Treatment Of Castration-resistant Prostate Cancer Research Articles

Single-cell analysis revealing the metabolic landscape of prostate cancer.

Tumor metabolic reprogramming is a hallmark of cancer development, and targeting metabolic vulnerabilities has been proven to be an effective approach for castration-resistant prostate cancer (CRPC) treatment. Nevertheless, treatment failure inevitably occurs, largely due to cellular heterogeneity, which cannot be deciphered by traditional bulk sequencing techniques. By employing computational pipelines for single-cell RNA sequencing, we demonstrated that epithelial cells within the prostate are more metabolically active and plastic than stromal cells. Moreover, we identified that neuroendocrine (NE) cells tend to have high metabolic rates, which might explain the high demand for nutrients and energy exhibited by neuroendocrine prostate cancer (NEPC), one of the most lethal variants of prostate cancer (PCa). Additionally, we demonstrated through computational and experimental approaches that variation in mitochondrial activity is the greatest contributor to metabolic heterogeneity among both tumor cells and nontumor cells. These results establish a detailed metabolic landscape of PCa, highlight a potential mechanism of disease progression, and emphasize the importance of future studies on tumor heterogeneity and the tumor microenvironment from a metabolic perspective.

[177Lu]Lu-PSMA-617 plus enzalutamide in patients with metastatic castration-resistant prostate cancer (ENZA-p): an open-label, multicentre, randomised, phase 2 trial

Enzalutamide and lutetium-177 [177Lu]Lu-prostate-specific membrane antigen (PSMA)-617 both improve overall survival in patients with metastatic castration-resistant prostate cancer. Androgen and PSMA receptors have a close intracellular relationship, with data suggesting complementary benefit if targeted concurrently. In this study, we assessed the activity and safety of enzalutamide plus adaptive-dosed [177Lu]Lu-PSMA-617 versus enzalutamide alone as first-line treatment for metastatic castration-resistant prostate cancer. ENZA-p was an open-label, randomised, controlled phase 2 trial done at 15 hospitals in Australia. Participants were men aged 18 years or older with metastatic castration-resistant prostate cancer not previously treated with docetaxel or androgen receptor pathway inhibitors for metastatic castration-resistant prostate cancer, gallium-68 [68Ga]Ga-PSMA-PET-CT (PSMA-PET-CT) positive disease, Eastern Cooperative Oncology Group performance status of 0-2, and at least two risk factors for early progression on enzalutamide. Participants were randomly assigned (1:1) by a centralised, web-based system using minimisation with a random component to stratify for study site, disease burden, use of early docetaxel, and previous treatment with abiraterone acetate. Patients were either given oral enzalutamide 160 mg daily alone or with adaptive-dosed (two or four doses) intravenous 7·5 GBq [177Lu]Lu-PSMA-617 every 6-8 weeks dependent on an interim PSMA-PET-CT (week 12). The primary endpoint was prostate-specific antigen (PSA) progression-free survival, defined as the interval from the date of randomisation to the date of first evidence of PSA progression, commencement of non-protocol anticancer therapy, or death. The analysis was done in the intention-to-treat population, using stratified Cox proportional hazards regression. This trial is registered with ClinicalTrials.gov, NCT04419402, and participant follow-up is ongoing. 162 participants were randomly assigned between Aug 17, 2020, and July 26, 2022. 83 men were assigned to the enzalutamide plus [177Lu]Lu-PSMA-617 group, and 79 were assigned to the enzalutamide group. Median follow-up in this interim analysis was 20 months (IQR 18-21), with 32 (39%) of 83 patients in the enzalutamide plus [177Lu]Lu-PSMA-617 group and 16 (20%) of 79 patients in the enzalutamide group remaining on treatment at the data cutoff date. Median age was 71 years (IQR 64-76). Median PSA progression-free survival was 13·0 months (95% CI 11·0-17·0) in the enzalutamide plus [177Lu]Lu-PSMA-617 group and 7·8 months (95% CI 4·3-11·0) in the enzalutamide group (hazard ratio 0·43, 95% CI 0·29-0·63, p<0·0001). The most common adverse events (all grades) were fatigue (61 [75%] of 81 patients), nausea (38 [47%]), and dry mouth (32 [40%]) in the enzalutamide plus [177Lu]Lu-PSMA-617 group and fatigue (55 [70%] of 79), nausea (21 [27%]), and constipation (18 [23%]) in the enzalutamide group. Grade 3-5 adverse events occurred in 32 (40%) of 81 patients in the enzalutamide plus [177Lu]Lu-PSMA-617 group and 32 (41%) of 79 patients in the enzalutamide group. Grade 3 events that occurred only in the enzalutamide plus [177Lu]Lu-PSMA-617 group included anaemia (three [4%] of 81 participants) and decreased platelet count (one [1%] participant). No grade 4 or 5 events were attributed to treatment on central review in either group. The addition of [177Lu]Lu-PSMA-617 to enzalutamide improved PSA progression-free survival providing evidence of enhanced anticancer activity in patients with metastatic castration-resistant prostate cancer with risk factors for early progression on enzalutamide and warrants further evaluation of the combination more broadly in metastatic prostate cancer. Prostate Cancer Research Alliance (Movember and Australian Federal Government), St Vincent's Clinic Foundation, GenesisCare, Roy Morgan Research, and Endocyte (a Novartis company).

TAS3681, an androgen receptor antagonist, prevents drug resistance driven by aberrant androgen receptor signaling in prostate cancer.

