Light-directed reprogramming of tumor-associated macrophages via STING agonist delivery

Macrophages play a pivotal role in immune regulation and disease progression through their ability to polarize into pro-inflammatory M1 or anti-inflammatory M2 phenotypes. In solid tumors, tumor-associated macrophages (TAMs) are predominantly M2-like and support tumor growth, metastasis, and immune suppression. Reprogramming these macrophages toward the M1 phenotype is a promising therapeutic strategy. STING (Stimulator of Interferon Genes) agonists have emerged as potent agents for inducing M1 polarization and enhancing anti-tumor immunity. However, their clinical use is limited, since it is hard to achieve therapeutic concentration of the agonist within the tumor without causing undesired systemic side effects. In this study, we present internalizable light-responsive carriers of varied sizes - 4.1 μm (Mic) and 0.7 μm (Sub) - for in situ controlled macrophage reprogramming using a light-triggered shift from the M2 to M1 phenotype in melanoma tissues through localized release of a STING agonist (AgST). Near-infrared (NIR) laser pulses enabled effective local heating of Mic and Sub up to 43 and 40 °C at 1035 mW/cm² with a consequent release about 60 % of the compounds loaded in carriers within 24 h. Both carrier types were efficiently internalized by RAW264.7 macrophages, with an increase of CD86 expression confirming 85-88 % M1-polarized phenotype after irradiation with light. In vivo studies on a murine melanoma model demonstrated significant M1 polarization of TAMs following intratumoral injection of AgST-loaded Mic carriers and subsequent NIR laser irradiation, as evidenced by CD86 expression increased up to 28.3 %. These findings underscore the potential of light-activated carriers for spatiotemporally controlled delivery of immunotherapeutic agents, providing a non-invasive and tunable method for macrophage reprogramming.