostate biopsy as a strong predictor of abiraterone efficacy in advanced PCa. These insights will assist clinicians in anticipating clinical outcomes and refining treatment decisions for PCa patients.

Prostate cancer across four countries in the Middle East: a multi-centre, observational, retrospective and prognostic study.

Prostate cancer (PC) is the second most prevalent cancer in males, with a steadily increasing incidence in the Middle East (ME). The aim of this study was to capture real-world data on the characteristics, disease progression, and treatment patterns among PC patients in the ME. This was a retrospective, observational, multi-centre study conducted across ten hospitals/research centers in Lebanon, Kingdom of Saudi Arabia, Iraq and Kuwait. Data were abstracted from medical records of 615 male patients who were diagnosed with PC between January 2012 and the site initiation date (December 2018-May 2019) and received at least one PC treatment/intervention. The observation period ranged between 84 and 88 months. Data were collected on demographics, clinical characteristics, time to progression to the subsequent clinical state or therapy (progression from localised/locally advanced PC to castration and to metastatic PC (metastatic castration-sensitive PC (mCSPC) or metastatic castration-resistant PC (mCRPC)), progression from mCSPC to mCRPC, and mCRPC patients' progression to first subsequent line of therapy), treatment patterns, and mortality. Most patients had localised/locally advanced PC (57.7%), followed by mCSPC (37.4%), and mCRPC (4.1%) at the time of inclusion in the study. Most patients were at tumours, nodes and metastases (TNM) stage IIIa (40.1%) or TNM stage IVb (27.8%) at study entry. Median time to metastatic disease, castration-resistance and next line therapy was 84 months (95% CI: 68-84), 41 months (95% CI: 30-56) and 7 months (95% CI: 0-41), respectively. The mortality rate was 3.6%. Disease progression was most common among patients with mCSPC (35.1%) or mCRPC (14.8%), and treatment discontinuation was most common among patients with mCRPC (36.6% treatments discontinued). The results show that most patients were at an advanced TNM stage at study entry, suggestive of a lack of awareness regarding PC. Disease progression was most common among patients with metastatic disease, reflecting the challenge of treating metastatic disease and highlighting the need for novel treatments.

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.

Abstract CT138: Evaluating nivolumab (nivo) plus ipilimumab (ipi) in patients with metastatic castration-resistant prostate cancer (mCRPC): Clinical and translational results from the AMADEUS prostate expansion cohort

