PLK1-IN-10 (Compound 4Bb), an orally active inhibitor of the PLK1 PBD (polo-box domain), inhibits the interaction between PLK1 and the cell division regulator protein 1 (PRC1) and reduces the protein expression of the CDK1-Cyclin B1 complex. Additionally, PLK1-IN-10 interacts with glutathione (GSH), enhancing cellular oxidative stress and promoting cell death [1].

PLK1-IN-10 significantly induces cell cycle arrest at the G2/M phase in A549 and A549/DDP cells, inhibiting their proliferation when used at concentrations ranging from 0 to 6 μM over 48 hours [1]. At 20 μM, PLK1-IN-10 stabilizes the PLK1 protein in A549/DDP cells across various temperatures [1]. Additionally, a 5 μM concentration of PLK1-IN-10 over 24 hours reacts with GSH, yielding a dose- and time-dependent fluorescence response, which is more pronounced in A549/DDP cells [1]. Exposure to 0 to 9 μM of PLK1-IN-10 for 48 hours elevates intracellular ROS levels in A549/DDP cells [1]. The interaction between PLK1 and PRC1 is inhibited by a 10 μM dose of PLK1-IN-10 over 48 hours, resulting in multinucleation [1]. PLK1-IN-10 exhibits anticancer activity against NCI-H1975 cells, with an IC50 value of 7.83 μM [1]. In Western blot analysis, PLK1-IN-10 treatment of A549 and A549/DDP cells at concentrations of 0, 1.5, 3, and 6 μM for 48 hours resulted in the downregulation of PLK1, CDK1, Cyclin B1, the CDK1-Cyclin B1 complex, and Cdc25 protein expression [1]. Cell cycle analysis of A549 and A549/DDP cells exposed to the same concentrations for 48 hours indicated a significant increase in cells in the G2/M phase, leading to mitotic catastrophe [1].

PLK1-IN-10 administered at doses of 30 and 50 mg/kg intraperitoneally every other day for 32 days significantly inhibited tumor growth in a A549/DDP resistant xenograft mouse model, with the higher dose inducing tumor regression [1]. Additionally, an oral administration of PLK1-IN-10 at 30 mg/kg on the same schedule effectively suppressed tumor growth in the NCI-H1975 resistant xenograft model over a period of 20 days [1]. Efficacy studies in these animal models revealed that the 30 mg/kg dose group achieved a total tumor inhibition (TGI) rate of 42%, while the 50 mg/kg group attained a TGI of 62%, significantly extending median survival times from 38 days in the control group to 53 and 62 days in the 30 and 50 mg/kg groups, respectively. Furthermore, the compound did not cause significant changes in mouse body weight or major organ function, except for a slight difference observed in the heart index at 30 mg/kg. A significant reduction in Ki-67 positive cells and no noteworthy changes in H&E staining of major organs further confirmed the compound’s biosafety.