IL-6 signaling is involved in the pathogenesis of a number of serious diseases, including chronic inflammation and cancer. Targeting of IL-6 receptor (IL-6R) by small molecules is therefore an intensively studied strategy in cancer treatment. We describe the design, synthesis, and characteristics of two new bis-pentamethinium salts 5 and 6 (meta and para) bearing indole moieties. Molecular docking studies showed that both compounds have the potential to bind IL-6R (free energy of binding -9.5 and -8.1 kcal/mol). The interaction with IL-6R was confirmed using microscale thermophoresis analyses, which revealed that both compounds had strong affinity for the IL-6R (experimentally determined dissociation constants 26.5 ± 2.5 nM and 304 ± 27.6 nM, respectively). In addition, both compounds were cytotoxic for a broad spectrum of cancer cell lines in micromolar concentrations, most likely due to their accumulation in mitochondria and inhibition of mitochondrial respiration. In summary, the structure motif of bis-pentamethinium salts represents a promising starting point for the design of novel multitargeting compounds with the potential to inhibit IL-6 signaling and simultaneously target mitochondrial metabolism in cancer cells.

BIOCEV 1st Faculty of Medicine Charles University CZ 252 42 Vestec Czech Republic

Department of Dermatovenerology 1st Faculty of Medicine Charles University and General University Hospital CZ 128 08 Prague Czech Republic

Department of Paediatrics and Inherited Metabolic Disorders 1st Faculty of Medicine Charles University and General University Hospital Ke Karlovu 455 2 CZ 128 08 Prague Czech Republic

Department of Pathological Physiology and Department of Physiology Faculty of Medicine Masaryk University Kamenice 5 CZ 625 00 Brno Czech Republic

Institute of Anatomy 1st Faculty of Medicine Charles University CZ 120 00 Prague Czech Republic

Institute of Biochemistry and Experimental Oncology 1st Faculty of Medicine Charles University CZ 120 00 Prague Czech Republic

Institute of Molecular Genetics Academy of Sciences CZ 140 00 Prague Czech Republic

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