Novel fusion superkine, IL-24S/IL-15, enhances immunotherapy of brain cancer.

Background: Glioblastoma (GBM) is a rapidly growing, aggressive brain tumor with very poor prognosis without currently effective therapies. The immunosuppressive nature of the tumor microenvironment (TME) in GBM hinders the development of effective tumor-eradicating immunotherapies. This hostile TME can be modulated by administering immune-activating cytokines in combination with agents inducing tumor cell death. To achieve these objectives, we sought to harness the cancer-selective cell death-inducing properties of an enhanced "Superkine" version of melanoma differentiation associated gene-7/interleukin-24, IL-24S, and the immune-activating properties of IL-15 to modulate the TME of GBM to maximize therapeutic outcomes.

Methods: A fusion "Superkine" (FSK) comprised of IL-24S linked to IL-15 was generated, and antitumor effects were evaluated when transduced by a type 5 adenovirus (Ad.5) in a GBM immunocompetent mouse tumor model. To target the delivery of Ad.5 FSK systemically, we employed an innovative approach of focused ultrasound (FUS) paired with microbubbles (MBs), FUS-DMB (FUS plus double MB), to safely transport the FSK engineered Ad.5 construct into mouse brain to overcome limitations of systemic viral delivery and selectivity of the blood-brain barrier.

Results: The FSK stimulated higher tumor regression and enhanced survival in vivo than the individual "Superkine" or cytokine in GBM cancer models. Apoptosis of GBM cells was induced, as well as increased tumor infiltration of T cells, dendritic cells, macrophages and natural killer (NK) cells. The antitumor-inducing activity of FSK is a consequence of induction of cancer-specific growth suppression and induction of apoptosis (IL-24S) as well as diverse effects on immune cells (IL-15 and IL-24S). Antibody neutralization indicates that a primary immune mediator of anticancer activity of FSK is through recruitment and activation of NK cells. Global cytokine analyses indicated no changes in inflammatory cytokines during therapy, suggesting that this strategy will be safe.

Conclusion: In summary, treatment with an FSK, consisting of a fusion of IL-24S to IL-15, promotes GBM cell killing and remodeling of the TME by recruiting and activating immune cells supporting the feasibility of developing safe and effective cancer immunotherapeutic fusion proteins and selective delivery in the brain for the therapy of GBM.