Cancer remains one of the leading causes of mortality despite decades of research. One reason is that radiation therapy and chemotherapy are highly invasive techniques, which may limit their therapeutic benefits. Cellular- or molecular-targeted therapies, which are less invasive techniques, are receiving increased attention. Photoimmunotherapy is a treatment method that synergistically enhances the therapeutic effect by combining immunotherapy and phototherapy. Immunotherapy enhances tumor immunity by increasing the immunogenicity of the tumor microenvironment and reducing immunoregulatory suppression, resulting in the destruction of tumors in the body. Phototherapy destroys primary tumors with a combination of photosensitizers and light rays, and tumor-specific antigens released from the tumor cells enhance tumor immunity. Tumors can be selectively treated using photosensitizers as they are specific and selective for the target cells. The modality of phototherapy includes photodynamic therapy (PDT), photothermal therapy (PTT), and photochemistry-based therapies1.
Near-infrared photoimmunotherapy (NIR-PIT) is a recently developed method of antitumor phototherapy that combines photochemical-based therapy and immunotherapy1,2. NIR-PIT is a molecularly targeted therapy that targets specific cell surface molecules through the conjugation of a near-infrared silicon phthalocyanine dye, IRdye 700DX (IR700), to a monoclonal antibody (mAb). The cell membrane of the target cell is destroyed upon irradiation with NIR light (690 nm)3.
The concept of using targeted light therapy by combining conventional photosensitizers and antibodies or targeted PDT is over three decades old4,5. Previous studies have attempted to target conventional PDT agents by conjugating them to antibodies. However, there was limited success because these conjugates were trapped in the liver, owing to the hydrophobicity of the photosensitizers6,7. Moreover, the mechanism of NIR-PIT is completely different from that of conventional PDT. Conventional photosensitizers generate oxidative stress that results from an energy conversion that absorbs light energy, dislocates to an excited state, transitions to the ground state, and causes apoptosis. However, NIR-PIT causes rapid necrosis by directly destroying the cell membrane by aggregating photosensitizers on the membrane through a photochemical reaction8. NIR-PIT is superior to conventional targeted PDT in many ways. Conventional photosensitizers have low extinction coefficients, requiring the attachment of large numbers of photosensitizers to a single antibody molecule, potentially reducing binding affinity. Most conventional photosensitizers are hydrophobic, making it difficult to bind the photosensitizers to antibodies without compromising their immunoreactivity or in vivo target accumulation. Conventional photosensitizers typically absorb light in the visible range, reducing tissue penetration.
Several studies on NIR-PIT targeting intrathoracic tumors such as lung cancer and malignant pleural mesothelioma (MPM) cells have been reported9,10,11,12,13,14,15,16,17. However, only a few reports have described the efficacy of NIR-PIT in pleural disseminated MPM or lung cancer models9,10,11,12. Subcutaneous tumor xenograft models are thought to be standard tumor models and are currently widely used to evaluate the antitumor effects of new therapies18. However, the subcutaneous tumor microenvironment is not permissive for the development of an appropriate tissue structure or a condition that properly recapitulates a true malignant phenotype19,20,21,22. Ideally, orthotopic disease models should be established for a more precise evaluation of the antitumor effects.
Here, we demonstrate a method of efficacy evaluation in a mouse model of pleural disseminated lung cancer, which was treated using NIR-PIT. A pleural dissemination mouse model is generated by injecting tumor cells into the thoracic cavity and confirmed using luciferase luminescence. The mouse was treated with an intravenous injection of mAb conjugated with IR700 and NIR irradiation to the chest. The therapeutic effect was evaluated using luciferase luminescence.