**Acknowledgements**

**3.8. Muscarinic acetylcholine receptors as pharmacological targets in breast cancer**

receptor antagonist), and tropicamide (M<sup>4</sup>

chol-induced MAPK/ERK phosphorylation [118].

the absence of muscarinic acetylcholine receptors [140].

brain cancers), no clinical trials have been done [109].

calcium channels, TRP channels, STIM/Orai proteins, hEag1 K<sup>+</sup>

breast cancer would simultaneously target several molecular players.

Carbachol, an agonist of muscarinic acetylcholine receptors, acts on M<sup>1</sup>

4-DAMP (M<sup>3</sup>

180 Calcium and Signal Transduction

**4. Conclusion**

IgG purified from the serum of breast cancer patients mimics the effect of carbachol by activating muscarinic acetylcholine receptors in MCF-7 breast cancer cells [136]. Moreover, these autoantibodies purified from the serum of breast cancer patients regulate the MCF7 breast cancer cell migration and the MMP-9 activity, and these effects are reduced by atropine,

the MCF7 breast tumor cells and potentiates tumor progression, by activating nitric oxide synthase via phospholipase C and protein kinase C signaling pathways [114]. Carbachol also elicits the mobilization of intracellular-free Ca2+ and induces the phosphorylation of MAPK/ ERK in MCF-7 human breast cancer cells, while pretreatment with wortmannin or LY294002 (selective inhibitors of phosphoinositide 3-kinase), with genistein (nonselective inhibitor of tyrosine kinases) or with PP2 (specific Src tyrosine kinase inhibitor), diminished the carba-

Moreover, carbachol upregulates the vascular endothelial growth factor-A in MCF7 tumor cells and determines angiogenesis, while atropine reverts its effects [136]. Carbachol treatment (20 hours) increased the tumor cell death and its administration in subthreshold concentrations in conjunction with paclitaxel potentiates cell death [138, 139], while atropine reverts these combined effects [138]. Interestingly, the combined treatment with carbachol (low doses) and paclitaxel induced the death of breast tumor MCF-7 cells, via the increased activity of nitric oxide synthase 1 and 3, and the reduced activity of arginase II, but the drug combination was ineffective against the nontumorigenic epithelial MCF-10A cell line, due to

Although several preclinical studies indicated the pharmacological potential of M<sup>3</sup>

nists in inhibiting tumor growth (e.g., melanoma, pancreatic, breast, ovarian, prostate, and

In conclusion, calcium signaling alterations occur in multiple cellular components, human breast stem cells, human breast epithelial cells, human breast myoepithelial cells, human breast adipocytes, human breast telocytes, etc., including those which contribute to the development and progression of breast cancer. Moreover, several molecular actors (e.g., voltage-gated

potassium channels, calcium-activated chloride channels, muscarinic acetylcholine receptors, etc.) are playing an important role in calcium-altered homeostasis associated with breast cancer that might be considered as potential pharmacological targets. Considering the interplay between the above-described calcium signaling pathways, the most efficient strategy against

receptor antagonist) [137].

and M<sup>3</sup>

receptors in

antago-

channels, calcium-activated

This work was supported by a grant of the Romanian Ministry of Research and Innovation, CCCDI—UEFISCDI, project number PN-III-P1—1.2-PCCDI-2017-0833/68/2018, within PNCDI III.
