Leelamine Mediates Cancer Cell Death through Inhibition of Intracellular Cholesterol Transport

Abstract

Leelamine is a promising compound for the treatment of cancer; however, the molecular mechanisms leading to leelamine-mediated cell death have not been identified. This report shows that leelamine is a weakly basic amine with lysosomotropic properties, leading to its accumulation inside acidic organelles such as lysosomes. This accumulation leads to homeostatic imbalance in the lysosomal endosomal cell compartments that disrupts autophagic flux and intracellular cholesterol trafficking as well as receptor-mediated endocytosis. Electron micrographs of leelamine-treated cancer cells displayed accumulation of autophagosomes, membrane whorls, and lipofuscin-like structures, indicating disruption of lysosomal cell compartments. Early in the process, leelamine-mediated killing was a caspase-independent event triggered by cholesterol accumulation, as depletion of cholesterol using β-cyclodextrin treatment attenuated the cell death and restored the subcellular structures identified by electron microscopy. Protein microarray–based analyses of the intracellular signaling cascades showed alterations in RTK–AKT/STAT/MAPK signaling cascades, which was subsequently confirmed by Western blotting. Inhibition of Akt, Erk, and Stat signaling, together with abnormal deregulation of receptor tyrosine kinases, was caused by the inhibition of receptor-mediated endocytosis. This study is the first report demonstrating that leelamine is a lysosomotropic, intracellular cholesterol transport inhibitor with potential chemotherapeutic properties leading to inhibition of autophagic flux and induction of cholesterol accumulation in lysosomal/endosomal cell compartments. Importantly, the findings of this study show the potential of leelamine to disrupt cholesterol homeostasis for treatment of advanced-stage cancers.

A non-cytotoxic N-dehydroabietylamine derivative with potent antimalarial activity

“…Therefore, optimally designed abietane diterpenoid compounds that specifically inhibit heme polymerization and kill malaria parasites may prove to be effective antimalarial drugs. Additionally, as reported previously for cancer cells (Kuzu et al, 2014), abietane diterpenoids having amine basicity may interfere with the cholesterol transport in parasites, causing membrane dysfunction and death. Therefore, based on the foregoing discussion, it appears that abietane diterpenoids target multiple functions in parasites.…”

“…In cancer cells, it has been shown that dehydroabietylamine is lysomotropic, thus accumulates in lysosomes causing disruption of lysosomal compartments (Gowda et al, 2014; Kuzu et al, 2014). Dehydroabietylamine has also been shown to interfere with intracellular cholesterol transport, affecting membrane functions and leading to cell death.…”

“…The cell lines were periodically monitored for genotypic characteristics and tumorigenic potential to confirm cell line identity and phenotypic behavior (Gowda et al, 2014; Kuzu et al, 2014; Robertson et al, 2014). …”

“…The cytotoxic activity of compounds has previously been measured by assessing the viability of normal human fibroblast FF2441 cells and human melanoma UACC 903 cells by the MTS assay (Promega, Madison, WI) (Gowda et al, 2014; Kuzu et al, 2014; Robertson et al, 2014). …”

“…Recently, dehydroabietylamine (also called leelamine), abietic acid, and their synthetic derivatives have been studied for potential anti-cancer activity (Huang et al, 2013; Kuzu et al, 2014; Robertson et al, 2014). Some of these compounds exhibited potent melanoma cell killing activity, while others had a negligible effect (Robertson et al, 2014).…”