In Vitro and In Vivo Evaluation of Photocontrolled Biologically Active Compounds - Potential Drug Candidates for Cancer Photopharmacology

Photocontrolled, biologically active compounds are an emerging class of "smart" drug candidates. They provide additional safety in systemic chemotherapy due to their precise spatiotemporal activation by directing a benign, non-ionizable light to a specific location within the patient's body. This paper presents a set of methods to evaluate the in vitro potency and ex vivo efficiency of the photoactivation of photocontrolled, biologically active compounds as well as the in vivo efficacy at early stages of drug development. The methodology is applied to anticancer cytotoxic peptides, namely, the diarylethene-containing analogs of a known antibiotic, gramicidin S. The experiments are performed using 2D (adherent cells) and 3D (spheroids) cell cultures of a cancer cell line (Lewis lung carcinoma, LLC), live tissue surrogates (pork meat mince), and an allograft cancer model (subcutaneous LLC) in immunocompetent mice. The selection of the most effective compounds and estimation of realistic phototherapeutic windows are performed via automated fluorescence microscopy. The photoactivation efficiency at varying illumination regimens is determined at different depths in a model tissue, and the optimal light dosage is applied in the final therapeutic in vivo experiment.