This study is a first-in-human, Phase 1, open-label, multicenter study to assess the safety, tolerability, pharmacokinetic (PK), pharmacodynamic (PD), and the preliminary efficacy of JANX014 in adults with metastatic castration-resistant prostate cancer (mCRPC).

Inclusion Criteria:

• Male ≥18 years of age at the time of signing informed consent
• Histologically or cytologically confirmed adenocarcinoma of the prostate
• For Dose Escalation: 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.
• Adequate organ function
• For Dose Expansion Part: Have received ≤ 2 anti-androgen therapies in either the HSPC or CRPC setting and no more than 1 prior taxane regimen in the HSPC setting. Participants who have actively refused a taxane regimen or are medically unsuitable to receive taxane are eligible.

Exclusion Criteria:

• Prior solid organ transplant
• Prior treatment with any CAR-T cell therapy, approved or investigational T-cell engager therapy, and prior receipt of radioligand therapy
• Clinically significant cardiovascular disease