Second-generation androgen receptor (AR) signaling inhibitors (ARSIs), such as abiraterone and enzalutamide, prolong the life of patients with castration-resistant prostate cancer (CRPC). However, patients receiving ARSIs ultimately develop resistance through various complex mechanisms, including AR mutations, constitutively active AR-splice variants (AR-Vs), and AR overexpression. Here, we characterized a novel AR pure antagonist, TAS3681, which inhibits AR transcriptional activity and downregulates AR-full length (AR-FL) and AR-Vs. TAS3681 reduced the protein levels of AR-FL and AR-Vs including AR-V7 in enzalutamide-resistant cells (SAS MDV No. 3-14), in vitro and in vivo, showing strong antitumor efficacy in an AR-V7-positive xenograft model. In AR-overexpressing VCaP (prostate cancer) cells, conversely to enzalutamide, TAS3681 effectively suppressed cell proliferation and downregulated AR expression. Importantly, TAS3681 blocked the transcriptional activity of various mutant ARs, including mutations F877L/T878A and H875Y/T878A, which confer resistance to enzalutamide, and V716M and H875Y mutations, which confer resistance to darolutamide. Our results demonstrate that TAS3681 suppresses the reactivation of AR signaling, which causes resistance to ARSIs, via a newly identified mechanism of action. Therefore, TAS3681 could be a new therapeutic option for CRPC treatment.

Preclinical efficacy of a PSMA-targeted actinium-225 conjugate (225Ac-macropa-pelgifatamab) - a targeted alpha therapy for prostate cancer.

Initially, prostate cancer responds to hormone therapy but eventually resistance develops. Beta emitter-based PSMA (prostate-specific membrane antigen)-targeted radionuclide therapy is approved for the treatment of metastatic castration-resistant prostate cancer. Here we introduce a targeted alpha therapy (TAT) consisting of the PSMA antibody pelgifatamab covalently linked to a macropa chelator and labeled with actinium-225 and compare its efficacy and tolerability with other TATs. The in vitro characteristics and in vivo biodistribution, antitumor efficacy, and tolerability of 225Ac-macropa-pelgifatamab (225Ac-pelgi) and other TATs were investigated in cell line- and patient-derived prostate cancer xenograft models. The antitumor efficacy of 225Ac-pelgi was also investigated in combination with the androgen receptor inhibitor darolutamide. Actinium-225-labeling of 225Ac-pelgi was efficient already at room temperature. Potent in vitro cytotoxicity was seen in PSMA-expressing (LNCaP, MDA-PCa-2b, and C4-2) but not in PSMA-negative (PC-3 and DU-145) cell lines. High tumor accumulation was seen for both 225Ac-pelgi and 225Ac-DOTA-pelgi in the MDA-PCa-2b xenograft model. In the C4-2 xenograft model, 225Ac-pelgi showed enhanced antitumor efficacy with a T/Cvolume (treatment/control) ratio of 0.10 compared with 225Ac-DOTA-pelgi, 225Ac-DOTA-J591, and 227Th-HOPO-pelgifatamab (227Th-pelgi) (all at 300 kBq/kg) with T/Cvolume ratios of 0.37, 0.39, and 0.33, respectively. 225Ac-pelgi was less myelosuppressive than 227Th-pelgi. 225Ac-pelgi showed dose-dependent treatment efficacy in the patient-derived KuCaP-1 model and strong combination potential with darolutamide in both cell line- (22Rv1) and patient-derived (ST1273) xenograft models. These results provide a strong rationale to investigate 225Ac-pelgi in patients with prostate cancer. A clinical phase 1 study has been initiated (NCT06052306).

Abstract CT224: Preliminary efficacy and safety results from the (TATCIST) trial: A PSMA-directed targeted alpha therapy with FPI-2265 (225Ac-PSMA-I&amp;T) for the treatment of metastatic castration-resistant prostate cancer (mCRPC)

Abstract INTRODUCTION: Targeted α therapy (TAT) in mCRPC is a rapidly advancing class of radiotherapeutics that can effectively deliver potent and local radiation selectively to cancer cells while sparing the surrounding normal cells. Retrospective studies of 225Ac PSMA-RLT (radioligand therapy), have shown promise in pts with mCRPC, where activity correlates with disease characteristics and prior therapies. FPI-2265 (225Ac-PSMA-I&amp;T) consists of a small-molecule PSMA-targeting ligand coupled with a 225Ac radionuclide. Here we present the initial results from TATCIST, an ongoing, open-label, single-arm study (NCT05219500) to evaluate the efficacy and safety of FPI-2265 in pts with mCRPC that was initiated as an investigator-sponsored study then converted into an industry-sponsored trial with more stringent eligibility criteria. METHODS: Eligible pts are required to have progressive mCRPC with PSMA-positive PET. Prior radioligand therapy is permitted. Pts with skeletal metastases presenting as a superscan were excluded upon protocol amendment and excluded from this analysis. Four doses of FPI-2265 at 100 kBq/kg (±10%) are administered at 8-week intervals; de-escalation in cycle 2 and beyond is allowed. Proportion of pts with PSA ≤50%, maximum %PSA decrease, and safety and tolerability of FPI-2265 were assessed. RESULTS: At the time of the data cut (30Jan2024) 30 pts have received ≥1 dose FPI-2265, with 25 pts having ≥12 weeks follow up. For this analysis, 21 pts were evaluable for safety and 20 pts were evaluable for PSA response: 4 pts with superscan were excluded and 1 pt was excluded due to uninterpretable PSA data. In general, pts were heavily pretreated in terms of prior lines of therapy. Most pts (17/21 [81%]) had received a prior taxane, including 8 pts who received ≥2 lines of taxanes. Eight pts received prior 177Lu PSMA-RLT (Lu). PSA50 was achieved in 10/20 pts (50%); In a subset of pts with the baseline PSMA SUVmean &amp;gt;6 (n=13 overall; post-Lu, n=6), PSA50 was achieved in 9 pts (69%). Treatment-related adverse events (TRAEs) included dry mouth (18/21 [86%]), fatigue (10/21 [48%]) dry eye (6/21 [28%]), and anemia (6/21 [28%]). All were Grade 1-2 in severity, expect anemia Grade 3 which was observed in (5/21 [24%]). Other Grade 3 TRAEs included decreased platelet count (3/21 [14%]). No Grade 4 or 5 TRAEs were reported. Dry mouth was primarily Grade 1 (13/21 [62%]) with only 5 patients (24%) experiencing Grade 2 dry mouth; there were no related discontinuations. CONCLUSION: Preliminary efficacy and safety data as of 30Jan24 suggest that FPI-2265 is active in heavily pretreated pts with progressive mCRPC, including pts who received prior Lu therapy. Higher PSMA SUVmean was associated with improved PSA responses, Safety and tolerability were consistent with other published studies of 225Ac-PSMA-RLTs. These initial results support further investigation of FPI-2265 and a new phase 2/3 trial will begin enrolling soon. Citation Format: Ebrahim S. Delpassand, Mohammad Jawed Hashmi, Julia Kazakin, Omer Nawaz, Gabriella Garufi, Joanne Schindler, Luke Nordquist. Preliminary efficacy and safety results from the (TATCIST) trial: A PSMA-directed targeted alpha therapy with FPI-2265 (225Ac-PSMA-I&amp;T) for the treatment of metastatic castration-resistant prostate cancer (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 CT224.

