JK-1201I Compared with Topotecan in Patients with Relapsed Extensive Stage Small Cell Lung Cancer

Inclusion Criteria: Participants must meet all the following criteria to be eligible for randomization into the study: 1. Sign and date the informed consent form prior to the start of any study-specific qualification procedures. 2. Male or female aged ≥18 years and ≤70 years. 3. Histologically or cytologically documented SCLC. 4. Has received prior therapy with only one prior platinum-based line as systemic therapy for ES SCLC and Disease progression on or after first-line platinum-based regimens (≤ 6 months). 5. Has at least 1 measurable lesion according to RECIST v1.1. 6. Has ECOG PS of ≤1. Exclusion Criteria: Participants who meet any of the following criteria will be disqualified from entering the study: 1. Hypersensitivity to any ingredient of JK-1201I and Topotecan. 2. Has received prior treatment with DNA topoisomerase I inhibitor agents. 3. Has received prior therapy with ≥2 line as systemic therapy for extensive-stage SCLC. 4. Chemotherapy-free interval within 4 weeks before the first use of the study drug. Radiotherapy with a limited field of radiation for palliation within 2 weeks before the first use of the study drug. Used biotherapy drugs within 2 weeks before the first use of the study drug. 5. Severe gastrointestinal illnesses as defined in the protocol within 6 months before the first use of the study drug. 6. Local symptoms of tumors requiring radiotherapy or surgical treatment as defined in the protocol. 7. Untreated or symptomatic brain metastases with exceptions defined in the protocol. 8. Severe pulmonary illnesses within 6 months before the first use of the study drug. 9. Uncontrolled hydrothorax and ascites. 10. Unresolved toxicity from prior anti-tumor therapy, defined as not having resolved to Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 grade 1 with exceptions defined in the protocol. 11. Severe infections within 4 weeks before the first use of the study drug.