Background:
The re-emerging of targeting dihydroorotate dehydrogenase (DHODH) in cancer treatment particularly acute myelogenous leukemia (AML) have corroborated the substantial role of DHODH in cancer and fascinated the attention of many pharmaceutical industries.
Objective:
The effects brequinar sodium (BQR) and 4SC-101 in lymphoblastoid cell lines were investigated.
Method:
DHODH expression and cell proliferation inhibition of lymphoblastoid and lymphoma cell lines were analysed using Western blot analysis and XTT assay respectively. JC-1 probe and ATP biochemiluminescence kit was used to evaluate
the mitochondrial membrane potential and ATP generation in these cell lines. Furthermore, we explored the cell cycle progression using Muse™ Cell Cycle Kit.
Results:
Ramos, SUDHL-1 and RPMI-1788 cells are fast-growing cells with equal expression of DHODH enzyme and sensitivity to DHODH inhibitors that showed that the inhibition of DHODH was not cancer specific. In ATP depletion assay,
the non-cancerous RPMI-1788 cells showed only a minor ATP reduction compared to Ramos and SUDHL-1 (cancer) cells.
In the mechanistic impact of DHODH inhibitors on non-cancerous vs cancerous cells, the mitochondrial membrane potential
assay revealed that significant depolarization and cytochrome c release occurred with DHODH inhibitors treatment in Ramos but not in the RPMI-1788 cells, indicating a different mechanism of proliferation inhibition in normal cells.
Conclusion:
The findings in this study provide evidence that DHODH inhibitors perturb the proliferation of non-cancerous
cells via a distinct mechanism compared to cancerous cells. These results may lead to strategies for overcoming the impact
on non-cancerous cells during treatment with DHODH inhibitors, leading to better therapeutic window in patients.
Brequinar sodium (BQR) is a well-studied inhibitor of the dihydroorotate dehydrogenase (DHODH) enzyme. Both the DHODH and uridine-cytidine kinase 2 (UCK2) enzymes have been reported to be over-expressed in cancer cells to maintain the cells high demand for DNA and RNA for their proliferation. In this study, we aim to further sensitize cells to the effects of BQR by knocking down the UCK2 activity. In DLD-1 UCK2 knockdown cells, no change in the sensitivity of cells to BQR was observed. Uridine is known to reverse the anti-proliferative effect of DHODH inhibitors via the salvage pathway. We observed abrogation of approximately 30% of the uridine reversal effect in UCK2 knockdown cells compared to the wild type cells. Our finding indicates that the loss of UCK2 activity in the salvage pathway did not enhance the BQR-mediated cell proliferation inhibition but it abrogates the uridine reversal in the cells.
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