Favorable Response of 225Ac-PSMA in the Treatment of Castration-Resistant Prostate Cancer With High Bone Metastasis Burden.

225Ac-PSMA treatment demonstrated low hematologic toxicity for prostate cancer with diffuse red marrow infiltration. A 70-year-old man with diffuse bone metastases of castration-resistant prostate cancer received 225Ac-PSMA radiation therapy. After 1 treatment cycle, the patient's skeletal lesions demonstrated a significant response and a significant decrease in PSA. 225Ac-PSMA may be a promising therapeutic option for metastatic castration-resistant prostate cancer patients with high bone metastatic burden.

Genomic profiling and clinical utility of circulating tumor DNA in metastatic prostate cancer: SCRUM-Japan MONSTAR SCREEN project

BackgroundCirculating tumor DNA (ctDNA) testing has emerged as a novel tool for cancer precision medicine. This study investigated the genomic profiling and clinical utility of ctDNA in metastatic prostate cancer.MethodsThis is a nation-wide prospective observational study. Patients treated with systemic treatment for metastatic castration-sensitive prostate cancer (mCSPC) and metastatic castration-resistant prostate cancer (mCRPC) were included. ctDNA was analyzed using FoundationOne Liquid®CDx at enrollment. In a subset of patients, ctDNA after disease progression and tissue prior to the initiation of treatment were examined using FoundationOne Liquid®CDx and FoundationOne®CDx, respectively.ResultsThe frequency of AR alterations and homologous recombination repair (HRR) defect was higher in mCRPC compared with mCSPC. Tumor mutational burden was correlated between tissue and ctDNA at pre-treatment, as well as ctDNA between at pre-treatment and at post-treatment. Patients with HRR defect were associated with shorter time to castration resistance in androgen deprivation therapy/combined androgen blockade, but not in androgen receptor pathway inhibitor, compared with patients without HRR defect in mCSPC. Time to treatment failure in patients with AR amplification or AR mutation was shorter compared with patients without AR alterations in mCRPC.ConclusionsThis study revealed valuable findings for the clinical care of metastatic prostate cancer. Especially, predictive factors such as HRR defect in mCSPC should be validated in the future.

Targeted interleukin-2 enhances the in vivo anti-cancer activity of Pluvicto™.

Pluvicto™ ([177Lu]Lu-PSMA-617), a radioligand therapeutic targeting prostate-specific membrane antigen (PSMA), has been recently approved for the treatment of metastatic castration-resistant prostate cancer (mCRPR). The drug suffers from salivary gland and kidney uptake that prevents its dose escalation to potentially curative doses. In this work, we sought to potentiate the in vivo anti-cancer activity of Pluvicto™ by combining it with L19-IL2, a clinical-stage investigational medicinal product based on tumor-targeted interleukin-2. We established a new PSMA-expressing model (HT-1080.hPSMA) and validated it using a fluoresceine analogue of PSMA-617 (compound 1). The HT-1080.hPSMA model was used to study the saturation and tumor retention of Pluvicto™ (compound 2) and to run combination therapy studies with L19-IL2. To complement our understanding of the mechanism of action of this novel combination, we conducted proteomics experiments on tumor samples after therapy with Pluvicto™ alone or in combination with the immunocytokine. High, selective, and long-lived tumor uptake was observed for Pluvicto™ (2) in the novel HT-1080.hPSMA model. Therapy studies in HT-1080.hPSMA tumor-bearing mice revealed that the combination of Pluvicto™ (2) plus L19-IL2 mediated curative and durable responses in all animals. Potent in vivo anti-cancer activity was observed solely for the combination modality, at doses that were well tolerated by treated animals. Proteomics studies indicated that L19-IL2 boosts the activation of the immune system in animals pre-treated with Pluvicto™. The therapeutic efficacy of Pluvicto™ at low radioactive doses can be effectively enhanced by the combination with L19-IL2. Our findings warrant further clinical exploration of this novel combination modality.

Tolerability of Olaparib Combined with Abiraterone in Patients with Metastatic Castration-resistant Prostate Cancer: Further Results from the Phase 3 PROpel Trial

