LAUSR

Photodynamic therapy (PDT) is a treatment that utilizes photosensitizers and light of a specific wavelength to kill cancer cells [1]. Additionally, the therapy may offer long term protection through activation of antitumor immune responses. Although PDT is an attractive therapeutic option for several types of cancer, there are several limitations that prevent its implementation as a universal cancer treatment. First, most of the currently used photosensitizers do not target tumors efficiently or avoid normal cells. Second, typical photosensitizers are most effectively excited by light with an approximate wavelength of 400 nm and less efficiently by light in the 600 to 800 nm range, limiting the treatment of deep tumors. Third, the generated immune responses are not robust enough to eliminate tumors due to the immunosuppressive tumor microenvironment [2]. Hence, the development of active compounds and/or therapeutic strategies that can overcome these shortcomings are of utmost importance for cancer treatment. Kobayashi's group has described a target-selected PDT strategy, named photoimmunotherapy (PIT) that uses antibodies conjugated to the photosensitizer IR700 [3]. Unlike conventional photosensitizers, the new highly hydrophilic IR700 induces cell death only when bound to the target cells and presents no cytotoxicity in the absence of light exposure. Moreover, its absorption peak in the nearinfrared (NIR) spectrum constitutes a significant advantage of this agent as it permits increased light penetration across tissues. IR700 is versatile enough to be conjugated to any targeting moieties (e.g. antibodies, peptides, small molecules). A clinical trial using cetuximabtargeted IR700 is being conducted in patients with recurrent or metastatic head and neck cancer (NCT03769506). Cetuximab targets the epidermal growth factor receptor (EGFR), which is overexpressed in multiple tumor types [4].