Abstract Background: Immune checkpoint inhibitors (ICIs) have transformed cancer treatment, offering durable responses for some patients. However, response to ICIs remains limited for many solid tumors, including metastatic castration-resistant prostate cancer (mCRPC). The AMADEUS primary cohort (NCT03651271) and CheckMate 650 (NCT02985957) trials demonstrated promising durable antitumor responses in a subset of mCRPC patients treated with nivo in combination with ipi at 1 mg/kg or 3 mg/kg, respectively. The AMADEUS prostate expansion cohort was initiated to evaluate the safety and efficacy of a higher ipi dose (5 mg/kg) in combination with nivo. Methods: This open-label, multicenter cohort enrolled mCRPC patients with no restriction on the number of prior treatments. The first 10 patients with &amp;lt; 15% tumoral CD8 T cells were randomized 1:1 to receive either ipi at 3 mg/kg (ipi3) or 5 mg/kg (ipi5) IV Q6W for up to 2 doses. In addition, all patients received nivo 1 mg/kg IV Q3W for 4 doses, followed by nivo 480 mg IV Q4W until PD or intolerable toxicity. After a safety pause, 10 additional patients were enrolled to the ipi5 arm. Co-primary endpoints were DCR (CR, PR, or SD ≥ 6 months) and conversion of tumor %CD8 T cells from low (&amp;lt; 15%) to high (≥ 15%). Baseline and on-treatment tumor and blood samples were analyzed for multi-omic biomarkers. This cohort was not powered for formal statistical analysis. Results: DCR was 20% in both ipi3 (N=1/5) and ipi5 (N=3/15) arms. In patients with an on-treatment biopsy, CD8 conversion from low to high occurred in 33% (1/3) of patients in ipi3 and 13% (1/8) in ipi5. However, 50% (4/8) of patients in ipi5 had on-treatment CD8 ≥ 14.8%. Baseline CD8 T cell frequencies and CD8 conversion were not associated with disease control or PSA reduction. The frequency and severity of AEs was consistent with the known safety profile of ipi/nivo, although more patient in ipi5 discontinued treatment owing to an AE (33% vs 0% in ipi3). Both arms showed increased activated (ICOS+, CD38+) and proliferating (Ki67+) CD4 T cells, CD8 T cells, Tregs, inflammatory cytokines (IFNg), chemokines (CXCL9, CXCL10), and soluble PD-1 in circulation. Conclusions: Across both arms, ipi/nivo induced clinical responses and increased %CD8 in a subset of “cold” mCRPC tumors with low CD8 cells. Additionally, the safety profile of ipi 5 mg/kg combined with nivo was consistent with previous trials that tested lower doses of ipi. Further translational analyses may inform which mCRPC patients could benefit from immunotherapy treatment. Trial registration: ClinicalTrials.gov (NCT03651271) Citation Format: Apostolia M. Tsimberidou, Alexandra Drakaki, Danny N. Khalil, Kwame Okrah, Mike Schachter, Shikha Gautam, Diane M. Da Silva, Farah A. Alayli, Christine N. Spencer, Wai Chin Foo, Matthew Adamow, Phillip Wong, Justin Fairchild, Jamie Arnott, Ute Dugan, Silvia Boffo, Lisa Salvador, Christopher R. Cabanski, Sumit K. Subudhi, Padmanee Sharma. Evaluating nivolumab (nivo) plus ipilimumab (ipi) in patients with metastatic castration-resistant prostate cancer (mCRPC): Clinical and translational results from the AMADEUS prostate expansion cohort [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 CT138.

Abstract ND09: Actinium-225 -PSMA-Trillium (BAY 3563254): Preclinical evaluation and clinical imaging study of a novel 225Ac-labeled PSMA-targeting small molecule triad for the treatment of mCRPC

Abstract With the approval of a PSMA-targeting small molecule labeled with the beta-emitter lutetium-177, PSMA is considered a clinically validated target for the treatment of mCRPC. Although effective, many patients treated with this therapeutic experience only transient clinical benefit, and G1/2 xerostomia is common due to salivary gland toxicity. Since the linear energy transfer and degree of induced DNA damage of alpha particles far exceeds that of beta particles, several investigational PSMA-targeting small molecules labeled with the alpha-emitter 225Ac have generated encouraging preliminary efficacy signals, but with severe xerostomia as a common dose-limiting toxicity. 225Ac-PSMA-Trillium is a novel PSMA-targeting radioligand consisting of a triad of important features: (1) a high-affinity PSMA inhibitor for specific tumor-targeting; (2) a customized albumin-binding domain designed to prolong plasma residence time and increase the therapeutic index by improving tumor uptake while reducing salivary gland uptake; and (3) a “macropa” chelator for efficient and stable radiolabeling with actinium-225. A series of compounds containing the same high-affinity PSMA-targeting moiety, but different chain lengths and albumin-binding domains, were evaluated to identify the optimal combination of features required to achieve the best therapeutic index. In vitro preclinical characterization was performed to test affinities for PSMA and albumin, compound stability and cell-killing potential in LNCaP and 22Rv1 CDX models as well as KuCaP-1 PDX model. Preclinical in vivo investigation of selected compounds showed increased plasma residence time, reduced uptake in normal organs, strong uptake and retention in PSMA-expressing tumors and robust anti-tumor activity. These analyses led to the selection of compounds for further evaluation in a Phase 0 imaging and PK study in mCRPC patients (NCT05773703). In this Phase 0 study, PSMA-Trillium compounds were labeled with indium-111 via a DOTA chelator and used as surrogates to facilitate longitudinal imaging. In patients, 111In-PSMA-Trillium demonstrated targeting to PSMA-expressing tumors as defined by PET/PSMA scans and a plasma residence time consistent with albumin-binding affinities. Importantly, 111In-PSMA-Trillium showed robust uptake and prolonged retention in tumors, and reduced uptake and relatively fast washout from salivary glands. Based on these preclinical data and clinical imaging results, a therapeutic first-in-human trial to evaluate 225Ac-PSMA-Trillium in patients with prostate cancer is anticipated to begin enrolling patients in the first half of 2024. Citation Format: Sabine Zitzmann-Kolbe, Jacob Hesterman, Patricia E. Cole, Nicolas Salem, Alex Papple, Michael Jeffers, Goekben Koca, Thorsten Poethko, Miroslav Dostalek, Shawn Hillier, John W. Babich. Actinium-225 -PSMA-Trillium (BAY 3563254): Preclinical evaluation and clinical imaging study of a novel 225Ac-labeled PSMA-targeting small molecule triad for the treatment of mCRPC [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 ND09.

