This is a 3-arm, parallel-group, active- and placebo-controlled, double-blind, randomized study, to compare treatment with intravenous custirsen at 640 mg (highest intended therapeutic dose) with placebo. The purpose of this study is to assess the effect of custirsen treatment on cardiac conduction and repolarization (electrical activity of the heart) in healthy subjects. The positive control employed to demonstrate assay sensitivity consists of a group receiving a single oral dose of 400 mg moxifloxacin on day 7. The moxifloxacin arm is un-blinded but the ECG readings are blinded.