A Phase 1/1b of RNDO-564 Single Agent or in Combination With Pembrolizumab in Bladder Cancer and Other Solid Tumors Associated With Nectin-4

The study will consist of four stages: 1) single agent dose escalation, 2) single agent dose optimization, 3) combination dose escalation and 4) combination dose optimization. Stages 1 and 3 are dose escalation to investigate the safety and tolerability of increasing doses of RNDO-564 as a single agent and in combination with standard pembrolizumab treatment. Participants will be enrolled who have one of the following advanced solid tumors associated with Nectin-4: locally advanced/metastatic urothelial cancer (la/m UC), cervical cancer (CC), head and neck cancer (HNSCC), esophageal cancer (EC), gastric (GC) and gastroesophageal junction cancer (GEJ), triple negative breast cancer (TNBC), and non-small cell lung cancer (NSCLC). The cancer must not have responded well to previous cancer treatments. Stages 1, and 3 will be non-randomized. Stages 2 (i.e., RNDO-564 single agent) and 4 (i.e., RNDO-564 in combination with pembrolizumab) are dose optimization and proof-of-concept stages to further investigate the safety and tolerability of at least 2 doses of RNDO-564 as a single agent and in combination with standard pembrolizumab treatment, and to investigate preliminary anti-tumor activity. Stages 2 and 4 will enroll participants with advanced urothelial cancer only. The cancer must not have responded well to previous cancer treatments. Participants will be randomized (1:1) into one of two arms which will evaluate two dose levels (as selected from Stages 1 and 3). The study consists of a screening period, a treatment period, an end of treatment visit, a safety follow-up visit, and 60 and 90 days telephone follow-up after ending treatment. The treatment period will last for a maximum of 2 years.