JNJ-6143 shows 75% tumour response rate in Phase I advanced prostate cancer study

Johnson & Johnson has reported early Phase I results showing that JNJ-6143 produced substantial anti-tumour activity in patients with advanced prostate cancer who had received multiple previous treatments.

JNJ-6143, formerly known as HLD-0915, is an investigational once-daily oral small molecule developed using the company’s Regulated Induced Proximity Targeting Chimera, or RIPTAC, platform.

Among patients with measurable disease receiving the 50 mg dose, 75% achieved a confirmed complete or partial tumour response according to RECIST criteria.

This represented 12 of 16 evaluable patients.

The same dose also produced deep reductions in prostate-specific antigen levels.

Among 38 patients treated with JNJ-6143 at 50 mg once daily, 77% achieved a confirmed PSA reduction of at least 50%.

Nearly half of patients, or 48%, experienced a PSA decline of at least 90%.

The findings were presented during a Proffered Paper session at the 2026 European Society for Medical Oncology Congress.

JNJ-6143 is designed to trigger cancer cell death through a dual-protein interaction involving BRD4 and the androgen receptor.

The RIPTAC mechanism brings BRD4, an essential protein involved in cell survival, into proximity with androgen receptor, which is highly expressed in many prostate cancer cells.

Johnson & Johnson said this targeted interaction is intended to disrupt cancer cell function and induce cell death through a mechanism that differs from existing androgen receptor-directed therapies.

The Phase I study included patients with advanced prostate cancer whose disease had progressed despite multiple previous lines of treatment.

Participants had received a median of four prior therapies, including chemotherapy and prostate-specific membrane antigen-targeted radioligand treatment.

PSA reductions were also observed among patients with molecular characteristics associated with higher-risk and more difficult-to-treat disease.

At the time of analysis, 71% of patients receiving the 50 mg dose remained on treatment.

Median follow-up in this group was 5.6 months.

Most treatment-related adverse events were mild or moderate.

The most commonly reported treatment-related events were elevated cholesterol levels in 18% of patients, nausea in 16% and increased triglyceride levels in 16%.

Four patients, representing 11%, temporarily interrupted treatment because of adverse events.

One patient reduced their dose and one discontinued treatment, representing 3% of patients in each category.

Johann de Bono, MD, Head of the Prostate Cancer Targeted Therapy Group at the Institute of Cancer Research in London, said the early findings suggest meaningful anti-tumour activity in patients whose disease had already progressed through several previous therapies.

Yusri Elsayed, MD, MHSc, PhD, Global Therapeutic Area Head of Oncology at Johnson & Johnson, said the results provide early clinical support for the RIPTAC approach and its potential as a different treatment strategy in prostate cancer.

Based on the Phase I findings, Johnson & Johnson has selected the 50 mg once-daily dose for continued development.

JNJ-6143 is set to advance into a Phase II study evaluating the treatment in patients with metastatic prostate cancer.

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