Synergistic Efficacy of CDK4/6 Inhibitor Abemaciclib and HDAC Inhibitor Panobinostat in Pancreatic Cancer Cells

The current 5-year survival rate of pancreatic cancer is about 12%, making it one of the deadliest malignancies. The rapid metastasis, acquired drug resistance, and poor patient prognosis necessitate better therapeutic strategies for pancreatic ductal adenocarcinoma (PDAC). Multiple studies show that combining chemotherapeutics for solid tumors has been successful. Targeting two distinct emerging hallmarks, such as non-mutational epigenetic changes by panobinostat (Pan) and delayed cell cycle progression by abemaciclib (Abe), inhibits pancreatic cancer growth. HDAC and CDK4/6 inhibitors are effective but are prone to drug resistance and failure as single agents. Therefore, we hypothesized that combining Abe and Pan could synergistically and lethally affect PDAC survival and proliferation. Multiple cell-based assays, enzymatic activity experiments, and flow cytometry experiments were performed to determine the effects of Abe, Pan, and their combination on PDAC cells and human dermal fibroblasts. Western blotting was used to determine the expression of cell cycle, epigenetic, and apoptosis markers. The Abe-Pan combination exhibited excellent efficacy and produced synergistic effects, altering the expression of cell cycle proteins and epigenetic markers. Pan, alone and in combination with Abe, caused apoptosis in pancreatic cancer cells. Abe-Pan co-treatment showed relative safety in normal human dermal fibroblasts. Our novel combination treatment of Abe and Pan shows synergistic effects on PDAC cells. The combination induces apoptosis, shows relative safety, and merits further investigation due to its therapeutic potential in the treatment of PDAC.