New Selenonapthaquinone-Based Copper (II) Complexes as the Next-Generation Photochemotherapeutic Agents

Photoactive transition metal complexes like copper complexes find great interest in promoting metal-based photochemotherapeutic agents. In the present study, we explored the photocytotoxic efficacy of new selenylnaphthoquinone-based copper (II) complexes that provide a phenomenal platform in making an effective photo-chemotherapeutic agent via PDT in the clinical field of cancer therapy.

Three new copper(II) complexes (1-3) were synthesized in 40-60% yield and characterized analytically/ spectroscopically. ATCC® Normal Adult Human Primary Epidermal Keratinocytes were grown in Dermal Cell Basal Media supplemented with Keratinocyte Growth Kit components, to propagate keratinocytes in serum- free (not animal free) conditions. Anticancer activity of the complexes was studied using MTT (3- [4,5- dimethyltiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) assay. The intracellular ROS (¹O₂) generation was studied by using Flow Cytometric Analysis (FACS) on HaCaT cells using cell accessible non-polar 2',7'- Dichlorofluorescein Diacetate (DCFH-DA) dye. The Acridine Orange/Ethidium Bromide (AO/EB) dual staining assay was performed for detecting apoptosis in HaCaT cells. Several photophysical studies probing the generation of singlet oxygen was also carried out. We have performed Time-Dependent Density Functional Theory (TD-DFT) calculations using unrestricted B3LYP to understand the mechanism of type-II process.

All the complexes were remarkably cytotoxic in HaCaT cells with IC₅₀, 1-4μM under visible light with comparing lower dark toxicity. The presence of low-lying and long-lived triplet excited state allowed effective intersystem crossing and subsequent generation of singlet oxygen, which was the primary cytotoxic species responsible for oxidative stress and apoptosis. The experimental findings are in good agrrement with the computational analysis (TD-DFT).

The remarkably enhanced cytotoxicity of the new selenyl copper (II) complexes under the visible light probed the role of Se in photosensitized generation of singlet oxygen which was responsible for apoptosis in HaCaT cells. The results in the present work are of paramount importance in developing next generation copper(II)-based PDT agents.