Polymeric cloak stabilizes cytokine complex to generate tumor-targeted nanosuperagonist

Innovation Center for NanoMedicine (iCONM; Center Director: Prof. Kazunori Kataoka), a research institute of the Kawasaki Institute of Industrial Promotion (KIIP), has announced that a group led by Prof. Horacio Cabral (Visiting Scientist of iCONM / Associate Professor of the Department of Bioengineering, Graduate School of Engineering, University of Tokyo) discovered a new method to construct protein complex-based therapeutics in collaboration with iCONM, and published a paper entitled " Nano-enabled IL-15 superagonist via conditionally stabilized protein-protein interactions eradicates solid tumors by precise immunomodulation" in the Journal of the American Chemical Society on October 2nd, 2024.

Protein complexes are critical regulators of diverse biological processes, exhibiting unique functions that make them promising candidates for therapeutic applications. For example, interlukin-15 (IL-15) can bind with its receptor α domain (IL-15Rα) to form a superagonistic complex, which can effectively activate antitumoral immunity by facilitating the trans-presentation of IL-15 to immune cells. However, protein complexes are mainly formed by dynamic non-covalent interactions, leading to the instability and transient effective time in biological environments. Thus, delivery strategies are needed to mediate stable delivery of protein complexes. Current study presents a polymer cloak that was designed to assist the use of protein complexes as therapeutic agents, as illustrated by the prototype formulation loading IL-15/IL-15Rα complex. The polymer coating stabilized the protein-protein interaction between IL-15 and IL-15Rα, which effectively immobilized the complex, isolating it from the surroundings and yielding an IL-15 nanosuperagonist with enhanced efficacy. In mouse models, the nanosuperagonist displayed improved pharmacokinetics and stably delivered the intact protein complex upon intravenous injection. Moreover, due to the pH-sensitivity of the polymer cloak, the nanosuperagonist could sense the acidic tumor microenvironment and ensured a tumor-selective activation. In murine colon cancer models, the nanosuperagonist profoundly inflamed the tumor to eliminate the cancer cells without inducing immune-related side effects.

What is the novelty of this study?

Protein complexes are important bioactive entities with the potential to be utilized for therapeutic applications. However, the inherent instability and transient nature of protein complexes pose significant challenges for achieving in vivo efficacy. Current mainstream delivery strategy for protein complexes is based on protein engineering technology to construct fusion proteins. The polymer cloak introduced in this study is the first example using polymeric materials to modulate the protein-protein interaction for stabilizing the delivery of protein complexes. The highlighted findings and features of the study are:

1. The polymer coating strategy simplifies the delivery of protein complexes, bypassing the need for protein engineering.
2. The polymer cloak maintains the protein-protein interaction and protects the protein complex in harsh biological environments.
3. The selective disassembly of the polymer-based nanosuperagonist in tumor tissues simultaneously addresses both efficacy and safety challenges for cancer immunotherapy.

Why are these findings important and how is the study going to improve the current technology landscape?

Protein complexes are mainly formed through dynamic non-covalent interactions, making them unstable and sensitive to factors like pH, temperature, ionic strength, mechanical stress, denaturants, and proteolysis. As illustrated in this study, IL-15/IL-15Rα complex could be disrupted by external reactive species like monomeric IL-15 or proteases, leading to the rapid disintegration of the complex in vivo. In contrast, the polymer cloak interlocked the complex and protect its integrity in harsh environment like blood stream. Thus, the polymeric cloak could promote the stability and function of the protein complex in in vivo conditions, which is critical for attaining therapeutic activity. Comparing to the reported methods for delivering protein complexes, which focus on engineering protein structures to create stable fusion proteins, this polymer cloak detours the complexity in design and manufacture of protein engineering technology. Meanwhile, the system can be easily extended to apply to other protein complex payloads beyond the illustrated IL-15/IL-15Rα complex, serving as a universal platform. Moreover, benefiting from the pH-sensitive nature of the polymer cloak, the system not only mediated a stable delivery of the intact protein complexes systemically, but further achieved a tumor-targeted release of the cargos. In the case of IL-15-based nanosuperagonist, the polymer coating stabilized the IL-15/IL-15Rα complex to provide antitumor superagonistic potency, and the pH-controlled de-coating of the polymer allowed a tumor-specific bioactivity, which mitigated the toxicity. Thus, comparing to the conventional fusion protein-based IL-15 superagonist formulations, the nanosuperagonist realized a safer therapy. In summary, the polymer cloak presents a streamlined platform for tumor-targeted delivery of protein complexes, and it will inspire further research into polymer- and nano-based approaches to facilitate the translation of protein complexes as therapeutic agents.