The invention encompasses novel compounds and pharmaceutically acceptable salts thereof and compositions including therapeutically or prophylactically effective amounts of such compounds or pharmaceutically acceptable salts thereof. The invention also encompasses methods for treating or preventing diseases and disorders associated with abnormal cell growth, for example, treating or preventing cancer or tumor growth, which methods include administering to a mammal in need thereof a composition comprising a therapeutically or prophylactically effective amount of a compound of the invention or a pharmaceutically acceptable salt thereof.