ASCO24: J&J Reports Four Deaths in Early Prostate Cancer Trial

Four patients have died in a Phase I clinical trial conducted by Johnson & Johnson (J&J) for their investigational drug, JNJ-6420. This drug is being studied as a targeted radiopharmaceutical treatment for metastatic castration-resistant prostate cancer. The findings were disclosed just ahead of the American Society of Clinical Oncology's annual meeting.

The study involved 57 participants, each receiving at least one dose of JNJ-6420. Of these, 31 patients continued the treatment for a minimum of 24 weeks. The interim analysis revealed that three patients exhibited a confirmed objective response, with one patient achieving a complete response.

Nearly half of the patients administered a 150-μCi dose of JNJ-6420 experienced a 50% reduction in prostate-specific antigen levels. Furthermore, 14% of the patients reached this threshold. By the six-month mark, the disease control rate was recorded at 28.1%.

The abstract suggests that one or two doses of the 150-μCi JNJ-6420 can induce significant and lasting biochemical and radiographic responses in patients. Nevertheless, the safety profile of JNJ-6420 raises concerns. Over 60% of the participants experienced treatment-emergent adverse events (TEAEs) of at least grade 3 severity, while almost 37% encountered serious TEAEs. Common adverse events included anemia, low platelet count, and significant reductions in white blood cells. Nine patients withdrew from the study due to severe side effects attributed to the drug.

JNJ-6420 is a potentially pioneering targeted radiopharmaceutical that employs an anti-hK2 antibody to deliver an actinium-based radioligand. This radioligand emits high-energy alpha particles across short ranges, providing targeted treatment to prostate cancer cells.

With the latest data release, J&J joins a growing number of companies investing in the emerging field of targeted radiopharmaceuticals. Bristol Myers Squibb, for instance, acquired RayzeBio for $3.6 billion in December 2023. RayzeBio also employs actinium-based payloads, with its lead program, RYZ101, being developed for gastroenteropancreatic neuroendocrine tumors and small-cell lung cancer.

In March 2024, AstraZeneca made a significant move in the radiopharmaceutical sector by potentially acquiring Fusion Pharmaceuticals for $2.4 billion. Fusion is also developing an actinium-based candidate, FPI-2265, which will compete with JNJ-6420 in treating metastatic castration-resistant prostate cancer.

Earlier this month, Novartis invested $1 billion in the radiopharmaceuticals sector by acquiring Mariana Oncology. Following this, Eli Lilly entered into a $1.1 billion partnership with Aktis Oncology.

The increasing interest and investment in targeted radiopharmaceuticals underscore the potential these treatments hold for addressing various forms of cancer, despite the associated risks and challenges evidenced by the high rate of adverse events in J&J’s trial.

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