Abstract LB177: Discovery of HC-4955, a novel AR-V7-targeting PROTAC for the treatment of mCRPC

Abstract Prostate cancer is the second most commonly diagnosed cancer and the second leading cause of cancer death among men worldwide. Androgens play an important role in the development and progression of prostate cancers and targeting androgen receptor (AR) signaling axis over decades has remained a mainstay of prostate cancer therapy. Next generation hormonal agents (NHAs) enzalutamide and abiraterone have brought clinical benefits for metastatic castrate-resistant prostate cancer (mCRPC) patients, AR axis-targeted therapy resistance is inevitable due to AR gene amplification or mutations. AR-V7 is the most clinically relevant AR splice variant associated with endocrine resistance and poor prognosis. AR-V7 constitutively activates AR signaling and lacks the ligand binding domain (LBD) where hormones and AR antagonists interact, resulting in resistance to AR signaling inhibitors (ARSi). Thus, AR-V7 is a promising therapeutic target to address ARSi resistance in mCRPC. We have discovered a highly potent AR-V7 proteolysis targeting chimera (PROTAC), HC-4955 that degrades both the wild-type AR (WT-AR) and AR-V7 mutant. HC-4955 degrades AR-V7 with DC50 &amp;lt; 5 nM. In silico molecular docking analysis predicts the binding of HC-4955 to the N-terminal domain of AR and then the essential amino acids contributed to HC-4955 binding are validated by mutational analysis studies. HC-4955 also potently degrades mutants of AR-LBD mutations including L702H and T878A and these mutations are also associated with ARSi resistance. HC-4955 strongly inhibits proliferation of ARSi-resistant prostate cancer cell lines with IC50 &amp;lt; 10 nM. HC-4955 shows a robust anti-tumor activity in the AR-V7-bearing 22Rv1 cell line derived tumor xenograft (CDX) and patient-derived xenograft (PDX) mouse models, with majority of the tumors completely regressed and &amp;gt; 90% AR-V7 expression decreased at 1-5 mg/kg (QD, PO) in these models. The pre-clinical results support the clinical development of HC-4955 for the treatment of mCRPC. Selected pre-clinical data along with the chemical structure of HC-4955 will be presented. Citation Format: Jing Li, Zhilin Tu, Wu Du, Xi Xiang, Zeyu Wen, Yang You, Lijuan Zhao, Yin Chen, Chengcheng Yang, Hongwei Yuan, Xinghai Li. Discovery of HC-4955, a novel AR-V7-targeting PROTAC for the treatment of mCRPC [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 LB177.

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.