BackgroundThe PROpel study (NCT03732820) demonstrated a statistically significant progression-free survival benefit with olaparib plus abiraterone versus placebo plus abiraterone in the first-line metastatic castration-resistant prostate cancer (mCRPC) setting, irrespective of homologous recombination repair mutation status. ObjectiveWe report additional safety analyses from PROpel to increase clinical understanding of the adverse-event (AE) profiles of olaparib plus abiraterone versus placebo plus abiraterone. Design, setting, and participantsA randomised (1:1), double-blind, placebo-controlled trial was conducted at 126 centres in 17 countries (October 2018–January 2020). Patients had mCRPC and no prior systemic mCRPC treatment. InterventionOlaparib (300 mg bid) or placebo with abiraterone (1000 mg od) plus prednisone/prednisolone (5 mg bid). Outcome measurements and statistical analysisThe data cut-off date was July 30, 2021. Safety was assessed by AE reporting (Common Terminology Criteria for Adverse Events v4.03) and analysed descriptively. Results and limitationsThe most common AEs (all grades) for olaparib plus abiraterone versus placebo plus abiraterone were anaemia (46.0% vs 16.4%), nausea (28.1% vs 12.6%), and fatigue (27.9% vs 18.9%). Grade ≥3 anaemia occurred in 15.1% versus 3.3% of patients in the olaparib plus abiraterone versus placebo plus abiraterone arm. The incidences of the most common AEs for olaparib plus abiraterone peaked early, within 2 mo, and were managed typically by dose modifications or standard medical practice. Overall, 13.8% versus 7.8% of patients discontinued treatment with olaparib plus abiraterone versus placebo plus abiraterone because of an AE; 3.8% versus 0.8% of patients discontinued because of anaemia. More venous thromboembolism events were observed in the olaparib plus abiraterone arm (any grade, 7.3%; grade ≥3, 6.8%) than in the placebo plus abiraterone arm (any grade, 3.3%; grade ≥3, 2.0%), most commonly pulmonary embolism (6.5% vs 1.8% for olaparib plus abiraterone vs placebo plus abiraterone). ConclusionsOlaparib plus abiraterone has a manageable and predictable safety profile. Patient summaryThe PROpel trial showed that in patients who had not received any previous treatment for metastatic castration-resistant prostate cancer, olaparib combined with abiraterone was more effective in delaying progression of the disease than abiraterone alone. Most side effects caused by combining olaparib with abiraterone could be managed with supportive care methods, by pausing olaparib administration for a short period of time and/or by reducing the dose of olaparib.

Symptoms and quality of life among men starting treatment for metastatic castration-resistant prostate cancer – a prospective multicenter study

BackgroundMen with metastatic castration-resistant prostate cancer (mCRPC) have an incurable disease. Along with prolonging life, symptom management is one of the main goals with treatment. This is also important from a palliative care perspective where the life prolonging outcomes should be balanced with quality of life (QoL) in this late phase. It is also essential in symptom management to view different dimensions of symptoms, for example how severe or distressing symptoms are, to support best QoL. Therefore, more knowledge is needed about the symptom experience when these treatments are initiated and thus the aim of this study was to describe different dimensions of symptoms in men with mCRPC starting their first-line of life-prolonging treatment, and to describe the association between symptom burden and QoL.MethodsBaseline data from a prospective longitudinal study of 143 men with mCRPC starting their first-line life-prolonging treatment were used. Symptoms were measured using the Memorial Symptom Assessment Scale (MSAS) and global QoL was measured by the EORTC QLQ C-30. Data was analyzed using descriptive- and multivariable linear regression analyses.ResultsOn average, the men had more than 10 symptoms (range 0–31 of 33). 50% or more reported sweats, lack of energy, pain, problems with sexual activity and sexual desire. The symptoms they reported as most severe, or most distressing were not always the ones that were reported as most frequent. There was an association between QoL and physical symptoms, and also between QoL, and analgesic use and prostate-specific antigen (PSA) values.ConclusionEven if some men with mCRPC report many symptoms, the dimensions of severity and distress levels vary, and the most frequent symptoms was not always the most burdensome or distressing. There was an association between high physical symptom burden and QoL, suggesting that it is not the number of symptoms that affects QoL but rather the subjective perceived impact of the physical symptoms experienced. The knowledge of how men with mCRPC experience and perceive their symptoms may help health care professionals in symptom management aiming to improve QoL, which is a cornerstone in integrating early palliative care.

SC912 inhibits AR-V7 activity in castration-resistant prostate cancer by targeting the androgen receptor N-terminal domain.

Androgen deprivation therapies (ADT) are the mainstay treatments for castration-resistant prostate cancer (CRPC). ADT suppresses the androgen receptor (AR) signaling by blocking androgen biosynthesis or inhibiting AR with antiandrogens that target AR's ligand-binding domain (LBD). However, the ADT's effect is short-lived, as the AR signaling inevitably arises again, which is frequently coupled with AR-V7 overexpression. AR-V7 is a truncated form of AR that lacks the LBD, thus being constitutively active in the absence of androgens and irresponsive to AR-LBD-targeting inhibitors. Though compelling evidence has tied AR-V7 to drug resistance in CRPC, pharmacological inhibition of AR-V7 is still an unmet need. Here, we discovered a small molecule, SC912, which binds to full-length AR as well as AR-V7 through AR N-terminal domain (AR-NTD). This pan-AR targeting relies on the amino acids 507-531 in the AR-NTD. SC912 also disrupted AR-V7 transcriptional activity, impaired AR-V7 nuclear localization and DNA binding. In the AR-V7 positive CRPC cells, SC912 suppressed proliferation, induced cell-cycle arrest, and apoptosis. In the AR-V7 expressing CRPC xenografts, SC912 attenuated tumor growth and antagonized intratumoral AR signaling. Together, these results suggested the therapeutic potential of SC912 for CRPC.

Abstract 4504: Discovery of CBPD-409 and CBPD-268 as highly potent and orally efficacious CBP/p300 PROTAC degraders for the treatment of castration-resistant prostate cancer

