Exploring the Role of Target Expression in Treatment Efficacy of Antibody-Drug Conjugates (ADCs) in Solid Cancers: A Comprehensive Review.

PURPOSE OF REVIEW: Antibody-drug conjugates (ADCs) offer a promising path for cancer therapy, leveraging the specificity of monoclonal antibodies and the cytotoxicity of linked drugs. The success of ADCs hinges on precise targeting of cancer cells based on protein expression levels. This review explores the relationship between target protein expression and ADC efficacy in solid tumours, focusing on results of clinical trials conducted between January 2019 and May 2023. RECENT FINDINGS: We hereby highlight approved ADCs, revealing their effectiveness even in low-expressing target populations. Assessing target expression poses challenges, owing to variations in scoring systems and biopsy types. Emerging methods, like digital image analysis, aim to standardize assessment. The complexity of ADC pharmacokinetics, tumour dynamics, and off-target effects emphasises the need for a balanced approach. This review underscores the importance of understanding target protein dynamics and promoting standardized evaluation methods in shaping the future of ADC-based cancer therapies.

Activity of Lutetium-177 Prostate-specific Membrane Antigen and Determinants of Outcomes in Patients with Metastatic Castration-resistant Prostate Cancer Previously Treated with Cabazitaxel: The PACAP Study.

BACKGROUND: Both cabazitaxel and lutetium-177 prostate-specific membrane antigen (Lu-PSMA) improve survival in metastatic castration-resistant prostate cancer (mCRPC) after an androgen receptor pathway inhibitor and docetaxel, but there are limited data regarding Lu-PSMA activity after cabazitaxel. OBJECTIVE: To assess the activity of Lu-PSMA and determinants of outcomes after cabazitaxel in mCRPC. DESIGN, SETTING, AND PARTICIPANTS: A retrospective analysis was conducted of consecutive mCRPC patients from eight European centers treated with Lu-PSMA after cabazitaxel. INTERVENTION: Lu-PSMA every 6-8 wk at a dose of 6-7.6 GBq. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The primary endpoint was radiographic progression-free survival (rPFS). The secondary endpoints included time to prostate-specific antigen (PSA) progression (TTPSA), overall survival (OS), PSA decline, objective response rate (ORR), clinical benefit, and safety. RESULTS AND LIMITATIONS: Of 126 patients, 68% had International Society of Urological Pathology (ISUP) grade 4-5 disease, 21% had visceral metastases, and 7% had lymph node disease only. DNA damage repair (DDR) alterations were detected in 11/50 (22%) patients with available testing. Patients received a median number of 3 Lu-PSMA cycles (interquartile range 2-4). With a median follow-up of 12.0 mo, the median rPFS was 4.4 mo (95% confidence interval [CI] 3.2-5.4), TTPSA 3.5 mo (95% CI 3.0-4.6), and OS 8.9 mo (95% CI 6.5-12.7). The ORR was 35%, and 55 patients (44%) experienced a PSA decline of ≥50%. The time to castration resistance of <12 mo was associated with shorter rPFS (p = 0.01). A similar trend was observed for ISUP grade 4-5 (p = 0.08), and baseline positron-emission tomography parameters including PSMA mean standardized uptake value (SUV) and maximum SUV (respectively, p = 0.06 and 0.05). The duration of previous cabazitaxel or DDR status did not impact outcomes. Patients experiencing a PSA decline of ≥ 50% on therapy demonstrated longer rPFS, TTPSA, and OS (all p < 0.0001). Limitations include retrospective data collection and investigator-based rPFS assessment. CONCLUSIONS: Lu-PSMA demonstrated a substantial PSA decline but limited rPFS after cabazitaxel in a real-life setting. Adverse baseline characteristics, baseline positron-emission tomography parameters, and quality of PSA response may help identify patients less likely to benefit from Lu-PSMA. PATIENT SUMMARY: Lutetium-177 prostate-specific membrane antigen (Lu-PSMA) improved outcomes in patients with castration-resistant prostate cancer, but there are limited data about its activity after cabazitaxel, a chemotherapy that is also the standard of care in this setting. We conducted a study across eight European centers and showed substantial responses on Lu-PSMA after cabazitaxel, although activity was short lived in a heavily pretreated population. Our findings prompt for real-life evaluation of Lu-PSMA in earlier settings to define the best therapeutic sequence.

Development of Novel Models of Aggressive Variants of Castration-resistant Prostate Cancer.

BACKGROUND: Genomic studies have identified new subsets of aggressive prostate cancer (PCa) with poor prognosis (eg, neuroendocrine prostate cancer [NEPC], PCa with DNA damage response [DDR] alterations, or PCa resistant to androgen receptor pathway inhibitors [ARPIs]). Development of novel therapies relies on the availability of relevant preclinical models. OBJECTIVE: To develop new preclinical models (patient-derived xenograft [PDX], PDX-derived organoid [PDXO], and patient-derived organoid [PDO]) representative of the most aggressive variants of PCa and to develop a new drug evaluation strategy. DESIGN, SETTING, AND PARTICIPANTS: NEPC (n = 5), DDR (n = 7), and microsatellite instability (MSI)-high (n = 1) PDXs were established from 51 patients with metastatic PCa; PDXOs (n = 16) and PDOs (n = 6) were developed to perform drug screening. Histopathology and treatment response were characterized. Molecular profiling was performed by whole-exome sequencing (WES; n = 13), RNA sequencing (RNA-seq; n = 13), and single-cell RNA-seq (n = 14). WES and RNA-seq data from patient tumors were compared with the models. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Relationships with outcome were analyzed using the multivariable chi-square test and the tumor growth inhibition test. RESULTS AND LIMITATIONS: Our PDXs captured both common and rare molecular phenotypes and their molecular drivers, including alterations of BRCA2, CDK12, MSI-high status, and NEPC. RNA-seq profiling demonstrated broad representation of PCa subtypes. Single-cell RNA-seq indicates that PDXs reproduce cellular and molecular intratumor heterogeneity. WES of matched patient tumors showed preservation of most genetic driver alterations. PDXOs and PDOs preserve drug sensitivity of the matched tissue and can be used to determine drug sensitivity. CONCLUSIONS: Our models reproduce the phenotypic and genomic features of both common and aggressive PCa variants and capture their molecular heterogeneity. Successfully developed aggressive-variant PCa preclinical models provide an important tool for predicting tumor response to anticancer therapy and studying resistance mechanisms. PATIENT SUMMARY: In this report, we looked at the outcomes of preclinical models from patients with metastatic prostate cancer enrolled in the MATCH-R trial (NCT02517892).

