Phase Ib of L-NMMA and Pembrolizumab

The purpose of this Phase Ib study is to test the safety of NG-monomethyl-L-arginine (L-NMMA) and pembrolizumab when used together in participants with melanoma, non-small cell lung cancer (NSCLC), head and neck squamous cell carcinoma (HNSCC), classical Hodgkin lymphoma (cHL), urothelial carcinoma, Cervical Cancer, Esophageal Cancer, Gastric Cancer, Hepatocellular Carcinoma, Merkel Cell Carcinoma, Primary Mediastinal Large B-cell Lymphoma, Renal Cell Carcinoma, Small Cell Lung Cancer, microsatellite instability-high (MSI-H)/mismatch repair deficient (dMMR) cancer or for the Treatment of Adult Patients with Unresectable or Metastatic Tumor Mutational Burden-High Solid Tumors. Pembrolizumab is a type of treatment that stimulates the immune system to attack cancer cells. The immune system is normally the body's first defense against threats like cancer. However, sometimes cancer cells produce signals like PD-L1 that prevent the immune system from detecting and killing them. Pembrolizumab blocks programmed death-1 (PD-1) so your immune system can detect and attack cancer cells. To help further boost the cancer-fighting ability of your immune system, L-NMMA will be used along with pembrolizumab. L-NMMA is a nitric oxide synthase inhibitor. The presence of nitric oxide synthase in the area around the cancer cells blocks the cancer-fighting ability of the immune system. Thus, the use of L-NMMA and pembrolizumab together may make the immune system work harder to attack and destroy the cancer cells. In this study, up to 3 different doses of L-NMMA will be studied (12.5, 15, and 20 mg/kg). Participants will only receive one of the three L-NMMA doses. The first several study participants will receive the 15 mg/kg dose. If the 15 mg/kg dose of L-NMMA causes serious side effects, L-NMMA will be given to other study participants at the lower dose of 12.5 mg/kg. If the 15 mg/kg dose of L-NMMA does not cause serious side effects, L-NMMA will be given to other study participants at the higher dose of 20 mg/kg. All study participants will be given the same dose of pembrolizumab (200 mg). This study will allow us to see the highest dose of L-NMMA that can be used safely with pembrolizumab in participants with melanoma, NSCLC, HNSCC, cHL, urothelial carcinoma, or MSI-H/dMMR cancer.