• Male or female subjects over 18 years of age.

• The subject must have a solid tumor confirmed by histology or cytology, and belong to one of the following categories: 1) locally advanced or metastatic SCLC, which has received standard treatment in the past and developed progress or intolerance; 2) Low-grade, medium-grade or high-grade locally advanced or metastatic GEP-NET, who has previously received first-line or multi-line anti-tumor treatment and developed progress or intolerance (unless there is no standard treatment available or such treatment is not suitable); 3) Metastatic or locally advanced unresectable TNBC, which is confirmed by histological examination, is characterized by the lack of expression of human epidermal growth factor 2(HER2), estrogen receptor (ER) and progesterone receptor (PR), and recurs/is refractory after standard treatment or has no standard treatment (which must include paclitaxel chemotherapy). 4) Other locally advanced or metastatic solid tumor subjects who have failed or are intolerant of standard treatment.

• ECOG PS is 0-1.

• Life expectancy ≥3 months.

• Organ function is normal, which is defined as follows: 1) Bone marrow (not treated with blood transfusion or hematopoietic stimulating factors within 14 days): absolute neutrophil (ANC) ≥ 1.5× 10 9/L, platelet count ≥ 100× 10 9/L, hemoglobin ≥ 90 g/L. 2) Liver: total bilirubin (TBIL) ≤1.5× upper limit of normal value (ULN), or TBIL\>1.5×ULN with direct bilirubin (DBIL) ≤ ULN; Alanine aminotransferase (ALT) and aspartate aminotransferase (AST)≤3×ULN (≤5×ULN if accompanied by liver metastasis). 3) Kidney: serum creatinine concentration ≤1.5×ULN or creatinine clearance ≥50 mL/min(Cockcroft-Gault formula) 4) Coagulation function: partial thromboplastin activation time (APTT) or ≤ 1.5× ULN; International normalized ratio (INR) or prothrombin time (PT)≤1.5×ULN (INR\<3.0 if the subject uses anticoagulant).

• Detection requirements for biomarkers: 1) For the dose escalation and backfill cohort in Phase I study, biomarkers are not detected when they are selected, and the subjects need to provide archived or fresh tumor tissues within 2 years (if the archived tissue samples are more than 2 years and fresh tumor tissues are difficult to obtain, they can communicate with the applicant to decide whether to exempt them); During the study, the biomarker detection results of subjects in the follow-up dose expansion cohort may be added as additional selection criteria according to the obtained clinical data; 2) For Phase II study, the subjects should provide archived or fresh tumor tissues within 2 years (if the archived tissue samples are more than 2 years and fresh tumor tissues are difficult to obtain, they can communicate with the sponsor to decide whether to exempt them), and at baseline, the biomarkers should be detected by IHC in the central laboratory.

• According to the RECIST version 1.1 standard, there is at least one target lesion (the target lesion must have not received radiotherapy before, or there is clear evidence of disease progression after radiotherapy).

• Male or female subjects who are infertile, not in pregnancy or agree to use at least one effective contraceptive method during the study intervention period (from 14 days before the first administration to at least 180 days after the last administration of the study intervention) are eligible to participate in the study, and abide by the following contents: 1) Avoid donating fresh unwashed sperm or eggs. 2) Women who are breastfeeding should stop breastfeeding during the study period.

• An informed consent form (ICF) that can be understood and signed, including compliance with ICF and the requirements and restrictions listed in this plan.