The present invention provides novel compounds of Formula (I) and Formula (II) and pharmaceutically acceptable salts, solvates, hydrates, tautomers, stereoisomers, isotopically labeled derivatives, and compositions thereof. Also provided are methods and kits involving the compounds or compositions for treating or preventing proliferative diseases, e.g., cancers (e.g., breast cancer, prostate cancer, lymphoma, lung cancer, pancreatic cancer, ovarian cancer, neuroblastoma, or colorectal cancer), benign neoplasms, angiogenesis, inflammatory diseases, fibrosis (e.g., polycystic kidney disease), autoinflammatory diseases, and autoimmune diseases in a subject.