Local immunotherapy with interleukin-2 delivered from biodegradable polymer microspheres combined with interstitial chemotherapy: a novel treatment for experimental malignant glioma

OBJECTIVE: Local delivery of carmustine (BCNU) from biodegradable polymers prolongs survival against experimental brain tumors. Moreover, paracrine administration of interleukin-2 (IL-2) has been shown to elicit a potent antitumor immune response and to improve survival in animal brain tumor models. We report the use of a novel polymeric microsphere delivery vehicle to release IL-2. We demonstrate both in vitro release of cytokine from the microspheres and histological evidence of the inflammatory response elicited by IL-2 released from the microspheres in the rat brain. These microspheres are used to deliver IL-2, and biodegradable polymer wafers are used to deliver BCNU, directly at the site of an intracranially implanted glioma in the rat. The two agents administered locally show a synergistic effect. METHODS: Fischer 344 rats challenged intracranially with 9L gliosarcoma received an intracranial implant of either empty microspheres or microspheres containing IL-2 (IL-2 MS). Five days later, animals in each group were randomized to receive polymer implants loaded with 0, 3.8, or 10% BCNU at the tumor site. RESULTS: Animals that received the combination of IL-2 MS and 3.8% BCNU polymer (median survival, 28.5 d) or IL-2 MS and 10% BCNU polymer (median survival, 45.5 d) showed significantly improved survival compared with animals that received monotherapy with IL-2 microspheres (median survival, 24 d), 3.8% BCNU polymer (median survival, 24 d), or 10% BCNU polymer (median survival, 32.5 d). Control animals had a median survival of 18 days. The combination of either 3.8 or 10% BCNU polymer with IL-2 MS resulted in 7 and 25% long-term survivors, respectively. CONCLUSION: By showing synergy of IL-2 and BCNU in an animal glioma model and using a reproducible synthetic delivery system for each agent (i.e., one that did not rely on genetically engineered cells or viruses), we hope that the combination of local immunotherapy and chemotherapy can take an important step closer to clinical application in patients with malignant brain tumors.