Treatment Patterns and Clinical Outcomes Among Patients With Metastatic Prostate Cancer Harboring Homologous Recombination Repair Mutations

BackgroundThere is currently limited literature assessing the real-world treatment patterns and clinical outcomes of patients with metastatic castration-resistant prostate cancer (mCRPC) and homologous recombination repair (HRR) mutations. MethodsMedical charts were abstracted for mCRPC patients with ≥ 1 of 12 HRR somatic gene alterations treated at US oncology centers participating in the American Association for Cancer Research Project Genomics Evidence Neoplasia Information Exchange. Treatment patterns and clinical outcomes were assessed from the initiation of first-line or later (1L+) mCRPC therapy received on or after July 1, 2014. ResultsAmong 138 patients included in the study, the most common somatic HRR mutations were CDK12 (47.8%), BRCA2 (22.5%), and ATM (21.0%). Novel hormonal therapy and taxane chemotherapy were most commonly used in 1L; taxane use increased in later lines. Median overall survival (95% confidence interval [CI]) was 36.3 (30.7-47.8) months from initiation of 1L therapy and decreased for subsequent lines. Similarly, there was a trend of decreasing progression-free survival and prostate-specific antigen response from 1L to 4L+ therapy. ConclusionsTreatment patterns identified in this study were similar to those among patients with mCRPC regardless of tumor HRR mutation status in the literature.

Abstract 6563: PSMA-based detection and global proteome-based analysis of circulating tumor cells in castration resistant prostate cancer patients

Abstract In recent years, many new targeted and immuno-therapies have entered the cancer treatment landscape with the potential to drastically improve patient outcomes; however, selecting the optimal drug target especially as the disease progresses becomes increasingly important. Liquid biopsies show great promise in providing insights on the current disease state, but generally rely on a small number of protein markers identified through immunofluorescence staining or genomic mutations determined from cell-free DNA which limits the amount of information available to make treatment decisions. One way to better select the optimal drug target is to generate unbiased mass-spectrometry based proteomic data from the circulating tumor cells (CTCs) isolated from blood. In this study, we collaborated with Astrin Biosciences using their patented isolation technology to enrich CTCs with high purity from the blood of 57 metastatic castration resistant prostate cancer (mCRPC) patients. The CTC-enriched sample (along with a patient-matched control sample consisting primarily of white blood cells) was analyzed in real time for either PSMA protein (Lutetium-PSMA-617 study, n=32) or via mass-spectrometry (CTC proteomics study, n=25). Over 1,500 peptides corresponding to greater than 600 proteins were identified from each patient’s CTCs. These included increased epithelial cell markers in the CTC-enriched sample and increased WBC markers in the control sample. Specifically, detection of the androgen receptor protein was identified in the CTC-enriched sample which is of particular interest in mCRPC patients. Furthermore, this method is able to detect and quantify PSMA expression, which is of clear relevance in the context of PSMA-directed therapeutics. This study demonstrates the feasibility of obtaining large scale proteomic data from a liquid biopsy. Future studies will focus on cancer signaling mechanisms and biomarkers to elucidate the clinical utility of such data. As more patients are analyzed, we will compare proteomic data with known tissue proteome information when available and to correlate these with drug response to improve treatment selection and patient outcomes. Citation Format: Justin M. Drake, Ali Arafa, Alec Horrmann, Kaylee J. Kamalanathan, Catalina Galeano-Garces, Zoi Sychev, Nicholas Heller, Mahdi Ahmadi, Megan Ludwig, Olivia Hedeen, Alexa Hesch, Grant Schaap, Joel Hapke, Jeff Miller, Ivo Babris, Tuan Lee, Tony Clacko, Justin Hwang, Jiarong Hong, Badri Konety, Jayant Parthasarathy, Emmanuel Antonarakis. PSMA-based detection and global proteome-based analysis of circulating tumor cells in castration resistant prostate cancer patients [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 6563.

