The overall objective of this Phase 1 study is to evaluate the safety, PK, and anti-tumor activity of 12 weeks of daily oral dosing with HP518 after selecting the RP2D of HP518 based on assessments of multiple dose escalation in patients with progressive mCRPC.

This First in Human dose escalation and expansion study of HP518 in patients with mCRPC is being conducted not only to evaluate the safety and tolerability of orally administered HP518, but also to provide necessary information for efficacy analysis in future studies.

Inclusion Criteria:

1. Has histologically confirmed adenocarcinoma of the prostate.
2. Has metastatic disease at study entry documented by 2 or more bone lesions on bone scan or by soft tissue disease observed by CT/MRI.
3. Has disease progression while receiving any ADT, androgen biosynthesis inhibitors, or second-generation AR inhibitors.
4. Must have recovered from toxicities related to any prior treatments
5. Ongoing ADT with LHRH agonist/antagonist therapy or history of bilateral orchiectomy.
6. ECOG performance status score of 0 to 1.

Exclusion Criteria:

1. Has received more than 1 line of chemotherapy for prostate cancer.

2. Use of enzalutamide, and/or other second-generation AR inhibitors and/or abiraterone as follows:

   • Received any agent within 4 weeks prior to the start of study drug.
   • Discontinued agent without evidence of radiographic or PSA progression.

3. Has had any anticancer treatments, including immunotherapy, chemotherapy, or radiotherapy (eg, 177Lu-PSMA-617, radium 223, PARP inhibitor) within 4 weeks prior to the first dose of HP518.

4. Has gastrointestinal disorder affecting absorption (e.g., gastrectomy).

5. Has significant cardiovascular disease.

6. Use of an investigational agent, without evidence of radiographic or PSA progression, within 4 weeks prior to the first dose of HP518 or a period required by local regulation, whichever is longer.