Nanatinostat Plus Valganciclovir in Advanced EBV+ Solid Tumors and in Combination With Pembrolizumab in EBV+ RM-NPC

Key Inclusion Criteria: * Recurrent or metastatic EBV+ nasopharyngeal carcinoma (RM-NPC) for whom no potentially curative options are available, who have received at least 1 prior line of platinum-based chemotherapy and no more than 3 prior lines of therapy for RM-NPC. * Phase 1b exploratory proof-of-concept cohort only: Advanced/metastatic EBV+ non-NPC solid tumors with no available curative therapies. * Measurable disease per RECIST v1.1 * ECOG performance status 0 or 1 * Adequate bone marrow and liver function Key Exclusion Criteria: * Anti-tumor treatment with cytotoxic drugs, biologic therapy, immunotherapy, or other investigational drugs within 4 weeks or \>5 half-lives, whichever is shorter * Active CNS disease * Inability to take oral medication, malabsorption syndrome or any other gastrointestinal condition (nausea, diarrhea, vomiting) that may impact the absorption of nanatinostat and valganciclovir * Active infection requiring systemic therapy * Active autoimmune disease that has required systemic therapy with modifying agents, corticosteroids, or immunosuppressive agents * Positive hepatitis B or hepatitis C