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

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 and Backfill: Having mCRPC that progressed after at least onenovel anti-androgen therapy and at least one taxane containing regimen. Participantswho have actively refused a taxane containing regimen or are medically unsuitable toreceive taxane are eligible

• Adequate organ function

• For Monotherapy Expansion Part a: Have received ≤ 2 anti-androgen therapies ineither the HSPC or CRPC setting and no more than 1 prior taxane regimen in the HSPCor CRPC setting. Participants who have actively refused a taxane regimen or aremedically unsuitable to receive taxane are eligible.

• For Monotherapy Expansion Part b: Have received ≤ 2 anti-androgen therapies ineither the HSPC or CRPC settings

• For Monotherapy Expansion Part d: Have received ≤ 1 anti-androgen therapy and apoly(ADP-ribose) polymerase (PARP) inhibitor for mCRPC and have progressed followingtreatment with the PARP inhibitor

• For Combination Expansion: Have received ≤ 1 anti-androgen therapy other thandarolutamide in the HSPC setting and ≤ 1 taxane in the mCRPC setting. Participantswho have actively refused a taxane regimen or are medically unsuitable to receivetaxane are eligible.

Exclusion Criteria:

• Prior solid organ transplant

• Prior treatment with PSMA-targeted CAR-T cell therapy or PSMA-CD3, PSMA-CD28 orother CD3 T-cell engaging bispecific antibodies or radioligand therapy

• Clinically significant cardiovascular disease

• For Monotherapy Expansion Part a: Prior receipt of any treatment other than an ARPIor taxane in the mCRPC setting

• For Monotherapy Expansion Part b: Prior receipt of any treatment other than ananti-androgen therapy or prior receipt of a taxane containing regimen or more than 1prior line of therapy for mCRPC

• For Monotherapy Part d: More than 1 prior line of therapy for mCRPC or prior receiptof any treatment other than an anti-androgen therapy and PARP inhibitor for mCRPC orprior receipt of a taxane in the mCRPC setting

• For Combination expansion: More than 1 prior line of therapy for mCRPC or priorreceipt of any treatment other than a taxane for mCRPC or prior receipt ofDarolutamide or prior receipt of a taxane for HSPC

• Active clinically significant infection (bacterial, viral, fungal, mycobacteria orother)

• Any medical condition or clinical laboratory abnormality likely to interfere withassessment of safety or efficacy of study treatment