Ribosome-Inactivating Proteins from Salsola soda L. and Saponaria officinalis L. Are Promising Candidates for Targeted Therapy of Colon Cancer

Background/Objectives: Ribosome-inactivating proteins (RIPs) are plant-derived enzymes with potent cytotoxic activity, widely studied as anticancer agents, particularly as toxic payloads in immunoconjugates. Despite numerous encouraging results reported, their clinical application has been limited by their immunogenicity. RIPs from edible plants have been proposed as potentially more suitable candidates due to their possible improved tolerability. However, this aspect still requires validation in vivo in animal models. This study investigated the cytotoxic activity, mechanisms of action and translational potential of sodin 5 (a recently characterized type 1 RIP derived from the edible plant Salsola soda L.) in human colon cancer models, comparing it to the well-known type 1 RIP saporin-S6. Methods: The effects of sodin 5 and saporin-S6 on cell viability, cell death mechanisms and epithelial barrier integrity were assessed on HT29 and Caco-2 cell lines. Sodin 5 cross-reactivity with other anti-type 1 RIP sera was evaluated by ELISA. Finally, its structural characteristics were analyzed. Results: Sodin 5 showed a cytotoxic effect comparable to that of saporin-S6 in HT29 and Caco-2 colon cancer cells, with time- and concentration-dependent reductions in viability. Both type 1 RIPs disrupted the integrity of the intestinal epithelial barrier in mono- and co-culture models and predominantly activated the apoptotic pathway, without inducing necrosis. Sodin 5 exhibited limited immunological cross-reactivity and a conserved catalytic core, supporting its potential relevance as a therapeutic payload for intestinal cancer therapy. Conclusions: Our results indicate that sodin 5 possesses promising characteristics for anticancer applications, particularly in the treatment of intestinal malignancies, where local exposure and repeated administration are often required.