Photodynamic therapy is an innovative treatment approach broadly directed towards oncological diseases. Its applicability and efficiency are closely related to the interaction of three main components, namely a photosensitizer, light and molecular triplet oxygen, which should drive cell death. Recently, several studies have demonstrated that squaraine cyanine dyes have a set of photophysical and photochemical properties that have made of these compounds' potential photosensitizers for this therapeutic modality. In the present research work, we describe the synthesis and characterization of four quinoline‑ and benzoselenazole‑derived unsymmetrical squaraine cyanine dyes. Except for the precursor of aminosquaraine dyes, i.e., O‑methylated derivative, all dyes were evaluated for their behavior and absorption capacity in different organic and aqueous solvents, their ability to form singlet oxygen, their light‑stability, and in vitro phototherapeutic effects against two human breast cancer cell cultures (BT‑474 and MCF‑7). Regardless of the nature of the used solvents, the synthesized dyes showed intense absorption in the red and near‑infrared spectral regions, despite the formation of aggregates in aqueous media. Dyes showed high light‑stability against light exposure. Despite the low ability to produce singlet oxygen, aminosquaraine dyes demonstrated worthy in vitro phototherapeutic activity.
Keywords: benzoselenazole; breast cancer; light‑stability; phototherapeutic effects; quinoline; singlet oxygen; unsymmetrical squaraine dyes.