SON-DP in Participants with Relapsed/Refractory Intolerant to Standard of Care Therapies for Advanced/Metastatic Solid Tumors

Inclusion Criteria:

1. Male or female participants aged 18 to 75 years (inclusive).

2. For Phase Ia: Participants with histologic diagnosis and confirmed solid tumor; ForPhase Ib: Participants with one of the two tumor types: Group 1: advanced primaryliver cancer; Group 2: Advanced primary gastric cancer (including gastroesophagealjunction adenocarcinoma).

3. There must be at least one measurable lesion defined by RECIST v1.1. Lesionsintended for biopsy should generally not be selected as target lesions, unless theinvestigator assesses that the biopsy of the lesion will not affect subsequent tumorevaluations. Lesions that have previously undergone radiation therapy,interventional therapy, or other local treatments should generally not be selectedas target lesions, unless the lesion shows clear radiological progression afterlocal treatment.

4. The ECOG performance status ≤ 1.

5. Able to understand and willing to sign the informed consent form (ICF) and complywith all the requirements of the protocol.

6. The investigator assesses that the subject's expected lifespan is greater than 3months.

7. Subjects must be candidates for and agree to the placement of a central venousaccess line and further must be able, in the opinion of the Investigator, to managecare of this line.

8. Subjects with treated brain metastases are allowed but should be neurologicallystable (for 4 weeks post-treatment as assessed by CNS imaging and prior to studyenrollment) and off steroids for at least 2 weeks before administration of any studytreatment.

9. All subjects in Phase Ia (with partial exceptions for the first 2 dose levels anddesignated subjects in Phase Ib must be prepared to undergo 2 or more tumorbiopsies, one during the screening period and 1-2 biopsy during therapy. In theInvestigator's assessment, these biopsies should be feasible considered, safe by theinvestigator, and not expected to interfere with all other study assessments.

10. Adequate hepatic/renal function as evidenced by meeting all the followingrequirements:

11. Total bilirubin ≤ 1.5 × ULN except for subjects with Gilbert's syndrome who areexcluded if TBIL > 3.0×ULN or direct bilirubin < 1.5×ULN. And there is noevidence of sustained liver function elevation (within 7 days) or acute hepaticdecompensation, as assessed by the investigator.

12. AST < 3.0×ULN, except for subjects that have tumor involvement of the liver,who are included if AST ≤ 5×ULN. And there is no evidence of sustained liverfunction elevation (within 7 days) or acute hepatic decompensation, as assessedby the investigator.

13. ALT ≤ 3.0×ULN, except for subjects that have tumor involvement of the liver,who are included if ALT ≤ 5×ULN. And there is no evidence of sustained liverfunction elevation (within 7 days) or acute hepatic decompensation, as assessedby the investigator.

14. Blood Urea Nitrogen (BUN) < 2.5×ULN.

15. The calculated creatinine clearance (CrCL) using the Cockcroft-Gault formulamust be ≥ 60 mL/min.

16. Primary liver cancer: Child-Pugh class A or class B with a score of 7, and nohistory of hepatic encephalopathy.

17. The subject must have adequate bone marrow function (no blood transfusions orhematopoietic growth factor support within 14 days prior to the first dose ofSON-DP), with special circumstances to be jointly evaluated by the study team,sponsor, and CRO medical team:

18. Absolute neutrophil count (ANC) ≥ 1.5 × 10⁹/L;

19. Hemoglobin (HGB) ≥ 80 g/L;

20. Platelet count (PLT) ≥ 75 × 10⁹/L.。

21. Coagulation tests within an acceptable range defined by the following:

22. Activated partial thromboplastin time (APTT) ≤ 1.5×ULN.

23. International normalized ratio (INR) or Prothrombin Time (PT) ≤ 1.5×ULN.Exception: INR 2 to ≤ 3 ULN is acceptable for subjects on stable therapeuticanticoagulants without active bleeding within 14 days prior to the first doseof the study drug.

24. Toxicity related to previous antitumor treatments must have returned to baseline or ≤ grade 1 (NCI-CTCAE 5.0), except for toxicities judged by the investigator to poseno safety risk, such as: hair loss, ≤ grade 2 peripheral neuropathy, thyroiddysfunction stabilized by hormone replacement therapy, or other toxicities that arestill grade 2 but are assessed by the investigator as chronic, stable, and with noclear safety concerns.

25. Female participants must agree not to breastfeed starting at screening andthroughout the study period and for 90 days after final SON-DP administration.

26. Fertile, eligible subjects (both male and female) must agree to use reliablecontraception methods (hormonal, barrier methods, or abstinence) during the trialand for at least 90 days after the last dose of the medication.

Exclusion Criteria:

1. Pregnant or breastfeeding women. Pregnancy is defined as the state from conceptionuntil the termination of pregnancy, confirmed by a positive human chorionicgonadotropin (hCG) laboratory test. Unless one of the following criteria is met:permanent sterilization (hysterectomy, bilateral salpingectomy, or bilateraloophorectomy), or documented biological or physiological evidence of postmenopausalstatus (defined as no menstruation for more than 12 months without otherconditions), or women who have been menopausal for 6-12 months must have a serumfollicle-stimulating hormone (FSH) level > 40 mIU/mL to confirm menopause;otherwise, female subjects will be considered fertile.

