This study will explore the efficacy and safety of a regimen of ON 01910.Na as a 48-hour continuous intravenous infusion once a week for 3 weeks of a 4-week cycle in MDS patients with Trisomy 8 or classified as Intermediate-1, -2 or High Risk who are not responding to current therapeutic options. The rationale for this trial is based upon data from laboratory studies with ON 01910.Na and upon activity that has been observed in other clinical trials with ON 01910.Na in patients with MDS.