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Dihydroorotate Dehydrogenase Inhibitors Promote Cell Cycle Arrest and Disrupt Mitochondria Bioenergetics in Ramos Cells

Kadir MFA, Othman S, Nellore K

Curr Pharm Biotechnol, 2020;21(15):1654-1665.
PMID: 32525770 DOI: 10.2174/1389201021666200611113734

BACKGROUND: The re-emerging of targeting Dihydroorotate Dehydrogenase (DHODH) in cancer treatment particularly Acute Myelogenous Leukemia (AML) has corroborated the substantial role of DHODH in cancer and received the attention of many pharmaceutical industries.
OBJECTIVE: The effects of Brequinar Sodium (BQR) and 4SC-101 on lymphoblastoid cell lines were investigated.
METHODS: DHODH expression and cell proliferation inhibition of lymphoblastoid and lymphoma cell lines were analyzed using Western blot analysis and XTT assay, respectively. JC-1 probe and ATP biochemiluminescence kit were 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 of 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 a better therapeutic window in patients.
Fulltext Synergistic inhibition of melanoma xenografts by Brequinar sodium and Doxorubicin

Dorasamy MS, Ab A, Nellore K, Wong PF

Biomed Pharmacother, 2019 Feb;110:29-36.
PMID: 30458345 DOI: 10.1016/j.biopha.2018.11.010

Malignant melanoma continues to be a fatal disease for which novel and long-term curative breakthroughs are desired. One such innovative idea would be to assess combination therapeutic treatments - by way of combining two potentially effective and very different therapy. Previously, we have shown that DHODH inhibitors, A771726 and Brequinar sodium (BQR) induced cell growth impairment in melanoma cells. Similar results were seen with DHODH RNA interference (shRNA). In the present study, we showed that combination of BQR with doxorubicin resulted in synergistic and additive cell growth inhibition in these cells. In addition, in vivo studies with this combination of drugs demonstrated an almost 90% tumor regression in nude mice bearing melanoma tumors. Cell cycle regulatory proteins, cyclin B1 and its binding partner pcdc-2 and p21 were significantly downregulated and upregulated respectively following the combined treatment. Given that we have observed synergistic effects with BQR and doxorubicin, both in vitro and in vivo, these drugs potentially represent a new combination in the targeted therapy of melanoma.
Dihydroorotate dehydrogenase Inhibitors Target c-Myc and Arrest Melanoma, Myeloma and Lymphoma cells at S-phase

Dorasamy MS, Choudhary B, Nellore K, Subramanya H, Wong PF

J Cancer, 2017;8(15):3086-3098.
PMID: 28928900 DOI: 10.7150/jca.14835

Dihydroorotate dehydrogenase (DHODH) is a rate-limiting enzyme in the de novo biosynthesis pathway of pyrimidines. Inhibition of this enzyme impedes cancer cell proliferation but the exact mechanisms of action of these inhibitors in cancer cells are poorly understood. In this study, we showed that cancer cells, namely melanoma, myeloma and lymphoma overexpressed DHODH protein and treatment with A771726 and Brequinar sodium resulted in cell cycle arrest at S-phase. Transfection with DHODH shRNA depleted DHODH protein expression and impeded the proliferation of melanoma cells. shRNA knockdown of DHODH in combination with DHODH inhibitors further reduced the cancer cell proliferation, suggesting that knockdown of DHODH had sensitized the cells to DHODH inhibitors. Cell cycle regulatory proteins, c-Myc and its transcriptional target, p21 were found down- and up-regulated, respectively, following treatment with DHODH inhibitors in melanoma, myeloma and lymphoma cells. Interestingly, knockdown of DHODH by shRNA had also similarly affected the expression of c-Myc and p21 proteins. Our findings suggest that DHODH inhibitors induce cell cycle arrest in cancer cells via additional DHODH-independent pathway that is associated with p21 up-regulation and c-Myc down-regulation. Hence, DHODH inhibitors can be explored as potential therapeutic agents in cancer therapy.
Benzimidazole derivatives as potential dual inhibitors for PARP-1 and DHODH

Abdullah I, Chee CF, Lee YK, Thunuguntla SSR, Satish Reddy K, Nellore K, et al.

Bioorg Med Chem, 2015 Aug 01;23(15):4669-4680.
PMID: 26088338 DOI: 10.1016/j.bmc.2015.05.051

Poly (ADP-ribose) polymerases (PARPs) play diverse roles in various cellular processes that involve DNA repair and programmed cell death. Amongst these polymerases is PARP-1 which is the key DNA damage-sensing enzyme that acts as an initiator for the DNA repair mechanism. Dihydroorotate dehydrogenase (DHODH) is an enzyme in the pyrimidine biosynthetic pathway which is an important target for anti-hyperproliferative and anti-inflammatory drug design. Since these enzymes share a common role in the DNA replication and repair mechanisms, it may be beneficial to target both PARP-1 and DHODH in attempts to design new anti-cancer agents. Benzimidazole derivatives have shown a wide variety of pharmacological activities including PARP and DHODH inhibition. We hereby report the design, synthesis and bioactivities of a series of benzimidazole derivatives as inhibitors of both the PARP-1 and DHODH enzymes.