Phase 2a Study to Evaluate Suppression of 5-Fluorouracil -Induced Mucositis by TK112690

Patients expected to receive a 500 mg/m2 of Leucovorin by iv & 500 mg/m2 of Fluorouracil (5FU) by iv bolus for their Colorectal Cancer. The patients will receive a one-hour infusion of TK-90 or equivalent TK-90 placebo depending on randomization at 5 hours & 11 hours post 5-FU iv bolus. This treatment cycle will continue weekly for 6 weeks. The TK112690 dose will be 45 mg/kg.