Lack of Impact of Trace Amine-Associated Receptor Type 1 Ligands on In Vitro Proliferation of Triple-Negative Breast Cancer-Derived Cell Line BT-20

Objective: Triple-negative breast cancer (TNBC) accounts for 10–20% of all invasive breast cancers characterizing by mostly poor outcome and resistance to therapies compared to other breast cancer subtypes. New class monoamine receptors, trace amine-associated ones (TAARs) are known to be associated with overall survival of breast cancer patients, and, for instance, stimulation of trace amine-associated receptor type 1 (TAAR1) in ovarian cancer cell lines with 3-iodothyronamine reduces cell viability in vitro. In this regard, we studied the effects of TAAR1 agonist tyramine hydrochloride and TAAR1 antagonist EPPTB (N-(3-ethoxyphenyl)-4-pyrrolidin-1-yl-3-trifluoromethyl-benzamide) on in vitro proliferation of TNBC-derived cell line BT-20. Methods: To measure in vitro cell proliferation, sulforhodamine B staining assay in 96-well plates was applied. The expression of pro-apoptotic factors BAK and BAX, and anti-apoptotic Bcl2 mRNAs was estimated by qPCR. Results and Discussion: TAAR1 agonist tyramine hydrochloride showed no antiproliferative action at all. In its turn TAAR1 antagonist EPPTB had a weak cytostatic effect (IC50 = 647.2 µM). However, in in vitro combination chemotherapy experiments, EPPTB did not augment the cytostatic effect of classic chemotherapeutic agents 5-fluorouracil and doxorubicin hydrochloride. Treatment of BT-20 cells with IC50 and IC80 of EPPTB did not result in significant changes of BAK and BAX gene expression; however, Bcl2 expression was suppressed by IC80, which may indicate the compound’s slight anti-apoptotic effect. Conclusion: We are able to state the lack of in vitro antiproliferative action of TAAR1 ligands tyramine hydrochloride and EPPTB on triple-negative breast cancer-derived cell line BT-20.