Inclusion Criteria:
1. Voluntarily sign a written informed consent form (ICF).
2. Aged ≥18 years and ≤75 years, male or female.
3. ECOG performance status score of 0 or 1.
4. Life expectancy ≥ 3 months.
5. Histologically or cytologically confirmed recurrent or metastatic nasopharyngeal carcinoma that is not amenable to curative treatment.
6. Have failed prior treatment with PD-(L)1 inhibitors and at least two lines of chemotherapy.
7. Suitable for treatment with investigator's choice of chemotherapy (docetaxel, capecitabine, or gemcitabine).
8. At least one measurable lesion according to RECIST v1.1.
9. Subjects are willing to provide the archived or freshly obtained tumor tissue (freshly obtained or archived) for detection of B7-H3 expression
10. Adequate organ function.
Exclusion Criteria:
1. History of other malignant tumors within 5 years prior to the first dose of study drug. Subjects who have been cured of other tumors by local therapy, such as basal cell carcinoma, squamous cell carcinoma of skin, bladder cancer in situ, cervical carcinoma in situ, or breast cancer in situ, are not excluded.
2. Previously received B7-H3-targeted drug therapy, including antibody, antibody-drug conjugate (ADC), and chimeric antigen receptor T cell (CAR-T).
3. Prior treatment with a topoisomerase I inhibitor or an antibody-drug conjugate containing a topoisomerase I inhibitor.
4. Inadequate washout period for prior anti-tumor treatment before the first dose of study drug.
5. Received radical radiotherapy within 4 weeks prior to the first dose of study drug; local palliative radiation for symptom control is allowed, but treatment must be completed at least 2 weeks prior to the first dose of study drug, and there is no plan for additional radiotherapy to the same lesion.
6. Received systemic steroids or other immunosuppressive therapy within 2 weeks before the first dose of study drug.
7. Received any live vaccine within 4 weeks before the first dose of study drug or intend to receive a live vaccine during the study.
8. Presence of brain stem or meningeal metastases, spinal cord metastases or compression.
9. Presence of central nervous system (CNS) metastasis. Participants with treated brain metastases are eligible if the metastases are asymptomatic and stable, and no immediate local or systemic treatment is needed within 2 weeks before the first dose.
10. Has an uncontrolled concurrent disease.
11. Presence of severe uncontrolled cardiovascular disorder.
12. History of interstitial lung disease (ILD) or pneumonitis that required corticosteroids, or current ILD/ pneumonitis.
13. Concomitant pulmonary disorder leading to clinically severe respiratory impairment.
14. Chronic autoimmune or inflammatory diseases requiring systemic therapy within 2 years prior to the first dose or currently receiving systemic therapy.
15. Clinical symptoms of pleural effusion, pericardial effusion, or ascites or requiring relevant repeated drainage.
16. Serious infections within 4 weeks prior to the first dose.
17. Known active pulmonary tuberculosis (TB).
18. Active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection.
19. Unresolved toxicities from previous antitumor therapy.
20. Known allergy to any component of the study drug; history of severe allergic reactions or known history of severe hypersensitivity to other monoclonal antibodies or recombinant proteins, or history of severe infusion reactions.
21. Pregnancy, breastfeeding, or women planning to become pregnant or breastfeed during the study.
22. Any illness, medical condition, organ system dysfunction, or social situation deemed by the investigator to be likely to interfere with a subject's ability to sign ICF, adversely affect the subject's ability to cooperate and participate in the study, or compromise the interpretation of study results.
