Colon cancer is a solid tumor with strong immunogenicity that is prone to metastasis in its early stages. Traditional single-treatment methods have limited efficacy; therefore, the development of new, safe, effective treatment strategies has become urgent. Natural killer (NK) cell-mediated immunotherapy can kill tumor cells in a nonspecific antigen manner and has good prospects for the treatment of malignant tumors. However, because of the common immune escape mechanism in malignant tumor tissues, the activity and infiltration of NK cells in tumor tissues are insufficient, making it difficult to effectively eliminate tumor cells. Recently, it was found that photothermal therapy (PTT) and photodynamic therapy (PDT), which induce local hyperthermia or reactive oxygen species in tumor tissues via laser-induced phototherapy, not only directly induce apoptosis and necrosis of tumor cells but also improve the immunosuppressive environment in tumor tissues by inducing immunogenic death of tumor cells. This promotes the infiltration and activity of immune cells, including NK cells, in tumor tissues. As a pure natural edible substance and a potential anticancer molecule in plants, lupeol directly promotes tumor cell apoptosis and NK cell activity, making it easier for NK cells to recognize and eliminate tumor cells. In this study, we investigated the synergistic effect and mechanism of a nanoliposome carrier combined with FDA-approved indocyanine green (ICG)-mediated optical therapy and the natural molecule, lupeol, in enhancing NK cell activity for colon cancer cell inactivation. The results show that Lip-Lupeol & ICG reduced colon cancer cell activity to 59.6% after 20 min of irradiation and 43.4% after 20 min+10 min of irradiation. When NK cells are added after 20 min+10 min of irradiation, the activity decreased to 16.7%, providing a new approach for colon cancer treatment.

The use of nanoliposomes as carriers to encapsulate the photosensitizer, ICG, and the natural anticancer product, lupeol, in fruits and vegetables to prepare nanoliposome drugs with uniform particle size and good stability (Lip-Lupeol & ICG) was used to achieve the synergistic amplification of PTT and PDT with lupeol-mediated NK cell immunotherapy. Lip-Lupeol & ICG can induce apoptosis of colon cancer cells and trigger immune responses through ICG-PDT under 808 nm laser radiation. In addition, it can release encapsulated lupeol to activate NK cells, thereby facilitating the accurate identification of colon cancer cells. Lip-Lupeol & ICG exhibits excellent tumor-killing effects and stimulates NK cell immune responses, achieving a synergistic therapeutic effect of NK cell immune enhancement and photodynamic therapy mediated by lupeol.

The prepared Lip-Lupeol & ICG has a typical phospholipid bilayer liposome structure, with bilayer vesicles for drug encapsulation and intracellular delivery. The particle size is approximately 144?153 nm, and the stability is good for 14 d. Lupeol and ICG were successfully encapsulated. Next, under the irradiation of an 808 nm laser on the liposome causing structural rupture, the encapsulated Lip-Lupeol & ICG were released rapidly. After 18 min, the accumulation of ICG reached 82.1%, indicating the photothermal response of Lip-Lupeol & ICG to laser irradiation. ICG-encapsulated liposomes enter tumor cells through endocytosis and induce severe cytotoxicity through PTT and PDT under a laser irradiation of 808 nm. In addition, lupeol synergistically enhances NK cell activity-mediated immunotherapy to achieve synergistic photodynamic immune antitumor effects.

In this study, a lipid nanocarrier system was designed to synergistically integrate the NK immune enhancement of lupeol-and ICG-mediated optical therapy and achieve controlled release. Both were effectively integrated to achieve precise targeting of lupeol and ICG to colon cancer cells, thereby enhancing the indirect immune response and anticancer effects of lupeol by promoting NK cell activity.