Nicotinic receptors modulate antitumor therapy response in triple negative breast cancer cells

BACKGROUND Triple negative breast cancer is more aggressive than other breast cancer subtypes and constitutes a public health problem worldwide since it has high morbidity and mortality due to the lack of defined therapeutic targets.Resistance to chemotherapy complicates the course of patients’treatment.Several authors have highlighted the participation of nicotinic acetylcholine receptors(nAChR)in the modulation of conventional chemotherapy treatment in cancers of the airways.However,in breast cancer,less is known about the effect of nAChR activation by nicotine on chemotherapy treatment in smoking patients.AIM To investigate the effect of nicotine on paclitaxel treatment and the signaling pathways involved in human breast MDA-MB-231 tumor cells.METHODS Cells were treated with paclitaxel alone or in combination with nicotine,administered for one or three 48-h cycles.The effect of the addition of nicotine(at a concentration similar to that found in passive smokers’blood)on the treatment with paclitaxel(at a therapeutic concentration)was determined using the 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.The signaling mediators involved in this effect were determined using selective inhibitors.We also investigated nAChR expression,and ATP“binding cassette”G2 drug transporter(ABCG2)expression and its modulation by the different treatments with Western blot.The effect of the treatments on apoptosis induction was determined by flow cytometry using annexin-V and 7AAD markers.RESULTS Our results confirmed that treatment with paclitaxel reduced MDA-MB-231 cell viability in a concentration-dependent manner and that the presence of nicotine reversed the cytotoxic effect induced by paclitaxel by involving the expression of functionalα7 andα9 nAChRs in these cells.The action of nicotine on paclitaxel treatment was linked to modulation of the protein kinase C,mitogen-activated protein kinase,extracellular signal-regulated kinase,and NF-κB signaling pathways,and to an up-regulation of ABCG2 protein expression.We also detected that nicotine significantly reduced the increase in cell apoptosis induced by paclitaxel treatment.Moreover,the presence of nicotine reduced the efficacy of paclitaxel treatment administered in three cycles to MDA-MB-231 tumor cells.CONCLUSION Our findings point to nAChRs as responsible for the decrease in the chemotherapeutic effect of paclitaxel in triple negative tumors.Thus,nAChRs should be considered as targets in smoking patients.

Breast cancer:Muscarinic receptors as new targets for tumor therapy

The development of breast cancer is a complex process that involves the participation of different factors.Several authors have demonstrated the overexpression of muscarinic acetylcholine receptors(mAChRs)in different tumor tissues and their role in the modulation of tumor biology,positioning them as therapeutic targets in cancer.The conventional treatment for breast cancer involves surgery,radiotherapy,and/or chemotherapy.The latter presents disadvantages such as limited specificity,the appearance of resistance to treatment and other side effects.To prevent these side effects,several schedules of drug administration,like metronomic therapy,have been developed.Metronomic therapy is a type of chemotherapy in which one or more drugs are administered at low concentrations repetitively.Recently,two chemotherapeutic agents usually used to treat breast cancer have been considered able to activate mAChRs.The combination of low concentrations of these chemotherapeutic agents with muscarinic agonists could be a useful option to be applied in breast cancer treatment,since this combination not only reduces tumor cell survival without affecting normal cells,but also decreases pathological neo-angiogenesis,the expression of drug extrusion proteins and the cancer stem cell fraction.In this review,we focus on the previous evidences that have positioned mAChRs as relevant therapeutic targets in breast cancer and analyze the effects of administering muscarinic agonists in combination with conventional chemotherapeutic agents in a metronomic schedule.