Novel chloropyridazine sulfonamides as aromatase inhibitors and apoptotic inducers in breast cancer

Aromatase catalyzes the rate-limiting and final step in the biosynthesis of estrogen. Inhibitors of this enzyme are effective targeted therapy for breast cancer. Molecular hybridization is a promising strategy in drug discovery that combines two or more biologically active moieties in a single structure. In this work, we aim at combining sulfonamide, chloropyridazine and pyrrole in a single design as potential aromatase inhibitors for breast cancer. The synthesized compounds were subjected to in vitro cytotoxic screening against MCF-7 breast cancer cell line, then were assessed for their ability to inhibit aromatase enzyme. Compound 10 exhibited a promising cytotoxic activity (IC₅₀ 1.83 μM) that nearly equal to the reference drug (doxorubicin, IC₅₀ 1.94 μM) on MCF-7 cells. Also, compound 10 was the most potent aromatase inhibitor with the lowest IC₅₀ (0.06 μM) compared to letrozole (IC₅₀ 0.05 μM). Based on the promising results of compound 10, it was selected to investigate its apoptotic effect that disclosed a marked increase in Bax level to 5.42 folds and down-regulation in Bcl-2 expression to 0.34 folds in MCF-7 cells compared to letrozole. Moreover, compound 10 increased caspase 9 level by 4.84 folds. Also, compound 10 arrested the cell cycle at G1 phase and caused induction of early and late apoptosis in an AnnexinV-FITC assay. Compound 10 had been evaluated to study its synergistic effect with γ-radiation by evaluating the cytotoxicity against MCF-7 after exposure to gamma rays (8 Gy). In addition, compound 10 showed low toxicity against human normal breast (MCF-10 A) cell line. Docking study of compound 10 was performed and showed binding with the key amino acids in aromatase active site.