A Phase I Study of Acapatamab, a Half-life Extended, PSMA-Targeting Bispecific T-cell Engager for Metastatic Castration-Resistant Prostate Cancer.

PURPOSE: Safety and efficacy of acapatamab, a prostate-specific membrane antigen (PSMA) x CD3 bispecific T-cell engager were evaluated in a first-in-human study in metastatic castration-resistant prostate cancer (mCRPC). PATIENTS AND METHODS: Patients with mCRPC refractory to androgen receptor pathway inhibitor therapy and taxane-based chemotherapy received target acapatamab doses ranging from 0.003 to 0.9 mg in dose exploration (seven dose levels) and 0.3 mg (recommended phase II dose) in dose expansion intravenously every 2 weeks. Safety (primary objective), pharmacokinetics, and antitumor activity (secondary objectives) were assessed. RESULTS: In all, 133 patients (dose exploration, n = 77; dose expansion, n = 56) received acapatamab. Cytokine release syndrome (CRS) was the most common treatment-emergent adverse event seen in 97.4% and 98.2% of patients in dose exploration and dose expansion, respectively; grade ≥ 3 was seen in 23.4% and 16.1%, respectively. Most CRS events were seen in treatment cycle 1; incidence and severity decreased at/beyond cycle 2. In dose expansion, confirmed prostate-specific antigen (PSA) responses (PSA50) were seen in 30.4% of patients and radiographic partial responses in 7.4% (Response Evaluation Criteria in Solid Tumors 1.1). Median PSA progression-free survival (PFS) was 3.3 months [95% confidence interval (CI): 3.0-4.9], radiographic PFS per Prostate Cancer Clinical Trials Working Group 3 was 3.7 months (95% CI: 2.0-5.4). Acapatamab induced T-cell activation and increased cytokine production several-fold within 24 hours of initiation. Treatment-emergent antidrug antibodies were detected in 55% and impacted serum exposures in 36% of patients in dose expansion. CONCLUSIONS: Acapatamab was safe and tolerated and had a manageable CRS profile. Preliminary signs of efficacy with limited durable antitumor activity were observed. Acapatamab demonstrated pharmacokinetic and pharmacodynamic activity.

Targeted Inhibition of CYP11A1 in Castration-Resistant Prostate Cancer.

BACKGROUND: Prostate cancer is regulated by steroid hormones, even in castration-resistant disease. ODM-208, a novel inhibitor of cytochrome P450 11A1 (which catalyzes the first step of steroid-hormone biosynthesis), was investigated in patients with heavily pretreated metastatic castration-resistant prostate cancer (mCRPC). METHODS: CYPIDES is a first-in-human phase 1 (3 + 3 design) and phase 2 study. We administered ODM-208 twice daily with glucocorticoid/mineralocorticoid replacement and ongoing androgen deprivation therapy to adults with previously treated mCRPC, regardless of androgen receptor gene (AR) ligand-binding domain mutations (phase 1) and with activating AR ligand-binding domain mutations (ARmut; phase 2). Safety, pharmacokinetics, steroid-hormone pharmacodynamics, and preliminary efficacy were the key outcomes. RESULTS: Ninety-two patients received one or more doses of ODM-208: 47 in phase 1 (20 [42.6%] with ARmut) and 45 in phase 2 (all ARmut). A dose of ODM-208 of 5 mg twice a day with dexamethasone 1 mg/fludrocortisone 0.1 mg provided a balance between decreased steroidogenesis and toxicity. Treatment-related adrenal insufficiency was the most common toxicity in phase 1 (n=17, 36.2%; necessitating ODM-208 discontinuation in one patient); this toxicity occurred in six patients (13.3%) at 5 mg twice a day in phase 2. Median circulating testosterone levels declined from 3.0 ng/dl (interquartile range, 1.3 to 6.2 ng/dl) at baseline to undetectable levels within the first week of ODM-208 5 mg twice a day treatment in 46 of 53 (87%) patients. A decrease in prostate-specific antigen levels of 50% or more occurred in 14 of 19 (73.7%) patients with ARmut and 2 of 23 (8.7%) patients with AR wild type in phase 1 and in 24 of 45 (53.3%) patients with ARmut in phase 2. CONCLUSIONS: ODM-208 potently inhibited steroid-hormone biosynthesis with the expected toxicity of adrenal insufficiency. Evidence of antitumor activity was observed in this heavily pretreated mCRPC population, especially in those with ARmut. (Funded by Orion Pharma; ClinicalTrials.gov number, NCT03436485.)