The Use of Polyethylene Glycol-Modified Interleukin-2 (PEG-IL-2) in the Treatment of Patients with Metastatic Renal Cell Carcinoma and Melanoma A Phase I Study and a Randomized Prospective Study Comparing IL-2 Alone versus IL-2 Combined with PEG-IL-2

Background. Conjugation of polyethylene glycol to recombinant human interleukin-2 (IL-2) results in a compound, polyethylene glycol-modified IL-2 (PEG-IL-2) that retains the in vitro and in vivo activity of IL-2, but exhibits a markedly prolonged circulating half-life. In mice, one dose of PEG-IL-2 results in tumor regression comparable to that achieved with multiple bolus doses of IL-2. Based on these preclinical studies, a Phase I study with PEG-IL-2 was undertaken in patients with metastatic renal cell carcinoma (RCC) and melanoma. Then, to exploit the higher peak levels attained with IL-2 and the improved trough levels of PEG-IL-2, a combination regimen beginning with bolus IL-2 followed by low dose maintenance PEG-IL-2 was devised and tested for efficacy. Methods. Patients with measurable metastatic melanoma or RCC were entered in a Phase I dose escalation trial of PEG-IL-2 given once a week by intravenous bolus. This trial then was repeated using a twice-a-week schedule. After determining the maximum tolerated dose (MTD) and a safe outpatient regimen for PEG-IL-2, a hybrid regimen combining an initial high dose IL-2 cycle followed by chronic maintenance with weekly PEG-IL-2 was devised. This regimen was compared with a standard regimen consisting of two cycles of high dose unconjugated IL-2 in a randomized prospective clinical trial. Results. When given by intravenous bolus once a week, the MTD of PEG-IL-2 was 12 million IU/mZ, with