New cytotoxic rosamine derivatives selectively accumulate in the mitochondria of cancer cells

Abstract

Conventional cytotoxic anticancer drugs that target all rapidly dividing cells are nonselective in their mechanism of action, because they disrupt essential components that are crucial to both malignant and proliferating normal cells. Instead, targeting cellular functions that are distinctly different between normal and cancer cells may provide a basis for selective killing of tumor cells. One such strategy that is still largely unexplored is to utilize the relatively higher negative mitochondrial membrane potential in carcinoma cells compared with adjacent normal epithelial cells to enhance accumulation and retention of cytotoxic lipophilic cations in the former. In this study, the anticancer activities of a new class of rosamines with cyclic amine substituents and their structure-activity relationships were investigated. From an in-vitro cell growth inhibition assay, 14 of the rosamines inhibited the growth of human leukemia HL-60 cells by 50% at micromolar or lower concentrations. Derivatives containing hydrophilic substituents had less potent activity, whereas aryl substitution at the meso position conferred extra activity with thiofuran and para-iodo aryl substitutions being the most potent. In addition, both compounds were at least 10-fold more cytotoxic than rhodamine 123 against a panel of cell lines of different tissue origin and similar to rhodamine 123, exhibited more cytotoxicity against cancer cells compared with immortalized normal epithelial cells of the same organ type. In subsequent experiments, the para-iodo aryl substituted rosamine was found to localize exclusively within the mitochondria and induced apoptosis as the major mode of cell death. Our results suggest that these compounds offer potential for the design of mitochondria-targeting agents that either directly kill or deliver cytotoxic drugs to selectively kill cancer cells.

Rosamines Targeting the Cancer Oxidative Phosphorylation Pathway

“…This is consistent with our previous data for 2-methylbenzenes unsymmetrically substituted with piperidine and morpholine which showed nearly 2-fold lower IC 50 values compared with the symmetrical hydrophobic structure containing only piperidine [10]. Meanwhile for the meso -thiofuran 5 , substitution of one of the piperidine groups with morpholine gives 8 , which has a slightly decreased activity, contrary to our expectations.…”

“…Even though these rosamines (i.e 2 and 5 ) are more cytotoxic against cancer cells compared with normal epithelial cells (previously published data [10]), their effects on normal cells could still lead to undesirable side effects as a result of increase lactic acid accumulation in cells following decreased ATP synthase activity and a shift in metabolic pathways from aerobic to anaerobic metabolism. Accumulation of lactic acid has been shown to cause depressive cardiovascular function, cardiac arrhythmias and multiple organ failure.…”

“…We have previously demonstrated that rosamines primarily localize in the mitochondria [10] and that accumulation of cytotoxic DLC is known to alter mitochondrial transmembrane potentials [24], [25]. Thus, alterations of mitochondrial membrane potential caused by rosamines 2 and 5 were monitored based on the accumulation of potential-dependent JC-1 dye which resulted in a shift of fluorescence emission from green (∼525 nm) to red (∼590 nm) due to the formation of J-aggregates.…”

“…Intracellular imaging on representative examples indicated these compounds accumulate in the mitochondria. These compounds (i.e rosamine 2 and 5 ) are also found to be more cytotoxic against cancer cells compared with immortalized normal epithelial cells of the same organ type [10].…”

“…1A) [10], [11]. These compounds are delocalized lipophilic cations (DLC) with peripheral cyclic amines and various groups at the meso position; the majority of these cations are substantially more potent than rhodamine-123 which is a well-studied delocalized lipophilic cation.…”