Singly and doubly modified analogues of C20-epi-salinomycin: A new group of antiparasitic agents against Trypanosoma brucei

Assessment of Salinomycin's Potential to Treat Microcotyle sebastis in Korean Rockfish (Sebastes schlegelii)

Aquaculture, a crucial sector of the global food industry, faces a myriad of issues due to parasitic invasions. One such parasite, Microcotyle sebastis, which afflicts Korean rockfish in South Korea, has a significant economic impact. The impending danger of resistance to traditional anthelmintics necessitates the exploration of new antiparasitic candidates. Although the efficacy of salinomycin against aquatic parasites such as ciliates and sporozoans is known, its influence on monogeneans has yet to be studied. Therefore, this study investigated the efficacy and safety of salinomycin for the treatment of M. sebastis infections, presenting the first exploration of salinomycin's therapeutic potential against monogeneans. In vitro examinations revealed a minimum effective concentration of salinomycin of 5 mg/kg, which led to necrosis of the haptor upon dislodging from the gill filaments. The one-time oral administration of the drug at concentrations of 5 mg/kg and 10 mg/kg showed a significant dose-dependent reduction in parasite counts, with no apparent behavioral side effects in Korean rockfish. Biochemical analyses monitored the liver, heart, and kidney enzymes, specifically aspartate transaminase (AST), alanine transaminase (ALT), blood urea nitrogen (BUN), and creatine kinase-myocardial band (CK-MB). At both 20 °C and 13 °C, no significant differences were observed in the levels of AST and ALT. However, at 20 °C, alterations in BUN levels were evident on Day 14, a deviation not observed at 13 °C. The CK-MB analysis revealed elevated enzyme levels at both temperatures when compared to the control group, reflecting the similar changes observed in terrestrial animals administered salinomycin. The biochemical data suggest that the oral administration of salinomycin is potentially more favorable at 13 °C than at 20 °C. Although our findings warrant further comprehensive studies, including on the long-term and potential effects on nontarget species and water quality, they also suggest that salinomycin could be considered as an alternative or adjunctive treatment if resistance to the currently used praziquantel against M. sebastis is confirmed.

Synthesis of urea and thiourea derivatives of C20-epi-aminosalinomycin and their activity against Trypanosoma brucei

Salinomycin (SAL) is a natural polyether ionophore that exhibits a very broad spectrum of biological effects, ranging from anticancer to antiparasitic activities. Our recent studies have shown that the chemical modification of the SAL biomolecule is a fruitful strategy for generating lead compounds for the development of novel antitrypanosomal agents. As a continuation of our program to develop trypanocidal active lead structures, we synthesized a series of 14 novel urea and thiourea analogs of C20-epi-aminosalinomycin (compound 2b). The trypanocidal and cytotoxic activities of the derivatives were assessed with the mammalian life cycle stage of Trypanosoma brucei and human leukemic HL-60 cells, respectively. The most antitrypanosomal compounds were the two thiourea derivatives 4b (C20-n-butylthiourea) and 4d (C20-phenylthiourea) with 50% growth inhibition (GI₅₀) values of 0.18 and 0.22 μM and selectivity indices of 47 and 41, respectively. As potent SAL derivatives have been shown to induce strong cell swelling in bloodstream forms of T. brucei, the effect of compounds 4b and 4d to increase the cell volume of the parasite was also investigated. Interestingly, both derivatives were capable to induce faster cell swelling in bloodstream-form trypanosomes than the reference compound SAL. These findings support the suggestion that C20-epi-aminosalinomycin derivatives are suitable leads in the rational development of new and improved trypanocidal drugs.

Activity of singly and doubly modified derivatives of C20-epi-salinomycin against Staphylococcus strains

Natural polyether ionophore salinomycin (Sal) has been widely used in veterinary medicine as an antibiotic effective in the treatment of coccidian protozoa and Gram-positive bacteria. Moreover, chemical modification of the Sal structure has been found to be a promising strategy to generate semisynthetic analogs with biological activity profiles improved relative to those of the native compound. In this context, we synthesized and thoroughly evaluated the antibacterial potential of a library of C1/C20 singly and doubly modified derivatives of C20-epi-salinomycin, that is, analogs of Sal with inversed stereochemistry at the C20 position. Among the synthesized analog structures, the most promising antibacterial active agents were those obtained via regioselective O-acylation of C20-epi-hydroxyl, particularly esters 7, 9, and 11. Such C20 singly modified compounds showed excellent inhibitory activity against planktonic staphylococci, both standard and clinical strains, and revealed potential in preventing the formation of bacterial biofilms. In combination with their non-genotoxic properties, these Sal derivatives represent attractive candidates for further antimicrobial drug development.

Evaluation of the anticancer activity of singly and doubly modified analogues of C20-epi-salinomycin

In developed countries, cancer is the second leading cause of death, with colon and prostate cancer belonging to the group of most often diagnosed types of neoplastic diseases. The search for new treatment strategies against these types of cancer is thus of top current interest. In this context, salinomycin (SAL), a naturally occurring polyether ionophore, has been identified recently as a very promising anticancer drug candidate towards several tumour cells. In the present work, a broad library of 24 derivatives of C20-epi-salinomycin (2), including C1 singly, C20 singly and C1/C20 doubly modified analogue structures, was screened to identify compounds with improved activity against colon and prostate cancer cells. Our study demonstrated that the growth inhibitory potency of the parent compound on both primary and metastatic colon cancer cells was similar to that of the semisynthetic products derived from SAL, and simultaneously the SAL analogues showed more potent toxic action on metastatic prostate cancer cells than that of the chemically unmodified ionophore. In contrast to the widely used oncological drug doxorubicin, some of the SAL derivatives demonstrated promising anticancer activity with no toxic effects on non-tumour cells, and with more favourable cytotoxicity than that of a reference agent 5-fluorouracil. Mechanistically, the SAL analogues induced late apoptosis in colon cancer cells and necrosis in prostate cancer cells, as well as reduced secretion of interleukin 6 (IL-6) in these cells.