Abstract A87: Nanoparticle-mediated systemic delivery of immune agonists to tumors enabling anti-tumor efficacy without toxicity

Systemic administration of immunomodulatory cytokines and antibodies (Ab) is often accompanied by serious toxicities that limit dosing and efficacy. Combining immune agonists can demonstrate synergistic enhancement of anti-tumor immunity, but exhibits further escalated toxicities; an example is co-treatment with interleukin-2 (IL-2) and agonistic antibodies for the T cell costimulatory receptor CD137 (αCD137). In order to reduce their in vivo toxicity and increase the therapeutic window, anti -CD137 and an engineered IL-2-Fc fusion protein were anchored on the surface of PEGylated liposomes (Lipo-αCD137/IL2-Fc) which served as a scaffold to deliver immunomodulatory antibodies systemically to mice bearing either primary melanoma or lung metastasis melanoma. In aggressive B16F10 melanoma model, combination treatment with αCD137 and IL-2-Fc (αCD137/IL2-Fc) suppressed tumor growth, but simultaneously induced lethal toxicity and all mice died within 6 days after repeated intravenous (IV) dosing. In striking contrast, Lipo-αCD137/IL2-Fc showed significant tumor growth inhibition without in vivo toxicity. αCD137/IL2-Fc induced dramatic elevation of systemic proinflammatory cytokines, but, little or undetectable amounts of proinflammatory cytokines were observed in Lipo-αCD137/IL2-Fc-treated animals. Lipo-αCD137/IL2-Fc enhanced the infiltration of cytotoxic T lymphocytes (CTL) and natural killer (NK) cells in tumors and increased the CD8 to regulatory T cell ratio. In addition, immuno-liposome therapy triggered a significant production of IFN-γ in CTL upon ex vivo polyclonal stimulation, increased CTL proliferation and cytolytic degranulation in tumors and peripheral blood as evidenced by the enhanced expression of Ki67, CD107, and surface granzyme B. Mechanistically, Lipo-αCD137/IL2-Fc quickly entered tumors through their leaky vasculature but cleared from the blood rapidly following bolus IV administration, which allowed repetitive dosing of the immunoliposomes without systemic toxicity; while free αCD137 and IL2-Fc showed a prolonged blood circulation profile, which persistently activated circulating lymphocytes, leading to severe cytokine storm, vascular leak syndrome and decreased survival. Lipo-αCD137/IL2-Fc exhibited greatly increased accumulation in tumors at early time points compared to the free drugs, as observed by confocal imaging. αCD137/IL2-Fc also failed to elicit therapeutic efficacy in lung metastasis melanoma model, while Lipo-CD137/IL2-Fc showed superior antitumor immunity in both primary and metastasis melanoma models. In summary, we designed nanoparticle-IL-2/αCD137 formulations that rapidly accumulate in tumors while minimizing systemic exposure and preserving antitumor efficacy comparable to their soluble form. The improved biodistribution and pharmacokinetic profiles offered by the liposome scaffold contribute to the decreased toxicity. The liposome scaffold allows high density of Ab binding to their receptors and multivalent receptor engagement, leading to more effective T-cell stimulation. This strategy of hitchhiking immunomodulators on liposomes as a delivery vehicle makes the clinical in vivo application of therapeutic cytokines and immune agonists promising. Citation Format: Yuan Zhang, Darrell J. Irvine. Nanoparticle-mediated systemic delivery of immune agonists to tumors enabling anti-tumor efficacy without toxicity. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr A87.