Opto-chemical and laser properties of FLTX1, a novel fluorescent tamoxifen derivative, and its potential applications in breast cancer photodynamic chemotherapy

Tamoxifen is the most common antiestrogen used in the chronic treatment of breast cancer. In these cells, it mainly binds to intracellular receptors (estrogen receptor alpha, ERα) and antagonizes the binding of its cognate ligand, 17β-estradiol, thereby preventing uncontrolled hormone-dependent cellular proliferation and growth. In the last decade, in our laboratories we have developed and characterized different tamoxifen derivatives, including a novel fluorescent tamoxifen conjugate: FLTX1. FLTX1 is formed by the covalent binding of tamoxifen to a common fluorescent biomarker NBD. This new prodrug was originally designed as a fluorescent biomarker to localize intracellular targets, which not only keeps the pharmacological activity of tamoxifen but also adds a luminescent functionality. Strikingly, the quantum efficiency of FLTX1 is so high that laser emission has been obtained as an emerging property. In this review, we will show its laser properties under three different configurations. First, as amplified spontaneous emission or mirrorless laser; second, through the evanescent field of WGMs of a ring resonator around an optical fiber; and finally as random laser in uterine tissues impregnated with the prodrug. Further, we observed another emergent property for FLTX1: this molecule, but not tamoxifen alone or NBD, was able to generate reactive oxygen species (ROS) upon irradiation. This property is extremely interesting as FLTX1 might be used for photodynamic therapy. Under this paradigm, FLTX1 would act as a sensitizer in ERα-overexpressing cells (which feature the most prevalent form of hormone-dependent breast cancer), causing cell death in ERα+ cells but reducing damage to other non-cancer (healthy) cells or surrounding tissues. We show here time resolved fluorescence results that suggest molecular aggregations, which could explain the subsequent generation of ROS. This is an original cancer therapy strategy that combines the pharmacological properties of a new tamoxifen derivative and its laser dye features with a highly selective photodynamic therapy.