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Janux Therapeutics has started Phase Ib expansion trials with JANX007 in the first-in-human ENGAGER-PSMA-01 clinical trial, aimed at treating advanced metastatic castration-resistant prostate cancer (mCRPC).
The open-label, multicentre Phase I trial is aimed at assessing JANX007’s tolerability, pharmacodynamics, safety, preliminary efficacy, and pharmacokinetics as a monotherapy or as a combo therapy in adults with advanced mCRPC.
The first Phase Ib study is set to enrol mCRPC subjects who are taxane-naïve. The trial will further assess the efficacy and safety of JANX007 in the first and second line (1L/2L) subject population, with JANX007 as monotherapy at two dosing regimens, 0.3/2/6mg and 0.3/2/9mg, being tested.
The dosing is given once a week or once every two weeks in these subjects who have advanced on or after novel hormonal therapy (NHT), stated the company.
Plans are underway by the company to begin three additional Phase Ib expansion studies focusing on different combinations and patient groups, including the evaluation of the therapy as a single agent in those resistant to poly(ADP-ribose) polymerase (PARP) inhibitors, and in conjunction with an androgen receptor inhibitor in inhibitor in subjects who experienced taxane.
The company also noted that JANX007 will be tested as a single agent in subjects experiencing NHT and taxane to support OPTIMUS dose selection for registrational trials.
In December 2024, the company announced promising interim data from the Phase Ia dose escalation segment of the trial and reported a median radiographic progression-free survival (rPFS) of 7.4 months from the Phase Ia portion of the trial, involving 16 mCRPC subjects with a median of four previous therapy lines.
Updated outcomes as of this April indicate a median rPFS of 7.5 months across the same patient group, backing the commencement of current Phase Ib expansion trials.
Subjects receiving 6mg and 9mg target doses experienced a median rPFS of 7.9 months, with a six-month rPFS rate of 78%.
The safety data was found to be consistent with last year’s data. Janux has also developed a strategy to mitigate cytokine release syndrome (CRS), supporting the new Phase Ib studies while maintaining the December-reported CRS profile.
Janux Therapeutics CEO and president David Campbell said: “Improved efficacy and durability of responses have been observed by other prostate cancer drugs and T-cell engagers (TCEs) when moving into earlier lines of therapy.
“There are also indications that safety with TCEs improves in earlier lines of therapy where disease burden is lower. We believe that these observations, coupled with the data seen in our Phase Ia dose escalation in later line patients, strongly support our decision to develop JANX007 in earlier lines of therapy.”