Abstract 983: Epigenomic analysis of plasma cell-free DNA identifies stemness features associated with worse prognosis in AR-altered lethal metastatic castration resistant prostate cancer

Abstract Background: Metastatic castration-resistant prostate cancer (mCRPC) resistant to androgen receptor (AR)-targeted agents is often lethal. Unfortunately, biomarkers for this deadly disease remain under investigation, and underpinning mechanisms are ill-understood. Here, we applied epigenomic approaches to identify cell-free (cf) DNA features associated with these lethal AR-resistant mCRPC patients. Methods: Plasma from 99 mCRPC patients was collected from two independent institutions, either prior to first-line AR-targeted therapy (n = 63) or during treatment (n = 36). We applied EnhanceAR-Seq to detect alterations in the AR locus including the upstream enhancer. We then applied genome-wide cfDNA epigenomics to 43 pre-treatment plasma samples and performed both fragmentomics and methylation sequencing to delineate the biology of AR/enhancer-altered lethal mCRPC. Finally, we identified stemness genes by applying CytoTRACE to external single-cell RNA-seq data from mCRPC, and applied these to cfDNA via promoter-level methylation analysis. We then assessed these stem-associated genes in tumor bulk RNA-seq data from an independent mCRPC cohort. Results: AR/enhancer alterations were detected in 44% of pre-treatment cfDNA samples and correlated with significantly worse progression-free survival (PFS) (HR = 2.12, P = 0.01) and overall survival (OS) (HR = 2.48; P = 0.02). AR/enhancer alterations were detected in 19% of on-treatment cfDNA samples and were also associated with profoundly worse PFS (HR = 15.38, P = 0.0003) and OS (HR = 15.53, P = 0.002). Further, genome-wide cfDNA fragmentomic analysis revealed that binding sites for developmentally relevant transcription factors such as FOXA1, NKX-3 and HOXB13 were significantly more accessible in AR/enhancer-altered lethal mCRPC patients. Gene set enrichment analysis of the 20 most accessible transcription factors revealed several pathways associated with stem cell development. Interestingly, the 10 most stem-associated genes obtained using CytoTRACE applied to an external cohort of single-cell RNA-seq data from mCRPC (He et al. 2021) were promoter-hypomethylated in the plasma cfDNA of AR/enhancer-altered lethal mCRPC patients (P = 0.005). Further, metagene analysis of these stem-associated genes revealed worse PFS by Kaplan-Meier analysis (P = 0.04), which was confirmed by multivariate cox proportional hazards modeling. Our stemness metagene further stratified overall survival (P = 0.03) when applied to an external cohort of 80 mCRPC patients from Abida et al. 2019. Conclusions: Alterations in AR including the upstream enhancer are remarkably prognostic in mCRPC with pre-treatment predictive potential. The mechanism can be inferred via cfDNA epigenomic analysis and appears to involve increased tumor cell stemness in AR-altered lethal mCRPC. Citation Format: Pradeep Singh Chauhan, Irfan Alahi, Savar Sinha, Ryan Mueller, Alexander L. Shiang, Jace Webster, Ha X. Dang, Debanjan Saha, Lilli Greiner, Breanna Yang, Elisa M. Ledet, Ramandeep K. Babbra, Wenjia Feng, Peter K. Harris, Faridi Qaium, Ellen B. Jaeger, Patrick J. Miller, Sydney A. Caputo, Oliver A. Sartor, Russell K. Pachynski, Christopher A. Maher, Aadel A. Chaudhuri. Epigenomic analysis of plasma cell-free DNA identifies stemness features associated with worse prognosis in AR-altered lethal metastatic castration resistant 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 983.

Abstract 6205: Identify drugs for metastatic castration-resistance prostate cancer (mCRPC) patients with high glycolytic activity through in silico approach

