An injectable chitosan hydrogel localizes and tunably releases immunotherapeutics intratumorally eliminating both treated and abscopal murine triple negative breast tumors

Systemic delivery of immunotherapy is dose-limited and often causes serious immune-related adverse events. Intratumoral injections can reduce systemic immunotoxicities and increase immunotherapy concentrations within a tumor. However, high pressures associated with direct tumor injection limits injectate retention, as low viscosity, saline-based solutions rapidly leak out of tumors. Viscoelastic solids, such as hydrogels, can improve local retention of co-formulated immunotherapies and provide sustained delivery. Prior work demonstrated that a chitosan-based hydrogel, XCSgel, was shear-thinning, self-healing, injectable, biocompatible, and clinically imageable. Here, we investigated XCSgel as a localized intratumoral delivery platform in the context of murine models of orthotopic triple-negative breast cancer. The intratumoral retention of immunotherapeutics co-formulated in XCSgel was characterized both ex vivo and in vivo via fluorescence imaging. Histopathological responses to intratumoral injections of XCSgel alone were scored by a veterinary pathologist. Initial antitumor studies evaluated a range of antitumor cytokines co-formulated with XCSgel. Subsequent antitumor and rechallenge studies evaluated the efficacy of a single intratumoral injection of interleukin-12 (IL-12) co-formulated in XCSgel (XCSgel-IL12) to control the growth of primary and abscopal tumors while inducing protective immunity. Pharmacokinetics studies quantified the systemic dissemination of IL-12 and consequent production of interferon-gamma following intratumoral injection with XCSgel co-formulation. Spectral flow cytometry was used to document changes in the tumor-immune microenvironment (TIME). XCSgel resisted tumor leakage and slowly released three model cytokines. XCSgel could be tuned for faster or slower release of embedded therapeutics. XCSgel-IL12 outperformed XCSgel formulations with other commonly used antitumor cytokines. A single injection of XCSgel-IL12 eliminated 86% E0771 and 20% mWnt orthotopic primary TNBC tumors. Mice rendered tumor-free resisted a live tumor challenge. XCSgel-IL12 also eliminated 67% untreated abscopal E0771 tumors. XCSgel-IL12 induced profound changes to the TIME, including a 3-fold reduction in the frequency of exhausted CD8+ T cells and a 3.2-fold increase in activated, proliferating CD8+ T cells. XCSgel is a promising localized delivery platform well-suited to enhance the retention and antitumor activity of potent immunotherapeutics. A single injection of XCSgel-IL12 can eliminate both primary and abscopal solid tumors, indicating that systemic immunotherapy may not be required for systemic control of cancer. SynopsisA novel injectable hydrogel, XCSgel, can localize and slowly release immunotherapies to eliminate primary and abscopal murine triple negative breast cancer tumors with a single injection.