This study will examine the safety and tolerability of IGN523 administered as an IV infusion. The main purpose of the study is to determine the maximum tolerated dose (MTD), which is the highest dose that does not cause unacceptable side effects of IGN523 in patients with acute myeloid leukemia (AML). The MTD will be determined by observing the dose-limiting toxicities (the side effects that prevent further increases in dose) of IGN523. In addition, the pharmacokinetic profile and anti-leukemia activity of IGN523 will be assessed. A recommended Phase 2 dose (RP2D) of IGN523 will be identified, on the basis of safety, pharmacokinetic (PK), and pharmacodynamic (PD) data.