A Phase 1/2a, Multicenter, Open-Label, First in Human Study to Assess the Safety, Tolerability, Pharmacokinetics, and Preliminary Antitumor Activity of DB-1305 in Subjects with Advanced/Metastatic Solid Tumors

• Male or female adults (defined as ≥ 18 years of age or acceptable age according to local regulations at the time of voluntarily signing of informed consent).
• Histologically or cytologically confirmed unresectable advanced/ metastatic solid tumors who have relapsed or progressed on or after standard systemic treatments or for which no standard treatment is available.
• At least one measurable lesion as assessed by the investigator according to response evaluation criteria in solid tumors (RECIST) version 1.1 criteria.
• Has a life expectancy of ≥ 3 months.
• Has an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0-1.
• Has LVEF ≥ 50% by either echocardiography (ECHO) or multiple-gated acquisition (MUGA) within 28 days before enrollment.
• Has adequate organ functions within 7 days prior to Day 1 of Cycle 1.
• Has adequate treatment washout period prior to Day 1 of Cycle 1.
• Is willing to provide pre-existing resected tumor samples or undergo fresh tumor biopsy for the measurement of Trop-2 level and other biomarkers if no contraindication.
• Is capable of comprehending study procedures and risks outlined in the informed consent and able to provide written consent and agree to comply with the requirements of the study and the schedule of assessments.

• Has a medical history of symptomatic congestive heart failure (CHF) (New York Heart Association [NYHA] classes II-IV) or serious cardiac arrhythmia requiring treatment.
• Has a medical history of myocardial infarction or unstable angina within 6 months before enrollment.
• Has an average of Fredericia's formula-QT corrected interval (QTcF) prolongation to > 470 millisecond (ms) in males and females based on a 12-lead electrocardiogram (ECG) in triplicate.
• Has a medical history of interstitial lung diseases (e.g., non-infectious interstitial pneumonia, pneumonitis, pulmonary fibrosis, and severe radiation pneumonitis) or current interstitial lung diseases or who are suspected to have these diseases by imaging at screening.
• Has an uncontrolled infection requiring IV injection of antibiotics, antivirals, or antifungals.
• Subjects have human immunodeficiency virus (HIV) infection with acquired immune deficiency syndrome (AIDS) defining illness are not eligible for enrollment; However, subjects have had HIV infection with a cluster of differentiation 4 (CD4)+ T cell count > 350 cells/µL and no history of an AIDS-defining illness are eligible for entry.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.