2. Participation in an interventional, investigational study within 2 weeks or 5half-lives, whichever is shorter of the first dose of study treatment.

3. Presence of overt leptomeningeal or active central nervous system (CNS) metastasesor primary tumors or CNS metastases that require local CNS-directed therapy (e.g.,radiotherapy or surgery) or increasing doses of corticosteroids within the prior 2weeks.

4. Impaired cardiac function or clinically significant cardiac disease, including anyof the following:

5. Clinically significant and/or uncontrolled heart disease such as congestiveheart failure requiring treatment (New York Heart Association [NYHA] Grade ≥ 2), left ventricular ejection fraction (LVEF) < 50% as determined by multiplegated acquisition (MUGA) or echocardiogram (ECHO), uncontrolled hypertension,or clinically significant arrhythmia.

6. QT interval corrected for heart rate using Fridericia's formula (QTcF) > 470 msECG or congenital long QT syndrome at the Screening Visit, except subjects withpacemaker.

7. Acute myocardial infarction or unstable angina pectoris < 6 months prior tostudy entry.

8. Uncontrolled hypertension (systolic blood pressure >160 mmHg and diastolic bloodpressure >100 mmHg), or in the opinion of the Investigator: a recent history ofhypertension crisis, or a recent history of hypertensive encephalopathy.

9. History of stroke or clinically significant intracranial hemorrhage within 6 monthsbefore first dose of study drug.

10. Concurrent severe pulmonary diseases, including but not limited to pulmonaryembolism within 3 months prior to enrollment, severe asthma, severe chronicobstructive pulmonary disease (COPD), restrictive lung disease, or pneumoniaconsidered based on imaging examination or investigator assessment at screening, aswell as a history of non-infectious pneumonia requiring steroid treatment within 12months prior to signing informed consent.

11. Subject with active human immunodeficiency virus (HIV) infection or a history of HIVinfection; subjects with active chronic hepatitis B or active chronic hepatitis C (excluding hepatitis B virus carriers, those with stable hepatitis B after antiviraltreatment [HBV DNA negative/ below the lower limit of detection in hospital'squantitative testing or < 500 IU/mL], and HCV-Ab positive but HCV-RNA negativesubjects); subject with active syphilis.

12. Other primary malignancies, past or present, except for the enrollment indicationsof this study. However, this does not include: malignancies that have been curedwithin 2 years prior to the first dose of SON-DP with no signs of recurrence, fullytreated and completely resected cervical carcinoma in situ, completely resected skinbasal cell carcinoma or squamous cell carcinoma, any malignancy considered indolentand not requiring treatment, or any type of carcinoma in situ that has beencompletely resected.

13. The presence of clinically symptomatic, poorly controlled pleural effusion,pericardial effusion, or ascites that requires repeated drainage.

14. Anticancer therapy within 5 half-lives or 3 weeks (whichever is shorter) prior tostudy entry. Chinese anticancer medicine, three weeks prior first dosing.

15. Received radical radiation therapy or radiation to an area where the bone marrowproportion is greater than 30% within 4 weeks prior to the first dose of SON-DP.Exceptions include: palliative radiation therapy for localized lesions (e.g.,radiation therapy for bone lesions aimed at symptom relief) or local interventionaltreatments (such as transarterial chemoembolization [TACE] and others) assessed bythe investigator as posing no safety risks.

16. Subjects receiving systemic chronic steroid therapy or any immunosuppressive therapy (≥ 10 mg/day prednisone or equivalent) two weeks prior first SON-DP dosing. Topical,inhaled, nasal, and ophthalmic steroids are allowed.

17. The use of any live vaccines or live attenuated vaccines against infectious diseaseswithin 4 weeks prior to the first dose of SON-DP and during the study treatmentperiod.

18. Subjects with a history of stroke or having active neurological symptoms, with theexception of chronic conditions or sequelae which in the opinion of the neurologist,Investigator, and the Sponsor, would not impact ongoing neurologic assessments whileon study treatment. a) This includes subjects with active sickle-cell disease with CNS involvement andactive intracranial bleeding.

19. Subjects who are using medications that cannot be used concurrently with urea;subjects who are using medications that require special caution or carefulconsideration when used with urea. Enrollment may be allowed if the investigatorassesses that the risks can be controlled.

20. Subjects with diseases affecting the thirst recognition center, such as centraldiabetes insipidus, syndrome of inappropriate antidiuretic hormone secretion (SIADH), etc.

21. Active infection requiring intravenous systemic antibiotic or antiviral therapywithin 14 days prior to the first dose of SON-DP.

22. Major surgery within 4 weeks of the first dose of study treatment (mediastinoscopy,insertion of a central venous access device, and insertion of a feeding tube are notconsidered major surgery).

23. Subjects who have undergone solid organ or hematopoietic stem cell transplantationwithin 5 years prior to signing the informed consent for this study.

24. Any medical condition that would, in the Investigator's judgment, prevent thesubject's participation in the clinical study due to safety concerns, compliancewith clinical study procedures, or interpretation of study results.

25. Allergy to study protein drug or components of its formulation such as PEI and urea.

26. History of a Grade 3 to 4 allergic reaction to treatment with another proteinproduct.