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J&J's experimental prostate cancer drug shrinks tumors in most patients

J&J's experimental prostate cancer drug shrinks tumors in most patients

New Capabilities

Phase 1 data shows a 75% response rate with JNJ-6143, a first-in-class dual-protein lock molecule, in heavily pretreated disease

3 days ago: J&J reports PSA responses for a separate prostate cancer combination

Overview

Updated 3 days ago

Johnson & Johnson's experimental prostate cancer drug JNJ-6143 shrank tumors in 12 of 16 patients with measurable disease in a Phase 1 trial. The results were presented October 24 at the European Society for Medical Oncology Congress, and J&J's press release followed a day later.

The drug locks two proteins together inside cancer cells, trapping BRD4, which those cells need to survive. Patients in the trial had received a median of four prior treatments, including chemotherapy and PSMA-targeted radiation. On October 31, Prostate Warriors reported a registered randomized Phase 3 trial of JNJ-6143 with an overall survival endpoint.

Why it matters

If the drug holds up in Phase 2, it could give late-stage prostate cancer patients a daily oral option after standard therapies stop working.

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Key Indicators

75%
Confirmed tumor response rate
12 of 16 patients with measurable disease had complete or partial responses per RECIST criteria, per J&J. The ESMO abstract reports 69% (11 of 16) as the confirmed objective response rate.
77%
Confirmed PSA50 rate at 50 mg dose
Patients whose prostate-specific antigen (PSA) fell by at least half, among 31 PSA-evaluable patients at the 50 mg dose.
48%
Confirmed PSA90 rate at 50 mg dose
Nearly half of patients saw PSA levels drop by at least 90 percent.
50 mg
Recommended Phase 2 dose
Once-daily oral dosing selected for further development based on activity, safety and pharmacokinetics.
4
Median prior therapies
Patients had received a median of four prior treatments, including chemotherapy and PSMA-targeted radioligand therapy.

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Organizations Involved

Johnson & Johnson
Johnson & Johnson
Pharmaceutical company
Developer of JNJ-6143; presented Phase 1 data at ESMO 2026

Global pharmaceutical company that acquired Halda Therapeutics in December 2025, gaining JNJ-6143 and the RIPTAC platform.
Halda Therapeutics
Halda Therapeutics
Biotechnology company
Acquired by Johnson & Johnson in 2025

Biotechnology company that developed the RIPTAC platform and the investigational molecule HLD-0915, now known as JNJ-6143.
European Society for Medical Oncology (ESMO)
European Society for Medical Oncology (ESMO)
Professional medical society
Hosted presentation of JNJ-6143 Phase 1 data at 2026 Congress

Professional organization for oncology specialists; its annual congress is a major venue for cancer clinical data.

Timeline

2025 November 2026

5 events Latest: 3 days ago
Tap a bar to jump to that date

  1. J&J reports PSA responses for a separate prostate cancer combination

    Latest Clinical data

    J&J said a regimen combining pasritamig and JNJ-9401, which targets the KLK2 and PSMA proteins to activate T cells against cancer, produced PSA responses in 73% of patients on every-six-week dosing. This is a different program from JNJ-6143, and the release did not give the number of patients the rate is based on.

  2. Randomized Phase 3 trial reported as registered

    Trial registration

    Prostate Warriors reported a newly registered randomized Phase 3 trial of JNJ-6143 with an overall survival endpoint in metastatic castration-resistant prostate cancer. The report is secondary and was not checked against a trial registry.

  3. Phase 1 results presented at ESMO 2026

    Clinical data

    Proffered Paper presented at ESMO; J&J announced 75% confirmed response and 77% PSA50 at 50 mg the next day. The 50 mg daily dose was selected for Phase 2.

  4. Phase 1 data cutoff

    Clinical data

    The ESMO data cutoff for the JNJ-6143 Phase 1 study. At that point 69 of 105 patients remained on treatment, including 27 of 38 at 50 mg.

