Janux Therapeutics Starts Phase 1b Expansion Studies of JANX007 for Prostate Cancer and Shares Updates

Janux Therapeutics, Inc., a clinical-stage biopharmaceutical company, has announced the commencement of Phase 1b expansion studies within the ongoing ENGAGER-PSMA-01 trial. This trial represents a significant step in the development of their innovative immunotherapies, which harness the power of the immune system to target and destroy cancer cells.

ENGAGER-PSMA-01, the first trial of its kind for Janux, focuses on evaluating the safety and effectiveness of JANX007. This drug is being tested as both a standalone treatment and in combination therapies for patients suffering from advanced metastatic castration-resistant prostate cancer (mCRPC). The trial is being conducted across multiple centers and operates under an open-label, multicenter design, allowing for comprehensive data collection on various aspects such as safety, tolerability, pharmacokinetics, and preliminary therapeutic effectiveness.

Janux had previously shared interim results from the Phase 1a dose escalation segment of the study, involving 16 mCRPC patients who had undergone, on average, four prior therapy lines. By December 2024, the median radiographic progression-free survival (rPFS) for these patients was recorded at 7.4 months. As of April 2025, updated findings indicated an improvement, with the median rPFS reaching 7.5 months for all patients and 7.9 months for those administered target doses of 6mg and 9mg. The six-month rPFS rates were 65% overall and 78% for the specified doses, respectively, maintaining consistency with previous safety data.

A critical component of the Phase 1b expansion includes a CRS-mitigation strategy, aiming to preserve the favorable CRS (cytokine release syndrome) profile observed in prior data. The first expansion study within Phase 1b targets taxane-naïve mCRPC patients. It is designed to produce further safety and efficacy data, focusing on those who have progressed after receiving novel hormonal therapy (NHT). The study will evaluate JANX007 as a monotherapy at various dosages with different administration frequencies.

Dr. Zachariah McIver, Janux's Chief Medical Officer, highlighted the significance of this phase, stating that exploring JANX007 in earlier-line mCRPC patients is a pivotal step. Despite advances in mCRPC treatments, there remains an urgent need for innovative non-chemotherapeutic strategies. The expansion into earlier treatment lines could potentially enhance the efficacy and durability of responses, as observed in other prostate cancer treatments and TCEs (Tumor-Activated T Cell Engagers).

Janux is planning additional Phase 1b studies to explore various combinations and monotherapy regimens of JANX007. These studies will investigate its use alongside androgen receptor inhibitors in taxane-experienced patients, as well as its efficacy in PARP inhibitor-resistant and NHT- and taxane-experienced mCRPC patients. The aim is to refine dose selection for future pivotal studies.

According to Dr. David Campbell, President and CEO of Janux, the decision to develop JANX007 for early-line therapies is strongly supported by the data from the Phase 1a results. The goal is to enhance both the treatment's effectiveness and safety profile when used earlier in the cancer treatment timeline.

Further updates on JANX007 and another candidate, JANX008, are anticipated in the latter half of 2025. Additionally, Janux plans to host an R&D Day in mid-2025 to showcase the progress of its preclinical pipeline as it transitions to clinical evaluation.

Janux Therapeutics continues to advance its TRACTr and TRACIr platforms, with JANX007 and JANX008 as its leading clinical candidates. These platforms aim to deliver safe and effective cancer treatments by strategically engaging the immune system to combat various solid tumors.