M2 Receptor Activation Counteracts the Glioblastoma Cancer Stem Cell Response to Hypoxia Condition

Abstract

Glioblastoma multiforme (GBM) is the most malignant brain tumor. Hypoxic condition is a predominant feature of the GBM contributing to tumor growth and resistance to conventional therapies. Hence, the identification of drugs able to impair GBM malignancy and aggressiveness is considered of great clinical relevance. Previously, we demonstrated that the activation of M2 muscarinic receptors, through the agonist arecaidine propargyl ester (Ape), arrests cell proliferation in GBM cancer stem cells (GSCs). In the present work, we have characterized the response of GSCs to hypoxic condition showing an upregulation of hypoxia-inducible factors and factors involved in the regulation of GSCs survival and proliferation. Ape treatment in hypoxic conditions is however able to inhibit cell cycle progression, causing a significant increase of aberrant mitosis with consequent decreased cell survival. Additionally, qRT-PCR analysis suggest that Ape downregulates the expression of stemness markers and miR-210 levels, one of the main regulators of the responses to hypoxic condition in different tumor types. Our data demonstrate that Ape impairs the GSCs proliferation and survival also in hypoxic condition, negatively modulating the adaptive response of GSCs to hypoxia.

Functional Characterization of Cholinergic Receptors in Melanoma Cells

“…An inhibitory effect on tumor progression was demonstrated for M2 receptor subtype. In particular in human glioblastoma, the M2 receptor stimulation by the preferential orthosteric agonist arecaidine propargyl ester, was reported to inhibit cell proliferation and survival in stable cell lines and in glioblastoma cancer stem cells isolated from human biopsies [92][93][94][95][96][97][98]. The same effect has been described in neuroblastoma cell lines [99], in urothelial bladder cancer cells [100], and in breast cancer [101].…”

“…The data presented in this review clearly indicate the relevant roles played by cholinergic receptors in the cancer [21]. Comprehensive data have been reported in relation to different tumor types, such as colon and urothelial cancers [100], glioblastoma [92][93][94][95][96][97][98], neuroblastoma [99], and breast cancer [101]. Unfortunately, studies reporting the role of cholinergic receptors in melanoma are, at this stage, still limited.…”

“…The M1 receptor is involved in the progression of the prostate cancer, where it regulated cell migration and invasion through hedgehog signaling regulation [91][92][93][94]. An inhibitory effect on tumor progression was demonstrated for M2 receptor subtype.…”

“…Interestingly, research by Hua and collaborators proved that R2HBJJ, a novel mAChRs antagonist, can block the cholinergic autocrine loop in non-small-cell lung cancer, antagonizing the M3 receptors [109]. M3R is also involved in growth and progression of several tumors when co-expressed with epidermal growth factor receptor (EGFR) [92][93][94]. The activation of M3R results in transactivation of EGFR, thus promoting cell proliferation and inducing phosphorylation of ERK1/2 and AKT; conversely EGFR inhibition arrests the acetylcholine-induced gastric cancer proliferation [110][111][112].…”

Hypoxia Induces DPSC Differentiation versus a Neurogenic Phenotype by the Paracrine Mechanism

“…In fact, human cells can sense and respond to O 2 fluctuations as they change from normal (normoxia) to subnormal levels (hypoxia) [45]. Hypoxia is defined as a state of low availability of O 2 that limits or even abolishes the functions of organs, tissues, and cells [46]. Although hypoxia is commonly studied related to a wide variety of pathological conditions such as tissue ischemia, inflammation, and tumors, it is known to play an important role in physiological processes such as embryogenesis and the regulation of stem cell proliferation and differentiation [46,47].…”