Abstract Prostate cancer remains the leading cause of cancer-related death globally in men. While current AR-targeted therapies are effective for the treatment of prostate cancer and improve patient survival, resistance in patients typically develops within 18 months. CBP/p300 are AR transcriptional co-activators and are promising therapeutic targets for the treatment of castration-resistant prostate cancer (CRPC). We developed a series of highly potent, selective, and orally efficacious CBP/p300 PROTAC degraders, with CBPD-409 being the best compound. CBPD-409 induces robust CBP/p300 degradation with DC50 0.2-0.4 nM and displays strong anti-proliferative effects with IC50 1.2-2.0 nM in VCaP, LNCaP and 22Rv1 AR+ cell lines. It has a favorable oral pharmacokinetic profile and achieves 50% of oral bioavailability in mice. A single oral administration of CBPD-409 at 1 mg/kg achieves &amp;gt;95% depletion of CBP/p300 proteins in the VCaP tumor tissue at 3 h and 24 h time points. CBPD-409 exhibits strong and dose/schedule-dependent tumor growth inhibition and is more potent and efficacious than two CBP/p300 inhibitors CCS1477 and GNE-049 and the AR antagonist Enzalutamide. To further improve the degradation potency and the oral bioavailability in rats, we developed a new class of CBP/p300 degraders based on our optimized CRBN ligand TX-16. Our efforts led to the discovery of CBPD-268 as an exceptionally potent, effective, and orally efficacious degrader of CBP/p300 proteins. In the VCaP, LNCaP and 22Rv1 cell lines, CBPD-268 induces consistent and robust CBP/p300 degradation with DC50 of ≤0.03 nM and Dmax &amp;gt;95%, leading to potent cell growth inhibition. CBPD-268 has excellent oral bioavailability in both mice and rats and has a good ADME profile. Oral administration of CBPD-268 at 0.3-3 mg/kg resulted in profound and persistent depletion of CBP and p300 proteins in tumor tissues and achieved strong antitumor activity in the VCaP and 22Rv1 xenograft tumor models in mice, including tumor regression in the VCaP tumor model. CBPD-268 was well tolerated in mice and rats and displayed a therapeutic index of &amp;gt;10. Taken together, CBPD-409 and CBPD-268 are highly promising CBP/p300 degraders for further extensive evaluations for the treatment of CRPC and other types of human cancers. Citation Format: Zhixiang Chen, Mi Wang, Dimin Wu, Lijie Zhao, Tianfeng Xu, Hoda Metwally, Yu Wang, Donna McEachern, Wei Jiang, Longchuan Bai, Jie Luo, Meilin Wang, Ruiting Li, John Takyi-Williams, Lu Wang, Qiuxia Li, Bo Wen, Duxin Sun, Arul M. Chinnaiyan, Shaomeng Wang. Discovery of CBPD-409 and CBPD-268 as highly potent and orally efficacious CBP/p300 PROTAC degraders for the treatment of 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 4504.

Abstract 7277: Discovery of INV-9956, an orally available and highly selective Cyp11A1 inhibitor for the treatment of castration-resistant prostate cancer with drug resistant AR mutations

Abstract Androgen Receptor (AR) signaling plays a profound role in prostate cancer and development. Efforts in harnessing androgen and AR axis for castration-resistant prostate cancer treatment have led to discovery of several therapeutics, including AR antagonists and Cyp17 inhibitors. However, resistance to these approved therapeutics has emerged, and remained a significant unmet medical need. Among the prominent resistance mechanisms of action are restored androgen signaling via AR amplification and overexpression, and gain-of-function mutations occurring at AR ligand binding domain that can be agonized by existing AR antagonists and/or non-androgenic steroids such as glucocorticoids. Targeting Cyp11A1 that catalyzes the formation of pregnenolone is effective to ablate biosynthesis of androgens and all steroids and thus holds promise to deliver coverage of a significant percentage of drug resistant AR mutations and benefit CRPC patients post treatment with AR antagonists or Cyp17 inhibitors. Here we present discovery and characterization of INV-9956, an orally available, selective, and potent Cyp11A1 inhibitor with well-acceptable pharmacokinetic properties. INV-9956 potently inhibits biosynthesis of pregnenolone and other androgens in H295R cells with IC50 at single-digit nanomolar, suppresses proliferation of prostate cancer cell lines harboring major clinically acquired drug resistant AR LBD mutations, such as AR L702H using coculture assays. Orally administered INV-9956 showed consistent dose dependent PK/PD correlations across animal species. Particularly, INV-9956 displayed pronounced tumor inhibition superior to known competitors in a CRPC VCaP xenograft model and in a “humanized” animal model. Furthermore, INV-9956 displayed a good tox profile in 14-day repeated dosing rat and dog studies, supported by a high selectivity to Cyp11A1 over other Cyp family members, clean hERG and mini-Ames, and no significant off-target activity in a safety panel screen. The promising preclinical profiles of INV-9956 lend strong support to its potentials in addressing unmet needs in CRPC treatments and warrant clinical development. Citation Format: Chang Bai, Danqi Chen, Zilei Xia, Shujuan Huang, LIshan Lin, Zhaopie Zeng, Jing Su, Yongkui Sun. Discovery of INV-9956, an orally available and highly selective Cyp11A1 inhibitor for the treatment of castration-resistant prostate cancer with drug resistant AR mutations [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 7277.

Abstract 4487: Simple modifications of 3-HPT for improved in-vivo activtiy

Abstract One of the key targets in the treatment of castration resistant prostate cancer is HDAC6. HDAC6 removes acetyl groups from Heat shock protein 90 (HSP90), which is a protein chaperone that folds the androgen receptor. By inhibiting HDAC6 it is possible to prevent the expression of mutated androgen receptors, that are no longer responsive to androgen deprivation therapy, treating castration resistant prostate cancer. The Oyelere lab has previously demonstrated that 3-Hydroxypyridin-2-thione (3-HPT) can serve as a scaffold for HDAC6 inhibitors. While the unaltered 3-HPT has been shown on its own to inhibit HDAC6 in enzyme specific assays. The unaltered 3-HPT had no effect in whole cell assays. This work investigated simple modification of the 3-HPT scaffold to improve the in-vivo activity of 3-HPT. This work is an extension of work previously done in the Oyelere lab. The aim of this work is to apply simple modifications to the 3-HPT scaffold to improve the in-vitro activity. Previously 3-HPT was shown on its own to inhibit HDAC6 with an IC50 of 681nM but have no effect on cell assays. The hypothesis was that by converting the secondary amine into a tertiary amine the pharmacokinetic-properties of 3-HPT allowing can be improved focusing on cellular entry. The specific modification was the addition of alkanes and fluorinated alkanes at the secondary amine. This addition should improve the charge of the compounds improving the invitro activity. Based on molecular docking studies using Autodock vina, the introduction of fluorines improves the binding to HDAC6 by interacting with a hydrophilic pocket near the zinc ion. The preliminary in-vivo results in LnCAP and DU145 cells demonstrate that the addition of fluorinated alkanes has substantially improved the IC50 compared to the base 3-HPT compound. The base 3-HPT compound has an IC50 of greater than 100µM while the compounds with fluorinated alkanes have IC50 values in the range of 2-15µM. this data indicates improved drug likeness. Preliminary IC50 values of compounds in prostate cancer cell lines Compound Name LNCaPIC50 (µM) DU145IC50 (µM) Vero IC50 (µM) SH-1-78 &amp;gt;100 &amp;gt;100 &amp;gt;100 SH-1-94 2.50 19.29 22.53 RK-1-187 96.95 95.45 88.57 SH-1-110 1.27 21.47 17.41 RK-2-16 2.09 62.86 18.76 RK-2-17 &amp;gt;100 &amp;gt;100 &amp;gt;100 RK-2-64 78.36 &amp;gt;100 76.45 RK-2-67 14.19 26.95 11.38 Citation Format: Ryan E. Kern, Susanna Huang, Uche Arunsi, Adegboyega Oyelere. Simple modifications of 3-HPT for improved in-vivo activtiy [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 4487.

