Circumventing the Crabtree effect: forcing oxidative phosphorylation (OXPHOS) via galactose medium increases sensitivity of HepG2 cells to the purine derivative kinetin riboside

Abstract

Small-molecule compound-based therapies have provided new insights into cancer treatment against mitochondrial impairment. N6-furfuryladenosine (kinetin riboside, KR) is a purine derivative and an anticancer agent that selectively affects the molecular pathways crucial for cell growth and apoptosis by interfering with mitochondrial functions and thus might be a potential mitotoxicant. Metabolism of cancer cells is predominantly based on the Crabtree effect that relies on glucose-induced inhibition of cell respiration and thus on oxidative phosphorylation (OXPHOS), which supports the survival of cancer cells in metabolic stress conditions. The simplest way to circumvent this phenomenon is to replace glucose with galactose in the culture environment. Consequently, cells become more sensitive to mitochondrial perturbations caused by mitotoxicants. In the present study, we evaluated several cellular parameters and investigated the effect of KR on mitochondrial functions in HepG2 cells forced to rely mainly on OXPHOS. We showed that KR in the galactose environment is a more potent apoptosis-inducing agent. KR decreases the mitochondrial membrane potential, reduces glutathione level, depletes cellular ATP, and induces reactive oxygen species (ROS) production in the OXPHOS state, leading to the loss of cell viability. Taken together, these results demonstrate that KR directly acts on the mitochondria to limit their function and that the sensitivity of cells is dependent on their ability to cope with energetic stress.

Implications of Oxidative Stress in Glioblastoma Multiforme Following Treatment with Purine Derivatives

“…The current paper demonstrates the impact of N 6furfuryladenosine (kinetin riboside; KR) and its newly designed derivatives, 8-azakinetin riboside (8-azaKR) and 7-deazakinetin riboside (7-deazaKR), on the redox status of T98G GBM cells. Our previous study confirmed the complexity of the mechanism of action of KR, and we determined its effect on mitochondrial bioenergetics in HepG2 cells [12]. KR exerts a powerful anticancer effect and has an impact on molecular pathways that are crucial for cell increase, proliferation, and induction of cell death [12,13].…”

“…Our previous study confirmed the complexity of the mechanism of action of KR, and we determined its effect on mitochondrial bioenergetics in HepG2 cells [12]. KR exerts a powerful anticancer effect and has an impact on molecular pathways that are crucial for cell increase, proliferation, and induction of cell death [12,13]. It is also a member of the purine analogue family, in which every compound may show an inimitable mechanism of action in neoplastic cells.…”

“…There are findings that natural small compounds may influence various steps of intracellular signaling pathways that are crucial for cell growth, proliferation, and apoptosis. We found a connection between observed KR-induced rapid ATP depletion and the enzymatic reactions that KR is involved in, such as phosphorylation by adenosine kinase, a crucial enzyme of the purine salvage pathway [12]. The current paper demonstrates the impact of N 6furfuryladenosine (kinetin riboside; KR) and its newly designed derivatives, 8-azakinetin riboside (8-azaKR) and 7-deazakinetin riboside (7-deazaKR), on the redox status of T98G GBM cells.…”

“…Cancer cells develop various mechanisms to escape cell death and induce a high proliferation rate through their ability to repair DNA damage, cell-cycle arrest, variations in the expression of oncogenes, induction of autophagy, hypoxia [48], and alterations in tumor metabolism [12]. Glioblastoma cells have an increased level of ROS, which results from the impairment of the mechanisms related to the production and elimination of ROS [40]; these impairments are mainly based on the mitochondrial dysfunction or inefficient antioxidant systems [42].…”

“…Following the development of hypoxia in the tumor microenvironment, metabolic activities of cancer cells are altered comparative to normal cells [41]. These modifications support the maintenance of malignant properties and create an intrinsic cell resistance mechanism associated with "metabolic reprogramming" [12]. Regardless of the elevated ROS level, GBM cells can survive in such environments by relying on lactic acid fermentation, which is associated with the high rate of anaerobic glycolysis [49].…”