  5. J&J completes Halda acquisition

    Acquisition

    Johnson & Johnson completes purchase of Halda Therapeutics, adding the RIPTAC platform and JNJ-6143.

Scenarios

1

JNJ-6143 confirms signal, enters Phase 3 registration trial

Likely Resolves by End of 2028

Discussed by: J&J has already initiated Phase 2 (NCT07832292), indicating internal confidence in the 50 mg dose

J&J moves JNJ-6143 into a registrational Phase 3 study after Phase 2 replicates the Phase 1 response rates. A fast-track or breakthrough designation from the FDA would shorten the path to approval, given the unmet need in patients who have exhausted AR-targeted therapy, chemotherapy and radioligand therapy.

2

Safety signal stalls JNJ-6143 development

Unlikely Resolves by Q2 2028

Discussed by: J&J's own data — 11% of patients at 50 mg interrupted dosing, 3% discontinued due to adverse events

The most common side effects — elevated cholesterol (18%), nausea (16%) and high triglycerides (16%) — were manageable in early follow-up. If longer exposure produces liver toxicity or cardiovascular issues, regulators could place the trial on hold or J&J could halt the program.

3

Response rates moderate as the cohort grows

Possible Resolves by End of 2028

Discussed by: Historical pattern across oncology Phase 1 programs; the early signal comes from a small cohort of 16 patients

The 75% response rate reflects just 16 patients with measurable disease. The ESMO abstract reports a 69% (11/16) confirmed objective response rate. As Phase 2 enrolls more patients with longer follow-up, response rates typically drift toward a truer, often lower, estimate. The drug would still be valuable if PSA responses hold, but regulators may require more evidence.

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

March 2022

Pluvicto approval for mCRPC (2022)

The FDA approved Novartis's Pluvicto (177Lu-PSMA-617), a radioactive molecule that delivers radiation to prostate cancer cells expressing the PSMA protein. It was the first radioligand therapy for metastatic castration-resistant prostate cancer, aimed at patients who had progressed on both androgen receptor pathway inhibition and taxane chemotherapy.

Then

Pluvicto became a standard option in late-stage prostate cancer, with uptake limited by manufacturing capacity and isotope supply.

Now

It proved that a fundamentally new modality could help patients who had exhausted existing drug classes, reshaping how late-stage prostate cancer is sequenced.

Why this matters now

JNJ-6143 is attempting the same feat with an oral small molecule instead of a radioactive isotope — a new mechanism for patients who have already run through AR-targeted therapy, chemotherapy and PSMA-targeted radiation.

August 2012

Enzalutamide approval (2012)

The FDA approved enzalutamide for metastatic castration-resistant prostate cancer after chemotherapy. The drug blocks the androgen receptor from being activated by testosterone and other androgens.

Then

Enzalutamide extended survival and became a standard of care in mCRPC.

Now

It validated the androgen receptor as a durable target across the disease course, even where earlier anti-androgens had failed.

Why this matters now

JNJ-6143 also targets the androgen receptor, but through proximity-based sequestration rather than blockade. Its early results test whether the same axis can be attacked a different way in patients resistant to AR pathway drugs.

2019

PROTACs reach the clinic (2019)

Arvinas became the first company to bring a PROTAC — a molecule that hijacks the cell's degradation machinery to destroy a target protein — into clinical trials, with ARV-110 for prostate cancer and ARV-471 for breast cancer.

Then

PROTACs generated intense industry interest in 'protein degrader' pharmacology, but early prostate cancer data showed modest activity.

Now

The mixed results tempered expectations that proximity-based drugs would automatically outperform conventional inhibitors, even with a clever mechanism.

Why this matters now

RIPTACs and PROTACs both rely on induced proximity, but RIPTACs sequester a protein instead of marking it for destruction. JNJ-6143 is the first test of that variation, and the PROTAC precedent argues for caution before treating a Phase 1 signal as a cure.

Sources

(9)
+3
PR Newswire Johnson & Johnson J&J Medical Connect Investing.com (Reuters) Pharmaphorum UroToday Prostate Warriors Small Molecule News PR Newswire