Abstract 4750: The MNK inhibitor EB1 sensitizes AR-V7 positive castration-resistant prostate cancer to enzalutamide

Abstract Introduction: Resistance to androgen receptor signaling inhibitors (ARSI) like Enzalutamide is frequent in castration resistant prostate cancer (CRPC). The mechanisms driving drug resistance include the overexpression of androgen receptor (AR) and the presence of splice variants like androgen receptor splice variant 7 (AR-V7). Clinical studies (PROPHECY) have demonstrated that AR-V7 positive CRPC patients treated with Enzalutamide show poorer overall survival and thus lack an effective targeted line of treatment. Recently, AR signaling and the regulation of protein translation via the translation initiation factor 4E (eIF4E) and MAPK-interacting kinases (MNKs) have been shown to depend on each other and targeting eIF4E has been proposed to increase the efficacy of ARSI. Objectives: We have recently described EB1 as the first in class non-ATP competitive inhibitor of MNK1/2 (Bou-Petit et al. JMC, 2022) and have now tested its applicability in CRPC. In this work we describe the impact of EB1 on the efficacy of Enzalutamide treatment in CRPC. Methodology: Cell lines 22RV1 and LNCaP-95 were used as AR-V7 positive models of CRPC. Effects of EB1 and Enzalutamide alone and in combination on cell growth were studied through crystal violet assay. Drug combination Index was calculated following Chou-Talalay method using CompuSyn Software. Cell death was studied through propidium iodide (PI) staining. AR transcriptional activity was assessed through RT-qPCR of AR canonical target genes like PSA. A head-to-head study with eFT-508 (Tomivosertib, eFFECTOR Therapeutics, Inc.) as the most advanced Type I MNK inhibitor was performed. Lastly, spheroids obtained through centrifugation in ultra-low attachment plates were used for validating drug interaction in 3D growth and viability studies. Spheroid viability was assessed through PI and Calcein AM staining as well as MTT assay. Results: In vitro results demonstrate strong to moderate synergistic inhibition of cell growth through the induction of cell death by the combination of Enzalutamide and EB1 in AR-V7 positive CRPC cell lines, as well as reduction of AR transcriptional activity (PSA). Drug combination also reduced growth and viability of spheroids, indicating good tumor penetrating properties in 3D models and giving in vitro proof-of-concept for in vivo applications. Furthermore, drug synergy with Enzalutamide could only be observed with EB1 and not with Type-I MNK inhibitors like eFT-508, indicating that MNK1/2 functions beyond its kinase activity might be relevant for cancer progression. Conclusion: Here we demonstrate that the novel MNK inhibitor EB1 shows promising in vitro results, which cannot be obtained with Type-I MNK inhibitors. The combination of EB1 with the standard of care Enzalutamide provide a novel therapeutic opportunity for the treatment of CRPC, particularly in AR-V7 positive patients. Citation Format: Sara García-Ortega, Leticia Suárez-Cabrera, Joan Morote, Olga Méndez, Marta Cano-Galietero, Elena Muro-Blanc, Jose I. Borrell, Anna Santamaria, Santiago Ramón y Cajal, Stefan Hümmer. The MNK inhibitor EB1 sensitizes AR-V7 positive castration-resistant prostate cancer to enzalutamide [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 4750.

Abstract 6359: Development of PSMA x CD3 T-cell engagers using an integrated, functional approach

Abstract In this study, we used a functional approach to generate CD3 T-cell engager (TCE) molecules targeting prostate-specific membrane antigen (PSMA). We present data on the robust in vitro characterization of T-cell activity and selection of molecules for further assessment. TCE function is dictated by the interplay between multiple factors that form the immune synapse, including binding kinetics, binding geometry, and epitopes of the CD3- and tumor-binding arms. To diversify immune synapse parameters, we engineer hundreds of bispecific molecules from highly diverse parental antibodies, and employ a high-throughput process to select molecules with desired functional properties. We applied this approach to engineer CD3 TCEs targeting PSMA. PSMA is an attractive target for the treatment of castration-resistant prostate cancer due to its high expression in prostate cancer cells and low relative expression in other tissues. We discovered hundreds of diverse, fully human PSMA-binding antibodies using high-throughput single B-cell screening and selected human/cynomolgus cross-reactive binders with a broad range of affinities and epitopes. We paired these with human/cynomolgus cross-reactive CD3-binding antibodies from our TCE platform to generate 180 bispecific PSMA x CD3 TCEs. CD3-binding antibodies covered several orders of magnitude of affinity (nanomolar to micromolar) and included binders specific for different CD3 subunits. We used high-throughput T-cell dependent cellular cytotoxicity (TDCC) and cytokine release assays to identify molecules with desired functional profiles. Bispecifics selected for further assessment had functional profiles spanning a range of properties that have been observed in clinical molecules, including potent killing and low cytokine release. To profile T-cell properties that are associated with anti-tumor immune responses, we subjected selected molecules to a battery of additional in vitro functional assessments, including proliferation, cytokine and chemokine production, and TDCC using cynomolgus T cells. Results demonstrate that a functional approach that begins with highly diverse CD3- and tumor-binding antibodies can generate promising TCEs with minimal need for protein engineering and optimization. Citation Format: Valentine de Puyraimond, Matt Mai, Alaa Amash, Nathalie Blamey, Gabrielle Conaghan, Jessica Fernandes Scortecci, Allison Goodman, Ahn Lee, Irene Yu, Franziska von Bank, Kate Caldwell, Lauren Clifford, Ingrid Knarston, Kelly Bullock, Melissa Cid, Cindy-Lee Crichlow, Lindsay Devorkin, Fiona Dickson, Patrick Farber, Stefan Hannie, Courteney Lai, Vivian Li, Stephanie K. Masterman, Iwona Niemietz, Philippe Pouliot, Ping Xiang, Bryan C. Barnhart, Raffi Tonikian. Development of PSMA x CD3 T-cell engagers using an integrated, functional 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 6359.

