Additional Study Information: The purpose of this study is to find if PTC299 is safe to treat people with relapsed/refractory acute myeloid leukemia (AML) as well to determine the dose of PTC299 that can be given without causing severe side effects. AML is a cancer of the blood and bone marrow (spongy tissue inside bones where blood cells are made). PTC299 is being developed to potentially treat leukemias. Approximately 18-36 adult subjects (at least 18 years of age) with relapsed/refractory AML will take part in this study, at 3-8 sites in the US.