Study of JANX007 in Subjects With Metastatic Castration-Resistant Prostate Cancer (ENGAGER-PSMA-01)

Inclusion Criteria:

1. Male ≥18 years of age at the time of signing informed consent
2. Histologically or cytologically confirmed adenocarcinoma of the prostate
3. For Dose Escalation and Backfill: Having mCRPC that progressed after at least one novel anti-androgen therapy and at least one taxane containing regimen. Participants who have actively refused a taxane containing regimen or are medically unsuitable to receive taxane are eligible
4. Adequate organ function
5. For Monotherapy Expansion Part a: Have received ≤ 2 anti-androgen therapies in either the HSPC or CRPC setting and no more than 1 prior taxane regimen in the HSPC or CRPC setting. Participants who have actively refused a taxane regimen or are medically unsuitable to receive taxane are eligible.
6. For Monotherapy Expansion Part b: Have received ≤ 2 anti-androgen therapies in either the HSPC or CRPC settings
7. For Monotherapy Expansion Part d: Have received ≤ 1 anti-androgen therapy and a poly(ADP-ribose) polymerase (PARP) inhibitor for mCRPC and have progressed following treatment with the PARP inhibitor
8. For Combination Expansion: Have received ≤ 1 anti-androgen therapy other than darolutamide in the HSPC setting and ≤ 1 taxane in the mCRPC setting. Participants who have actively refused a taxane regimen or are medically unsuitable to receive taxane are eligible.

Exclusion Criteria:

1. Prior solid organ transplant
2. Prior treatment with PSMA-targeted CAR-T cell therapy or PSMA-CD3, PSMA-CD28 or other CD3 T-cell engaging bispecific antibodies or radioligand therapy
3. Clinically significant cardiovascular disease
4. For Monotherapy Expansion Part a: Prior receipt of any treatment other than an ARPI or taxane in the mCRPC setting
5. For Monotherapy Expansion Part b: Prior receipt of any treatment other than an anti-androgen therapy or prior receipt of a taxane containing regimen or more than 1 prior line of therapy for mCRPC
6. For Monotherapy Part d: More than 1 prior line of therapy for mCRPC or prior receipt of any treatment other than an anti-androgen therapy and PARP inhibitor for mCRPC or prior receipt of a taxane in the mCRPC setting
7. For Combination expansion: More than 1 prior line of therapy for mCRPC or prior receipt of any treatment other than a taxane for mCRPC or prior receipt of Darolutamide or prior receipt of a taxane for HSPC
8. Active clinically significant infection (bacterial, viral, fungal, mycobacteria or other)
9. Any medical condition or clinical laboratory abnormality likely to interfere with assessment of safety or efficacy of study treatment