Activation of β2-adrenergic receptor (β2AR) and deorphanized GPR55 has been shown to modulate cancer growth in diverse tumor types in vitro and in xenograft models in vivo. (R,R′)-4′-methoxy-1-naphthylfenoterol [(R,R′)-MNF] is a bivalent compound that agonizes β2AR but inhibits GPR55-mediated pro-oncogenic responses. Here, we investigated the molecular mechanisms underlying the anti-tumorigenic effects of concurrent β2AR activation and GPR55 blockade in C6 glioma cells using (R,R′)-MNF as a marker ligand. Our data show that (R,R′)-MNF elicited G1-phase cell cycle arrest and apoptosis, reduced serum-inducible cell motility, promoted the phosphorylation of PKA target proteins, and inhibited constitutive activation of ERK and AKT in the low nanomolar range, whereas high nanomolar levels of (R,R′)-MNF were required to block GPR55-mediated cell motility. siRNA knockdown and pharmacological inhibition of β2AR activity were accompanied by significant upregulation of AKT and ERK phosphorylation, and selective alteration in (R,R′)-MNF responsiveness. The effects of agonist stimulation of GPR55 on various readouts, including cell motility assays, were suppressed by (R,R′)-MNF. Lastly, a significant increase in phosphorylation-mediated inactivation of β-catenin occurred with (R,R′)-MNF, and we provided new evidence of (R,R′)-MNF-mediated inhibition of oncogenic β-catenin signaling in a C6 xenograft tumor model. Thus, simultaneous activation of β2AR and blockade of GPR55 may represent a novel therapeutic approach to combat the progression of glioblastoma cancer.
Various species of the Carlina genus have been used in traditional medicine in many countries to treat numerous skin disorders, including cancer. The objective of this work was to assess the anticancer properties of root and leaf extracts from Carlina acaulis subsp. caulescens and C. acanthifolia subsp. utzka. Anti-tumor properties of the extracts were explored using a tetrazolium-based cell viability assay and flow cytometric apoptosis analysis, followed by immunodetection of phosphoactive ERK1/2 in UACC-903, C32, and UACC-647 human melanoma cell lines. Normal human fibroblasts were used as a control. Leaf extracts inhibited the viability of all tested melanoma cell lines in a dose-dependent fashion while the fibroblasts were less sensitive to such extract. The root extracts inhibited the proliferation of UACC-903 and UACC-647 cells only at the highest doses (300 μg/mL). However, the C32 and fibroblast cells exhibited an increase in the cellular proliferation rate and no caspase activity was observed in response to the root extracts (100 μg/mL). An increase in caspase activity was observed in melanoma cells treated with the leaf extracts of both Carlina species. Leaf extracts from C. acaulis subsp. caulescens (100 μg/mL) inhibited proliferatory ERK1/2 in UACC-903 and C32 cells, as demonstrated by the decrease in ERK1/2 phosphorylation. No reduction in phospho-ERK1/2 was observed in the tested cell lines treated with the root extracts, apart from UACC-647 after incubation with the C. acanthifolia subsp. utzka root extract (100 μg/mL). There was no change in ERK1/2 phosphorylation in the fibroblasts. The extracts from the leaves and roots were analyzed by HPLC and the analysis showed the presence of triterpenes and phenolic acids as the main extract components. The research demonstrated that the extracts from the leaves of the plants were cytotoxic against the human melanoma line and induced apoptosis of the cells. The triterpene fraction present in the tested extracts may be responsible for this activity.
Targeted therapies are based on the use of compounds that inhibit a specific target molecule within the tissue of interest. The recent advances in the molecular etiology of cancer significantly shifted the therapeutic approach from nonspecific cytotoxic agents towards molecules directed either at individual receptors or acting simultaneously on multiple molecular targets. This article is an overview of recent literature on (R,R′)-4′-methoxy-1-naphthylfenoterol (MNF), a novel bifunctional ligand that activates β2 adrenergic receptor (β2AR) and blocks GPR55 receptor. These two activities are important for MNF-dependent inhibition of cancer cell proliferation in vitro and in vivo, highlighting the potential applicability of MNF in multitarget anticancer therapies.
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