 - Participants who have had chemotherapy or radiotherapy within 14 days 6 weeks for nitrosoureas or mitomycin C prior to entering the study or those who have not recovered from adverse events due to agents administered more than 14 days earlier. The use of steroids up the equivalent of 160 mg of dexamethasone is allowed within 14 days of screening, but the last dose has to be given at least 1 day prior to initiation of treatment. 