Abstract 7222: Antiandrogen equipped with HDAC inhibitors activates autophagy-mediated growth inhibition in castrate-resistant prostate cancer

Abstract Targeting androgen receptor (AR) by pharmacologic intervention is one of the practical approaches for the treatment of castration-resistant prostate cancer (CRPC). Hence, this study aimed to develop novel molecules that employ multiple mechanisms to inhibit AR expression and curtail the growth of CRPC. The target antiandrogen-equipped histone deacetylase inhibitors were synthesized, adapting the convergent chemistry we used to synthesize the first-generation compounds. The final compounds were characterized using 1H-NMR, 13C-NMR, and high-resolution mass spectrometry. We synthesized and analyzed several compounds, in which KK62 emerged as the lead compound. KK62 significantly inhibits a panel of CRPC cell lines in nanomolar concentrations without causing toxicity to healthy prostate epithelial cells. The molecular analysis suggested that inhibition of AR and AR-splice variants was evident, followed by downregulation of PSA expression in AR-positive CRPC cell lines. Further analysis confirmed that KK62 overcomes dihydrotestosterone (DHT) induced AR signaling and enzalutamide-resistant CRPC cells by downregulating AR and AR-splice variants in CRPC cells. Subsequent analysis confirmed that KK62 induces autophagy signaling by upregulating autophagosome (LC3B) and lysosome (LAMP1) markers expression and facilitating the autophagosome and lysosome fusion, which resulted in the induction of apoptosis in all AR-positive CRPC cell lines. The pro-apoptotic markers, such as BAX and cleaved caspase, were upregulated, whereas the downregulation of pro-survival markers was evident in KK62-treated CRPC cells. Our ongoing castrated and non-castrated xenotransplanted CRPC tumors and Patient-derived xenograft in vivo studies would validate our in vitro findings and confirm that KK62 is a potent compound that may improve therapeutic advances in treating CRPC. Citation Format: Balaji Chandrasekaran, Kiran Kumar Yalla, Ashish Tyagi, Vaibhav Shukla, Neha Tyagi, Bhawna Tyagi, Mohit Vashishta, Adegboyega K Oyelere, Chendil Damodaran. Antiandrogen equipped with HDAC inhibitors activates autophagy-mediated growth inhibition in castrate-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 7222.

Abstract 2011: MAOA Drives Anti Androgen Therapy Resistance in Advanced Prostate Cancer by Conferring Neuroendocrine Plasticity via a Twist1 BRN2 Signaling Pathway

Abstract Background: Therapy resistance in cancer is often linked to cancer cell state or lineage changes. In prostate cancer (PCa), a subset of castration-resistant prostate cancer (CRPC) loses reliance on the androgen receptor (AR) signaling and gains neuroendocrine (NE) traits through a lineage switch along disease progression. However, the molecular mechanisms driving such cellular lineage plasticity remain unclear. This study investigated the functional and mechanistic role of monoamine oxidase A (MAOA) in driving adenocarcinoma (adeno)-to-NE lineage conversion in CRPC cells upon enzalutamide (ENZ), a FDA-approved newer-generation antiandrogen drug, and evaluated the efficacy of MAOA inhibitors for treating CRPC and overcoming ENZ resistance.Methods: ENZ-resistant C4-2B and CWR-R1 cells (C4-2BENZR and CWR-R1ENZR) CRPC cells were transfected with a PSA promoter-driven GFP expression construct for isolating a PSAlo/− cell population distinct from PSAhi cells, which was used for manipulation of MAOA expression levels and subsequent functional assays in vitro and in vivo. The MAOA expression levels were determined and correlated with NE parameters in PCa clinical samples by immunohistochemistry and data mining of multiple publicly available clinical datasets. Results: MAOA protein expression was significantly upregulated in the PSAlo/− ENZ-resistant cell population, accompanied by concomitant activation of NE markers and downregulation of luminal markers including AR and AR targets, compared to the PSAhi counterpart. Elevated MAOA expression was also found in PCa patient samples associated with NE features from multiple independent cohorts. Silencing MAOA suppressed the proliferation, migration, invasion, stem-like properties and NE plasticity of both PSAlo/- C4-2BENZR and CWR-R1ENZR cells. Moreover, co-culturing adeno LNCaP or C4-2B cells with MAOA-silenced PSAlo/- cells exhibiting a repressed secretory phenotype attenuated acquired induction of NE markers and proliferation of adeno cells as compared to controls. Mechanistically, MAOA induces Twist1, which directly activates the transcription and expression of BRN2, a master neural transcription factor known to confer NE differentiation and anti-AR therapy resistance in CRPC. Further, pharmacological inhibition of MAOA greatly enhanced the growth-inhibitory efficacy of ENZ with ENZ sensitivity restored in ENZ-resistant LuCaP PC PDX-derived organoids as well as a PSAlo/− CWR-R1ENZR xenograft mouse model.Conclusion: Our results suggest MAOA as a potential therapeutic target for reversing ENZ resistance in CRPC treatment by blockade of NE transdifferentiation.Funding Acknowledgements: This work was supported by the NIH/NCI grants R37CA233658 and R01CA258634 (to B. Wu) and the DOD Department of Defense EIRA award W81XWH-21-1-0218 (to J. Wei) Citation Format: Jing Wei, Jing Wang, Chia-hui Chen, Wen Guan, Boyang Wu. MAOA Drives Anti Androgen Therapy Resistance in Advanced Prostate Cancer by Conferring Neuroendocrine Plasticity via a Twist1 BRN2 Signaling Pathway [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 2011.

