Inhibition of Carbohydrate Metabolism Potentiated by the Therapeutic Effects of Oxidative Phosphorylation Inhibitors in Colon Cancer Cells

Cancer cells undergo a significant level of "metabolic reprogramming" or "remodeling" to ensure an adequate supply of ATP and "building blocks" for cell survival and to facilitate accelerated proliferation. Cancer cells preferentially use glycolysis for ATP production (the Warburg effect); however, cancer cells, including colorectal cancer (CRC) cells, also depend on oxidative phosphorylation (OXPHOS) for ATP production, a finding that suggests that both glycolysis and OXPHOS play significant roles in facilitating cancer progression and proliferation. Our prior studies identified a semisynthetic isoflavonoid, DBI-1, that served as an AMPK activator targeting mitochondrial complex I. Furthermore, DBI-1 and a glucose transporter 1 (GLUT1) inhibitor, BAY-876, synergistically inhibited CRC cell growth in vitro and in vivo. We now report a study of the structure-activity relationships (SARs) in the isoflavonoid family in which we identified a new DBI-1 analog, namely, DBI-2, with promising properties. Here, we aimed to explore the antitumor mechanisms of DBIs and to develop new combination strategies by targeting both glycolysis and OXPHOS. We identified DBI-2 as a novel AMPK activator using an AMPK phosphorylation assay as a readout. DBI-2 inhibited mitochondrial complex I in the Seahorse assays. We performed proliferation and Western blotting assays and conducted studies of apoptosis, necrosis, and autophagy to corroborate the synergistic effects of DBI-2 and BAY-876 on CRC cells in vitro. We hypothesized that restricting the carbohydrate uptake with a KD would mimic the effects of GLUT1 inhibitors, and we found that a ketogenic diet significantly enhanced the therapeutic efficacy of DBI-2 in CRC xenograft mouse models, an outcome that suggested a potentially new approach for combination cancer therapy.

Mitochondrial Deoxyguanosine Kinase Regulates NAD+ Biogenesis Independent of Mitochondria Complex I Activity

Overexpression of DGUOK promotes mitochondria oxidative phosphorylation and lung adenocarcinoma progression. However, the role and mechanism of DGUOK in regulation of mitochondria function and lung cancer progression still poorly understood. Here we demonstrated that DGUOK regulated NAD⁺ biogenesis. Depletion of the DGUOK significantly decreased NAD⁺ level. Furthermore, knockout of the DGUOK considerably reduced expression of the NMNAT2, a key molecule controlling NAD⁺ synthesis, at both mRNA and protein levels. Ectopic expression of the NMNAT2 abrogated the effect of knockdown of DGUOK on NAD⁺. Notably, this regulation is independent of DGUOK -mediated mitochondria complex I activity. We also showed that NMNAT2 was highly expressed in lung adenocarcinoma and negatively correlated with the patient overall survival. Our study suggested that DGUOK regulates NAD⁺ in a NMNAT2 dependent manner and DGUOK-NMNAT2-NAD⁺ axis could be a potential therapeutic target in lung adenocarcinoma.

PET Imaging of Mitochondrial Complex I with 18F-BCPP-EF in the Brains of MPTP-Treated Monkeys

(18)F-BCPP-EF was applied to assess mitochondrial complex I (MC-I) activity in the brains of Parkinson disease model monkeys prepared by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and also presynaptic dopamine parameters.

METHODS

(11)C-β-CFT for the dopamine transporter; (11)C-3,4-dihydroxy-phenyl-L-alanine (β-(11)C-L-DOPA), L-6-(18)F-fluorodopa ((18)F-FDOPA), or 6-(11)C-methyl-m-tyrosine ((11)C-6MemTyr) for dopamine synthesis; or 2-tert-butyl-4-chrolo-5-{6-[2-(2-(18)F-fluoroethoxy)-ethoxy]-pyridin-3-ylmethoxy}-2H-pyridazin-3-one ((18)F-BCPP-EF) for MC-I was intravenously injected into normal and MPTP monkeys in order to analyze their uptake in the striatum.

RESULTS

Significant reductions in presynaptic dopamine parameters and MC-I activity were detected in the striatum of MPTP monkeys. Correlations were observed between MC-I activity and dopamine transporter as well as between MC-I activity and dopamine synthesis in the striatum. The order of detectability of impaired MC-I activity was (11)C-6MemTyr >> β-(11)C-L-DOPA > (18)F-FDOPA.

CONCLUSION

(18)F-BCPP-EF has potential as a PET probe for the quantitative imaging of MC-I damage in the living brains of Parkinson disease model monkeys using PET.

Novel PET probes 18F-BCPP-EF and 18F-BCPP-BF for mitochondrial complex I: a PET study in comparison with 18F-BMS-747158-02 in rat brain

We developed novel PET probes, 2-tert-butyl-4-chloro-5-{6-[2-(2-(18)F-fluoroethoxy)-ethoxy]-pyridin-3-ylmethoxy}-2H-pyridazin-3-one ((18)F-BCPP-EF) and 2-tert-butyl-4-chloro-5-[6-(4-(18)F-fluorobutoxy)-pyridin-3-ylmethoxy]-2H-pyridazin-3-one ((18)F-BCPP-BF), for quantitative imaging of mitochondrial complex I (MC-I) activity in the brain and preliminarily evaluated their properties in comparison with (18)F-BMS-747158-02 ((18)F-BMS).

METHODS

The affinity of (18)F-BCPP-EF, (18)F-BCPP-BF, and (18)F-BMS to MC-I was analyzed using in vitro binding assays with (3)H-dihydrorotenone and bovine cardiomyocyte submitochondrial particles. (18)F-BCPP-EF, (18)F-BCPP-BF, or (18)F-BMS was intravenously injected into rats, and the uptake (standardized uptake value) in each organ was determined by dissection method. The effects of rotenone, a specific MC-I inhibitor, on the uptake of each probe were assessed by whole-body PET imaging in rats. Ischemic brain model rats were imaged using (18)F-BCPP-EF.

RESULTS

The rank order of affinity to MC-I was (18)F-BCPP-BF > (18)F-BMS > (18)F-BCPP-EF. The uptake of (18)F-BCPP-EF and (18)F-BMS was high in the heart, intermediate in brain, and low in muscle and bone 60 min after the injection. (18)F-BCPP-BF provided increasing bone uptake with time after the injection. The uptake of (18)F-BCPP-EF and (18)F-BMS into the brain and heart was significantly decreased by preadministration of rotenone; however, the reduction degree of (18)F-BCPP-EF was more pronounced than that of (18)F-BMS. Rotenone did not affect (18)F-BCPP-BF uptake in either the brain or the heart. (18)F-BCPP-EF imaged the cortical ischemic neuronal damage without any disturbance by microglial activation even on day 7 when (18)F-FDG showed high uptake in the damaged area.

CONCLUSION

The present study demonstrated that (18)F-BCPP-EF could be a potential PET probe for quantitative imaging of MC-I activity and its ischemic damage in the living brain with PET.