New functionalized 6-thienylpyrimidine-5-carbonitriles as antiproliferative agents against human breast cancer cells

6-Thienylpyrimidine-5-carbonitrile derivatives were synthesized and screened for their in vitro antiproliferative activities against two human breast cancer cell lines in comparison to 5-fluorouracil as a reference. Compounds 2, 3a-c, and 6b evolved as the most active congeners against both cell lines, while others showed selectivity for only one cell line. Compound 2 exerted its effect through inhibition of the epidermal growth factor receptor (EGFR), while 6b showed less aromatase inhibitory activity than letrozole. The rest of the tested compounds did not show significant inhibition, and it can be assumed that they exert their antiproliferative activity through different target mechanisms. In addition, caspase-9 protein activation assays, cell cycle analysis using flow cytometry, and annexin V-fluorescein isothiocyanate-propidium iodide (FITC/PI) dual staining assays were performed for the most active compounds. All the tested compounds were found to be potent pyrimidine derivatives able to initiate apoptosis in MCF-7 and MDA-MB-231 cells.