Anticancer Effect of Nature-Inspired Indolizine-Based Pentathiepines in 2D and 3D Cellular Model

Background: 1,2,3,4,5-pentathiepines (PTEs) are compounds originally identified in marine ascidians and are currently under investigation for their promising pharmacological
properties, particularly as potential antineoplastic agents. Objectives: In this study, we investigated the antineoplastic properties of a series of ten indolizine-based PTEs, comprising
eight previously reported compounds and two newly synthesized derivatives. Methods:
These compounds were evaluated against a panel of human cancer cell lines of diverse
tissue origins, as well as, for the first time, on non-cancerous CR9 fibroblasts to assess their
cytotoxic selectivity. In addition, their effects were tested on 3D spheroid models, providing
preliminary insights into their potential in vivo efficacy. Initial screening focused on cell
viability, followed by a more detailed characterization of the most active compounds in
terms of their ability to induce apoptosis, necrosis, cell cycle arrest, and reactive oxygen
species (ROS) generation. The anti-migratory activity of PTEs and a newly adapted assay to
confirm sulfur species release in the cells were also performed for the first time. Results and
Conclusions: Our findings reveal that four PTEs bearing hydrophilic, hydrogen-bonding functional groups, particularly the two inspired by natural analogs, exhibited the most potent anticancer activity.