A Study of [225Ac]Ac-AKY-2519 in Patients With B7-H3 Expressing Solid Tumors

This Phase 1b study consists of two parts. Part 1 is the dose escalation portion and will investigate ascending doses of \[225Ac\]Ac-AKY-2519 in patients with locally advanced or metastatic solid tumors, including non-small cell lung cancer (NSCLC), extensive stage-small cell lung cancer (ES-SCLC), metastatic castration-resistant prostate cancer (mCRPC), head and necks squamous cell carcinoma (HNSCC), esophageal squamous cell carcinoma (ESCC), and colorectal cancer (CRC). Part 1 will also incorporate a backfill strategy to evaluate two dose levels further. Part 2 is the dose expansion portion and aims to assess the efficacy of \[225Ac\]Ac-AKY-2519 in two separate cohorts by indication: * Cohort A: NSCLC * Cohort B: Other solid tumors