Abstract 6059: Discovery of ETS-007, a first-in-class degrader targeting N-terminal domain of androgen receptor derived from AR liquid-liquid phase separation inhibitor

Abstract Patients with advanced prostate cancer inevitably acquire resistance to anti-androgen therapies, and progress to lethal castration-resistant prostate cancer (CRPC). The resistance mechanisms involve AR gene amplification and overexpression, constitutively active ligand-independent splice variants such as AR-V7, and the mutations in the AR ligand-binding domain (LBD). Our previous study has shown that the AR N-terminal domain (NTD) is responsible for AR liquid-liquid phase separation (LLPS) capability, which is essential for AR/AR-V7 transcriptional activity. We conducted a compound library screening using an AR LLPS phenotypic assay and identified ET0516 as a hit to specifically inhibit AR LLPS and its downstream gene expression, indicating that inhibition of AR. LLPS through targeting its NTD is a feasible approach to overcome the resistance to current anti-androgens therapy. Here we report the identification of a novel AR degrader, ETS-007 which is originated and evolved from internal LLPS phenotypic screening, that effectively degrades both AR and AR-V7 proteins with DC50 of single-digit nM by inducing a protein-protein interaction between AR NTD and an E3 ligase complex. ETS-007 induced AR and AR-V7 polyubiquitination, followed by degradation which could be blocked by the protease inhibitor MG132. ETS-007 significantly inhibited cell proliferation in AR and/or AR-V7 positive cell lines, e.g. LNCaP and 22RV1, and downregulated the androgen responsive genes such as PSA and TMPRSS2. Compared with enzalutamide and ARV-110, ETS-007 could block transcriptional activities of AR-V7, and AR mutants in luciferase report assay. Oral administration of ETS-007 in an enzalutamide-resistant 22RV1 xenograft model led to intratumoral AR-V7 degradation and concomitant decrease in PSA protein levels, resulting in a remarkable tumor regression. Taken together, our findings provide preclinical evidence that ETS-007 as a potent AR-NTD degrader derived from our LLPS platform can effectively block the transcriptional activities of both AR and AR-V7 for the treatment of metastatic CRPC. Citation Format: Yingjie Li, Mingyue Fei, Yingke Miao, Lijian Feng, Xiaofei Fan, Jinping Li, Yaozhong Chen, Ming Xu, Wenqi Cui, Qiangang Zheng, Jidong Zhu. Discovery of ETS-007, a first-in-class degrader targeting N-terminal domain of androgen receptor derived from AR liquid-liquid phase separation inhibitor [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 6059.

Abstract 1904: Preclinical development of MGC026, a glycan-linked, exatecan-based antibody-drug conjugate (ADC) targeting B7-H3 for solid cancer

Abstract Introduction: Antibody-drug conjugates (ADCs) have emerged as an important class of therapeutic agents for the treatment of cancer. A duocarmycin-based B7-H3-targeted DNA-alkylating ADC, vobramitamab duocarmazine (vobra duo), has shown encouraging clinical activity in the treatment of metastatic castration-resistant prostate cancer. Given the broad spectrum of tumor indications addressable by targeting B7-H3, we developed MGC026, an ADC incorporating a B7-H3-targeting antibody and a novel glycan-linked topoisomerase 1 inhibitor (TOP1i). With distinct mechanisms of action, vobra duo and MGC026 can address different cancers, tumor stages, or be used in combination with alternate agents to enhance their clinical utility. Methods: MGC026 is comprised of the cleavable linker-payload, bicyclononyne carbamoyl sulfamide Val-Ala-PABC exatecan (SYNtecan E™) site-specifically conjugated at asparagine 297 of the heavy chain through enzymatic glycan remodeling and metal-free click chemistry, using Synaffix’s GlycoConnect™ technology. In vivo efficacy studies were conducted in immunodeficient mice with human tumor cell-line or patient-derived xenografts to identify the spectrum of MGC026-sensitive tumors and the relationship between exposure and antitumor activity. A toxicology study was conducted in cynomolgus monkeys in which MGC026 was administered by 15-minute IV infusion once every three weeks. Pharmacokinetic (PK) analysis and detailed toxicology evaluation was performed. Results: MGC026 demonstrated specific, dose-dependent in vivo antitumor activity toward B7-H3-positive tumor xenografts representing lung, pancreatic, and prostate cancers, head and neck squamous cell carcinoma, and melanoma. Additionally, MGC026 demonstrated antitumor activity toward B7-H3-positive patient-derived xenograft models of lung and prostate cancer, with additional indications under investigation. MGC026, administered to cynomolgus monkeys at dose levels of 10, 30, and 50 mg/kg every 3 weeks for a total of 3 doses, exhibited approximate dose-proportional PK and high stability in circulation. MGC026 was well tolerated, with no lung toxicity observed, and the highest dose level tested (50 mg/kg) was declared as the highest non-severely toxic dose. Conclusions: MGC026 exhibited a favorable preclinical profile, with potent in vivo activity toward B7-H3-expressing tumor xenografts representing a range of cancer indications. MGC026 was tolerated in cynomolgus monkeys, a relevant toxicology model, at exposure levels exceeding those required for antitumor activity. These data support clinical development of MGC026 for the treatment of B7-H3-expressing solid cancers. Citation Format: Juniper A. Scribner, Jennifer G. Brown, Thomas Son, Linda Jin, Carroll McKenzie, Viktoriya Nam, Curtis Bush, Dienis Quinonez, James Tamura, Sergey Gorlatov, Hua Li, Shelley Butler, Ezio Bonvini, Deryk Loo. Preclinical development of MGC026, a glycan-linked, exatecan-based antibody-drug conjugate (ADC) targeting B7-H3 for solid 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 1904.