A research group from Japan Advanced Institute of Science and Technology (JAIST) developed light-activatable, liquid metal (LM) nanoparticles for cancer diagnosis and treatment via photoimmunotherapy. The LM nanoparticles can target and destroy cancer cells and can be fluorescently tagged to function as reporters to identify and eliminate tumors in vivo. Gallium (Ga)-based LM nanoparticles are promising nanoscale materials for biomedical applications due to their physicochemical properties, including flexibility, easy surface modification, efficient photothermal conversion, and high biocompatibility. One prominent application of LMs is photothermal cancer therapy, in which functional LM nanoparticles convert light energy to heat energy to kill cancerous cells. LM-based phototherapy is superior to traditional cancer therapy due to its high specificity, repeatability, and minimal side effects. According to the researchers, the JAIST study is the first to exploit the physicochemical properties of LM nanocomplexes for cancer immunotheranostics. The researchers believe that their approach can improve the theranostic effects of LM for the treatment of cancer and other diseases. A versatile liquid metal (LM) gallium-indium (Ga-In) alloy has been used to develop a novel LM nanoparticle that contains an immunomodulant and an immune checkpoint inhibitor called anti-PD-L1. Upon irradiation by near-infrared (NIR) light, anti-PD-L1 specifically binds to the cancer cell, while immunostimulants activate T and dendritic cells. This synergistic activation, coupled with the photothermal effect, effectively eliminates the cancer cell almost immediately. Courtesy of Eijiro Miyako/JAIST. To combine cancer phototherapy with immunotherapy, the researchers synthesized multifunctional LM nanoparticles containing a eutectic gallium-indium (EGaIn) LM alloy and an immunological modulator, which were embedded inside a biocompatible surfactant. They prepared water-dispersible LM nanoparticles through a sonication process and used the surfactant to introduce the immunological modulator. The researchers confirmed that the LM material disintegrated to ensure delivery of the immunological modulator to the target. They also found that the LM nanoparticles displayed a linear increase in absorbance in the NIR region at 808 nm, confirming that the LM particles were optically activatable. When the researchers irradiated the aqueous solution of the LM nanoparticle with an NIR laser at 808 nm, they observed a notable increase in the temperature of the solution, proportional to the increase in the nanoparticle concentration. This finding confirmed that LM nanoparticles with the immunological modulator could be robust, stable, photothermal drug carriers suitable for immunotherapy. Further experiments demonstrated that LM nanoparticles were safe and did not cause cytotoxicity in human fibroblast or mouse colon cancer cells. To assess the degree to which the nanoparticles were internalized and distributed, the researchers introduced a fluorescent dye into the nanoparticles through a sonication process. Using fluorescent microscopy with a laser, they demonstrated that the LM nanoparticles displayed strong fluorescence at various NIR wavelengths and immediately destroyed mouse colon cancer cells. Thus, the researchers showed that the LM nanoparticles could not only deliver the immunomodulator efficiently, but could also enable real-time tracking of the immunomodulator to show that it had the ability to eliminate specific cancer cells. “We believe that the convergence of nano-immuno engineering and LM technology could provide a promising modality to trigger ideal immune responses for advancing cancer immunotherapy,” said Eijiro Miyako, a professor at JAIST. “In this study, we report light-activatable, multifunctional LM nanoparticles with immunostimulants to combine photothermal therapy with immunotherapy.” To achieve a multifaceted LM immune nanostimulator for cancer theranostics, the researchers then added an immune checkpoint inhibitor to the fluorescent LM nanoparticles. The modified nanoparticles were dispersed efficiently and exhibited significant fluorescence. Also, the surface temperature of the tumor increased linearly as post-irradiation time increased, indicating that the fluorescent LM nanoparticles with an immune checkpoint inhibitor had an antitumor effect. Adding the immune checkpoint inhibitor to the LM nanoparticles enabled the nanoparticles to bind to programmed death-ligand 1, or PD-L1, proteins on the cancer cells. The PD-L1 proteins could not allow the cancer cells to escape an attack by the immune system, because the immune checkpoint inhibitor marked the cancer cells for destruction by macrophages and dendritic cells. The LM nanocomplex stimulated the T cells and dendritic cells due to its modified immunological modulators, thus increasing innate antitumor immunity. Once systemic administration occurred, the LM nanocomplex selectively accumulated at the targeted tumor site through enhanced penetration and retention effects. The immunological modulator was remotely released from the LM nanocomplex by NIR laser irradiation. The strong photothermal conversion property of LM was also activated under NIR light to induce a thorough denaturation of aggressive tumor cells. NIR laser-induced LM nanoparticles with the immune checkpoint inhibitor exhibited the highest, most comprehensive rate of cancer removal, with fast healing and recovery. Moreover, when a tumor recurred, mice treated with these nanoparticles displayed sustained antitumor effectiveness and prolonged survival. The LM nanoparticles show the potential to elicit antitumor immunity in a controlled manner and to regulate the cellular activity inside a tumor as well as systemic immunological activity. The combined effects of photothermal and control drug-releasing properties and immunological stimulations were shown to induce the infiltration and activation of cytotoxic T cells and dendritic cells in targeted tumors for enhanced cancer immunotherapy. “We believe that these synergistic immunological effects and optical nanofunctions of LMs have wide therapeutic applications and might contribute to innovative cancer theranostic technologies,” Miyako said. “We are hopeful that this technology will be available for clinical trials in 10 years.” The research was published in Advanced Functional Materials (www.doi.org/10.1002/adfm.202305886).