There will be no intra-patient dose escalation. Each treatment cycle consists of 21 days. Patients will receive a single IV dose of 2B3-101 on day 1 of each cycle. In order to minimize the risk of infusion reactions 5% of the total dose of 2B3-101 (in mg) should be infused slowly over the first 30 minutes. If tolerated, the infusion may then be completed over the next hour for a total infusion time of 90 minutes. Blood samples will be taken on day 1, 2, 3, 5, 8 and 11 of cycle 1 and day 1, 8 and 15 of cycle 2 to assess the PK profile during the first 2 cycles. The dose limiting toxicity (DLT) observation period for each dose level will be cycle 1 (day 1 to day 21). Patients who do not complete the DLT observation period (cycle 1) for other reasons than a DLT will be replaced.