Abstract Prostate cancer (PC) remains a prominent cause of cancer-related mortality among men in the United States. A significant factor contributing to the mortality of PC patients is the development of resistance to second-generation antiandrogen therapies, particularly androgen receptor-signaling inhibitors (ARSI), which is pronounced in patients with late-stage PC, metastatic castration-resistance prostate cancer (mCRPC). Therefore, there is an urgent need for novel therapeutics beyond AR signaling inhibition for patients with mCRPC. One of the key drivers of resistance to ARSI and a critical feature of CRPC is cancer metabolism reprogramming to elevated glycolysis. However, the current research on finding drugs to impede high-glycolytic tumor growth is hurdled by a resistance raised from metabolic plasticity. The aim of this research is to quickly repurpose existing drugs for inhibiting high-glycolytic mCRPC growth while proactively circumstancing resistance from metabolic plasticity through computational approaches. To do this, we imputed a large number of drug responses in patients with mCRPC using a computational algorithm (OncoPredict), identified drugs that were projected to show higher sensitivity in high-glycolytic tumors, and performed in vitro validation. Furthermore, to maximize drug efficacy, we identified biomarkers for drug candidates. By implementing this computational pipeline, we identified a number of drugs with various mechanisms of action that show higher efficacy in mCRPC with high glycolysis. Furthermore, we successfully validated the efficacy of these nominated drug candidates including an anti-parasitic agent, an HSP90 inhibitor, and a CDK inhibitor. These drug candidates exhibited superior tumor growth inhibition in in vitro models of high glycolysis-induced advanced PC. In conclusion, this study introduces an innovative in silico approach to unveil the existing drugs’ unknown potential for the treatment of patients with mCRPC. Our findings hold promise for development of effective therapeutics for combating this challenging disease. Citation Format: Mei-Chi Su, Adam M. Lee, R. Stephanie Huang. Identify drugs for metastatic castration-resistance prostate cancer (mCRPC) patients with high glycolytic activity through in silico approach [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 6205.

Abstract 5031: Identification of predictive/prognostic biomarkers in metastatic castration-resistant prostate cancer patients using plasma cell-free total RNA-sequencing

Abstract Background Metastatic castration-resistant prostate cancer (mCRPC) is a heterogeneous disease that is still lacking an optimal patient selection strategy and a validated sequence of therapies. Therefore, there is an urgent need to identify non-invasive biomarkers to guide treatment choice in a perspective of personalized medicine. Plasma cell-free RNA profiling has emerged as a tool to investigate potential liquid biopsy biomarkers. In this study, we aimed to evaluate a method to capture total RNA content deriving from plasma and to identify potential biomarkers for mCRPC. Methods Plasma samples of 41 mCRPC patients treated with first line Abiraterone or Enzalutamide and 7 healthy donors were collected and stored from 2015 to 2022. Plasma cell-free RNA was purified using miRNeasy Serum/Plasma Advanced Kit (Qiagen) with DNase treatment. Bioanalyzer (Agilent) was used for the evaluation of RNA content and integrity profile of the samples. Sequencing libraries were generated using SMARTer Stranded Total RNA-Seq Kit v3 - Pico Input Mammalian (Takara Bio). An average of 80 millions reads pairs were sequenced on Novaseq 6000 (Illumina) using 100 bpx2 approach. After demultiplexing, reads were trimmed and aligned on hg19. Sequencing metrics were evaluated using Picard. Kallisto was used for gene expression analysis. Results A median of 10x109 bases per sample were aligned on hg19, of which a mean of 45% were located on coding or UTR regions. Storage time was investigated as a potential variable for RNA content and sequencing metrics, but no difference related to the year of storage was found. Unsupervised principal component analysis confirmed the absence of batch effects (including storage and sequencing analysis). PC1 seemed to reflect the different tumor RNA content of each sample, in which healthy donors and cancer patients were distinguished. Higher androgen receptor (AR) gene expression was found in mCRPC patients compared to healthy donors. Conclusions Despite enormous interest in extracellular nucleic acids, RNA-sequencing methods for total RNA content outside cells are rare and not standardized. In this study, we found a method to identify plasma non-invasive RNA biomarkers in mCRPC samples, retrieving coding and non-coding RNAs. Case series enlargement and differential gene expression analyses are ongoing. Citation Format: Giorgia Gurioli, Milena Urbini, Alessandra Virga, Chiara Casadei, Emilio Francesco Giunta, Nicole Brighi, Michela Cortesi, Michele Zanoni, Sara Bravaccini, Giovanni Martinelli, Paola Ulivi, Ugo De Giorgi. Identification of predictive/prognostic biomarkers in metastatic castration-resistant prostate cancer patients using plasma cell-free total RNA-sequencing [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 5031.