SKL35501

This Phase 1, open-label study will evaluate two investigational radiopharmaceuticals in adults with selected advanced or metastatic solid tumors. SKL35502 is an imaging agent used with SPECT scans to identify tumors with neurotensin receptor 1 (NTSR1), a protein found on some cancer cells, and to assess where the agent travels in the body and the radiation dose delivered to tissues. Participants with sufficient SKL35502 tumor uptake may receive SKL35501, a treatment designed to deliver targeted alpha radiation to NTSR1-expressing tumor cells. Part A will evaluate the safety and imaging performance of SKL35502 and the safety, tolerability, pharmacokinetics, biodistribution, dosimetry, and biologically active dose range of SKL35501, as well as preliminary antitumor activity. Part B will further evaluate selected SKL35501 dose levels, including randomized low- and high-dose groups in participants with colorectal cancer, and will expand evaluation in selected tumor types. The study will also examine relationships among SKL35502 imaging, NTSR1 expression, SKL35501 tumor uptake, and treatment outcomes.