Galactokinase 1 Inhibition-Induced Cell Cycle Arrest and Apoptosis in Bladder Cancer Cells Is Associated with AKT Signaling Downregulation.

Bladder cancer (BCa) is the second most common cancer of the genitourinary tract globally. It has limited treatment options, high recurrence rate, and acquires resistance to platinum-based therapy. Therefore, identifying novel therapeutic targets is urgently needed. Analysis of the TCGA data revealed that the enzyme galactokinase-1 (GALK1) is overexpressed (p < 0.0001) in bladder tumors compared to normal tissue. Our data also confirmed GALK1 protein upregulation in multiple human BCa cell lines and rodent bladder tumors. However, the precise role of GALK1 in BCa progression and effects of its specific inhibitor remain unexamined. In this study, we demonstrate that GALK1 gene silencing using shRNA resulted in a significant reduction in BCa cell proliferation, migration, and invasion. Pharmacological inhibition of GALK1 using small molecule Cpd36 resulted in anticancer efficacy against BCa. Cpd36 inhibited proliferation, migration, and invasion of BCa cells. Further, Cpd36 induced G1 phase cell cycle arrest, apoptosis, mitochondrial membrane depolarization, and ROS production in the BCa cells. Mechanistically, Cpd36-induced reduction in cell proliferation was associated with a decrease in expression of GALK1, PCNA proteins. Inhibition of metastatic potential was accompanied by decreased migration, invasion, and MMP-9 expression. Cell cycle arrest was associated with decrease in Cyclin D1 and increased expression of p21 and p27. Induction of apoptosis was linked with increased expression of cleaved caspase-3 and cleaved PARP, while downregulating p-AKT. Additionally, Cpd36 in combination with cisplatin or gemcitabine showed a strong synergistic effect on BCa cells. Taken together, our findings suggest that GALK1 plays a significant role in BCa cell survival and validates its inhibitors as promising therapeutic options for managing this disease.