Novel oxindole/benzofuran hybrids as potential dual CDK2/GSK-3β inhibitors targeting breast cancer: design, synthesis, biological evaluation, and <i>in silico</i> studies

Abstract

The serine/threonine protein kinases CDK2 and GSK-3β are key oncotargets in breast cancer cell lines, therefore, in the present study three series of oxindole-benzofuran hybrids were designed and synthesised as dual CDK2/GSK-3β inhibitors targeting breast cancer (<b>5a-g</b>, <b>7a-h</b>, and <b>13a-b</b>). The <i>N¹</i> -unsubstituted oxindole derivatives, <b>series 5</b>, showed moderate to potent activity on both MCF-7 and T-47D breast cancer cell lines. Compounds <b>5d-f</b> showed the most potent cytotoxic activity with IC₅₀ of 3.41, 3.45 and 2.27 μM, respectively, on MCF-7 and of 3.82, 4.53 and 7.80 μM, respectively, on T-47D cell lines, in comparison to the used reference standard (staurosporine) IC₅₀ of 4.81 and 4.34 μM, respectively. On the other hand, the <i>N¹</i> -substituted oxindole derivatives, <b>series 7</b> and <b>13</b>, showed moderate to weak cytotoxic activity on both breast cancer cell lines. CDK2 and GSK-3β enzyme inhibition assay of <b>series 5</b> revealed that compounds <b>5d</b> and <b>5f</b> are showing potent dual CDK2/GSK-3β inhibitory activity with IC₅₀ of 37.77 and 52.75 nM, respectively, on CDK2 and 32.09 and 40.13 nM, respectively, on GSK-3β. The most potent compounds <b>5d-f</b> caused cell cycle arrest in the G2/M phase in MCF-7 cells inducing cell apoptosis because of the CDK2/GSK-3β inhibition. Molecular docking studies showed that the newly synthesised <i>N¹</i> -unsubstituted oxindole hybrids have comparable binding patterns in both CDK2 and GSK-3β. The oxindole ring is accommodated in the hinge region interacting through hydrogen bonding with the backbone CO and NH of the key amino acids Glu81 and Leu83, respectively, in CDK2 and Asp133 and Val135, respectively, in GSK-3β. Whereas, in series <b>7</b> and <b>13</b>, the <i>N¹</i> -substitutions on the oxindole nucleus hinder the compounds from achieving these key interactions with hinge region amino acids what rationalises their moderate to low anti-proliferative activity.