Neoadjuvant therapy with interleukin-12-loaded polylactic acid microspheres reduces local recurrence and distant metastases

Background. We previously demonstrated that the intratumoral injection of biodegradable polylactic acid microspheres that were loaded with interleukin (IL)-12 can induce a systemic antitumor immunity. We sought to investigate the clinical potential as neoadjuvant therapy. Methods. Mice were inoculated with 5 × 10⁷ Line-1 cells subcutaneously. Six days later, a single intratumoral injection of IL-12- or BSA-loaded microspheres were given; 14 days later, autopsy was performed to document metastases. Mice were inoculated with 5 × 10⁷ Line-1 cells and 10 days later either treated with IL-12- or BSA-loaded microspheres or resected. Treated tumors were resected 6 days after treatment. Mice were observed 45 days for local recurrence before autopsy. Results. Intratumoral injection of IL-12 microspheres resulted in significant suppression of tumor growth compared with controls (599 ± 255 mm³ vs 1591 ± 372 mm³; P = .001) and pulmonary metastases (0.4 vs 3.8 nodules per mouse; P = .003). Given before the operation, IL-12-loaded microspheres both decreased the local recurrence rate (100% to 40%) and pulmonary metastases (5.2 vs 0.6 nodules per mouse; P = .06). Earlier resection did not improve local recurrence or distant metastases. Conclusions. Intratumoral injection of IL-12-loaded polylactic acid microspheres promotes the development of systemic antitumor immunity that can eradicate micrometastases. As a neoadjuvant therapy, this can result in decreased local and distant recurrence.