This is a phase 2, study in which 14 MDS patients with Trisomy 8 or classified as Intermediate-1, -2 and High risk who meet all other inclusion/exclusion criteria will receive ON 01910.Na 800 mg/m^2/24h as an continuous intravenous infusion (CIV) over 48 hours once a week for 3 weeks of a 4-week cycle. As of Amendment 3 to the Protocol, the regimen is changed to 1800 mg/24h for 72 hours every other week for the first four 2-week cycles and every 4 weeks afterwards. The total study duration is 31 weeks, which includes a 2-week screening phase, a 27-week dosing phase, and a 4-week follow-up phase that begins after the last dose of ON 01910.Na. Beginning at week 4, and every 2 weeks thereafter, patients will be assessed for response. Patients who drop out for any reason will not be replaced. Patients who achieve by week 29 a complete or partial response or stabilization of their disease are eligible to receive an additional 24 weeks of ON 01910.Na 1800 mg/24 h over 72 hours per week of a 4-week cycle.