This is an open-label, dose-escalation and expansion Phase I clinical trial designed to evaluate the safety, tolerability, pharmacokinetic (PK) profile, immunogenicity, and preliminary antitumor activity of QLF4113 monotherapy in participants with metastatic prostate cancer.

The Phase I trial consists of two parts: Phase Ia and Phase Ib. Phase Ia is a dose-escalation study of QLF4113 monotherapy to determine the recommended phase two dose and assess safety and PK. Then the study will proceed to Phase Ib, a dose-expansion study to further evaluate the preliminary efficacy and safety of QLF4113 monotherapy under the selected doses.

Inclusion Criteria:

• Participants voluntarily agree to participate and sign the informed consent form.
• Male, aged ≥18 years.
• Eastern Cooperative Oncology Group (ECOG) performance status score of 0-1.
• Life expectancy ≥ 3 months.
• Histologically or cytologically confirmed adenocarcinoma of the prostate without evidence of neuroendocrine carcinoma or small cell carcinoma features.
• Confirmed metastatic Castration-Resistant Prostate Cancer (mCRPC).
• Failed or are intolerant to standard therapies
• Adequate function of major organs as defined by the protocol.
• Agreement to use effective contraception during the study (except for subjects who have undergone bilateral orchiectomy).
• Prior to the first use of the investigational drug, recovery from all reversible adverse events (AEs) related to prior anticancer treatments

Exclusion Criteria:

• Previously treated with drugs targeting CD3 or CD2.
• Significant Cardiovascular Diseases
• Active, Uncontrolled Infections
• Immunosuppressive Treatment before the first dose of the investigational drug
• Clinically Uncontrolled Third-Space Fluid Accumulation
• History of Other Malignancies within 5 years prior to the first dose of the investigational drug
• Moderate to Severe Pulmonary Diseases significantly affecting lung function,
• Current Hepatic Encephalopathy, Hepatorenal Syndrome, or Cirrhosis classified as Child-Pugh B or worse.
• Allergy to the Investigational Drug or its Components.
• Any Condition deemed by the investigator to increase study-related risks, interfere with the interpretation of study results, or otherwise render the participant unsuitable for inclusion.