Design and Characterization of an NQO1‐Activated Spiroisoindolinone Derivative for Glioma Treatment
Authors: Punganuru Surendra Reddy , Madala Hanumantha Rao , Srivenugopal Kalkunte 
Published: June 2021

Primary brain tumors and cancers metastasizing to CNS are most challenging and lethal malignancies to treat. Chemotherapy with radiation has been a mainstay in their treatment, however, the adverse effects such as the bone marrow suppression, inefficient drug entry through the BBB, intratumoral heterogeneity, overexpression of MGMT repair protein are all impediments for successful treatment. Therefore, there is a great need for innovative exploitation of targets selectively expressed in CNS cancers for effective therapy. Such an approach is also likely to spare the normal tissues from the therapeutic insult and prevent the adverse effects. A potential cancer‐specific target is the antioxidant enzyme NAD(P)H quinone oxidoreductase 1 (NQO1). NQO1 is a 2‐electron reductase responsible for the detoxification of quinones. Its expression is typically quite low in normal tissues but is highly overexpressed in many solid tumor types, including brain cancers. Based on these observations, we have designed a BBB permeable small molecule NQO1–directed drug, spiroisoindolinone GNQ‐9 for glioma therapy. GNQ‐9 was prepared through rhodium(III)‐catalyzed redox‐neutral coupling reaction of N‐acyl ketimine generated in situ from 3‐hydroxyisoindolinone with benzoquinone. GNQ‐9 exhibited potent antiproliferative activities against a variety of cancer cell lines, particularly, the NQO1 overexpressing tumor cells and showed minimal cytotoxicity towards a panel of normal cell counterparts (astrocytes, HIVECs, and fibroblasts from lung, pancreatic, breast, and colon). Cytotoxicity studies revealed a strong correlation between NQO1 bioreduction and anticancer activity of GNQ‐9. Further, cotreatment with dicoumarol (DIC) significantly reversed the cytotoxic effect of GNQ against U87MG cells demonstrating the NQO1 dependent‐cytotoxicity. The ability of GNQ‐9 to participate in a redox cycle with NQO1 allows for outstanding potency, as one molecule of GNQ‐9 processed by NQO1 generates several ROS molecules and induce oxidative stress and DNA damage. This was confirmed by GNQ‐9 generated ROS production using the DCF‐DA and DHE. GNQ‐9 was also an intercalator and a topo II inhibitor. Other studies revealed that GNQ‐9 induces autophagy and apoptosis through ROS with an increased expression of LC3‐II and beclin‐1 proteins. A marked loss of mitochondrial membrane potential was also noted. Further, the efficacy of GNQ‐9 was tested in intracranial xenograft model developed by injecting the luciferase‐expressing and NQO1‐proficient U87 glioblastoma cells; a significant reduction in the tumor growth was noted with GNQ‐9 as a single agent. Serum ALT and AST levels in the tumor‐bearing nude mice were not altered, suggesting a lack of toxicity. We conclude that GNQ‐9, as an NQO1‐targeted drug heightens the tumor redox and induces selective apoptosis in gliomas.Support or Funding Informationsupported by CPRIT grants RP130266 and RP170207This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.