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

Overview

Updated 1 hour ago

Johnson & Johnson's experimental prostate cancer drug shrank tumors in 75 percent of patients with measurable disease in a Phase 1 trial. The results, presented at ESMO on October 25, are the first clinical data for JNJ-6143 — a molecule J&J acquired with its December 2025 purchase of Halda Therapeutics.

The trial enrolled patients who had already run through a median of four treatments, including chemotherapy and PSMA-targeted radiation therapy. For them, median survival is about two to three years. JNJ-6143 works through an approach no approved drug uses: it locks two proteins together inside the cancer cell, trapping one the cell needs to survive.

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.

Questions about this story

Free account needed to ask — your question is kept and asked for you right after sign-up. Answers are public.

No questions yet — be the first to ask.

Key Indicators

75%

Confirmed tumor response rate

12 of 16 patients with measurable disease had complete or partial responses per RECIST criteria.

77%

Confirmed PSA50 rate at 50 mg dose

Patients whose prostate-specific antigen fell by at least half, among 38 receiving 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.

Median prior therapies

Patients had received a median of four prior treatments, including chemotherapy and PSMA-targeted radioligand therapy.

Voices

Curated perspectives — historical figures and your fellow readers.

Ever wondered what historical figures would say about today's headlines?

Organizations Involved

Johnson & Johnson

Multinational 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

Biotechnology company

Acquired by Johnson & Johnson in December 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)

Medical society / congress organizer

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

December 2025 October 2026

2 events Latest: Today

October 2026
Phase 1 results presented at ESMO 2026
Today Clinical data

75% confirmed response rate, 77% PSA50; 50 mg daily selected as Phase 2 dose.
Today
December 2025
J&J completes Halda acquisition
Acquisition

Johnson & Johnson completes purchase of Halda Therapeutics, adding the RIPTAC platform and JNJ-6143.
December 2025

Scenarios

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.

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.

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, and the company's own slide deck reports 69% (11/16) at a different cutoff. 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.