AUTHOR=Miyazaki Yukiko , Inaoka Daniel K. , Shiba Tomoo , Saimoto Hiroyuki , Sakura Takaya , Amalia Eri , Kido Yasutoshi , Sakai Chika , Nakamura Mari , Moore Anthony L. , Harada Shigeharu , Kita Kiyoshi 

TITLE=Selective Cytotoxicity of Dihydroorotate Dehydrogenase Inhibitors to Human Cancer Cells Under Hypoxia and Nutrient-Deprived Conditions

JOURNAL=Frontiers in Pharmacology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2018.00997

DOI=10.3389/fphar.2018.00997

ISSN=1663-9812

ABSTRACT=<p>Human dihydroorotate dehydrogenase (HsDHODH) is a key enzyme of pyrimidine <italic>de novo</italic> biosynthesis pathway. It is located on the mitochondrial inner membrane and contributes to the respiratory chain by shuttling electrons to the ubiquinone pool. We have discovered ascofuranone (<bold>1</bold>), a natural compound produced by <italic>Acremonium sclerotigenum</italic>, and its derivatives are a potent class of HsDHODH inhibitors. We conducted a structure–activity relationship study and have identified functional groups of <bold>1</bold> that are essential for the inhibition of HsDHODH enzymatic activity. Furthermore, the binding mode of <bold>1</bold> and its derivatives to HsDHODH was demonstrated by co-crystallographic analysis and we show that these inhibitors bind at the ubiquinone binding site. In addition, the cytotoxicities of <bold>1</bold> and its potent derivatives <bold>7</bold>, <bold>8</bold>, and <bold>9</bold> were studied using human cultured cancer cells. Interestingly, they showed selective and strong cytotoxicity to cancer cells cultured under microenvironment (hypoxia and nutrient-deprived) conditions. The selectivity ratio of <bold>8</bold> under this microenvironment show the most potent inhibition which was over 1000-fold higher compared to that under normal culture condition. Our studies suggest that under microenvironment conditions, cancer cells heavily depend on the pyrimidine <italic>de novo</italic> biosynthesis pathway. We also provide the first evidence that <bold>1</bold> and its derivatives are potential lead candidates for drug development which target the HsDHODH of cancer cells living under a tumor microenvironment.</p>