Comprehensive Evaluation of Biological Effects of Pentathiepins on Various Human Cancer Cell Lines and Insights into Their Mode of Action

Abstract

Pentathiepins are polysulfur-containing compounds that exert antiproliferative and cytotoxic activity in cancer cells, induce oxidative stress and apoptosis, and inhibit glutathione peroxidase (GPx1). This renders them promising candidates for anticancer drug development. However, the biological effects and how they intertwine have not yet been systematically assessed in diverse cancer cell lines. In this study, six novel pentathiepins were synthesized to suit particular requirements such as fluorescent properties or improved water solubility. Structural elucidation by X-ray crystallography was successful for three derivatives. All six underwent extensive biological evaluation in 14 human cancer cell lines. These studies included investigating the inhibition of GPx1 and cell proliferation, cytotoxicity, and the induction of ROS and DNA strand breaks. Furthermore, selected hallmarks of apoptosis and the impact on cell cycle progression were studied. All six pentathiepins exerted high cytotoxic and antiproliferative activity, while five also strongly inhibited GPx1. There is a clear connection between the potential to provoke oxidative stress and damage to DNA in the form of single- and double-strand breaks. Additionally, these studies support apoptosis but not ferroptosis as the mechanism of cell death in some of the cell lines. As the various pentathiepins give rise to different biological responses, modulation of the biological effects depends on the distinct chemical structures fused to the sulfur ring. This may allow for an optimization of the anticancer activity of pentathiepins in the future.

Synthesis of Seven Indolizine-Derived Pentathiepines: Strong Electronic Structure Response to Nitro Substitution in Position C-9

“…Notably, in all seven cases, both the ethoxy substituent and the five sulfur atom chains extend from the aromatic plane towards the same side of this plane. A search of the CSD [ 45 ] for a pentathiepine moiety fused to a five-membered ring with an adjacent ethoxy substituent gave five hits, all from our group [ 21 , 23 , 24 ]. The number of available ethoxy-substituted indolizine-derived pentathiepine molecular structures is, hence, with the present study, more than doubled.…”

“…Another important aspect in this regard is the fact that the literature-known pentathiepines are somehow limited in their number and variation, while a larger available library would broaden, for instance, their use as monomers in electrochemical polymerization applications [ 22 ] and thereby provide an access to polymers with a wide range of characteristics. The milder protocol has the potential to change the limits of the present situation quite dramatically as was already indicated [ 23 , 24 , 25 ], and as is currently being explored by us intensively.…”

Liposomal formulation of model pentathiepin improves solubility and stability toward glutathione while preserving anticancer activity

“…In recent studies, we characterized the features that lead to antiproliferative effects of pentathiepins in cancer cells, such as inducing apoptosis, altering the mitochondrial membrane potential, causing oxidative stress, and inhibiting GPx1 as well as inducing DNA strand breaks. [11,12] The results of Wolff et al [12] and Chatterji and Gates [10] showed that the presence of thiols, such as GSH, are necessary for the induction of cytotoxic effects, for example, DNA cleavage, while at the same time leading to degradation of the pentathiepin. Still, a better understanding of the mechanism of action of pentathiepins will require further experimentation.…”

“…A well‐investigated and characterized [ 12 ] pentathiepin is (6‐ethoxy‐[1,2,3,4,5]pentathiepino[6,7‐ a ]indolizin‐9‐yl)[4‐(4‐flourobenzoyl)piperazinyl]methanone, shown in Figure 1. The compound possesses the greatest activity with regard to ROS formation in the presence of GSH, and is one of the most potent pentatheipins regarding antiproliferative activity and GPx1 inhibition, while possessing adequate solubility in organic solvents used for preparing stock solutions in biological testing.…”

“…The compound possesses the greatest activity with regard to ROS formation in the presence of GSH, and is one of the most potent pentatheipins regarding antiproliferative activity and GPx1 inhibition, while possessing adequate solubility in organic solvents used for preparing stock solutions in biological testing. [ 12 ] Here, we have formulated this compound into 1,2‐dioleoyl‐ sn ‐glycero‐3‐phosphocholine liposomes and compared the chemical stability in the presence of GSH, water solubility and antiproliferative activity on two human cancer cell lines of the liposomal pentathiepin to the free pentathiepin. Our studies indicate that liposomes are ideal delivery systems for use in biological studies, as well as for parenteral application in in vivo testing of pentathiepins as anticancer drugs.…”