SU5416 is a small molecule antiangiogenic agent that inhibits vascular endothelial growth factor (VEGF) stimulation of the KDR tyrosine kinase receptor. In this Phase I dose escalation trial, a weekly dose schedule of SU5416 was tested whereby an initial 5-day loading dose was followed by weekly maintenance infusions. The start dose was 20 mg/m(2) for the loading dose followed by 65 mg/m(2) for the weekly infusions. Dose escalations occurred at 33% until a final dose of 65 mg/m(2) (loading dose) and 190 mg/m(2) (weekly infusion) was obtained. Twenty-two patients were treated at five dose levels; tumor types included gastrointestinal (8), breast (3), lung (4), sarcoma (2), and other (5). The most common serious drug-related toxicity was headache, often associated with nausea and vomiting. Grade 1 and 2 toxicities included headache, nausea, vomiting, asthenia, pain at the infusion site, phlebitis, change in voice, and fevers. Of 19 evaluable patients, 4 obtained clinical benefit as defined by tumor regression (1) or disease stabilization for at least 12 weeks (3). Pharmacokinetic data revealed that the weekly infusion schedule prevented the reported 50-60% induction in SU5416 clearance observed with either daily or twice weekly dosing. Higher baseline levels of urine VEGF were observed in the 4 patients who gained clinical benefit, suggesting this may be a useful marker for predicting response to anti-VEGF therapies. Our results suggest that a weekly schedule of SU5416 shows signs of biological activity and is well tolerated at doses up to 145 mg/m(2).