Imaging of Primary and Metastatic Tumors and Their Treatment through Abscopal Effects and Cancer Immunotherapy Using Encapsulated, Radiation Therapy Directed Antigen-Capturing Nanoparticles

We investigated the combination of antigen-capturing nanoparticles (AC-NPs; 224 ± 32 nm) encapsulated in nanocapsules (945 ± 31 nm) that release its contents upon exposure to radiation from two radiotherapy sessions for tumor imaging. The AC-NPs achieved successful immune-radiotherapy of primary tumors and treated metastases by abscopal effects, which led to the recruitment of dendritic cells (DCs) by MIP-3α, DC-mediated T-cell priming, and the PD-L1 blockade. For session one, nanocapsules generated by modifying iopamiron and 400 mg anti-PD-L1 antibody (Ab) with a single-chain variable fragment (scFv)-Ab against CD4, were mixed with a 1.0 mL solution containing 4.0% alginate, 3.0% hyaluronate, 1 mg ascorbate, and 1 μg/mL P-selectin and sprayed into 0.5 mmol/L FeCl2 supplemented with 1 μg/mL anti-VEGFR-1/2 Ab. For session two, AC-NPs generated via nanoprecipitation of 4 mg/ml polylactic-co-Glycolic acid (PLGA) and 500 mg/ml MIP-3α, was mixed with the abovementioned cocktail and sprayed into 0.5 mmol/L FeCl2 supplemented with 1 μg/mL anti-P-selectin Ab, to encapsulate MIP-3α and AC-NPs. In session one, 1 × 1010 nanocapsules were intravenously (iv) injected into C57BL/6 mice with primary B16F10 murine melanoma in the left hind leg and lung metastases. Tumor accumulation was monitored by computed tomography (CT). Subsequently, 10 or 20 Gy 60Co γ-radiation was locally administered to primary tumors. In session two, 1 × 1010 nanocapsules were injected via iv and allowed to interact with P-selectin for 9 h, after which 10 or 20 Gy 60Co γ-radiation was locally administered. In session one, anti-VEGFR-1/2 microcapsules accumulated around primary and metastatic tumors and were detected by CT. The microcapsules released P-selectin and Anti-PD-L1 Ab in response to initial irradiation. In session two, microcapsules accumulated around the primary tumor via a P-selectin antigen-antibody reaction. Subsequently, PLGA AC-NPs and MIP-3α were released, in response to the second radiation dose. PLGA AC-NPs captured tumor-derived protein antigens released by the second radiation dose and transported them to DCs recruited by MIP-3α, which intensified DC-associated cross-priming of CD8+ T-cells. The primed CD8+ T cells targeted primary and metastatic tumors, for which PD-L1 was suppressed in session one. These treatments significantly increased the antitumor effect (EF 1.6) and reduced metastasis by 82.3 ± 2.3 %. Our CT-detectable microcapsules exhibited targeted AC-NPs-mediated immunotherapy and consistently induced abscopal effects, which together improved tumor diagnosis and treatment.