This multi-center, Phase 2, Randomized, Double-Blind, Placebo Controlled, 3-Period Crossover, Positive Control study designed to evaluate the QT interval prolongation potential of 10 mg to 60 mg doses of APL-130277 compared to placebo and the positive control, 400mg moxifloxacin in subjects with Parkinson's Disease (PD) who experience motor fluctuations ("OFF" episodes) The patient is titrated to the highest tolerated dose from 10mg to 60mg, and then is randomized to one of six crossover sequences. Each sequence includes treatment with the following: