Page 86 - SRPSKO DRUŠTVO ISTRAŽIVAČA RAKA

Serbian Association for Cancer Research SDIRSACR

through alternative mechanisms [9],[10]. Notably, we discovered that Sal disrupts the function of the Golgi apparatus,
similarly to Mon, a known Golgi disruptor. This prompted further investigations to clarify whether salinomycin’s
selectivity is linked to its ability to impair Golgi function.
Effect of ionophores on ABCG2 activity.
Several studies have reported that natural ionophores (e.g., Sal, Mon, and Nig) sensitize resistant cancer cells to various
chemotherapeutics, an effect primarily attributed to their inhibitory activity on ABCB1 (P-gp). In contrast to this well-
documented P-gp-mediated multidrug resistance (MDR) reversal, our current study did not demonstrate any inhibitory
activity of these ionophores on ABCG2. Moreover, salinomycin may act as a substrate of ABCG2 rather than an inhibitor.
This implies that their CSC-selectivity is likely mediated by distinct, transporter-independent mechanisms [7].
Influence of salinomycin on Golgi function in EMT cells.
We further confirmed that Sal reduced the proportion of EMT cells in a mixed population. In proliferation assays,
Sal showed a more pronounced inhibitory effect on EMT cells compared to non-EMT cells. However, this selectivity
diminished at higher concentrations of Sal, which were cytotoxic to both cell types. These higher doses also caused
immediate mitochondrial depolarization, which was even more prominent in non-EMT HMLE-pBp cells. This suggests
selective toxicity toward EMT cells, albeit to a lesser extent than previously reported.
Notably, we demonstrated that Sal disrupts Golgi function, similar to Mon. Both compounds altered GA morphology,
but only EMT cells exhibited extensive fragmentation of the Golgi and ER-Golgi intermediate compartments, and were
sensitized to Sal and Mon treatment. Furthermore, Sal induced the expression of ER-Golgi-related genes predominantly
in EMT cells. Impaired Golgi function led to alterations in post-translational modifications—specifically, reduced
protein secretion and significant changes in the N-glycosylation profile of secreted proteins, most notably a reduction
in complex N-glycans.[8] Strikingly, cell adhesion emerged as the most affected biological process in EMT cells treated
with Sal, which was not the case in non-EMT cells.
Conclusions: Our data clearly establish salinomycin (Sal) as a Golgi-disrupting agent and support existing evidence that
cells undergoing EMT are particularly sensitive to Golgi perturbation. These findings further elucidate the mechanism
underlying the selective activity of Sal and related ionophores toward EMT/CSC cells and underscore the therapeutic
potential of Golgi-disrupting compounds in targeting cancer stem-like populations. Moreover, they point to a broader
and previously underappreciated role of the Golgi apparatus in regulating EMT plasticity.

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