Early prediction of prostate cancer biochemical recurrence and identification of disease persistence using PSA isoforms and human kallikrein-2

BACKGROUND: The role of isoforms of prostate specific antigen (PSA) and other kallikrein-related markers in early detection of biochemical recurrence (BCR) after radical prostatectomy (RP) is not well known and serum PSA is currently used in preoperative risk nomograms. OBJECTIVE: The aim of this research was to study pre- and early postoperative levels of important PSA isoforms and human kallikrein-2 to determine their ability to predict BCR and identify disease persistence (DP). METHODS: This study included 128 consecutive patients who underwent RP for clinically localized prostate cancer. PSA, fPSA, %fPSA, [–2]proPSA, PHI and hK2 were measured preoperatively, at 1 and 3 months after RP. We determined the ability of these markers to predict BCR and identify DP. RESULTS: The DP and BCR rate were 11.7%and 20.3%respectively and the median follow up was 64 months (range 3–76 months). Preoperatively, the independent predictors of BCR were PSA (p-value 0.029), [–2]proPSA (p-value 0.002) and PHI (p-value 0.0003). Post-RP, PSA was the single marker correlating with BCR, both at one (p-value 0.0047) and 3 months (p-value 0.0004). PSA, fPSA, [–2]proPSA and PHI significantly correlated to DP at 1 and 3 months post-RP (p-value < 0.05), although PSA had the most significant existing correlation (p-value < 0.0001). CONCLUSIONS: [–2]proPSA and PHI are preoperative predictors of BCR and DP that outperform the currently used serum PSA. At the early postoperative period there is no additional benefit of the other markers tested.

Phase 0 study to assess [111In]-DOTA-h11B6 to target human kallikrein-2 (hk2) in men with metastatic castration-resistant prostate cancer.

TPS249 Background: Human kallikrein-2 (hk2) is a member of the kallikrein family, is produced by prostatic epithelium, has 80% DNA sequence homology with PSA, is both circulating and bound to prostatic tissue, and is highly expressed even in high grade tumors. hK2 holds the promise of serving as a new therapeutic target for radiopharmaceuticals in prostate cancer. h11B6 is a humanized antibody directed to an epitope found on the catalytically active form of hK2, which is permanently internalized after binding. This is a first-in-human trial of [111In]-DOTA-h11B6 to determine the radio-immunotherapeutic potential of targeting hK2 with nanomolar affinity. The trial will determine the most favorable antibody mass as well as assess tumor targeting. Methods: To determine the optimal antibody mass, two cohorts of patients will be studied. All patients will receive 2 mg of [111In]-labeled h11B6. The first cohort consists of escalating amounts of antibody mass in 2-6 patients: 2, 10 and 20 mg total antibody respectively. Patients will undergo serial whole-body images for up to a week, along with assessments of serum clearance kinetics and normal organ residence time. The lowest mass amount of antibody that demonstrates favorable biodistribution and evidence of radioactivity accumulation in tumor will be used for the second cohort. Up to 6 patients will be studied in the second cohort, which will focus on assessment of antibody tumor targeting. Following this optimization and targeting imaging trial, a phase 1 dose-escalation radioimmunotherapy trial may be performed. Clinical trial information: NCT04116164.

Genetic signature of prostate cancer resistant to optimized hK2 targeted alpha-particle therapy

Hu11B6 is a monoclonal antibody that internalizes in cells expressing androgen receptor (AR)-regulated prostate specific enzyme human kallikrein 2 (hK2; KLK2). In multiple rodent models, Actinium-225 labeled hu11B6-IgG1 ([225Ac]hu11B6-IgG1) has shown promising treatment efficacy. In the current study we investigated options to enhance and optimize [225Ac]hu11B6 treatment. Firstly, we evaluated the possibility of exploiting IgG3, the immunoglobulin G (IgG) subclass with superior activation of complement and ability to mediate FC-gamma-receptor binding, for immunotherapeutically enhanced hK2 targeted alpha-radioimmunotherapy. Secondly, we compared the therapeutic efficacy of a single high activity vs. fractionated activity. Finally, we used RNA sequencing to analyze the genomic signatures of prostate cancer that progressed after targeted alpha therapy. [225Ac]hu11B6-IgG3 was a functionally enhanced alternative to [225Ac]hu11B6-IgG1 but offered no improvement of therapeutic efficacy. Progression free survival was slightly increased with a single high activity compared to fractionated activity. Tumor free animals succumbing after treatment revealed no evidence of treatment associated toxicity. In addition to upregulation of canonical aggressive prostate cancer genes, such as MMP7, ETV1, NTS and SCHLAP1, we also noted a significant decrease in both KLK3 (PSA) and FOLH1 (PSMA) but not in AR and KLK2, demonstrating efficacy of sequential [225Ac]hu11B6 in a mouse model.