Johnson & Johnson announced new data from a Phase 1 study evaluating pasritamig (JNJ-78278343), a first-in-class bispecific antibody that activates T-cells to harness the body's immune system against prostate cancer cells, showing promise in patients with advanced disease who have progressed after multiple lines of therapy. These first data on pasritamig, from the first-in-human study, demonstrate that pasritamig appears well-tolerated and exhibits a promising antitumor activity in patients with metastatic castration-resistant prostate cancer (mCRPC), highlighting the potential of KLK2 as a novel target for T-cell engagement in advanced disease.1 These data were presented as an oral presentation (Abstract #5017) at the 2025 American Society of Clinical Oncology Annual Meeting and published simultaneously in The Journal of Clinical Oncology.
Pasritamig is a novel T-cell engager designed to bind both CD3 on T-cells and KLK2—a prostate-specific antigen with minimal expression outside of the prostate. Pasritamig activates T-cells by binding to CD3 and directing them to KLK2- expressing tumor cells, engaging the body's immune system to specifically target these cancerous cells. This differentiated approach aims to deliver a targeted treatment for patients with advanced prostate cancer, while potentially reducing the high-grade toxicities historically associated with T-cell engagers.
"These first-in-human results for pasritamig are highly encouraging, demonstrating that KLK2 is a viable target for T-cell engagers in metastatic castration-resistant prostate cancer," said Capucine Baldini*, M.D., Ph.D., Drug Development Department (DITEP), Institut Gustave Roussy, and presenting author. "The data show a promising safety profile, with manageable adverse events and no AEs leading to treatment discontinuations or ICANS observed, with 40 percent of patients having no treatment-related AEs at all. Given the limited treatment options for mCRPC, these findings support further investigation of pasritamig and the role of KLK2-targeted T-cell therapies as a potential new approach for patients with aggressive disease."
"Metastatic castration-resistant prostate cancer remains one of the most difficult stages of prostate cancer to treat, particularly for patients who haven't responded well to previous treatments," said Jeff Infante, M.D., Vice President of Early Clinical Development and Translational Research at Johnson & Johnson Innovative Medicine. "This investigational approach underscores our commitment to developing innovative and practice-changing medicines that are well-tolerated and can be easily administered in community practice settings."
The Phase 1 first-in-human study (NCT04898634) evaluated 174 patients with ages ranging from 36 to 89 years old and on average having received four prior therapies (range 1-13). The recommended phase 2 dose (RP2D) of pasritamig was 3.5mg on day 1, 18mg on day 8, 300mg intravenously on day 15 and then once every six weeks. The RP2D safety group also included patients treated once every three weeks as the toxicity profiles were very similar. The RP2D efficacy group only included patients treated at the RP2D once every six weeks.1
Within the RP2D safety group (n=45), treated once every three or six weeks, 100 percent had previously received androgen receptor pathway inhibitors, 75.6 percent had undergone taxane chemotherapy, and 37.8 percent had been treated with Lutetium 177 vipivotide tetraxetan prostate-specific membrane antigen radioligand therapy.1 The most common treatment- related adverse events (TRAEs) were Grade 1/2 infusion-related reactions (24.4 percent), Grade 1 cytokine release syndrome (CRS) presenting as fever only (8.9 percent, no steroid or tocilizumab was administered) and no reports of higher grade CRS. No TRAEs leading to treatment discontinuation or dose reduction were reported and no immune effector cell-associated neurotoxicity syndrome (ICANS) was observed. Grade 3 TRAEs were infrequent with 4.4 percent of patients reporting transient AST/ALT increases and neutropenia. There were no dose-limiting toxicities reported. The favorable safety profile of the RP2D regimen enabled convenient outpatient administration on a patient-friendly, once-every-six-weeks schedule.1
Of the patients in the RP2D efficacy group (n=33), treated once every six weeks, 42.4 percent achieved a 50 percent or greater reduction in their prostate-specific antigen (PSA) levels with a median rPFS of 7.9 months (95 percent confidence interval [CI] 2.9, not estimable [NE]) and 21.2 percent of patients continuing therapy. Treatment with pasritamig showed durable disease control and rPFS that compares favorably to historical data in heavily pretreated patients with mCRPC.
Metastatic castration-resistant prostate cancer occurs in a significant portion of prostate cancer patients, with many progressing despite initial therapies. Overall survival from diagnosis of mCRPC patients ranges from 13.5 to 31.6 months, and lower in patients who have progressed on therapy. Treatment options remain limited, underscoring the urgent need for safer and more effective therapies.
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