The order of infusion will be gemcitabine first, immediately followed by ON 01910.Na (with the only exception being the first infusion for those patients undergoing PK sampling; where the ON 01910.Na infusion will be given first on this occasion). The dose of gemcitabine will be fixed at 1000 mg/m2 i.v. as a 30 minutes infusion on days 1, 8, and 15 every 28 days. As of Amendment 2, the starting dose of ON 01910.Na is 250 mg/m2 as a 24 hour intravenous (i.v.) infusion on days 1, 8 and 15 of a 28-day course. The dose of ON 01910.Na will be escalated in increments in successive cohorts (dose level (DL) 1 = 250 mg/m2, DL 2 = 650 mg/m2, DL 3 = 1050 mg/m2, DL 4= 1350 mg/m2) of new patients. A course is defined as 4 weeks in length. Toxicity will be graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE v3.0). A minimum of three new patients will be treated at each dose level with a minimum of a 1 week stagger between the dosing of the first and remaining patients in each new dose cohort. In exceptional circumstances (e.g. where there is one slot available in a cohort and two eligible patients have been screened), the Sponsor may allow four patients to enter a cohort (or seven patients to enter an expanded cohort). A DL -1A (ON 01910.Na = 125 mg/m2) is set in case dose de-escalation is required with the starting dose due to ON 01910.Na-related toxicity. A DL -1A gemcitabine = 750 mg/m2 and DL - 1B at 500 mg/m2 are set in case dose de-escalation is required with the starting and subsequent doses due to gemcitabine-related toxicity. If DLT is not observed in the first three patients, then the dose of ON 01910.Na will be increased to the next level. If DLT occurs in any of the first three new patients in the first course, at least three additional new patients will be treated. If no further DLT is encountered, dose escalation will proceed. Alternately, if DLT is noted in one or more of three additional patients, dose escalation will be terminated and the MTD will be defined as the highest dose level at which none of the first three patients or no more than one of six patients experienced DLT in course 1. All patients receiving doses exceeding the confirmed MTD will have their dose reduced to the MTD; even if apparently tolerating their current dose. Intra-patient dose escalation of ON 01910.Na will be permitted. There will be no limit to the number of courses that could be administered to a patient who is both tolerating and benefiting from therapy.

Escalation to the next dose level will occur only after the third evaluable patient (or sixth, if an expanded cohort), on the previous dose level has been observed for 4 weeks. Dose escalation decisions will be made by a Cohort Review Committee (CRC). Intra-patient dose escalation of ON 01910.Na will be allowed after the third evaluable patient on the next dose level has been observed for 4 weeks with acceptable tolerability.

Once the MTD has been defined, an expanded cohort of 9 to 12 additional patients (depending if 3 or 6 patients were enrolled on the previous cohort) will be enrolled at the MTD dose level in order to further define the safety and tolerability of this regimen, and characterize the pharmacokinetics of ON 01910.Na alone and after gemcitabine, and perform a tumor biomarker study.